Peter Armbruster

Shell effects in the properties of the heaviest nuclei

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.

Mass, charge, and energy distributions in very asymmetric thermal fission of 235U

Abstract The fission fragment separator “Lohengrin” of the Institut Laue-Langevin in Grenoble was used to determine the yields of the very asymmetric light fission products ( A = 84-69) as a function of A, Z, and the kinetic energy E. The proton pairing effect causes fine structures in the mass distribution, in the mean nuclear charge − Z and its variance σZ , and in the mean kinetic energies of the elements. The neutron pairing effect in the production yields is found for the first time of the same order of magnitude than the proton pairing effect. In the mass region investigated both are the largest observed in fission of 235 U . A decrease in the mean kinetic energy for the isotopes of Ni and Cu was observed. It points to a large deformation at scission. Our results support the view that very asymmetric low-energy fission is a weakly dissipative process. The highly deformed transient system breaks by a slow necking-in process.

Measurement of residual nucleus cross sections and recoil energies in p + Fe collisions at 300, 500, 750, 1000 and 1500 MeV

The production of residual nuclei in p + Fe collisions has been measured at GSI on the FRS facility by means of the reverse kinematic techniques at 300, 500, 750, 1000 and 1500 MeV/A. The cross‐sections larger than 0.01 mb of all isotopes with Z larger than 8 have been obtained. Velocity distributions were also measured. Comparisons to models describing spallation reactions and some empirical formulae often used in astrophysics are presented. These data are directly used to calculate impurety production and DPAs in a thin window as foreseen in spallation sources or accelerator‐driven systems.

Nuclide Cross‐Sections Of Fission Fragments In The Reaction 208Pb+p At 500 A MeV

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. 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 the experimental data, the characteristics of the average fissioning system can be reconstructed in charge, mass and excitation energy and the number of post‐fission neutrons can be inferred. The results are also compared to different models describing the spallation reaction.

Basic research at GSI for the transmutation of nuclear waste in Accelerator Driven Reactor Systems (ADS)

The still increasing and developing world population demands more energy. Further burning of coal, oil and gas produces still more CO2 deteriorating the climate. Anyhow, oil and gas will run out in the middle of the century. Planning a decent future with a minimum supply of energy for those who will follow us, requires re-examining all possibilities of non-polluting, renewable, and sustainable energies including nuclear options. There are two nuclear reactions which allow for a long-term exploitation: (i) converting H into He by fusion or (ii) converting U and Th into Pu and U to be burnt by fission. In this paper, the fission option is the target. The real long-term reserves of fission energy lie in the even-even isotopes U and Th, as the supplies of U, like fossil fuels, are restricted, as well. The remaining U and available Pu could be burnt in a 3 generation of reactors (EPR) using mixed U/Pu-fuel (MOX). Aiming at a contribution of fission energy to the world electricity production of one third, that is three times more nuclear power than today, reactors of a 4 generation should be envisaged, ready to wide technological applications in the middle of the century. Such an option could be foreseen as an implement of a peaceful future.

Measurements of spallation residues using inverse kinematics at GSI

The production cross sections and the kinematical properties of primary residual nuclei have been studied in reactions 197Au + p, 208Pb + p, d, 238U + p, d, and 238U + 208Pb at energies around 1 A GeV. 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.