Karl-Heinz Schmidt

Abstract: Based on a comprehensive set of fission-fragment distributions measured in low-energy fission, the even�odd staggering in the fission-fragment element yields is investigated. The well-established evolution of the global even�odd effect with the fissioning system is found to be only a partial aspect of the even�odd structure. Indeed, it is shown that the global even�odd effect varies systematically with the mean asymmetry of the fission-fragment distribution, and that the general increase of the even�odd staggering with asymmetry depends on the fissioning system. Thus, the dependence of the even�odd effect on the fissioning system is accredited in part to the asymmetry evolution of the charge distribution, and not solely to the dissipated energy as it has been done earlier. This interpretation is strongly supported by data measured in inverse kinematics, which cover the complete fission-fragment charge distribution and include precise yields at symmetry. The relevance of the ordering parameter for the description of the even�odd effect in fission-fragment yields as a general property is explored.

Abstract: A correlation between the production and kinematic properties of the fragments issued of fission and multifragmentation is established in the study of the reaction 136Xe+hydrogen at 1 GeV per nucleon, measured in inverse kinematics at the FRagment Separator (GSI, Darmstadt). Such observables are analysed in a comprehensive study, selected as a function of the decay mode, and related to the isotopic properties of the fragments in the intermediate-mass region. Valuable information can be deduced on the characteristics of the heaviest product in the reaction, which has been considered a fundamental observable for tagging the thermodynamic properties of finite nuclear systems.

Abstract: We study how the excitation energy of the fully accelerated fission fragments is built up. It is stressed that only the intrinsic excitation energy available before scission can be exchanged between the fission fragments to achieve thermal equilibrium. This is in contradiction with most models used to calculate prompt neutron emission where it is assumed that the total excitation energy of the final fragments is shared between the fragments by the condition of equal temperatures. We also study the intrinsic excitation- energy partition in statistical equilibrium for different level-density descriptions as a function of the total intrinsic excitation energy of the fissionning system. Excitation energies are found to be strongly enhanced in the heavy fragment, if the level density follows a constant-temperature behavior at low energies e.g. in the composed Gilbert-Cameron description.

Abstract: The thermodynamic properties of a dinuclear system are studied with the methods of statistical mechanics. A schematic model calculation shows that the excitation-energy transfer proceeds in energy steps of considerable amount which are subject to large fluctuations. As a consequence, thermal averaging is strong enough to assure the application of thermodynamical methods for describing the energy exchange between the two nuclei in contact. In particular, thermal averaging justifies the definition of a nuclear temperature. The division of excitation energy in thermal equilibrium is derived for several analytical descriptions of the level density.

Abstract: The fragmentation of neutron-rich 132Sn nuclei produced in the fission of 238U projectiles at 950 A MeV has been investigated at the FRagment Separator (FRS) at GSI. This work represents the first investigation of fragmentation of medium-mass radioactive projectiles with a large neutron excess. The measured production cross sections of the residual nuclei are relevant for the possible use of a two-stage reaction scheme (fission + fragmentation) for the production of extremely neutron-rich medium-mass nuclei in future rare-ion-beam facilities. Moreover, the new data will provide a better understanding of the �memory� effect in fragmentation reactions.

Abstract: On the basis of systematic measurements of fragmentation reactions, which provide a detailed overview on the velocity distributions of residual nuclei, an improved description of the kinematical properties of the fragmentation residues is established. This work is dedicated to the fluctuations of their momentum distributions. In contrast to previous investigations, limited to close-to-projectile fragments, we extended our study to the entire production range, down to the lightest observed fragments. In this context, beside the contribution of abrasion and evaporation processes, we considered the effect of the thermal break-up on the width of the momentum distributions. Using approximated theoretical descriptions of the different reaction stages, a new analytical formula for the variance of the momentum distribution is derived, which is well adapted to technical applications.

Abstract: Production cross sections and longitudinal velocity distributions of the projectilelike residues produced in the reactions 112Sn+112Sn and 124Sn+124Sn, both at an incident beam energy of 1A GeV, were measured with the high-resolution magnetic spectrometer, the Fragment Separator of GSI. For both reactions the characteristics of the velocity distributions and nuclide production cross sections were determined for residues with atomic number Z�10. A comparison of the results of the two reactions is presented.

Abstract: It is shown that the constant-temperature behavior of nuclei in the superfluid regime leads to an energy-sorting process if two nuclei are in thermal contact, as is the case in the fission process. This effect explains why an increase of the initial excitation energy leads an increase of the number of emitted neutrons from the heavy fission fragment, only. The observed essentially complete energy sorting may be seen as a new counterintuitive manifestation of quantum-mechanical properties of microscopic systems.

Abstract: Isospin properties of fragments measured in multifragmentation of 136Xe and 124Xe projectiles in midperipheral collisions with a lead target at 1 A GeV were studied within the statistical approach describing the liquidgas nuclear phase transition. By analyzing the isoscaling phenomenon and the mean NoverZ ratio of the fragments with Z = 10 to 13 we have concluded that the symmetry energy of hot fragments produced in multifragment environment at subnuclear densities at high temperatures decreases in comparison with cold nuclei.

Abstract: It is shown that the recently proposed sorting of intrinsic excitation energy in superfluid fission dynamics explains the complex features of even-odd structure in fission-fragment yields. A schematic dynamical scenario is proposed. It reveals that the variation of the even-odd effect with the Coulomb parameter of the compound nucleus and the increase towards asymmetric splits carries information on several dynamical times. This new insight stresses the importance of nuclear fission as a laboratory for studying the dynamics of non-equilibrium processes between mesoscopic superfluid objects.

Abstract: Peripheral collisions with radioactive heavy-ion beams at relativistic energies are discussed as an innovative approach for probing the transient regime experienced by fissile systems evolving towards quasi-equilibrium, and thereby studying the viscous nature of nuclear matter. A dedicated experiment using the advanced technical installations of GSI, Darmstadt, permitted to realize ideal conditions for the investigation of relaxation effects in the meta-stable well. Combined with a highly sensitive experimental signature, it provides a measure of the transient effects with respect to the flux over the fission barrier. Within a two-step reaction process, 45 proton-rich unstable spherical isotopes between At and Th produced by projectile-fragmentation of a stable 238U beam have been used as secondary projectiles which impinge on lead target nuclei. The fragmentation of the radioactive projectiles results in nearly spherical compound nuclei which span a wide range in excitation energy and fissility. The decay of these excited systems by fission is studied with a dedicated s et-up which, together with the inverse kinematics of the reaction, permits the detection of both fission products in coincidence and the determination of their atomic numbers with high resolution. The information on the nuclear charges of the two fragments is used to sort the data according to the initial excitation energy and fissility of the compound nucleus. The width of the fission-fragment nuclear charge distribution is shown to be specifically sensitive to pre-saddle transient effects and is used to establish a clock for the passage of the saddle point. The comparison of the experimental results with model calculations points to a fission delay tau_trans of (3.3 +- 0.7)10^-21s for initially spherical compound nuclei, independent of excitation energy and fissility. This value suggests a nuclear dissipation strength beta at small deformation of (4.5 +- 0.5)10^21s-1. The very specific combination of the physics and technical equipment exploited in this work sheds light on previous controversial conclusions, which were drawn without considering the influence of the initial conditions.

Abstract: The production of heavy neutron-rich nuclei has been investigated using cold fragmentation reactions of 238 U projectiles at relativistic energies. The experiment performed at the high-resolving-power magnetic spectrometer FRS at GSI allowed to identify 45 new heavy neutron-rich nuclei: 205Pt, 207�210Au, 211�216Hg, 213�217Tl, 215�220Pb, 219�224Bi, 221�227Po, 224�229At, 229�231Rn and 233Fr. The production cross sections of these nuclei were also determined and used to benchmark reaction codes that predict the production of nuclei far from stability.

Abstract: The analysis of experimental production cross-sections of intermediate-mass fragments (IMF) of several nuclear reactions at relativistic energy, measured at the FRS, GSI Darmstadt, revealed a very strong and complex even-odd staggering. The origin of this effect is related to the condensation process of hot nuclei while cooling down by evaporation. The characteristics of the staggering correlate strongly with the lowest particle separation energy of the final experimentally observed nuclei, but not with the binding energy. The study confirms the important role of the de-excitation process in multifragmentation reactions, and indicates that sequential decay strongly influences the yields of IMF, which are often used to extract information on the nature of nuclear reactions at high energies.

Abstract: Heavy neutron-rich nuclei close to N=126 were produced by fragmentation of a 1 A GeV 208Pb beam at the FRS at GSI. The beta-decay half-lives of 8 nuclides have been determined. The comparison of the data with model calculations including an approach based on the self-consistent ground-state description and continuum QRPA considering the Gamow-Teller and first-forbidden decays provide a first indication on the importance of first-forbidden transitions around A=195. The measured data indicate that the matter flow in the r-process to heavier fissioning nuclei is faster than previously expected.

Abstract: Measurements of prompt Doppler-corrected deexcitation gamma rays from uniquely identified fragments formed in fusion-fission reactions of the type 12C(238U,134Xe)Ru are reported. The fragments were identified in both A and Z using the variable-mode, high-acceptance magnetic spectrometer VAMOS. States built on the characteristic neutron configurations forming high-spin isomers (7- and 10+) in 134Xe are presented and compared with the predictions of shell-model calculations using a new effective interaction in the region of Z>=50 and N<=82.

Abstract: The fission barrier, given as the difference between the saddle-point and ground-state masses, plays a mandatory role in determining the survival probability of fissile nuclei. While the ground-state mass is strongly influenced by the shell correction, according to the topographic theorem the saddle-point mass should be rather close to its macroscopic value. In the present paper, the topographical properties of fission barriers have been investigated within the macro-microscopic approach. The range of the validity of the topographic theorem was studied in a quantitative way. It is shown that the conditions for the validity of the topographic theorem are fulfilled at the inner barrier, while at the outer saddle-point, deviations caused by the presence of shell effects of the nascent fragments have been found.

Abstract: This paper reports the first application of a new technique to measure the β-decay half-lives of exotic nuclei in complex background conditions. Since standard tools were not adapted to extract the relevant information, a new analysis method was developed. The time distribution of background events is established by recording time correlations in backward time. The β half-lives of the nuclides and the detection efficiency of the set-up are determined simultaneously from a least-squares fit of the ratio of the time-correlation spectra recorded in forward and in backward time, using numerical functions. The necessary numerical functions are calculated in a Monte-Carlo code using the known operation parameters of the experiment and different values for the two free parameters, half-life and detection efficiency, as input parameters.

Abstract: The nuclide cross sections and longitudinal velocity distributions of residues produced in the reactions of 136Xe and 124Xe at 1A GeV in a lead target were measured at the high-resolution magnetic spectrometer, the fragment separator (FRS) of GSI. The data cover a broad range of isotopes of the elements between Z=3 and Z=56 for 136Xe and between Z=5 and Z=55 for 124Xe, reaching down to cross sections of a few microbarns. The velocity distributions exhibit a Gaussian shape for masses above A=20, while more complex behavior is observed for lighter masses. The isotopic distributions for both reactions preserve a memory on the projectile N/Z ratio over the whole residue mass range.

Abstract: Electromagnetic-induced fission of several neutron-deficient actinides and pre-actinides was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multi-modal fission of nuclei around 226Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is presented. The positions of the asymmetric fission channels are found to be constant in atomic number over the whole range of systems investigated.

