A detector system for 'absolute' measurements of fission cross sections at n_TOF in the energy range below 200 MeV

TL;DR

This paper reports the development and deployment of a novel detector system at n_TOF for absolute measurements of the $^{235}$U(n,f) cross section in the 20-200 MeV neutron energy range, a previously underexplored domain.

Contribution

It introduces new detector setups, a parallel plate fission chamber and recoil proton telescope, optimized for high-energy neutron measurements at n_TOF, enabling more precise cross section data.

Findings

Detectors are effective above 30 MeV

Systematic effects are well-controlled

Path for future detector improvements

Abstract

A new measurement of the $^{235}$U(n,f) cross section was performed at the neutron time-of-flight facility n_TOF at CERN. The experiment focused on neutron energies from 20 MeV to several hundred MeV, and was normalized to neutron scattering on hydrogen. This is a measurement first of its kind at this facility, in an energy range that was until now not often explored, so the detector development phase was crucial for its success. Two detectors are presented, a parallel plate fission chamber (PPFC) and a recoil proton telescope (RPT), both dedicated to perform measurements in the incident neutron energy range from 30 MeV to 200 MeV. The experiment was designed to minimize statistical uncertainties in the allocated run time. Several efforts were made to ensure that the systematic effects were understood and under control. The results show that the detectors are suited for measurements at n_TOF above 30 MeV, and indicate the path for possible future lines of development.