Fission Fragment Angular Anisotropy in Neutron-Induced Fission of $^{235}$U Measured with a Time Projection Chamber

TL;DR

This paper reports the first use of a three-dimensional tracking detector to measure the angular anisotropy of fission fragments from $^{235}$U across a broad neutron energy range, enhancing data precision and understanding.

Contribution

It introduces the use of a fission time projection chamber for direct, high-precision measurement of fission fragment angular anisotropy over a wide energy spectrum.

Findings

Measured anisotropy data from 180 keV to 200 MeV neutron energies.

Achieved unprecedented measurement precision with systematic uncertainty analysis.

Provided new constraints for fission theory and modeling.

Abstract

Fission fragment angular distributions can provide an important constraint on fission theory, improving predictive fission codes, and are a prerequisite for a precise ratio cross section measurement. Available anisotropy data is sparse, especially at neutron energies above 5 MeV. For the first time, a three-dimensional tracking detector is employed to study fragment emission angles and provide a direct measurement of angular anisotropy. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration has deployed the fission time projection chamber (fissionTPC) to measure nuclear data with unprecedented precision. The fission fragment anisotropy of $^{235}$U has been measured over a wide range of incident neutron energies from 180 keV to 200 MeV; a careful study of the systematic uncertainties complement the data.