Fast neutron spectrometry using thick threshold detectors

G Medkour Ishak-Boushaki,K Boukeffoussa,M Allab,Z Idiri

doi:10.1051/epjconf/20122407009

Abstract

This paper discusses the use of thick threshold activation detectors for the characterization of low intensity neutron fields. This technique has been applied to the determination of the spectral emission of a low activity (37 GBq) Am-Be source. The reaction rates induced by the neutrons emitted by this source in different thick metallic targets (Al, Si, Fe, In) have been measured in the following reactions: 27Al(n,p)27Mg, 27Al(n,α)24Na, 28Si(n,p)28Al, 56Fe(n,p)56Mn, 115In(n, n′)115mIn and 115In(n, γ)116mIn. Each measured reaction rate corresponding to a threshold detector response depends on the spectral emission of the source via a correcting factor. This factor, which takes into account the source detector geometry, the neutron attenuation and diffusion by the detectors, has been determined by Monte Carlo simulation using MCNP5 code. The spectral emission of the neutron source has been generated from the response matrix of the threshold detectors by using different neutron spectrum unfolding methods (Stayn'l, Gravel and Maxed). A fairly good agreement with the assumed ISO spectrum has been achieved.

Highlights

For environmental and personal safety, it is necessary to have adequate techniques to monitor environmental radioactivity
We discuss the use of thick threshold activation foils to characterize low intensity neutron fields and by extension to measure environmental neutron energy spectra [2, 3]
The reaction rate ai induced in a threshold detector irradiated by the neutron source during ti and measured during tm after decay time td was determined from the following expression: ai

Summary

Introduction

For environmental and personal safety, it is necessary to have adequate techniques to monitor environmental radioactivity. We discuss the use of thick threshold activation foils to characterize low intensity neutron fields and by extension to measure environmental neutron energy spectra [2, 3]. – they present a good discrimination against gamma radiation Their sensitivity is usually rather low because of the small size of the detectors commonly used. The set of threshold detectors used in the present work, aimed for the characterization of lower fluxes, are, thicker. They present different geometric configurations and their responses vary with neutron energy. The aforementioned approach is tested; it has been applied for the determination of the spectral emission of a low activity (37 GBq) Am-Be neutron source

Experimental set-up

Reaction rates measurements

Analysis approach

Unfolding results and discussion

Conclusion