Abstract: The large body of experimental data on nuclear fission is analyzed with a semi-empirical ordering scheme based on the macro-microscopic approach and the separability of compound-nucleus and fragment properties on the fission path. We apply the statistical model to the non-equilibrium descent from saddle to scission, taking the influence of dynamics into account by an early freeze-out. The present approach reveals a large portion of common features behind the variety of the complex observations made for the different systems.

Abstract: Production cross sections of medium-mass neutron-rich nuclei obtained in the fragmentation of 136Xe projectiles at 1 A GeV have been measured with the FRagment Separator (FRS) at GSI. The measured cross sections are compared to 238U fission yields and model calculations to determine the optimum reaction mechanism to extend the limits of the chart of the nuclides around the r-process waiting point at N=82.

Abstract: We report on a novel experimental approach for studying the dissipative spreading of collective motion in a metastable nuclear system, using, for the first time, highly fissile nuclei with spherical shape. This was achieved by fragmentation of 45 radioactive heavy-ion beams at GSI, Darmstadt. The use of inverse kinematics and a dedicated experimental setup allowed for the identification in atomic number of both fission fragments. From the width of their nuclear-charge distributions, a transient time of (3.3±0.7)�10-21 s is deduced for initially spherical nuclei.

Abstract: Possibilities are studied for the optimization of EURISOL rare nuclide yields in specific regions of the nuclear chart by building the driver accelerator in a way that enables accelerating several additional beam species, to specific energies, besides the baseline 1 GeV proton beam. Nuclide production rates with these driver beams are compared to the production rates expected with the 1 GeV proton beam in the direct-production and the high-power-converter scenarios. Arguments are presented to show that several additional driver-beam scenarios could provide substantial benefit for the production of nuclides in specific regions of the nuclear chart. The quantitative values in this report are preliminary in the sense that they depend on assumptions on the values of some key parameters which are subject to technical development, e.g., maximum beam intensities or limits on the target heat load. The different scenarios are compared from the aspect of nuclide yields. The arguments presented here, when complemented by the corresponding technological and financial considerations, are intended to serve as a part of the basis for decisions on the design of the driver accelerator of EURISOL.

Abstract: Fission fragments of 1A GeV238U nuclei interacting with a deuterium target have been investigated with the Fragment Separator (FRS) at Gesellschaft für Schwerionenforschung (GSI) by measuring their isotopic production cross sections and velocities. Results, along with those obtained recently for spallation-evaporation fragments, provide a comprehensive analysis of the spallation nuclear productions in this reaction. Details about the experimental performance, data reduction and results are presented.

Abstract: The spallation residues produced in the bombardment of 56Fe at 1.5A,1.0A,0.75A,0.5A, and 0.3A GeV on a liquid-hydrogen target have been measured using the reverse kinematics technique and the fragment separator at GSI (Darmstadt). This technique has permitted the full identification in charge and mass of all isotopes produced with cross sections larger than 10-2 mb down to Z=8. Their individual production cross sections and recoil velocities at the five energies are presented. Production cross sections are compared with previously existing data and with empirical parametric formulas, often used in cosmic-ray astrophysics. The experimental data are also extensively compared with the results of different combinations of intranuclear cascade and deexcitation models. It is shown that the yields of the lightest isotopes cannot be accounted for by standard evaporation models. The GEMINI model, which includes an asymmetric fission decay mode, gives an overall good agreement with the data. These experimental data can be directly used for the estimation of composition modifications and damages in materials containing iron in spallation sources. They are also useful for improving high-precision cosmic-ray measurements.

Abstract: We propose a new formula for the saddle-to-scission time that is more general that the one based on Kramers' approach. Its validity and applicability is then studied in detail. Such a formula is useful for the evaluation of the fission time of very heavy nuclei.

Abstract: We present an extensive overview of production cross sections and kinetic energies for the complete set of nuclides formed in the spallation of 136Xe by protons at the incident energy of 1 GeV per nucleon. The measurement was performed in inverse kinematics at the GSI fragment separator. Slightly below the Businaro-Gallone point, 136Xe is the stable nuclide with the largest neutron excess. The kinematic data and cross sections collected in this work for the full nuclide production are a general benchmark for modeling the spallation process in a neutron-rich nuclear system, where fission is characterized by predominantly mass-asymmetric splits.

Abstract: The production cross sections of fragmentation�evaporation residues in the reaction Pb+p at 500 A MeV have been measured using the inverse-kinematics method and the FRS spectrometer (GSI). Fragments were identified in nuclear charge using ionisation chambers. The mass identification was performed event-by-event using the B��TOF��E technique. Although partially-unresolved ionic charge states induced an ambiguity on the mass of some heavy fragments, production rates could be obtained with a high accuracy by systematically accounting for the polluting ionic charge states. The contribution of multiple reactions in the target was subtracted using a new, partly self-consistent code. The isobaric distributions are found to have a shape very close to the one observed in experiments at higher energy. Kinematic properties of the fragments were also measured. The total and the isotopic cross sections, including charge-pickup cross sections, are in good agreement with previous measurements and models. The data are discussed in the light of previous spallation measurements, especially on lead at 1 GeV.

Abstract: Isotopic cross sections of all projectile residues with Z above 23 produced in collisions induced by 238U at 1A GeV on deuterium have been measured. The isotopic distributions reflect the role of evaporation and fission in the formation process of these nuclei. The comparison of the measured cross sections with Monte Carlo deexcitation codes including an analytical description of the dynamics of fission shows the sensitivity of the data to nuclear dissipation. Moreover, the large excitation-energy range covered in this experiment together with the high accuracy of the measured cross sections allowed to clearly separate and quantify the role of transient and quasistationary dissipative effects in the fission-decay width.

Abstract: The population of metastable states produced in relativistic-energy fragmentation of a 238U beam has been measured. For states with angular momentum greater-than or equivalent to20planck constant over two pi, a much higher population than expected has been observed. By introducing a collective component to the generation of angular momentum the experimental data can be understood. This is the first time that a collective degree of freedom has be shown to play a major role in such high-energy collisions.

Abstract: Recently, a series of dedicated inverse-kinematics experiments performed at GSI, Darmstadt, has brought an important progress in our understanding of proton and heavy-ion induced reactions at relativistic energies. The nuclear reaction code ABRABLA that has been developed and benchmarked against the results of these experiments has been used to calculate nuclide production cross-sections at different energies and with different targets and beams. These calculations are used to estimate nuclide production rates by protons in thick targets, taking into account the energy loss and the attenuation of the proton beam in the target, as well as the low-energy fission induced by the secondary neutrons. The results are compared to the yields of isotopes of various elements obtained from different targets at CERN-ISOLDE with 600 MeV protons, and the overall extraction efficiencies are deduced. The dependence of these extraction efficiencies on the nuclide half-life follows a simple pattern in many different cases. A universal function is proposed to parameterize this behavior in a way that quantifies the essential properties of the extraction efficiency for the element and the target�ion-source system in question.

Abstract: Isotopic production cross sections and momentum distributions of 602 residual nuclei produced in the collision of 238U(1A GeV) with deuterium have been measured. These data are relevant for a better understanding of spallation reactions for use as neutron sources for accelerator-driven systems or to produce radioactive nuclear beams. Access to primary residue production makes it possible to study the main reaction mechanisms involved: intranuclear cascade, particle evaporation, and fission. The characteristics of the reaction investigated and the high fissility of the 238U and the dinucleon projectile system are discussed and compared with other available experimental data.

Abstract: This review on second- and third-generation multidetectors devoted to heavy-ion collisions aims to cover the last twenty years. The presented list of devices is not exhaustive but regroups most of the techniques used during this period for nuclear reactions at intermediate energy (� 10A MeV to 1A GeV), both for charged-particle and neutron detection. The main part will be devoted to 4� multidetectors, projectile decay fragmentation, high-resolution magnetic spectrometers, auxiliary detectors and neutron detection. The last part will present the progress in electronics and detection in view of the construction of future-generation detectors.

Abstract: Different approaches for measuring nuclear temperatures are described. The quantitative results of different thermometer approaches are often not consistent. These differences are traced back to the different basic assumptions of the applied methods. Moreover, an overview of recent theoretical investigations is given, which study the quantitative influence of dynamical aspects of the nuclear-reaction process on the extracted apparent temperatures. The status of the present experimental and theoretical knowledge is reviewed. Guidelines for future investigations, especially concerning the properties of asymmetric nuclear matter, are given.

Abstract: The production cross-sections of proton-rich protactinium and thorium isotopes have been investigated for the fragmentation of 1 A GeV 238U in a beryllium target at the SIS/FRS facility at GSI Darmstadt. The experimental results are compared with the predictions of an abrasion�ablation model of nuclear fragmentation yielding good overall agreement. Weak evidence for first observation of the new isotopes 208Th and 211Pa is presented.

Abstract: Fission fragments from 1 A GeV 238U ions impinging a hydrogen target are investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing, and �E-ToF techniques. On the basis of the kinematics of the fragments, binary fission can be assigned as production process up to very heavy fragments. Fission fragments are separated and identified as far as 184Re for the first time. Cross sections are measured and found in the range of 500 μb to 5 μb. Isobaric cross sections decrease smoothly with increasing masses. Beyond tungsten, fission fragments are hidden in the more abundant spallation evaporation residues. 283 isotopes of elements gadolinium to rhenium in the mass range 147 to 184 are observed and cross sections measured. All the fragments are formed by fission of excited parent nuclei following emission of a cascade of secondary neutrons.

Abstract: Using available experimental data on fission barriers and ground-state masses, a detailed study of the predictions of different models concerning the isospin dependence of saddle-point masses is performed. Evidence is found that several macroscopic models yield unrealistic saddle-point masses for very neutron-rich nuclei, which are relevant for the r-process nucleosynthesis.

Abstract: The production of light and intermediate-mass nuclides formed in the reaction 1H+238U at 1 GeV was measured at the Fragment Separator at GSI, Darmstadt. The experiment was performed in inverse kinematics, by shooting a 1 A GeV 238U beam on a thin liquid-hydrogen target. A total of 254 isotopes of all elements in the range 7<=Z<=37 were unambiguously identified, and the velocity distributions of the produced nuclides were determined with high precision. The results show that the nuclides are produced in a very asymmetric binary decay of heavy nuclei originating from the spallation of uranium. All the features of the produced nuclides merge with the characteristics of the fission products as their mass increases.

Abstract: The isotopic distributions and recoil velocities of the fission fragments produced in the spallation reaction 208Pb + p at 500 A MeV have been measured using the inverse-kinematics technique, a lead beam onto a liquid-hydrogen target, and the high-resolution spectrometer FRS at GSI. The shapes of the different distributions are found in good agreement with previously published data while the deduced total fission cross-section is higher than expected from existing systematics and some previous measurements. From the experimental data, the characteristics of the average fissioning system can be reconstructed in charge, mass and excitation energy, and the average number of post-fission neutrons can be inferred. The results are also compared to different models describing the spallation reaction. The intranuclear cascade code INCL4 followed by the de-excitation code ABLA is shown to describe reasonably well the evolution of the isotopic distribution shapes between 500 and 1000 A MeV.

