Speaker
Description
The problem of scission neutron emission during fission is addressed in a microscopic approach. During scission, the internal degrees of neutrons are coupled to the fast-changing potential. This coupling depends on the time of transition ∆T between a deformed nucleus with a very thin neck and two just separated fragments. Each neutron
becomes a wave packet with components in the continuum and it is therefore partially emitted.
We present here scission neutron emission for the most probable mass division of $^{235}$U(n$_{th}$,f): $A_{L}$/$A_{H}$ = 96/140. In the sudden approximation, the neck rupture is instantaneous (∆T = 0 s) and the coupling is extremely diabatic. In a realistic case, the duration of the rupture is finite (e.g., ∆T = 2x10$^{-22}$ s). To follow the evolution of neutron-occupied states during scission, we solved the two-dimensional time-dependent Schrödinger equation with time-dependent potential. Some physical quantities such as primary fragment excitation energy, multiplicity and mean kinetic energy value of scission neutrons could be extracted; they are compared to those obtained in the sudden approximation approach.
In the particular case of ∆T = 2x10$^{-22}$ s, the experimental average neutron multiplicity (2.4 n/fission) could be reproduced as a sum of calculated scission and evaporated components. The scission neutron contribution to the total neutron multiplicity amounts to 18 %.
In addition, scission neutron spectrum is found to possess a high-energy tail extending beyond the limit of the evaporation spectrum (10 MeV). Thus, the existence of scission neutrons could be the source of the high energy (10 to 18 MeV) fission neutrons observed through high threshold dosimetry reactions.
| Session | Nuclear Fission (prompt particle emission, fission yields) |
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