Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors

TL;DR

This study compares boron-10 based Multi-Grid and helium-3 neutron detectors, focusing on their time and energy resolution, internal scattering, and pulse reconstruction, to evaluate their performance for neutron spectroscopy at the ESS.

Contribution

It provides the first detailed comparison of Multi-Grid and helium-3 detectors in terms of fine time- and energy-resolved effects, including internal scattering and pulse timing.

Findings

Multi-Grid detector shows comparable timing resolution to helium-3 tubes.

Internal scattering can be effectively reduced in the Multi-Grid detector.

Agreement between measured and calculated detection efficiency curves was confirmed.

Abstract

The boron-10 based Multi-Grid detector is being developed as an alternative to helium-3 based neutron detectors. At the European Spallation Source, the detector will be used for time-of-flight neutron spectroscopy at cold to thermal neutron energies. The objective of this work is to investigate fine time- and energy-resolved effects of the Multi-Grid detector, down to a few $\mu$eV, while comparing it to the performance of a typical helium-3 tube. Furthermore, it is to characterize differences between the detector technologies in terms of internal scattering, as well as the time reconstruction of ~ $\mu$s short neutron pulses. The data were taken at the Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube were installed at the ESS test beamline, V20. Using a Fermi-chopper, the neutron beam of the reactor was chopped into a few tens of $\mu$s wide pulses before reaching the detector, located a few tens of cm downstream. The data of the measurements show an agreement between the derived and calculated neutron detection efficiency curve. The data also provide fine details on the effect of internal scattering, and how it can be reduced. For the first time, the chopper resolution was comparable to the timing resolution of the Multi-Grid detector. This allowed a detailed study of time- and energy resolved effects, as well as a comparison with a typical helium-3 tube.