A dynamical model of surrogate reactions

TL;DR

This paper introduces a comprehensive dynamical model for surrogate nuclear reactions using multi-dimensional Langevin equations, capable of predicting various observables including spin distributions, aiding the understanding and validation of surrogate techniques.

Contribution

The model unifies multiple reaction stages and can calculate spin distributions and other observables, advancing the analysis of surrogate nuclear reactions.

Findings

Spin distributions are less than 10ħ, satisfying surrogate ratio method conditions.

The model accurately predicts energy and angular distributions of ejectiles.

It provides a framework for assessing surrogate reaction mechanisms.

Abstract

A new dynamical model is developed to describe the whole process of surrogate reactions; transfer of several nucleons at an initial stage, thermal equilibration of residues leading to washing out of shell effects and decay of populated compound nuclei are treated in a unified framework. Multi-dimensional Langevin equations are employed to describe time-evolution of collective coordinates with a time-dependent potential energy surface corresponding to different stages of surrogate reactions. The new model is capable of calculating spin distributions of the compound nuclei, one of the most important quantity in the surrogate technique. Furthermore, various observables of surrogate reactions can be calculated, e.g., energy and angular distribution of ejectile, and mass distributions of fission fragments. These features are important to assess validity of the proposed model itself, to understand mechanisms of the surrogate reactions and to determine unknown parameters of the model. It is found that spin distributions of compound nuclei produced in $^{18}$O+$^{238}$U $\rightarrow ^{16}$O+$^{240*}$U and $^{18}$O+$^{236}$U $\rightarrow ^{16}$O+$^{238*}$U reactions are equivalent and much less than 10$\hbar$, therefore satisfy conditions proposed by Chiba and Iwamoto (PRC 81, 044604(2010)) if they are used as a pair in the surrogate ratio method.