Fast- and thermal-neutron detection with common NaI(Tl) detectors

TL;DR

This paper shows that common NaI(Tl) detectors can be adapted for neutron detection using pulse-shape discrimination and gamma cascade analysis, enhancing their capabilities in radiation detection systems.

Contribution

It introduces methods to enable thermal and fast-neutron sensitivity in standard NaI(Tl) detectors through advanced signal processing techniques.

Findings

Neutron-induced nuclear recoils can be distinguished via pulse-shape discrimination.

Thermal neutron captures produce characteristic gamma cascades detectable in NaI(Tl).

Experimental analysis confirms the feasibility of these methods in commercial detectors.

Abstract

Radionuclide Identification Devices (RIDs) or Backpack Radiation Detection Systems (BRDs) are often equipped with NaI(Tl) detectors. We demonstrate that such instruments could be provided with reasonable thermal- and fast-neutron sensitivity by means of an improved and sophisticated processing of the digitized detector signals: Fast neutrons produce nuclear recoils in the scintillation crystal. Corresponding signals are detectible and can be distinguished from that of electronic interactions by pulse-shape discrimination (PSD) techniques as used in experiments searching for weakly interacting massive particles (WIMPs). Thermal neutrons are often captured in iodine nuclei of the scintillator. The gamma-ray cascades following such captures comprise a sum energy of almost 7 MeV, and some of them involve isomeric states leading to delayed gamma emissions. Both features can be used to distinguish corresponding detector signals from responses to ambient gamma radiation. The experimental proof was adduced by offline analyses of pulse records taken with a commercial RID. An implementation of such techniques in commercial RIDs is feasible.