10B+ZnS(Ag) as an alternative to ³He-based detectors for Radiation Portal Monitors.

Typical radiation portal monitor systems, RPM, deployed to detect illicit trafficking of radioactive materials include a set of gamma-ray detectors and neutron detectors. Usually the employed neutron detectors are pressurized ³He-based neutron detectors tubes. Due the shortage of ³He reported since 2009, the amount of ³He available for use in gas proportional counter neutron detectors has become limited, while the demand has significantly increased, especially for homeland security applications. For this reason, many different alternatives are being investigated for its use in RPM systems. The aim of this work is to study a scintillation detector ZnS(Ag) mixed with highly enriched ¹⁰B, ¹⁰B+ZnS(Ag). Using Monte Carlo methods, MCNPX code, the response of two neutron detectors based on 1^0B+ZnS(Ag), manufactured by BridgePort Instruments LLC with different geometries, were estimated by calculating the number of ¹⁰B(n,α)⁷Li reactions for 29 monoenergetic neutron sources. Measurements and models were made, and both detectors were compared. The importance of the distance with respect to the ground was studied. The response with a ²⁵²Cf moderated neutron source (0.5 cm lead and 2.5 cm polyethylene) was calculated in order to compare with other studied alternatives in the USA by Pacific National Northwest Laboratory, PNNL. With these results we conclude that neutron detectors using ¹⁰B+ZnS(Ag) are an interesting alternative for replacing ³He detectors. From the analysis with MCNPX we propose an improvement in the detector design. [ABSTRACT FROM AUTHOR]