Dynamical model calculation to reconcile the nuclear fission lifetime from different measurement techniques

Abstract

The pre-scission particle multiplicities suggest a lifetime of ∼ 10 −20 s for the nuclear fission to occur which is in contrast to the fission lifetime ∼ 10 −18 s as predicted by atomic probe. This long standing ambiguity, arising due to the orders of magnitude differences among the fission lifetime measured from the nuclear and atomic probes, has been addressed within a dynamical model which includes the contributions from the nuclear shell effects. We show that, at lower excitation energies, these two probes decouples as the fissioning system survives for a long time without any particle evaporation. We also consider a wide range of reactions to study the impact of the excitation energy of compound nucleus on the fission dynamics in general. Our model predicts the average fission life time of superheavy nucleus 302 120, to be more than 10 −18 s which is in reasonable agreement with the recent experiments.

Inference on fission timescale from neutron multiplicity measurement in 18O + 184W

“…We demonstrated the average fission time τ f in figure 4 and, as expected from the distributions in figure 3, τ f is strongly underestimated by τ nl . These results support the findings of reference [26] and reconfirm the importance of dynamics in predicting the actual fission lifetime τ f which is extracted here in coherence with the measured value of ν pre .…”

“…Specifically, as we have shown below, neutron multiplicity apparently predicts a shorter survival time [26] of a CN due to the lack of proper accounting of the post-neutron-emission delay. As claimed in reference [26], this perhaps resolves the long-standing discrepancy between the nuclear (neutron clock) and atomic (x-ray and crystal blocking techniques) [29][30][31][32][33] probes that prevents a conclusive determination of fission timescales.…”

“…Next, the time evolution of the compound nuclei is studied by using a one-dimensional Langevin dynamical model [26,45] governed by the Langevin equations,…”

“…Moreover, neutron emission is in general more probable compared to any charge-particle decay which is always suppressed by the Coulomb barrier [25]. Therefore, pre-scission neutron multiplicity is often used as a clock [26] to measure fission lifetime: the time taken by a CN to decay into two fission fragments. The critical part in such a measurement is the extraction of fission lifetime from the experimental multiplicities requires realistic modelling of the whole decay process, which is often accomplished within an approximate statistical prescription [27,28].…”

“…The critical part in such a measurement is the extraction of fission lifetime from the experimental multiplicities requires realistic modelling of the whole decay process, which is often accomplished within an approximate statistical prescription [27,28]. Specifically, as we have shown below, neutron multiplicity apparently predicts a shorter survival time [26] of a CN due to the lack of proper accounting of the post-neutron-emission delay. As claimed in reference [26], this perhaps resolves the long-standing discrepancy between the nuclear (neutron clock) and atomic (x-ray and crystal blocking techniques) [29][30][31][32][33] probes that prevents a conclusive determination of fission timescales.…”