Study of a 10B+ZnS(Ag) neutron detector as an alternative to 3He-based detectors in Homeland Security

Abstract The response of a scintillation neutron detector of ZnS(Ag) with 10 B was calculated, using the MCNPX Monte Carlo Code. The detector consists of four panels of polymethyl methacrylate (PMMA) and five thin layers of ~0.017 cm thick 10 B+ZnS(Ag) in contact with the PMMA. The response was calculated for the bare detector and with different thicknesses of High Density Polyethylene, HDPE, moderator for 29 monoenergetic sources as well as 241 AmBe and 252 Cf neutrons sources. In these calculations the reaction rate 10 B(n, α) 7 Li and the neutron fluence in the sensitive area of the detector 10 B+ZnS(Ag) was estimated. Measurements were made at the Neutron Measurements Laboratory, Universidad Politecnica de Madrid, LMN-UPM, to quantify the detections in counts per second in response to a 252 Cf neutron source separated 200 cm. The MCNPX computations were compared with measurements to estimate the efficiency of ZnS(Ag) for detecting the α that is created in the 10 B(n, α) 7 Li reaction. After validating new models with different geometries it will be possible to improve the detector response trying to achieve a sensitivity of 2.5 cps-ng 252 Cf comparable with the response requirements for 3 He detectors installed in the Radiation Portal Monitors, RPMs. This type of detector can be considered an alternative to the 3 He detectors for detection of Special Nuclear Material, SNM.