A COINCIDENCE BASED (GAMMA-ALPHA/BETA) SYSTEM FOR VERY-LOW BACKGROUND RADIATION MEASUREMENTS


  Sagi Nissim  ,  Michal Brandis [1]  ,  Ofer Aviv [1]  ,  Lior Arazi [2]  
[1] Radiation Protection Department Soreq Nuclear Research Center
[2] Unit of Nuclear Engineering, Ben-Gurion University of The Negev

High-accuracy measurements of nuclear and related materials are a useful tool in nuclear forensics, and in supporting the verification regime of the Comprehensive Test Ban Treaty Organization (CTBTO). In addition, low-background measurements can be valuable for studies in fundamental physics and environmental radioactivity. Traditionally, radionuclides are identified and quantified by directly detecting one of their decay emissions. Systems based on coincident multi-particle detection (a/g, b/g and g/g) hold the potential for providing excellent signal-to-noise ratio, compared to traditional single-detector schemes [1-3].

An innovative low-background multi-detector system is being developed in Soreq NRC in collaboration with Ben-Gurion University. The proposed setup comprises of a high-purity germanium (HPGe) detector, a liquid scintillator cell, a photo-multiplier tube and plastic scintillator panel (for cosmic radiation suppression). The system geometry aims to cover a solid angle of ~4π for a/b counting, thereby obtaining high detection efficiency. The combination of an HPGe detector and liquid scintillator allows for high-resolution g spectrometry augmented by a/b energy measurements for radionuclide identification and substantial background reduction. By incorporating dedicated electronics and software, it is possible to observe the different data aspects associated with the decay. Energy and timestamp are recorded event-by-event for each particle type, thereby allowing to perform off-line analysis of the entire dataset and make use of the various detection modes.

This work comprised the design and integration of the coincidence measurement system, development of a dedicated coincidence-based analysis algorithm, optimization of the liquid scintillator cell and sample preparation methods. This presentation will cover results from the characterization tests of the system, involving measurements of the counting efficiency and linearity, and evaluation of the minimum detectable activity.  We will further describe tests done using a Ra-226 source, providing multiple radionuclides and decay channels, and highlight several potential applications.

[1] J.L. Burnett et al. Journal of Radioanalytical and Nuclear Chemistry 312, 81-86 (2017). [2] A. Ringbom et al. Nuclear Instruments and Methods in Physics Research A 508, 542-553 (2003). [3] P.P. Povince. Journal of Radioanalytical and Nuclear Chemistry 316, 893-931 (2018).