A water-based neutron detector as a well multiplicity counter

Abstract

a b s t r a c tWe report the performance characteristics of a water-based neutron detecting multiplicity counter for the non-destructive assay of fissile sources. This technique could replace or supplement existing 3 Hebased multiplicity counters. The counter is a 1.02 m 3 tank containing pure deionized water doped with 0.5% GdCl 3 . It has highly reflective walls and eight 10-in. PMTs mounted at the top. An unshielded source well of 19 cm diameter, mounted at the top and center, extends 73 cm down into the detector. The counter was evaluated using low intensity 252 Cf and 60 Co sources, and a fast pulsing LED to simulate higher intensity backgrounds. At low gamma ray intensities ( $ 200 kBq or less) we report an absolute neutron detection efficiency of 28% and a 60 Co rejection/suppression factor of $ 10 8 to 1. For sources with high gamma ray intensities, the neutron efficiency was 22% 71% up to a 60 Co equivalent activity of 4 MBq. The detector background event rate, primarily due to muons and other cosmogenic particles, was found to be stable over a period of almost three months. The minimum detectable neutron source intensity above background was 3.1 n/s, assuming a one-hour data acquisition.

Gadolinium for neutron detection in current nuclear instrumentation research: A review

“…A high-energy threshold (140 photoelectrons, corresponding to 2.6 MeV gamma ray total absorption) accounts for gamma background without pile-up, and the detector segmentation serves the rejection of spallation neutron detection. With a frequency threshold at 130 Hz over triggering events, a 4-module water Cherenkov system with a 0.6 wt% GdCl 3 load is expected to have a 25% registration efficiency and a detection limit of 75 g of plutonium within 20 s. The prescriptions of the authors were implemented in a fullsize module prototype by Dazeley et al [91]: 8 PMTs with a 10-inch diameter were positioned on top of a 121.9 × 91.4 × 119.4 cm 3 stainless steel tank containing 1 tonne of Gd-doped water. The increase by a factor of 3 in GdCl 3 mass concentration from reference [89] lowers the mean neutron capture time from 28 µs down to 16 µs, and the inter-correlated neutron event period to 12.3 µs.…”

The Water Neutron Detector

“…The Fig. 2 The detector response spectrum from a 1 h run with a 5.9 microCurie cobalt-60 gamma and a 0.82 microCurie californium-252 neutron source [6]. The solid black line indicates the cobalt-60 spectrum prior to background subtraction.…”

“…The WaND (Water Neutron Detector) [6] is a non-helium-3 based neutron multiplicity counter under development at Lawrence Livermore National Laboratory. It is an efficient, stable, non-toxic, and non-flammable solution to some neutron multiplicity counting applications.…”

Enhancing neutron detection capabilities of a water Cherenkov detector

“…In this direction the experimental results presented in Section 3.1 show a clear improvement of the spectra (with background subtracted) of measurements performed using different amounts con NaCl in the water. The simplicity of the detector allows us to incorporate the necessary amount of additive to the active volume in a way we can gain detection efficiency.It is worth to notice that the neutron detector introduced in this work presents several advantages over previously used water Cherenkov detectors for neutron detection[4,5,40,41]. The main advantages are that the active volume of the detector employed in this work is simply pure water (an inexpensive material, abundant, and no contaminant) using NaCl as an additive.…”