Molecular-orbital study of late-fission times in deep-inelasticU238+

Abstract

The U-like AT-vacancy production probability in 7.5-MeV/nucleon deep-inelastic 238 U4-238 U collisions has been measured for no-fission, single-fission, and double-fission exit channels. The results are interpreted using quasimolecular orbital correlations for diatomic and triatomic configurations. This leads to the determination of lower limits for the time scale for late fission of U~like products (> 8 and > 4 as) and their probability (> 77% and > 52%), at mean initial-excitation energies of -40 and -105 MeV, respectively. PACS numbers: 25.70.Lm, 21.10.Tg, 25.85.Ge, 34.50.Fa PPAC FIG. details. 1. Schematic of the experimental setup. See text for

Nuclear temperatures from evaporation fragment spectra and observed anomalies

“…m. angular distribution for the heavier ions such as carbon are characteristics of statistical emission of the fragments [3,5] from an equilibrated compound nucleus. We have also studied the angle-integrated ratios of the yields of boron to carbon, beryllium to carbon and lithium to beryllium as a function of the exit channel excitation energy for both 16 In Fig. 14, we have overlayed the calculated (using the 'CASCADE' code) and the experimental alpha spectra from 16 O+ 89 Y reaction at E( 16 O) lab =96 MeV and find that the shapes of the calculated and experimental alpha spectra are almost identical.…”

“…We have also studied the angle-integrated ratios of the yields of boron to carbon, beryllium to carbon and lithium to beryllium as a function of the exit channel excitation energy for both 16 In Fig. 14, we have overlayed the calculated (using the 'CASCADE' code) and the experimental alpha spectra from 16 O+ 89 Y reaction at E( 16 O) lab =96 MeV and find that the shapes of the calculated and experimental alpha spectra are almost identical. A one source fitting of the experimental alpha spectrum (using eq.…”

“…We used the statistical model code 'CASCADE' [2] to calculate the spectra of the neutron, proton, alpha and heavier fragments from 16 O+ 89 Y reaction at E Lab ( 16 O) =96 MeV. In the 'CASCADE' code, the neutron, proton and alpha particles were the main particle emission channels and the lithium or boron or carbon particle was used as a fourth particle channel one at a time.…”

“…This is because the kinetic energies carried away by the heavy fragments are small compared to the excitation energy of the compound nucleus (E X = 212 MeV) and so the extracted temperatures from alpha and heavy ion fragments are about the same. The statistical model calculations were also performed for 16 O+ 93 Nb reaction at E Lab ( 16 O)=116 MeV and the evaporation spectra of alpha, lithium, beryllium, boron and carbon were generated using the statistical model codes ⎯ 'CASCADE' and 'GEMINI'. The calculated spectra were fitted with eq.…”

Long lifetime components in the decay of excited super-heavy nuclei

“…Considering the independent lifetimes of the electron vacancies and of the compound nucleus, sizable probabilities of X-ray fluorescence from the unified atom can only be observed when the compound nucleus lifetime is at least of the same order of magnitude as the vacancy lifetime. Nuclear lifetimes of excited uranium nuclei have been estimated with the fluorescence technique in good agreement [13,14] with those inferred from the blocking technique in single crystals [15]. Since the lifetime of a vacancy in the K shell of a super-heavy atom is of the order of 10 −18 s [16], the multiplicity of X K rays with an energy characteristic of the unified atom provides us with a sensitive probe for long lifetime components.…”