Angular momentum population in the projectile fragmentation ofU238at750MeV∕nucl

Abstract

A systematic study of the population probabilities of nanosecond and microsecond isomers produced following the projectile fragmentation of 238 U at 750 MeV/ nucleon has been undertaken at the SIS/FRS facility at GSI. Approximately 15 isomeric states in neutron-deficient nuclei around A ϳ 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 ␥ 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.

Properties of γ -decaying isomers and isomeric ratios in the Sn100 region

“…The experimental isomeric ratios R exp were compared to theoretical predictions R theo as described in other experimental literature with various primary beam energies and projectile masses of fragmentation reactions [46,65,66]. The initial step of the theoretical calculations involves the final spin distribution of the fragments.…”

“…The parameter ν is the mean number of evaporated nucleons per abrasion of one nucleon which varied depending on the projectile nuclei and the primary beam energy. ν = 2 was assumed for primary beams of 750 MeV/u 238 U [66] and 1 GeV/u 208 Pb, while ν = 0.5 was used for a 60 MeV/u 92 Mo beam [65]. In comparison to the cited works, the 345-MeV 124 Xe beam used in this experiment has intermediate quantities in both mass and energy.…”

Application of isochronous mass spectrometry for the study of angular momentum population in projectile fragmentation reactions

“…Recently, isomeric yield ratios have been obtained from γray spectroscopy investigations of angular momentum population of projectile fragments [9][10][11][12][13][14][15][16][17][18]. γ-ray spectroscopy is a powerful technique, which provides valuable contributions to nuclear structure investigations.…”

“…γ-ray spectroscopy is a powerful technique, which provides valuable contributions to nuclear structure investigations. However, it is typically limited to studies of excited states with half-lives between about 100 ns and several milliseconds [10,11]. The lower half-life limit is given by the time of flight through a beam line and the upper limit is determined by the need to correlate delayed γrays with individual ions in a segmented implantation detector with a technologically limited number of pixels [11].…”

“…The question of how the isomeric yield ratio depends on the mass loss is not only related to the understanding of the origin of angular momentum, but plays also an important role in the production and application of isomeric beams [31] as well as spin-aligned beams [32]. In previous works [9][10][11][12][13][14][15][16][17][18], nuclides with the same spin had different structure and different isomer excitation energies, which masked a possible dependence of the isomeric ratios versus the mass loss [11,33]. Thus, in order to remove the nuclear structure effects, we use the isomeric ratio values of the high-spin isomeric 19/2 state in 53 Fe produced using different projectiles: 58 Ni (Ref.…”