Fragment mass distributions in the fission of heavy nuclei by intermediate- and high-energy probes

Abstract

Recent experiments have shown that the multimode approach for describing the fission process is compatible with the observed results. A systematic analysis of the parameters obtained by fitting the fission-fragment mass distribution to the spontaneous and low-energy data has shown that the values for those parameters present a smooth dependence upon the nuclear mass number. In this work, a new methodology is introduced for studying fragment mass distributions through the multimode approach. It is shown that for fission induced by energetic probes (E > 30 MeV) the mass distribution of the fissioning nuclei produced during the intranuclear cascade and evaporation processes must be considered in order to have a realistic description of the fission process. The method is applied to study 208 Pb, 238 U, 239 Np and 241 Am fission induced by protons or photons.

Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission

“…Also, as shown in Figure 3, the excitation energy of the fissioning nuclei are in many cases around hundreds of MeV, and the parameters are not determined at these energies. In the present work we extend the analysis performed in Ref [17] and discuss also the possibility of symmetric fission dominance at high energies. It was believed that at low energies fission should be predominantly asymmetric, while at high energies the symmetric mode should be dominant because at these energies the effects due to nuclear structure would be washed out.…”

“…In recent papers [17,18] we discussed about the effects of the mass-and energy-distributions on the final fragment mass distributions. We have shown that in fission induced by high energy probes, as protons and photons, the fissioning nuclei are quite different from the target nucleus due to the emission of particles during intranuclear cascade and during the evaporation steps before fission occurs.…”

“…In [17,18] we have shown how to unfold the contributions due to fission modes and to fissioningnuclei distribution in the fragment-mass distribution by using Monte Carlo method. CRISP is a Monte Carlo code for simulating nuclear reactions [20] that uses a two step process.…”

“…For the other parameters, the values from the systematics [6] are used. Following [17], the second calculation (Type 2) is performed by using for K S , K 1 and K 2 the values found by Demekhina et al and Karapetyan et al [15,16], presented in Table 1 (lower part), to calculate the corresponding probabilities through equation (5), while keeping all other parameters unchanged. Finally, a third calculation (Type 3) is performed considering the probabilities p (S,1,2) as gaussian functions of the fissioning nucleus mass number, which are obtained by fitting the systematic values from Böckstiegel et al [6] and using linear extrapolation to lower masses (A < 220).…”

Evidence of subnucleonic degrees of freedom inJ/ψphotoproduction in ultraperipheral collisions at energies available at the CERN Large Hadron Collider

“…Both intranuclear cascade and evaporation/fission calculations with the CRISP model have been extensively investigated yielding good results for reactions induced by photons, electrons and protons and observables such as neutron or proton multiplicity, fission and spallation cross sections, and fragment mass distributions [14,16,17,[22][23][24][25][26][27].…”