Abstract: The feasibility of low-energy fragmentation experiments using a magnetic spectrometer is discussed. The main challenge is the multiplicity of the ionic charge states, which can hamper the identification in both Z and A of the fragments. Three topics are covered. First, a specific set-up for ionisation chambers, based on a very large gas thickness, is presented. Its satisfactory performances are discussed in light of the observations during a 500A MeV Pb+p experiment performed at the FRS (GSI). As a second topic, the possibility to use a thick layer of matter (a degrader) as a passive measurement device to identify the nuclear charge and the ionic charge state of fragments is discussed. This method, successfully used for Z identification in experiments such as Pb+p at 1A GeV, fails to measure the charge states at 500A MeV for the same system. It is shown that surface defects of the degrader are probably responsible for this failure. The third topic is the description of new analysis techniques developed in order to account for and subtract the contribution of polluting charge states in the spectrometer, thus making possible a clean estimation of the production cross-sections of all fragments. The combination of those new experimental and analysis techniques made the 500A MeV spallation experiment a success.

Abstract: We study neutrino-induced processes that might contribute to the observed patterns in the r-process abundances in low-metallicity, old galactical halo stars. The neutrino�nucleus interaction is calculated within the random phase approximation, while the decay of excited levels in the daughter nucleus is followed via the evaporation-fission code ABLA. We calculate the fission cross sections for selected neutron-rich progenitor nuclei with Zprog>80. More importantly, we calculate the mass and charge distributions of the fission fragments as well as the number of neutrons set free in the neutrino-induced reactions. We particularly study a sample of nuclei with Aprog>200 representing r-process progenitors during their decay towards the valley of stability after the r-process freeze-out.

Abstract: The time-dependent flux over the fission barrier of an excited nucleus under the influence of dissipation is investigated. Characteristic features of the evolution of the amplitude of the probability distribution and the velocity profile at the fission barrier are derived. Analytical results are compared to numerical Langevin calculations and used to develop a new analytical approximation to the solution of the Fokker�Planck equation for the time-dependent fission-decay width. This approximation is shown to be more realistic than previously proposed descriptions, which were widely used in the past.

Abstract: Relativistic projectile fragmentation of 208Pb has been used to produce isomers in neutron-rich, A ap 190 nuclides. A forward-focusing spectrometer provided ion-by-ion mass and charge identification. The detection of gamma-rays emitted by stopped ions has led to the assignment of isomers in 188Ta, 190W, 192Re, 193Re, 195Os, 197Ir, 198Ir, 200Pt, 201Pt, 202Pt and 203Au, with half-lives ranging from approximately 10 ns to 1 ms. Tentative isomer information has been found also for 174Er, 175Er, 185Hf, 191Re, 194Re and 199Ir. In most cases, time-correlated, singles gamma-ray events provided the first spectroscopic data on excited states for each nuclide. In 200Pt and 201Pt, the assignments are supported by gamma-gamma coincidences. Isomeric ratios provide additional information, such as half-life and transition energy constraints in particular cases. The level structures of the platinum isotopes are discussed, and comparisons are made with isomer systematics.

Abstract: A systematic study of the population probabilities of nanosecond and microsecond isomers produced following the projectile fragmentation of 238U at 750 MeV�nucleon has been undertaken at the SIS�FRS facility at GSI. Approximately 15 isomeric states in neutron-deficient nuclei around A�190 were identified and the corresponding isomeric ratios determined. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning γ cascades in the final nucleus (sharp cutoff). This model represents an upper limit for the population of isomeric states in relativistic projectile fragmentation. When the decay properties of the states above the isomer are taken into account, as opposed to the sharp cutoff approximation, a good agreement between the experimental and calculated angular momentum population is obtained.

Abstract: A new experimental approach is introduced to investigate the relaxation of the nuclear deformation degrees of freedom. Highly excited fissioning systems with compact shapes and low angular momenta are produced in peripheral relativistic heavy-ion collisions. Both fission fragments are identified in atomic number. Fission cross sections and fission-fragment element distributions are determined as a function of the fissioning element. From the comparison of these new observables with a nuclear-reaction code a value for the transient time is deduced.

Abstract: Complex structural effects in the nuclide production from the projectile fragmentation of 1 A GeV 238U nuclei in a titanium target are reported. The structure seems to be insensitive to the excitation energy induced in the reaction. This is in contrast to the prominent structural features found in nuclear fission and in transfer reactions, which gradually disappear with increasing excitation energy. Using the statistical model of nuclear reactions, relations to structural effects in nuclear binding and in the nuclear level density are demonstrated.

Abstract: New experimental results on the kinematics and the residue production are obtained for the interactions of 56Fe projectiles with protons and natTi target nuclei, respectively, at the incident energy of 1 A GeV . The titanium-induced reaction serves as a reference case for multifragmentation. Already in the proton-induced reaction, the characteristics of the isotopic cross sections and the shapes of the velocity spectra of light residues indicate that high thermal energy is deposited in the system during the collision. In the 56Fe+p system the high excitation seems to favor the onset of fast break-up decays dominated by very asymmetric partitions of the disassembling system. This configuration leads to the simultaneous formation of one or more light fragments together with one heavy residue.

Abstract: The conditions for the manifestation of transient effects in fission are carefully examined by analysing experimental data where fission is induced by peripheral heavy-ion collisions at relativistic energies. Experimental total nuclear fission cross sections of 238U at 1 A GeV on gold and uranium targets are compared with the predictions of a nuclear-reaction code, where transient effects in fission are modeled using different approximations to the numerical time-dependent fission-decay width: a new analytical description based on the solution of the Fokker�Planck equation and two widely used but less realistic descriptions, a step function and an exponential-like function. The experimental data are only reproduced when dissipation is considered. The influence of transient effects on the fission process, as well as the deduced value of the dissipation strength β, depends strongly on the approximation applied for the time-dependent fission-decay width. In particular, a meticulous analysis sheds severe doubts on the use of the exponential-like in-growth function. Finally, we investigate which should be the characteristics of experimental observables to be most sensitive to transient effects in fission. The pertinence of observables related to the excitation energy at saddle is discussed.

Abstract: Spallation residues and fission fragments from 1A��GeV��238U projectiles irradiating a liquid hydrogen target were investigated by using the fragment separator at GSI for magnetic selection of reaction products including ray-tracing, energy-loss and time-of-flight techniques. The longitudinal-momentum spectra of identified fragments were analyzed, and evaporation residues and fission fragments could be separated. For 1385 nuclides, production cross sections down to values of 10��μb with a mean accuracy of 15%, velocities in the uranium rest frame and kinetic energies were determined. In the reaction all elements from uranium to nitrogen were found, each with a large number of isotopes.

Abstract: Isotopically resolved cross sections and velocity distributions have been measured in charge-pickup reactions of 1A GeV 208Pb with proton, deuterium, and titanium targets. The total and partial charge-pickup cross sections in the reactions 208Pb+1H and 208Pb+2H are measured to be the same within the limits of the error bars. A weak increase in the total charge-pickup cross section is seen in the reaction of 208Pb with the titanium target. The measured velocity distributions show different contributions�quasielastic scattering and � -resonance excitation�to the charge-pickup production. Data on total and partial charge-pickup cross sections from these three reactions are compared with other existing data and also with model calculations based on the coupling of different intranuclear cascade codes and an evaporation code.

Abstract: Precise momentum distributions of identified projectile fragments, formed in the reactions 238U+Pb and 238U+Ti at 1A� ��GeV, are measured with a high-resolution magnetic spectrometer. With increasing mass loss, the velocities first decrease as expected from previously established systematics, then level off, and finally increase again. Light fragments are on the average even faster than the projectiles. This finding is interpreted as the response of the spectators to the participant blast. The reacceleration of projectile spectators is sensitive to the nuclear mean field and provides a new tool for investigating the equation of state of nuclear matter.

Abstract: The production of heavy nuclides from the spallation�evaporation reaction of 238U induced by 1 GeV protons was studied in inverse kinematics. The evaporation residues from tungsten to uranium were identified in-flight in mass and atomic number. Their production cross-sections and their momentum distributions were determined. The data are compared with empirical systematics. A comparison with previous results from the spallation of 208Pb and 197Au reveals the strong influence of fission in the spallation of 238U.

Abstract: Fission fragments from 1 A GeV 238U projectiles irradiating a hydrogen target were investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing and �E�ToF techniques. The momentum spectra of 733 identified fragments were analysed to provide isotopic production cross sections, fission-fragment velocities and recoil momenta of the fissioning parent nuclei. Besides their general relevance, these quantities are also demanded for applications. Calculations and simulations with codes commonly used and recently developed or improved are compared to the dat

Abstract: Different analytical approximations to the time-dependent fission-decay width used to extract the influence of dissipation on the fission process are critically examined. Calculations with a new, highly realistic analytical approximation to the exact solution of the Fokker�Planck equation sheds doubts on previous conclusions on the dissipation strength made on the basis of less realistic approximations.

Abstract: Isotopic series of 58 neutron-deficient secondary projectiles (205,206At, 205�209Rn, 208�212,217,218Fr, 211�223Ra, 215�226Ac, 221�229Th, 226�231Pa, 231�234U) were produced by projectile fragmentation using a 1 A GeV 238U beam. Cross sections of fission induced by nuclear and electromagnetic interactions in a secondary lead target were measured. They were found to vary smoothly as a function of proton and neutron number of the fissioning system, also for nuclei with large ground-state shell effects near the 126-neutron shell. No stabilization against fission was observed for these nuclei at low excitation energies. Consequences for the expectations on the production cross sections of super-heavy nuclei are discussed.

Abstract: A two-step reaction scheme for the production of extremely neutron-rich radioactive beams, fission followed by cold fragmentation, is considered. The cross-sections of the second step, the cold fragmentation of neutron-rich fission fragments, are estimated with different computer codes. Discrepancies between an empirical systematics and nuclear-reaction codes are found.

Abstract: The application of a secondary-electron transmission monitor for high-precision intensity measurements of relativistic heavy-ion beams is investigated. The basic requirements, a strictly linear response as a function of beam intensity and a reliable absolute calibration are discussed on the basis of experimental data. Statistical fluctuations and systematic uncertainties of the calibration method are determined.

Abstract: 197Au(800 A MeV)-on-proton collisions are used to investigate the fission dynamics at high excitation energy. The kinematic properties together with the isotopic identification of the fission fragments allow to determine the mass, charge and excitation energy of the fissioning nucleus at saddle. The comparison of these observables and the measured total fission cross section with model calculations evidences a clear hindrance of fission at high excitation energy that can be explained in terms of nuclear dissipation. Assuming a statistical evaporation for other de-excitation channels than fission, an estimated value of the transient time of fission of (3±1)�10�21 s is obtained.

Abstract: The production cross sections and the kinematical properties of primary residual nuclei have been studied in the reaction 208Pb(1 A GeV)+d. Isotopic distributions were measured for all elements from titanium (Z=22) to lead (Z=82). The measured kinematical properties of the residues were also used to disentangle the relevant reaction mechanisms, spallation�evaporation and spallation�fission. The fragment separator FRS at GSI, Darmstadt, was used to separate and identify the reaction products. The measured quantities are important for the design and planning of future radioactive-beam facilities and accelerator-driven systems. The measured data of the present work are comprehensively compared with the experimental data from the reaction 208Pb(1 A GeV)+p.

