Field-Deployable 6LiF:ZnS Neutron Detectors for Fission source Detection and Identification

The potential for in-field fission source detection and identification using Symetrica’s 6LiF:ZnS(Ag) thermal neutron detectors has been investigated using the Monte-Carlo code MCNP-PTA, and measurements at MTA EK (Centre for Energy Research), Hungary. A laboratory-based neutron coincidence counter using this 3He free technology has been successfully tested at JRC, Ispra for safeguards applications. In order to extend the capability to in-field measurements a two-module prototype has been designed consisting of 8 detectors per module. Simulated signatures obtained from these modules have been studied including D/S v S, where D and S are the doubles and singles rates respectively. This signature enables source types to be identified and a mass estimate to be made in well-defined situations. The challenges in applying this signature to in-field measurements include uncertainties in the source moderation, location and isotopic composition. These effects have been analysed in simulation studies alongside possible methods to mitigate them, enabled by the use of list- mode data and individual channel readout. The prototype modules have been tested at MTA EK, Hungary. A detection efficiency of 3.4% was obtained for a centrally located bare Cf-252 source, and detection of 0.2g of WGPu can be achieved within 30 minutes.