Neutron resonance densitometry has been proposed as a non-destructive analytical method for quantifying special nuclear material (SNM)in the rock- and particle-like debris that is to be removed from the Fukushima Daiichi nuclear power plant. The method is based on neutron resonance transmission analysis (NRTA) and neutron resonance captureanalysiscombinedwithprompt-γ-rayanalysis(NRCA/PGA). Although quantification of SNM will predominantly rely on NRTA, this will be hampered by the presence of strong neutron-absorbing matrix materials, in particular 10B. Results obtained with NRCA/PGA are used to improve the interpretation of NRTA data. Prompt γ rays originating from the 10B(n, αγ) reaction are used to assess the amount of 10B. The 478 keV γ raysfrom 10B, however, need to be measured under a high-radiation environment, especially because of 137Cs. To meet this requirement, we developed a well-shaped γ-ray spectrometer consisting of one cylindrical and four rectangular-cuboid LaBr3 scintillators combined with a fast data-acquisition system. Furthermore, to improve the gain stability of the main detector, a special high-voltage divider was developed. Because of the reduction in gain shift, a 3.8% resolution at 662 keV was obtained for long-term measurements. By using the data-acquisition system, which consists of eight 250 MHz digitizers, input signals of over 500kHz per channel were recorded. The work reported herein demonstrates that, with such a spectrometer, the impact of the Compton edge of 662 keV γ rays from 137Cs is significantly reduced, which allows the 10B amount to be determined with greater sensitivity.

KOIZUMI M.;  TSUCHIYA H.;  KITATANI F.;  HARADA H.;  HEYSE Jan;  KOPECKY Stefan;  MONDELAERS Willy;  PARADELA DOBARRO Carlos;  SCHILLEBEECKX Peter; 

2017-04-19

ELSEVIER SCIENCE BV

JRC106109

0168-9002,   

http://www.sciencedirect.com/science/article/pii/S016890021630938X,    https://publications.jrc.ec.europa.eu/repository/handle/JRC106109,   

10.1016/j.nima.2016.09.015,