Abstract: A new method to estimate the angular transmission in zero-degree magnetic spectrometers is presented. This method is based on a parameterisation of the angular aperture of the spectrometer for any possible value of the magnetic rigidity of the transmitted particles. This parameterisation of the angular aperture together with a description of the kinematics of the reaction mechanism allows to determine the angular transmission analytically, avoiding tedious Monte-Carlo calculations. The analytical solutions are implemented for residual nuclei produced in fission, projectile�fragmentation and fusion�evaporation reactions.

Abstract: Fragmentation of secondary beams of neutron-rich, unstable 19,20,21O isotopes at beam energies near 600 MeV/nucleon was studied by measuring the production cross sections for carbon, nitrogen, and oxygen fragments. Data for stable 17,18O beams were obtained as well. The measurements serve to illuminate the isospin dependence of the fragmentation process. The experimental results are compared to those from empirical parametrization and those from abrasion-ablation models.

Abstract: Isotope yields of heavy residues produced in collisions of 238U with lead at 1 A GeV show indications for a simultaneous break-up process. From the average N-over-Z ratio of the final residues up to Z=70, the average limiting temperature of the break-up configuration at freeze out was determined to T�5 MeV using the isospin-thermometer method. C

Abstract: A systematic study of the population probabilities of microsecond isomers produced following the fragmentation of 208Pb projectiles at 1 GeV/nucleon has been undertaken at the SIS/FRS facility at GSI Darmstadt. Gamma decays from approximately 20 isomeric states, mainly in the rare-earth and transitional nuclei with A�180, were identified and the corresponding isomeric ratios deduced. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning gamma cascades in the final nucleus (sharp cutoff). The model is found to represent an upper limit for the population of isomeric states in relativistic projectile fragmentation

Abstract: The secondary-beam facility at GSI allows to produce a large variety of exotic nuclei at relativistic energies. This technique offers a unique oportunity to investigate systematically fission in inverse kinematics. In the present experiment, the fission properties of more than 70 different actinides and preactinides were investigated at low excitation energy. The elemental yields and kinetic energies of the fission residues present new signatures of shell structure and pairing correlations.

Abstract: Heavy 65-70Co, 68-74Ni, 70-76Cu and 74-81Ga isotopes were produced at the LISOL facility by means of 30 MeV proton-induced fission of 238U. Production rates were deduced and compared to two types of cross-section calculations: the empirical model (V. Rubchenya, private communication) and the PROFI code. Comparison with experimental data favors the latter model. Yields using different beam-target combinations and different energies are calculated and discussed.

Abstract: The production of primary residual nuclei in the reaction 1 A GeV 208Pb on proton has been studied by measuring isotopic distributions for all elements from titanium (Z=22) to lead (Z=82). Kinematical properties of the residues were also determined and used to disentangle the relevant reaction mechanisms, spallation (projectile fragmentation) and fission. The fragment separator FRS at GSI, Darmstadt, was used to separate and identify the reaction products. The measured production cross sections are highly relevant for the design of accelerator-driven subcritical reactors and for the planning of future radioactive-beam facilities.

Abstract: Interactions of 197Au projectiles at 800 A MeV with protons leading to fission are investigated. We measured the production cross sections and velocities of all fission residues which are fully identified in atomic and mass number by using the in-flight separator FRS at GSI. The new data are compared with earlier measurements of the characteristics of fission in similar reactions. Both the production cross sections and the recoil energies are relevant for a better understanding of spallation reactions.

Abstract: The spallation of 197Au by 800 MeV protons was investigated in inverse kinematics at GSI, Darmstadt, by use of a 197Au beam bombarding a liquid-hydrogen target. The fragment separator (FRS) was used to select and identify the reaction products prior to β decay. The individual production cross sections and the kinematic properties of 380 isotopes for all elements between mercury (Z=80) and neodymium (Z=60) have been measured. A comparison with a Monte-Carlo calculation based on the two-step model of the spallation reaction is given. The isotopic cross-section distribution of iridium isotopes is compared to that resulting from the aluminium-induced fragmentation of 197Au. The mean kinetic energies of the fragments are deduced from the experimental data. The importance of the new data to improve our understanding of the spallation mechanism is discussed.

Abstract: The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even�odd effects and lead to an improved understanding of structure effects in nuclear fission. The relevance of these studies for some presently considered applications is described. Prospects for future experiments are discussed

Abstract: The secondary-beam facility of GSI Darmstadt was used to study the fission properties of 70 short-lived radioactive nuclei. Most of them have not been accessible so far in conventional fission experiments. Relativistic secondary projectiles were produced by fragmentation of a 1 A GeV 238U primary beam and identified in nuclear charge and mass number. Using these reaction products as secondary beams, the giant resonances, mostly the giant dipole resonance, were excited by electromagnetic interactions in a secondary lead target, and fission from excitation energies around 11 MeV was induced. The fission fragments were identified in nuclear charge, and their velocity vectors were determined. Elemental yields and total kinetic energies have been obtained for a number of neutron-deficient actinides and preactinides. The characteristics of multimodal fission of nuclei around 227Th were systematically investigated. The proton even�odd effect was determined for all systems.

Abstract: The probabilities of single-particle excitations that preserve completely paired configurations of the nuclear proton and neutron subsystems are formulated as a function of excitation energy in the framework of the superfluid nuclear model. These calculations are used to analyse measured data on even�odd structure in fission-fragment yields. Excitation energies acquired at scission are deduced. The strongly differing even�odd structures in proton and neutron numbers are explained within the assumption of thermal equilibrium of intrinsic excitations at scission.

Abstract: Spallation residues produced in 1 GeV per nucleon 208Pb on proton reactions have been studied using the Fragment Separator facility at GSI. Isotopic production cross sections of elements from 61Pm to 82Pb have been measured down to 0.1 mb with a high accuracy. The recoil kinetic energies of the produced fragments were also determined. The obtained cross sections agree with most of the few existing gamma-spectroscopic data. The data are compared with different intranuclear-cascade and evaporation-fission models. Drastic deviations were found for a standard code used in technical applications.

Abstract: A new statistical test procedure is described to evaluate whether a set of radioactive-decay data is compatible with the assumption that these data originate from the decay of a single radioactive species. Criteria to detect contributions from other radioactive species and from different event sources are given. The test is applicable to samples of exponential distributions with two or more events.

Abstract: The production cross sections and longitudinal-momentum distributions of very neutron-rich isotopes have been investigated in the fragmentation of a 950 A MeV 179Au beam in a beryllium target. Seven new isotopes (193Re, 194Re, 191W, 192W, 189Tl, 187Hf and 188Hf) and the five-proton-removal channel were observed for the first time. The reaction mechanism leading to the formation of these very neutron-rich isotopes is explained in terms of the cold-fragmentation process. An analytical model describing this reaction mechanism is presented.

Abstract: Projectile fragmentation and fission, induced in collisions of 238U at 1 A GeV with lead, have systematically been studied. A complete survey on the isotopic production cross sections of all elements between vanadium (Z = 23) and rhenium (Z = 75) down to a cross section of 0.1 mb is given. About 600 isotopes produced in fragmentation and about 600 isotopes produced in fission were identified in the GSI fragment separator FRS from magnetic rigidities, time-of-flight values, and the energy loss in an ionisation chamber. In addition, the velocity distributions of all these reaction products have been mapped, and the products are unambiguously attributed to the different reaction mechanisms due to their kinematical properties. The results are compared with empirical systematics and previous data. The velocity of the fragments obtained in the fission process by the Coulomb repulsion allows one to reconstruct the TKE-value of the break-up and to identify the atomic number of the fissioning nucleus in hot fission. The mean velocities of light projectile fragments were found to be higher than the beam velocity.

Abstract: Production cross sections of more than 270 isotopes ranging from Z = 59 to Z = 82 were measured in the reaction 208Pb(1 GeV A)+Cu. The method of identifying the projectile fragments and evaluating the production cross sections is described. The experimental data are compared with a modern version of the abrasion-ablation model and with the empirical parameterization EPAX. Apart from deviations in the details they both show an overall good agreement. The cross sections of those fragments which are produced by the removal of protons only test the lower part of the excitation energy distribution. For the first time, the four-proton removal channel could be observed.

Abstract: Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 � 52 and N2 � 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A � 180�220.

Abstract: In an experiment at the LISE3 facility of GANIL, we used the projectile fragmentation of a 36Ar primary beam at 95 MeV/nucleon to produce the isotope 24Si. The beta decay half-life of 24Si has been determined to be T1/2 = (140 ± 8) ms, in agreement with earlier measurements. In addition to the decay of the isobaric analog state, several proton peaks are observed for the first time allowing to identify most of the Gamow-Teller transitions to unbound states and to present a partial decay scheme for 24Si. These results are compared with shell-model predictions.

Abstract: Projectile fragmentation of 238U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30�53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues was used to determine an effective proton-evaporation barrier.

Abstract: Nuclear-charge yields of fragments produced by fission of 214,�,223Ac, 220,�,229Th, 224,�,232Pa, and 231,�,234U have been measured. These radioactive nuclei were produced as secondary beams, and fission was induced in flight at 420 A MeV by electromagnetic excitation in a lead target. The excitation-energy distribution at fission is estimated to be centered at 11 MeV. The nuclear-charge distributions of the fission fragments of odd-Z actinium and protactinium isotopes show a pronounced odd-even structure: in asymmetric charge splits, the unpaired proton predominantly sticks to the heavy fragment. A model is proposed which attributes this effect to the single-particle level densities of the nascent fission fragments. This model also explains the strongly enhanced odd-even effect observed in the most asymmetric parts of the nuclear-charge distributions after fission of the even-Z nuclei 220,�,229Th and 231,�,234U. It is concluded that proton pairs are broken in an early stage of the fission process.

Abstract: Fragments of relativistic 750 A.MeV U-projectiles were investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing and �E-ToF techniques. For elements between Ge and Sb, measurements of isotopic yield distributions and velocities revealed three processes: fragmentation, low-energy fission, and high-energy fission. The last of these regimes is presently reported. First and second moments of distributions of mass numbers, atomic numbers and velocities of the corresponding fragments allowed us to identify 101 43Tc56 as the most probable fragment of a high energy symmetric fission reaction. Moreover, we could deduce a hypothetical mean fissioning fragmentation product 208Rn and its highly excited pre-fragmentation parent 227Ra produced in a primary abrasion reaction at an excitation energy of about 290 MeV.

Abstract: A model calculation is presented which predicts the complex nuclide distribution resulting from peripheral relativistic heavy-ion collisions involving fissile nuclei. The model is based on a modern version of the abrasion-ablation model which describes the formation of excited prefragments due to the nuclear collisions and their consecutive decay. The competition between the evaporation of different light particles and fission is computed with an evaporation code which takes dissipative effects and the emission of intermediate-mass fragments into account. The nuclide distribution resulting from fission processes is treated by a semi-empirical description which includes the excitation-energy dependent influence of nuclear shell effects and pairing correlatios. The calculations of collisions between 238U and different reaction partners reveal that a huge number of isotopes of all elements up to uranium is produced. The complex nuclide distribution shows the characteristics of fragmentation, mass-asymmetric low-energy fission and mass-symmetric high-energy fission. The yields of the different components for different reaction partners are studied. Consequences for technical applications are discussed.

