Neutron spectrometer for fast nuclear reactors

TL;DR

This paper presents the development and testing of a neutron spectrometer suitable for high flux environments like fast nuclear reactors, utilizing $^6$Li conversion and diamond detectors for neutron energy measurement.

Contribution

The paper introduces a novel neutron spectrometer design based on $^6$Li conversion and diamond detectors, with calibration and efficiency validation in reactor-like conditions.

Findings

Detection efficiency matches simulations and estimates.

Energy resolution is better than 100 keV.

Effective in high flux environments.

Abstract

In this paper we describe the development and first tests of a neutron spectrometer designed for high flux environments, such as the ones found in fast nuclear reactors. The spectrometer is based on the conversion of neutrons impinging on $^6$Li into $\alpha$ and $t$ whose total energy comprises the initial neutron energy and the reaction $Q$-value. The $^6$LiF layer is sandwiched between two CVD diamond detectors, which measure the two reaction products in coincidence. The spectrometer was calibrated at two neutron energies in well known thermal and 3 MeV neutron fluxes. The measured neutron detection efficiency varies from 4.2$\times 10^{-4}$ to 3.5$\times 10^{-8}$ for thermal and 3 MeV neutrons, respectively. These values are in agreement with Geant4 simulations and close to simple estimates based on the knowledge of the $^6$Li(n,$\alpha$)$t$ cross section. The energy resolution of the spectrometer was found to be better than 100 keV when using 5 m cables between the detector and the preamplifiers.