Fission-Residues Produced in the Spallation Reaction 238U+p at 1 A GeV

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 DE-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 data.Comment: 60 pages, 21 figures, 4 tables, 2 appendices (15 pages

Nuclear-fission studies with relativistic secondary beams: analysis of fission channels

Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal 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 element number over the whole range of systems investigated.Comment: 16 pages, 3 figures, background information on http://www.gsi.de/charm

Electromagnetic-induced fission of 238U projectile fragments, a test case for the production of spherical super-heavy nuclei

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.Comment: 20 pages, 13 figure

Isotopic and isotonic effects in fission-fragment mass yields of actinide nuclei

AbstractFission-fragment mass distributions for the target nuclei 232Th, 233,235,236,238U, 238,239,240,242Pu, and 244Cm have been measured at an incident proton energy Ep=10.3 MeV, and proton and neutron-number distributions of the fragments have been deduced on the basis of the unchanged-charge-density assumption. It was revealed that the shape of the mass distribution in asymmetric fission strongly depends on the proton number of the compound nucleus and shows only a weak dependence on neutron numbers. It was shown that for nuclei with equal ZCN the asymmetric fission-fragment charge distributions practically coincide, i.e., they are almost independent on NCN. Moreover, for nuclei with equal NCN from isotonic pairs with NCN=144,146, and 148 the fragment neutron-number distributions vary with a change of ZCN. This behaviour of the mass, charge and neutron-number distributions is an evidence for the determinative influence of proton shells on the formation of fragments in asymmetric fission of actinide nuclei