Abstract: Production cross sections of several hundred nuclei produced in the fragmentation of uranium and lead projectiles are analysed with the abrasion-ablation model taking into account fission in the deexcitation chain. The survival probability against fission of excited compound nuclei is a sensitive probe for shell and collective effects in the nuclear level density. The expected stabilization against fission for neutron-deficient actinides near the magic number N = 126 due to large ground-state shell effects is not found in the experimental data. With the inclusion of collective enhancement in the level density the experimental data can be described well. The damping of the collective enhancement with excitation energy has to be treated as essentially independent of nuclear deformation, a new finding which contradicts the current theoretical picture. A schematic description of the vibrational enhancement in spherical nuclei is deduced from the data. The lack of shell stabilization against fission observed for the 126-neutron shell is expected to have consequences for the production cross sections of spherical superheavy elements around N = 184.

Abstract: The angular momentum induced in peripheral fragmentation reactions at relativistic energies is described on the basis of shell-model considerations. An analytical expression for the spincutoff parameter of prefragments is obtained, and numerical calculations in the framework of the abrasion-ablation model are performed in order to estimate the angular-momentum distribution of prefragments and final fragments. Additionally, an approximative formula is given to calculate the angular-momentum distribution of final fragments.

Abstract: For isotopically separated secondary beams of neutron-deficient nuclei delivered by the SIS-FRS facility at the GSI, electromagnetic fission-in-flight induced at 430 · A MeV in a secondary lead target was observed. Electromagnetic fission cross sections were measured for 232,233,234U, 232Pa, 220,221,222Th, 218,�,222Ac and 215,217,218,219Ra. By using a simple analysis, fission barrier were derived from the electromagnetic fission cross sections. For the U- and Pa-isotopes, these barriers agree with those measured previously by other methods. The new barriers for Th- and Ac-isotopes are smaller than predicted theoretically.

Abstract: In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope 22Al by the fragmentation of a 36Ar primary beam at 95 MeV/nucleon. After implantation in a detector telescope, the decay of 22Al via β-delayed proton emission, β-delayed two-proton emission as well as, for the first time, via β-delayed α emission has been studied. An α peak has been observed at (3.27 ± 0.04) MeV with a branching ratio of (0.31 ± 0.09) %. The comparison of the different decay channels to those of the mirror nucleus 22F and to shell-model calculations favor a 3+ state as being the ground state of 22Al. A half life of T1/2 = (59 ± 3) ms has been measured.

Abstract: 23Si isotopes have been produced as projectile fragments of a 36Ar primary beam at 95 MeV/nucleon at the LISE3 spectrometer of GANIL. After implantation in a detector telescope, beta-delayed one-proton and beta-delayed two-proton emission has been observed. The main one-proton peaks are at (1.32-0.04)MeV, (2.40-0.04)MeV, and (2.83-0.06)MeV. The total decay energy for the beta2p decay is (6.18-0.10)MeV for the decay to the ground state and (5.86-0.10)MeV for the decay to the first excited state in the daughter nucleus. However, energetically possible decays via beta-p! and beta-3p emission have not been identified. The spectra allowed us to determine the excitation energy of the isobaric analogue state in 23Al. This enabled us to calculate the coefficients of the T=5/2 isobaric multiplet mass equation for A=23. The mass excess of the 23Si ground state was deduced. This value is compared to different theoretical predictions. Additionally, we determined the branching ratios for the different decay branches. A half-life measurement yielded T1/2=(40.7-0.4)ms.

Abstract: For isotopically separated secondary beams of 233U delivered by the SIS-FRS facility at the GSI, fission-in-flight induced by electromagnetic excitations in a lead target and by nuclear interactions in a plastic target at beam energies of about 420 · A MeV was observed. The nuclear-charge yields and the total kinetic energies released during the fission process as a function of the nuclear charge of the fission fragments were measured. The results are compared to data measured by thermal-neutron-induced fission.

Abstract: The intensity of a 136Xe(600 A MeV) beam has been determined by simultaneously measuring the particle rate and the corresponding ionisation current with an ionisation chamber. The ionisation current of this self-calibrating device was compared at higher intensities with the current of a secondary-electron monitor and a calibration of the secondary-electron current was achieved with a precision of 2%. This method can be applied to all high-energy heavy-ion beams.

Abstract: The proton-rich nuclei 44Cr, 47Mn, 48,49Fe and 50Co have been produced by fragmentation of a 58Ni beam at 650 MeV/u. The isotopic separation of these nuclei has been achieved with the GSI Projectile-Fragment Separator FRS. The isotopes have been identified in flight by �E-ToF-Bvarrho measurements. After implantation in a stack of seven silicon detectors, the signals measured for implantation and radioactive decay were unambiguously correlated in time due to low counting rates. On the basis of the two proton peaks observed for 50Co at (2034±30) keV and (2740±41) keV with a half-life of (44±4) ms, a partial decay scheme is proposed for this nucleus. A single proton peak at (959±33) keV was observed for 48Fe with a half-life of (44±7) ms. This emission is attributed to the decay of the T = 2 isobaric analog state in 48Mn. No deviation from the quadratic form of the isobaric multiplet mass equation is observed. Additional information on β-delayed proton branches of 49Fe, 44Cr and 47Mn was also obtained.

Abstract: Charge distributions of fragments from low energy nuclear fission are investigated in reactions of highly fissile238U projectiles at relativistic energies (750 A·MeV) with a heavy (Pb) and a light (Be) target. The fully stripped fission fragments are separated by the Fragment Separator (FRS). Their high kinetic energies in the laboratory system allow the identification of all atomic numbers by using Multiple-Sampling Ionization Chambers (MUSIC). The elemental distributions of fragments observed at larger magnetic rigidities than the238U projectiles show asymmetric break-up and odd-even effects. They indicate a low energy fission process, induced mainly by dissociation in the electro-magnetic field for the U/Pb-system, or by peripheral nuclear interactions for the U/Be-system.

Abstract: In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope 22Si by the fragmentation of a 36Ar primary beam at 95 MeV/nucleon. After implantation in a detector telescope, we studied the decay of 22Si via a measurement of charged particles emitted during the decay. The most important β-delayed proton activity is observed at an energy of Ep = (1.99±0.05) MeV with a branching ratio of (20±2)%. The spectra allow us also to determine the half-life of 22Si to be T1/2 = (29±2) ms. These results are compared with theoretical estimates and model predictions

Abstract: Charge-loss and fission cross-sections of238U at 750 A·MeV were measured on Al, Cu and Pb targets. The charge-loss rate was obtained by the attenuation method. Fission was selected by detecting the pair of highly ionizing fragments. Since the neutron-loss cross sections were measured in a parallel experiment for the same projectiles, all cross sections contributing to238U collisions on nuclei are available now as function of the target mass number and can be compared with current models.

Abstract: Total nuclear charge-changing cross sections ��z in a CH2 target were measured for 54 isotopically identified secondary beams around A = 60 produced from a 1A·GeV86Kr beam via projectile fragmentation. With secondary beams between Image and �3, the isospin dependence of ��z was investigated systematically. Contrary to the predictions of so-called overlap formulae, the ��z values are not a function of the projectile mass alone, but are found to depend on the projectile isospin. A comparison of the data with the predictions of the statistical abrasion model reveals that this behaviour can be understood by the combined influence of the abrasion and the ablation phase in relativistic heavy-ion collisions. On the basis of this improved understanding, previous findings of anomalously large cross sections of secondary-reaction products are discussed.

Abstract: A method for measuring the cross sections for the neutron removal from relativistic secondary projectiles by means of a two-stage magnetic spectrometer is presented. Its application to the 1n- and 2n-removal from 56Ni and 52Fe at 470 A·MeV in an aluminum target is described. The results are compared to the intranuclear-cascade plus evaporation model and to the statistical abrasion-ablation model. The influence of the nuclear surface on the few-nucleon removal reactions is discussed. The neutron-removal cross sections are combined with total charge-changing cross sections to obtain the total interaction cross sections of 56Ni and 52Fe.

Abstract: A complete identification in mass and nuclear charge for relativistic projectile fragments up to uranium is possible at the fragment separator (FRS) at GSI by using the scintillation detector equipment described in this paper. It was successfully used in experiments with primary beams ranging from oxygen to uranium with energies from 300 to 1000 A MeV. A mass-resolving power of A/�A = 407 (FWHM) was obtained for 0.95 A GeV 238U fragments.

Abstract: The abrasion-ablation model widely used previously to describe peripheral nuclear reactions at relativistic energies has been generalized to be applicable to heavy reaction partners for which it is important to account for nuclear fission. It is shown that the changes of the fission widths and the transient times of the competing decay modes caused by the nuclear viscosity must be included to consistently describe the available experimental data. The model predictions are in good agreement with measured total fission cross sections for high-energy 238U projectiles impinging on different targets. Furthermore, recently measured production cross sections of neutron-deficient U and Pa isotopes in the fragmentation of 238U projectiles at 950A MeV are well described by the model, if a nuclear viscosity parameter of β = 1 � 1021 s�1 is chosen. The model predicts rather high production cross sections for a wide range of fissile exotic nuclei which may be produced by the fragmentation of 238U.

Abstract: The projectile fragmentation in peripheral nuclear collisions was studied using � 1 GeV·A of 208Pb and 238U from the SIS at GSI, impinging on a copper target. Lead and thallium isotopes from the fragmentation of 208Pb as well as uranium and protactinium isotopes from 238U, were selected by the fragment separator FRS. In contrast to the fragmentation of 208Pb, the cross sections for the production of heavy fragments from 238U are strongly reduced by fission. The measured isotopic yields may be explained quantitatively by calculations in the framework of the abrasion-ablation model, if fission is allowed to compete with particle evaporation in the deexcitation of the prefragments.

Abstract: At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of58Ni at 650 MeV/nucleon in a beryllium target. By means of aDeltaE�Brgr�TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH2, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations.

Abstract: At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of58Ni at 650 MeV/nucleon in a beryllium target. By means of aDeltaE�Brgr�TOF measurement, the fragments were identified and their charge-changing probabilities in targets of (CH2) n , C, Al, and Pb placed at the exit of the FRS were determined. Whereas a first article dealt with the total charge-changing cross sections, we describe in this second article the element distributions of these secondary fragments, which are found to depend strongly on the isospin of the secondary projectile as well as on the target material. In the case of the lead target, the influence of the electromagnetic dissociation is clearly visible in the one-proton and two-proton removal channels. The preference for the formation of even-Z fragments is much more pronounced for exotic secondary projectiles than for projectiles close to stability. Calculations with a geometrical abrasion-ablation model allow to understand the global features of the experimental data. However, far from stability, the discrepancies between calculations and experimental data increase.

Abstract: As part of a comprehensive study of uranium fragmentation at relativistic energies at the GSI projectile fragment separator, FRS, inclusive neutron-removal cross sections have been measured for severalxn channels at projectile energies of 600 and 950A MeV using targets of Al, Cu and Pb. The variation of the experimental cross sections with target nuclear charge is used to disentangle nuclear and electromagnetic contributions. The electromagnetic cross sections agree surprisingly well with a simple harmonic oscillator calculation of giant dipole resonances based on measured photonuclear cross sections and do not require an extra enhancement of the two-phonon giant dipole excitation as concluded from similar measurements with197Au.

Abstract: Using a primary beam of 58Ni at 650 MeV/nucleon impinging on a beryllium target, production cross sections of proton-rich fragments from projectile fragmentation have been measured at the projectile-fragment separator FRS at Gesellschaft für Schwerionenforschung Darmstadt m.b.H. The experimental data ranging from nickel to scandium for isotopes close to stability as well as for fragments at the proton drip line are compared to predictions of the microscopic ISApace code, to calculations with a revised abrasion-ablation model and with the statistical abrasion model, and to the results of the empirical parametrization EPAX. Besides these systematic measurements, evidence for the particle stability of 50Ni has been found for the first time, whereas the nuclei 49Co and 54Cu are shown to be unbound. These observations are compared to mass predictions.

