Description
It is well established that nuclear fission (the splitting of atomic nuclei) is strongly influenced by the quantum mechanical structure of the nucleus, determined by its constituent protons and neutrons. Nascent fission fragments with large energy gaps between nuclear states are more stable and therefore drive fission towards these configurations. An open question in nuclear fission is: why do the effects of nuclear shell structure persist at surprisingly large excitation energies? When the nucleus has significant excitation energy, it is expected that the effect of the shell structure should substantially diminish. However, experimental measurements observe the influence of shell effects up to tens of MeV of excitation energy. One contributing factor may be the rotational energy that the fissioning nucleus possesses due to its angular momentum, which reduces the excitation energy available for fission and extends the energy range where shell effects significantly affect fission characteristics.
To investigate this quantitatively, we present the results of experiments studying the fission of $^{172}$Os formed in $^{28}$Si+$^{144}$Sm reactions, performed at the Heavy Ion Accelerator Facility at the Australian National University. We combine precise measurements of the capture cross section for $^{28}$Si+$^{144}$Sm with high-statistics measurements of the fission mass distribution for this system at multiple energies. Using a statistical model for fission, we obtain detailed information about the distribution of angular momenta, and thus the rotational energy, of the compound system when it fissions. Alongside analysis of the shell effects present in the fission mass distribution, this provides new insights into interpreting the excitation energy dependence of fission.
| I am the presenting author | Yes |
|---|