Origin of the narrow, single peak in the fission-fragment mass distribution for $^{258}$Fm

TL;DR

This paper investigates the origin of the extremely narrow, single-peaked mass distribution in the spontaneous fission of $^{258}$Fm by employing a macroscopic-microscopic model and solving a Schrödinger equation with a microscopic inertial mass.

Contribution

It introduces a detailed microscopic model to explain the narrow mass distribution in $^{258}$Fm fission, linking potential energy and inertial mass to experimental observations.

Findings

Calculated mass yield matches the narrow experimental distribution.

Potential energy curve at symmetric scission explains the peak's narrowness.

Microscopic inertial mass influences the shape of the mass distribution.

Abstract

We discuss the origin of the narrowness of the single peak at mass-symmetric division in the fragment mass-yield curve for spontaneous fission of $^{258}$Fm. For this purpose, we employ the macroscopic-microscopic model, and calculate a potential-energy curve at the mass-symmetric compact scission configuration, as a function of the fragment mass number, which is obtained from the single-particle wave-function densities. In the calculations, we minimize total energies by varying the deformations of the two fragments, with constraints on the mass quadrupole moment and keeping the neck radius zero, as a function of mass asymmetry. Using the obtained potential, we solve the one-dimensional Schr\"odinger equation with a microscopic coordinate-dependent inertial mass to calculate the fragment mass-yield curve. The calculated mass yield, expressed in terms of the microscopic mass density, is consistent with the extremely narrow experimental mass distribution.