Abstract: Spatial isotopic separation of relativistic uranium projectile fragments has been achieved for the first time. The fragments were produced in peripheral nuclear collisions and spatially separated in-flight with the fragment separator FRS at GSI. A two-fold magnetic-rigidity analysis was applied exploiting the atomic energy loss in specially shaped matter placed in the dispersive central focal plane. Systematic investigations with relativistic projectiles ranging from oxygen up to uranium demonstrate that the FRS is a universal and powerful facility for the production and in-flight separation of monoisotopic, exotic secondary beams of all elements up to Z = 92. This achievement has opened a new area in heavy-ion research and applications.

Abstract: Projectile fission of 238U was investigated at a bombarding energy of 750 A·MeV using a Pb target. Forward emitted fragments from 80Zn up to 155Ce were analyzed with the Fragment Separator (FRS) and unambigously identified by their energy-loss and time-of-flight. The magnetic selection of the largest momenta acted as a trigger of the low-energy fission component. More than forty new nuclear species were identified. The related isotopic production cross-sections are presented.

Abstract: The SIS accelerator facilities at GSI in combination with a magnetic spectrometer allow the direct measurement of stopping powers for relativistic heavy ions up to uranium with high precision for the first time. Here, we report our representative results obtained for projectiles up to xenon in the energy range from 700 to 1000 MeV/u. Systematic deviations from the Bethe stopping-power theory are observed, whereas the data are in good agreement with theory once Mott and Bloch corrections and the Fermi density effect are included.

Abstract: Low-energy fission of neutron-deficient actinium, thorium, protactinium and uranium isotopes has been investigated using a new experimental technique. The isotopes were produced as secondary beams by projectile fragmentation from a 950 A MeV 238U primary beam. Their fission was induced by electromagnetic excitation and nuclear reactions in a lead and in a plastic target at energies between 510 A MeV and 150 A MeV. The transition from symmetric fission is shown to take place around N = 138.

Abstract: Experimental data on energy deposition for argon, krypton and xenon ions in the energy range from 100 to 950 MeV/u passing through an ionization chamber filled with an Ar (90%) + CH4 (10%) gas mixture of thickness equivalent to 60 mg/cm2 of argon are reported. Measured values are compared with the proposed model of energy deposition and with the model of Badhwar and Adams et al. The observed data support the picture of the escape of high energy δ rays from the active detector volume.

Abstract: A description of peripheral nuclear collisions at high energies in terms of quasi-free nucleon-nucleon collisions is proposed. The statistical removal of nucleons from diffuse nuclear-density distributions is formulated in the framework of the abrasion model. Based on the nucleon-nucleon cross sections, energy-dependent partial and total abrasion cross sections are obtained. The total abrasion cross section is found to be equivalent to the total interaction cross section resulting from a microscopic Glauber-type calculation. In contrast to geometrical and optical abrasion models, the statistical abrasion formalism describes the fluctuations of the prefragment neutron-to-proton ratio without need for further assumptions. The predictions of the statistical abrasion model are compared to experimental data.

Abstract: The isotope 52Ni has been produced by fragmentation of a 58Ni beam at 68 MeV/nucleon on a nickel target and separated using the LISE spectrometer at GANIL. We have measured the half-life of 52Ni and the energies of β-delayed protons emitted during the decay. Two proton lines have been observed at Ep=1.06±0.05 MeV and 1.34±0.06 MeV with branching ratios of 0.06±0.01 and 0.11±0.01, respectively. The measured half-life of 52Ni is T1/2=38±5 ms. A partial decay scheme is proposed.

Abstract: The longitudinal-momentum distributions of projectile fragments from 0.8 A GeV136Xe and 1 A GeV197Au projectiles impinging on targets of beryllium and aluminium, respectively, have been measured using the projectile-fragment separator FRS at GSI. Different momentum distributions have been found for two different classes of fragmentation processes: the abundant hot fragmentation with several nucleons evaporated from the prefragments, and the rare cold fragmentation with only protons removed from the projectile, but no nucleons evaporated. The data are compared to model calculations.

Abstract: The development of 207Pb, 208Pb and 209Bi target wheels and their applications in heavy-ion fusion reactions are reviewed. In both fabrication and use, the centers of the evaporator or accelerator beams are focussed at wheel radii of 155 mm to specially shaped frames which generate very homogeneous target layers and very constant reaction and counting rates in the experiment. Target areas of up to not, vert, similar98% of a wheel's circumference of 974 mm can be provided. The preparation procedures for the necessary C backings and protecting layers of C are described, and details are given for the development of high-vacuum evaporations of 207Pb, 208Pb and 209Bi with deposition yields of 35�55% from tantalum crucibles. Applications of the target wheels in heavy-ion fusion reactions with beams of 54Cr and 58Fe at energies near the Coulomb barrier and intensities of not, vert, similar1012 particles/s are reported. The target parameters for the production runs of the new chemical elements 107Ns, 108Hs and 109Mt are included.

Abstract: Cross sections of iridium and platinum isotopes have been measured, which were produced as fragments from 197Au projectiles interacting with aluminum target nuclei at 1 A GeV. The fragments were identified by a kinematic analysis (�E�B�-time-of-flight) and by an ion-optical separation at the projectile-fragment separator FRS at GSI. Indications are found for high excitation energies and weak proton-neutron correlations in the peripheral nuclear-collision process.

Abstract:

Abstract: Total interaction cross sections have been measured for 8Li on C and Pb targets, for 9Li on C, Al, Cu, Sn and Pb targets, as well as for 11Li on C, Sn and Pb targets at about 80 MeV/nucleon. In addition, 2n-removal cross sections for 11Li have been extracted. These measurements are used to determine the nuclear and the electromagnetic part of the cross sections for the different projectile-target combinations. The experimental results are compared to different model calculations. These comparisons allow one to draw conclusions on the matter density distribution of the neutron-rich lithium isotope 11Li. By comparing our data on the electromagnetic dissociation of 11Li with all the other data available in the literature, we are able to put constraints on the dipole-strength distribution in 11Li.

Abstract: Excitation functions in the vicinity of the Coulomb barrier have been measured for the formation of evaporation residues in100Mo-induced fusion reactions with90, 92, 96Zr,92, 96, 98, 100Mo,104Ru and110Pd as well as for the system96Zr+96Zr. From these data the fusion probability in central collisions was extracted covering a range of 4 orders of magnitude. At the fusion barriers expected from systematics we find that the fusion probability is suppressed by one to three orders of magnitude. It is rising very gradually at higher energies and reaches for the heaviest systems saturation only at energies as high as 30 MeV above the barrier. The observed hindrance of the fusion process increases roughly with the growing Coulomb repulsion between the collision partners, but there is also a distinct influence of their individual nuclear structure. The data are compared to the extra-push model, the surface-friction model and the diabatic fusion model. A parameterisation of the extra-push energy and its fluctuation in terms of a macroscopic quantity like the Coulomb repulsion combined with a microscopic quantity characterizing the nuclear structure is proposed. As a byproduct of this work a new alpha emitter,191Po, could be identified. Its half-life is (15.5 �2.5 +6 ) ms, the alpha energy is (7314±20) keV.

Abstract: The projectile-fragment separator FRS, recently installed at the heavy-ion synchrotron SIS18 at GSI, was used to measure the formation cross sections and longitudinal-momentum distributions of fragments produced by removing one, two or three protons from 0.8 GeV· A 136Xe and 1 GeV · A 197 Au projectiles impinging on targets of beryllium and aluminum, respectively. These data gave direct information on the high-energy nuclear collision with only little contribution from evaporation processes. The measured cross sections decrease by more than one order of magnitude per proton removed. They are well reproduced by the predictions of a statistical abrasion model and an intranuclear-cascade calculation. The momentum distributions are found to be much broader than predicted by empirical systematics. They are, however, in agreement with the momentum distribution of the abraded protons as calculated with the uniform-Fermi-gas model, if Fermi momenta as measured by quasi-elastic electron scattering are used.

Abstract: A method for calculating the motion of an ensemble of beam particles through an ion-optical system is presented. The collective motion of the ensemble which covers a finite phase-space volume is described by an analytical transformation of the corresponding particle density distribution in phase space. This density distribution is represented by a convolution of generating functions. It is transformed by applying the ion-optical matrix formalism tto the generating functions. Physical effects acting on the particle ensemble on its way through the ion-optical system are taken into account by additional generating functions. This method allows to calculate rare processes in ion-optical systems with low computational effort.

Abstract: The projectile fragment separator FRS designed for research and applied studies with relativistic heavy ions was installed at GSI as a part of the new high-energy SIS/ESR accelerator facility. This high-resolution forward spectrometer has been successfully used in first atomic and nuclear physics experiments using neon, argon, krypton, xenon, and gold beams in the energy range from 500 to 2000 MeV/u. For the first time relativistic xenon and gold fragments have been isotopically separated. In this contribution we describe first experiments characterizing the performance of this spectrometer.

Abstract: At the fragment separator FRS at GSI, relativistic secondary beams with nuclear mass numbers 50 less-than-or-equals, slant A less-than-or-equals, slant 62 were produced by the fragmentation of a 1 A circled dot operatorot GeV 86Kr beam in a 9Be production target. The nuclear charge and mass numbers of the secondary-beam particles were determined by a ��t.o.f�B-rho measurement. The fragmentation of stable and neutron-deficient manganese, iron, cobalt and nickel isotopes in a composite carbon-hydrogen target, placed behind the separator, was investigated. The element distributions of the secondary-fragmentation products were found to depend strongly on the neutron-to-proton ratio of the projectile. Calculations with a statistical abrasion model allow an explanation of the observed features by means of the different influences of the neutron-to-proton ratio of the projectile on the abrasion and ablation steps of the fragmentation reaction.

Abstract: Total charge-changing cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets, as well as for11Li on C, Sn and Pb targets at about 80 MeV/nucleon. These data are compared to measured total reaction cross sections and Glauber-type calculations using Hartree-Fock density distributions. These comparisons allow to draw conclusions on the proton density distribution of the neutronrich lithium isotopes. The results show that even for the most exotic nucleus11Li the proton distribution is only very weakly influenced by the long tail in the neutron density distribution already established in several experiments.

Abstract: The performance of the newly commissioned heavy-ion synchrotron SIS 18 is investigated. The fragment separator provides access to all six phase-space coordinates of the slowly extracted ion beam. Transverse beam emittances were found to be εxx� = 1.8� mm mrad and εyy� = 4.0� mm mrad for 40Ar at 1 GeV/nucleon. A change in longitudinal momentum over extraction time is discussed. The stability of mean position and angle during resonance extraction is investigated.

Abstract: At GSI accelerator beams are now available from 0.045 to 2000 MeV/u; therefore heavy-ion targets of a wide variety have to be prepared in thicknesses from not, vert, similar 2�10�3 to not, vert, similar 5�104 mg/cm2. Range values of 238U beams in various targets for energies up to 1 GeV/u are illustrated as well as ranges of 1-GeV/u projectiles in some targets, and practicable target thicknesses for relativistic ions are discussed. The new water-cooled target system with target screws and the ion-optical fragment energy degrader system consisting of plane plates, wedged plates and wedged discs to be used in the fragment separator are described in detail.

