https://doi.org/10.1140/epja/i2004-10130-9
Intranuclear-Cascade model calculation of photofission probabilities for actinide nuclei
1
Center for Nuclear Studies, Department of Physics, The George Washington University, D.C. 20052, Washington, USA
2
Institute for Nuclear Research, Russian Academy of Science, 117312, Moscow, Russia
* e-mail: briscoe@gwu.edu
Received:
11
August
2004
Accepted:
27
January
2005
Published online:
21
February
2005
We have calculated the fission probabilities for 237 Np, 233, 235, 238 U, 232 Th, and nat Pb following the absorption of photons with energies from 68 MeV to 3.77 GeV using the RELDIS Monte Carlo code. This code implements the cascade-evaporation-fission model of intermediate-energy photonuclear reactions. It includes multiparticle production in photoreactions on intranuclear nucleons, pre-equilibrium emission, and the statistical decay of excited residual nuclei via competition of evaporation, fission, and multifragmentation processes. The calculations show that in the GeV energy region the fission process is not solely responsible for the entire total photoabsorption cross-section, even for the actinides. The fission probabilities are 80-95% for 233 U, 235 U, and 237 Np, 70-80% for 238 U, and only 55-70% for 232 Th. This is because certain residual nuclei that are created by deep photospallation at GeV photon energies have relatively low fission probabilities. The results of those model calculations are in reasonable agreement (at the ∼ 10% level) with recent experimental data on relative photofission cross-sections for 237 Np and 233, 235, 238 U (but not for 232 Th or nat Pb) from the Saskatchewan and Jefferson Laboratories over a very wide range in photon energy. Using our calculated fission probabilities plus the total photoabsorption cross-sections per nucleon, estimated from previous cross-section data for nuclei from C to Pb, we can infer absolute photofission cross-sections for the actinide nuclei and compare them with the SAL and JLab results. The resulting discrepancies, however, clearly demonstrate the need for direct measurement of the total photoabsorption cross-sections for the heavy actinides.
PACS: 25.20.-x Photonuclear reactions – / 25.85.Jg Photofission – / 24.10.Lx Monte Carlo simulations (including hadron and parton cascades and string breaking models) –
© Società Italiana di Fisica and Springer-Verlag, 2005