E. Hanelt

Projectile fission at relativistic velocities: a novel and powerful source of neutron-rich isotopes well suited for in-flight isotopic separation

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.

Distribution of Ir and Pt isotopes produced as fragments of 1 A GeV 197Au projectiles: a thermometer for peripheral nuclear collisions

Abstract Cross sections of iridium and platinum isotopes have been measured, which were produced as fragments from 197 Au projectiles interacting with aluminum target nuclei at 1 A GeV. The fragments were identified by a kinematic analysis ( ΔE − Bρ -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.

Breakdown of the compound-nucleus model in the fusion-evaporation process for110Pd+110Pd

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.

Momentum distributions of projectile fragments produced in the cold and hot fragmentation of relativistic136Xe and197Au projectiles

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.

Low-energy fission investigated in reactions of 750 AMeV238U-ions with Pb and Be targets

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.

Few-neutron removal from238U at relativistic energies

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.

Beta-delayed proton spectroscopy of 24Si

Abstract In an experiment at the LISE3 facility of GANIL, we used the projectile fragmentation of a 36 Ar primary beam at 95 MeV/nucleon to produce the isotope 24 Si. The beta decay half-life of 24 Si has been determined to be T 1/2 = (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 24 Si. These results are compared with shell-model predictions.

Separation and implantation of relativistic86Kr-fragments at the FrS; half-life measurement by ion-? time-correlations

Neutron-rich Co and Fe isotopes produced by86Kr projectile fragmentation at 500 MeV/u were separated and identified using the fragment separator (FrS) in a bunched energy mode.66Co and65Fe ions were selectively implanted in a double PIN-diode array where theβ-decay signals were measured. The half-lives were deduced from time correlations between implantation andβ-decay signals. The remeasurement of the66Co half-life confirms the isotope identification. The value of the65Fe half-life was found to be 0.45±0.15 s.

Decay of the compound nucleus179Au formed in the cold fusion reaction90Zr+89Y

For the compound nucleus179Au formed at an excitation energy of 26 MeV in the fusion reaction90Zr+89Y, the energy spectra of promptly emitted protons,α particles andγ rays were measured in concidence with the evaporation residues. On the basis of the measured total decay energy, the 1p and 1α 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.

Spectroscopic measurements with a new method: The projectile‐fragments isotopic separation

A new method for the isotopic separation of projectile fragments is exposed. The application to the LISE spectrometer at GANIL provided radioactivity data on light neutron‐rich nuclei (mass range 14–40). The observation on 17B of the beta‐delayed four neutron decay mode is reported for the first time.