Abstract: The fusion of the massive systems110Pd+104Ru and110Pd+110Pd was uniquely identified by observing the a decay of the evaporation residues. The observed distribution of the fusion cross section on the different evaporation-residue channels is in clear contradiction to calculations based on the compound-nucleus model. As a possible explanation the precompound evaporation of a particles is proposed.

Abstract: 18C has been produced as a projectile fragment in the interaction of a 60 MeV/u 22Ne beam with a thick beryllium + carbon target. Using the LISE spectrometer of GANIL tuned according to the PFIS method allowed an unprecedented measurement of its β-delayed γ spectroscopy, along with redetermination of half-life and β-neutron branching ratio. A partial decay scheme is proposed. A comparison with theoretical predictions provides a qualitative understanding of the decay of 18C.

Abstract: In parallel to the attempts to synthesize the heaviest nuclei, systematic studies have been made to obtain better understanding of the reaction aspects. The most comprehensive data have been taken for nearly mass-symmetric massive systems. They combine high Coulomb forces in the entrance channel with evaporation-residue cross sections which are high enough to be easily detectable. With these systems, rather cold compound nuclei can be produced, and even radiative fusion was observed. While one of the most salient features of the thoroughly studied fusion of light and medium-heavy systems is the enhanced sub-barrier fusion, the massive systems exhibit a considerable deficit of fusion above the expected potential barrier. This hindrance to fusion may be attributed to the dynamical evolution of the composite system which may lead to immediate reseparation. The experimental data reveal that the hindrance to fusion is strongly influenced by the nuclear structure of the reaction partners. The high fission competition in the evaporation cascade of fissile excited compound systems as deduced from measured evaporation-residue cross sections is compared with the expectations of the statistical model. Experimental evidence is presented.

Abstract: The nuclear fragmentation reaction is studied as an important production mechanism for secondary beams. The geometrical abrasion model and a macroscopic evaporation model which describe the two steps of the reaction are reexamined. Several improvements and modifications of these models are discussed and a new model description incorporating these elements is proposed. In particular, the excitation energy and the angular-momentum distribution of the prefragments, the formulation of evaporation as a diffusion process and the role of microscopic structure in the production cross section are considered. The new model description preserves the simplicity and the transparency of the original models. The prediction of the new model are compared to those of the original models and to experimental cross sections. While the original models showed several systematic discrepancies in comparison to measured cross sections, the new model is able to reproduce the whole body of experimental data with satisfactory agreement.

Abstract: For the compound nucleus179Au formed at an excitation energy of 26 MeV in the fusion reaction90Zr+89Y, the energy spectra of promptly emitted protons,agr particles andgamma rays were measured in concidence with the evaporation residues. On the basis of the measured total decay energy, the 1p and 1agr decay channels were separated from all other evaporation-residue channels. The energy spectra and absolute cross sections, together with previously measured excitation functions for various decay channels, are successfully described by statisticalmodel calculations with the Monte Carlo code CODEX.

Abstract: In the fusion reactions90Zr(89Y,p)178Pt and90Zr(89Y,agr)175Ir the sum energy of all emittedgamma rays as well as the energy of the promptly emitted charged particle were measured. From these data the mass-excess values for the evaporation residues178Pt and175Ir were extracted to beDelta(178Pt)=(�32.4±1.1)MeV/c2 andDelta(175Ir)=(�32.0±1.2) MeV/c2. The method provides absolute mass values for nuclides far from stability which can be produced in fusion reactions as evaporation residues in the 1p or 1agr channel. The sources of the experimental uncertainties of the method are discussed, and the potential for considerable improvements is outlined.

Abstract: Total interaction cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets as well as for11Li on C, Sn and Pb targets. For each beam, we also used a plastic scintillator as target. The measurements with the scintillator targets are used to extract reduced nuclear radii of the lithium isotopes. These radii are then used for the calculation of the nuclear part of the total cross section for the other targets. The total electromagnetic-dissociation (EMD) cross sections have been deduced and are compared to different models. A strong target-charge-dependent EMD cross section is measured for11Li reaching 2.96 �0.82 +0.84 b for the Pb target. In the9Li case, a large EMD cross section for high-Z targets has been observed which amounts to 0.75 ± 0.45 b for the Pb target. The EMD cross sections of both,9Li and11Li, may be understood by the giantdipole-resonance model.

Abstract: Using the magnetic spectrometer SPES I at SATURNE, energy-loss measurements have been performed for projectiles of 40Ar (401 MeV/u), 36P (362 MeV/u), 15N (149 MeV/u), 11Li (131 MeV/u) and 8Li, 9Li (130 MeV/u) in carbon, aluminum and lead targets. The experimental results are compared to calculations based on a modified relativistic Bethe formula and to a semiempirical formula using a Z2 scaling law for the stopping power and an effective charge parametrization for the heavy ions.

Abstract: Projectile fragments were produced with a 403 MeV/u 40Ar beam from the SATURNE accelerator in a thick carbon target. By use of the spectrometer SPES I in combination with a shaped energy-degrader, a clean secondary beam of 36P was separated. The results of this first application of a momentum-loss achromat to relativistic projectile fragments confirm model calculation published previously. In particular, several experimental values for the energy loss and the energy-loss straggling have been found to agree with the predictions. The amount of cross-contaminants originating from secondary reactions proved to be very small. As an additional separation tool a range telescope has been successfully tested.

Abstract: The beta-gamma spectroscopic study of22O is presented. This nucleus, produced as a projectile-like fragment from the interaction of a 60 MeV/n40Ar beam with a Be target, has been separated by the LISE spectrometer. Several gamma rays from22O decay have been observed, from which a half-life of (2.25±0.15)s has been determined. Accurate excitation energies have been deduced for several states in22F. A partial beta decay scheme of22O has been established. Experimental results have been compared with shell model calculations.

Abstract: The progress in investigations of the heaviest known elements in the recent years was only possible with an elaborate target technology. Large area thin and homogeneous targets of Pb and Bi, mounted on a rotating wheel to allow high projectile currents, were used in the experiments performed at the velocity filter SHIP at GSI Darmstadt. Various techniques for the on-line monitoring of the targets will be described and their importance for the experiments will be discussed. The experimental results from the investigations of the heaviest elements will be summarized briefly.

Abstract: We identified two alpha-emitting isotopes of element 107 with masses of 261 and 262 respectively by parent-daughter correlations. For the isotope with mass 262 we found two transitions with (102±26) ms and (8.0±2.1) ms half-life, which we assign to the groundstate and to an isomeric transition, respectively. The half-life of the isotope with mass 261 is (11.8 �2.8 +5.3) ms. Spontaneous fission, which could be assigned to the decay of an isotope of element 107, was not detected in our experiments. This observation is in-line with our previous results, indicating a region of nuclei with strong microscopic stabilisation in the trans-actinides. Both new isotopes were produced by complete fusion of209Bi with54Cr. The production cross sections are (163±34) pb for262107 and (36 �14 +22 ) pb for261107

Abstract: Measured α-decay spectra of the isotopes 215Th and 213Ra were used to investigate the influence of energy summing of α-particles and conversion electrons, and Auger electrons, respectively, emitted after α-decays into excited daughter levels, on the shape of α-spectra. The isotopes were produced in heavy ion fusion reactions and were implanted into silicon surface barrier detectors after in-flight separation from the projectile beam. It was shown that the summing effects will cause (a) the occurrence of additional lines in the α-energy spectra and (b) a change in the relative intensities of α-lines belonging to the α-decay pattern of a certain isotope. The results for 215Th and 213Ra are used for a discussion of the α-decay properties of the isotope 255104 and its α-decay products 251No and 247Fm. Especially the large discrepancies of the α-energies of 247Fm measured in our experiments and literature values are interpreted as due to a summing between α and electron energies.

Abstract: Desirable and inevitable phase-space modifications for heavy ions propagating through matter and ion-optical systems are described. Some aspects of the interaction of energetic ions with matter incorporated in ion-optical devices and the use of profiled targets at relativistic energies are discussed. A variety of measured and calculated results is presented which demonstrates interesting applications, including the interaction of heavy ions under channeling conditions or with free electron targets, and the separation and implantation of radioactive beams. As examples, some of the new GSI projects are briefly presented which illustrate the growing importance of non-Liouvillian ion-optics.

Abstract: Shell effects are extracted in the following experimental quantities: mass, alpha-decay energy and half-life, spontaneous-fission barrier and lifetime. The heaviest even-even nuclei known experimentally, with Z = 92�108 are considered. This extraction is based on the Yukawa-plus-exponential model, used for the description of the macroscopic part of nuclear mass. The effects are found to be large; e.g. they increase the spontaneous-fission half-life of some nuclei by about 15 orders of magnitude. The sensitivity of these effects to changing the macroscopic model is discussed.

Abstract: Protons and α-particles emitted from the compound nucleus 179Auexcited to 26 MeV were detected in coincidence with the corresponding evaporation residues. The charged-particle spectra are shifted to lower energies than spectra from statistical-model calculations based on a spherical compound nucleus.

Abstract: The three nuclei 17B, 14Be, 19C have been produced and separated by the LISE spectrometer at GANIL. Half-lives and beta-delayed neutron multiplicities have been determined for these nuclei. The study of 17B has allowed us to observe for the first time the beta-delayed four-neutron decay mode with a branching ratio p4n=(4±3)�10�3.

Abstract: The experiment having led to the discovery of first isotopes of element 108, as published previously in Short Notes to this Journal [1, 2] are described and discussed in a final paper. Two isotopes of element 108 were produced by complete fusion of 207Pb and208Pb, respectively, with58Fe. Both isotopes are alpha-emitters. For the isotope with mass 265 three alpha-decay sequences were observed. The alpha-decay energy is (10.36±0.03) MeV, the half-life (1.8 �0.7 +2.2 ) ms. For the isotope with mass 264, which is the heaviest doubly even isotope known at present, the decay sequence of one atom was found. The measured half-life is (76 �36 +364 ) micro-s. Our experimental results point towards an enhanced stability of the heaviest elements against spontaneous fission, which was already observed for element 106.

Abstract: The application of the slowing-down process of relativistic heavy ions in a layer of matter in ion-optical devices is theoretically investigated. The modifications of the phase space of the ion beam due to the dissipative forces and the straggling phenomena are discussed. Methods are developed to study the properties of the momentum-loss achromat, an isotope separator consisting of an achromatic magnetic system with an energy degrader located in the intermediate dispersive focal plane. This device separates projectile fragments with respect to A and Z up to uranium over a wide energy range with an efficiency of the order of 50% and with separation times of several hundred nanoseconds.

Abstract: The thirteen above-listed isotopes have been produced at GANIL by fragmentation of a 40Ar beam at 60 MeV/nucleon. The LISE spectrometer allowed us to isotopically separate these nuclei. Beta-delayed gamma spectroscopy was carried out for the first time for eleven isotopes, and additional information was obtained for another two. More complete data and their interpretation will be presented in forthcoming papers.

