Scission neutrons and other scission properties as function of mass asymmetry in U235(nth,f)

Abstract

The emission of scission neutrons is studied in the frame of the sudden approximation, i.e., under the assumption that fission motion is adiabatic until the neck ruptures at finite radius and that this rupture is followed by a sudden absorbtion of the neck pieces by the fragments. We are therefore dealing with a transition between two different nuclear configurations (${\epsilon }_i\to {\epsilon }_f$) and we only need to know the corresponding two sets of neutron eigenstates. The accent in the present work is put on the dependence on the mass asymetry $A_L/A_H$ of the primary fission fragments during the thermal neutron fission of ${}^{235}\mathrm{U}$. At ${\epsilon }_i$, i.e., just before scission, the neutrons are considered both independent and pairing correlated. We estimate the scission neutron multiplicity ${\nu }_{\mathrm{sc}}$, the spatial distribution of the emission points $S_{\mathrm{em}}(\rho ,z)$ and the primary fragments’ excitation energy $E_{\mathrm{sc}}^{*}$. ${\nu }_{\mathrm{sc}}$ is found to depend only slightly on $A_L$. The multiplicity has an average value of 0.76 (which represents one third of the prompt neutron multiplicity) with a maximum deviation from this value of less than 0.1. $S_{\mathrm{em}}(\rho ,z)$ is mainly concentrated in the region between the fragments giving a useful detail of the emission mechanism. $E_{\mathrm{sc}}^{*}$ together with the extradeformation energy is used to evaporate neutrons and emit $\gamma$ rays from fully accelerated fragments. DOI: http://dx.doi.org/10.1103/PhysRevC.82.014617 © 2010 The American Physical Society