# 1H(n,el) as a Cross Section Reference in a White Source Neutron Beam With the fissionTPC

## TL;DR

This paper explores a method using the fission Time Projection Chamber to measure neutron-induced fission cross sections relative to elastic hydrogen scattering in a white-source neutron beam, aiming to improve precision in cross section measurements.

## Contribution

It proposes a novel approach to measure neutron-induced fission cross sections with reduced uncertainties by employing the H(n,el) cross section as a reference in a white-source neutron beam.

## Key findings

- Feasible measurement in 0.5 to 10 MeV neutron energy range.
- Current uncertainties hinder sub-percent precision.
- Enhanced precision possible with neutron time-of-flight or mono-energetic sources.

## Abstract

We provide a quantitative description of a method to measure neutron-induced fission cross sections in ratio to elastic hydrogen scattering in a white-source neutron beam with the fission Time Projection Chamber. This detector has measured precision fission cross section ratios using actinide references such as $^{235}$U(n,f) and $^{238}$U(n,f). However, by employing a more precise reference such as the H(n,el) cross section there is the potential to further reduce the evaluation uncertainties of the measured cross sections. In principle the fissionTPC could provide a unique measurement by simultaneously measuring both fission fragments and proton recoils over a large solid angle. We investigate one method with a hydrogenous gas target and with the neutron energy determined by the proton recoil kinematics. This method enables the measurement to be performed in a white-source neutron beam and with the current configuration of the fissionTPC. We show that while such a measurement is feasible in the energy range of 0.5 MeV to $\sim$10 MeV, uncertainties on the proton detection efficiency and the neutron energy resolution do not allow us to preform a fission ratio measurement to the desired precision. Utilizing either a direct measurement of the neutron time-of-flight for the recoil proton or a mono-energetic neutron source or some combination of both would provide a path to a sub-percent precision measurement.