Abstract: We have observed the decay of one atom of the doubly even isotope 108. We observed alpha-decay with a halflife, of (76 �36 +364 ) microseconds. The full alpha-decay energy could not be measured, as the alpha escaped the detector. With the knowledge of the halflife, an estimate on the alpha-decay energy can be made. From the formula of Rasmussen [9] and a reduced alpha-width of 1, a value which has been measured for 260-106 and also for the doubly even isotones of N=156, we obtain Q=(11.0 �0.3 +0.1) MeV. This value is higher than given by Moeller [10] (10.35 MeV), and agrees with that of Liran and Zeldes11 (10.9 MeV). A hindrance factor w-alpha of 0.5 increases the Q-alpha-value by 0.14 MeV. The mass excess of 264-108 follows as (120.0±0.3) MeV. The ground-state shell effect amounts to (�5.0±0.3) MeV using the macroscopic mass values of Ref. [10]. The formation cross section of (3.2 �2.6 +6.1 ) pb overlaps with the value of about 5 pb from Dubna for the 6 ms sf-activity mentioned initially but is considerably lower than an extrapolation from the reaction 58Fe (208Pb,n) 265-108 which gave 10 pb with the lower limit of 4 pb.

Abstract: The gamma rays emitted in the radiative fusion reaction 90Zr+90Zr�180Hg+xy were measured. No indication was found for a specific direct capture process associated with a high-energy gamma ray. The shape of the observed gamma spectrum is compatible with a statistical deexcitation of the compound nucleus.

Abstract: The gamma decay in the radiative fusion reaction 90Zr+90Z -> 180Hg+xgamma has been observed in an array of NaI detectors. States up to 6+ in the yrast sequence of 180Hg are tentatively assigned and suggest the coexistence of weakly oblate and strongly prolate nuclear shapes. The difference in potential energy between the two inferred shapes has dropped to about 200 keV, continuing the downward trend observed in the heavier even isotopes 188�182Hg.

Abstract: Excitation functions for evaporation residues were measured for the reactions 90Zr + 89Y, 90Zr, 92Zr, 96Zr, and 94Mo. Deexcitation by γ-radiation only was found for the compound nuclei 179Au, 180Hg, 182Hg and 184Pb. Fusion probabilities as well as fusion-barrier distributions were deduced from the measured cross sections. There are strong nuclear-structure effects in subbarrier fusion. For energies far below the fusion barrier, the increase of the fusion probabilities with increasing energy is found to be much steeper than predicted by WKB calculations. As a by-product of this work new alpha-spectroscopic information was obtained for neutron-deficient isotopes between Ir and Pb.

Abstract: The isotopic separation of intermediate-energy (30 to 100 MeV per nucleon) heavy-ion projectile fragments is theoretically and experimentally investigated. Physical separation of nuclides is achieved through magnetic analysis (Image sensitivity) and differential stopping-power effects (Z² sensitivity). Depending on the specific case, a complete mass and charge separation may be achieved or a few nuclides may be selected simultaneously. The projectile fragments isotopic separation method described allows us to obtain an experimental mass separation A/Delta_A of approximately 100. Simple formulae are given to determine the optimum factors for the best separation and transmission of the device. First applications to the spectroscopy of exotic nuclei lead to the new observation of the beta decay of 37P at GANIL and 15B at CERN.

Abstract: Evaporation residues produced in heavy-ion fusion-reactions of 50Ti and 207Pb, 208pb have been investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into position-sensitive surface-barrier detectors, where their alpha decay or their decay by spontaneous fission was measured. The production of weakly excited compound nuclei in reactions of projectiles and targets close to the doubly magic 48Ca and 208Pb was confirmed by the observation of the 1n deexcitation channel in the reaction 50Ti +208Pb. The spontaneous fission activities of 255-104 and 256-104 could be confirmed; improved halflives are (1.4 �0.2 +0.2 )s and (7.4 �0.7 +0.9 )ms. Furthermore alpha-decay of 255-104 (b-alpha =0.48 ±0.07) and an indication for a small alpha-branch (b-alpha = 0.022 �0.018 +0.073 ) of 256-104 was found. A total kinetic energy of (207±13)MeV released in spontaneous fission of 256-104 was measured. A statistical model analysis of the evaporation-residue cross sections is shown to give evidence for a dynamic hindrance to complete fusion in the system 50Ti + 208Pb, as well as for non-equilibrium components in the deexcitation mechanism.

Abstract: Evaporation-residue excitation functions for the reactions 86Kr + 70,76Ge, 92,100Mo, 99,102,104Ru have been measured using activation methods and the velocity filter SHIP. The data span the region from well below the fusion barrier up to, and beyond, the energy where limitation by fission competition takes place. The data are shown to be compatible with the concept of complete fusion followed by the statistical decay of the equilibrated compound nucleus. Information on both the fusion probability at and below the fusion threshold and the fissionability of the compound nuclei formed, is extracted. The model dependence of the extracted fission barriers is discussed in detail. In analogy to studies involving lighter projectiles, strong correlations between the low-energy nuclear-structure properties of the nuclei and the subbarrier fusion probability are found. A relative shift of the fusion barrier to higher energies, that increases with the number of valence neutrons in the target nuclei, is observed.

Abstract: Fusion excitation functions for the systems 40Ar + 112, 116, 122Sn and 40Ar + 144, 148, 154Sm have been determined, covering cross sections ranging from several hundred mb down to the μb level. The data show a pronounced correlation of the subbarrier behaviour with low-energy collective properties of the nuclei involved and are well reproduced by simplified coupled-channel calculations coupling fusion to inelastic channels. The possibilities of parameterizing the data in terms of a simple dynamic barrier-fluctuation phenomenon are discussed and result in the prediction of remarkably diffuse partial-wave distributions above the barrier. This is shown to be important for the analysis of deexcitation phenomena following fusion reactions.

Abstract: In irradiations of 207Pb and 208Pb, respectively, with54Cr the alpha-decay of the isotopes 259-106,260-106, and261-106 could be observed for the first time. For260-106 a spontaneous fission branch of (50 �20 +30 )% was observed. The isotopes were identified by genetic relationships of alpha-decay after separation in-flight with the velocity filter SHIP and implantation into a position-sensitive silicon surface-barrier detector. The measured partial fission halflife of the doubly even isotope260-106 of (7.2 �2.7 +4.8 )ms exceeds the predicted values by at least a factor of 40. This result could be explained by the high shell corrections of the ground state mass, derived from the measured alpha-decay energies. The experimental results show evidence for an island of purely shell stabilized nuclei in the region of deformed isotopes beyond the actinides.

Abstract: Evaporation residues from the heavy-ion fusion reaction50Ti on209Bi were investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into an array of position-sensitive surface-barrier detectors by analyzing theiragr-decay chains. Spontaneous fission was also observed. Four newagr emitters,258105 (T1/2=4.4 �0.6 +0.9 s),257105 (T1/2= 1.4 �0.3 +0.6 s),254Lr (T 1/2= 13 �2 +3 s), and253Lr (T 1/2=1.3 �0.3 +0.6 s) could be identified. For the isotope257105 we obtained a spontaneous-fission branch of about 20%. A spontaneous-fission activity with a halflife comparable to that for theagr decay of258105 was explained as fission of258104, formed by electron capture from258105. An excitation function for evaporation-residue production was measured for bombarding energies in the range of E_CM=184.4 MeV to E_CM=196.6 MeV. Nearly all evaporation residues we observed, could be attributed to the 1n and 2n deexcitation channels. The maximum cross sections were sigma(1n)=(2.9±0.3) nbarn, and sigma(2n)=(2.1±0.8) nbarn, respectively. We could measure the total kinetic energy of the fission fragments of 258-104 to be TKE=(220±15) MeV, a value that fits into empirical systematics based on a Z^2/A^1/3 dependence.

Abstract: Cross sections were measured for the formation of evaporation residues in 48Ca-, 86Kr- and 124Sn-induced reactions with Yb, Sb and Zr isotopes. For the nearly symmetric systems, the energy dependence of the fusion probability in central collisions was determined. The fusion probability at the expected fusion barrier as calculated from a one-dimensional heavy-ion potential was found to be reduced by several orders of magnitude. The fusion cross sections increase gradually, and only at energies appreciably above the expected fusion barrier the major part of the cross section of central collisions leads to fusion. The observed hindrance of the fusion process is compared with model predictions.

Abstract: For the reactions 40Ar + 165Ho. 169Tm, 174Yb. 115Lu, 176�180Hf, 181Ta, 208Pb and 50Ti + 208Pb, 209Bi the cross sections for the fusion-fission process were determined by measuring energy and time-of-flight of the reaction products. In addition, the neutron-evaporation-residue cross sections were measured by using the velocity filter SHIP. A � versus 1/E analysis of the fusion-fission cross sections is used to determine fusion barriers and fusion radii. The evaporation- residue cross sections are used to extract in an approximate way barriers for compound-nucleus formation. These barriers are found to agree with the fusion barriers determined from the fission cross sections. For all systems investigated the neutron-evaporation-residue cross sections reach their maximum close to the fusion barrier as calculated from the Bass potential.

Abstract: Cross sections for compound residues from the fusion reaction 90Zr+90Zr were measured. No "extra push" is necessary to describe the data. Below the fusion barrier, the cross section decreases much faster than observed previously in 40Ar-induced fusion reactions with tin and samarium targets. The present data are incompatible with recently published data for the same system.

Abstract: An experiment to synthesize element 109 is presented. Decay patterns characteristic of complete fusion products were searched for in an irradiation of 209Bi targets with 58Fe projectiles at specific incident energies of 4.95, 5.05, and 5.15 MeV/u. A total dose of 7 �10^17 particles was obtained. The experimental method involves in-flight separation of forward peaked reaction products with a static-field velocity filter, their passage through a time-of-flight device and their final implantation into position sensitive solid state detectors to measure their kinetic energy, approximate mass and their time and position of incidence. The subsequent decay of the narrowly localised reaction products by cascades of alpha particles and/or spontaneous fission is also registered in terms of the energies and times of all the emitted particles. One outstanding decay sequence that started with the emission of two alpha particles within subsequent time intervals of 5 ms and 22 ms and ended with spontaneous fission after 13 s was found at 5.15 MeV/u. The first alpha particle had a kinetic energy of (11.10±0.04) MeV. A detailed analysis of all the alternative interpretations of this observation, such as a purely random correlation of signals, the decay of a product from a transfer reaction or of any of the various energetically possible evaporation residues, shows that the isotope with mass 266 of element 109, i.e. the one neutron evaporation channel after complete fusion, is the statistically most significant assignment. The outlook for new element synthesis is also briefly discussed.

Abstract: In fusion reactions of 40Ar with isotopes of Ho, Tm, Yb, Lu, Hf, and Ta, cross sections for the production of proton-rich evaporation-residues near the 126 neutron shell were measured. This first comprehensive study of very fissile spherical residues reveals a surprisingly low stabilizing influence of the spherical N=126 shell on the survival probability. The experimental results are compared with evaporation calculations. Conclusions for the production of superheavy nuclei are drawn.

Abstract: A prescription for the error analysis of experimental data in the case of stochastic background is formulated. Several relations are given which allow to establish the significance of mother-daughter relationships obtained from delayed coincidences. Both, the probability that a cascade is produced randomly and the probability that the parameters of an observed event chain are incompatible with known properties of a given species are formulated. The expressions given are applicable also in cases of poor statistics down even to single events.

Abstract: The interplay of shell structure and rotational motion in the nuclear level density is discussed. The result of a schematic calculation reveals a washing out of spherical shell effects at much lower excitation energies than expected if only the intrinsic level density in the independent particle model is considered.