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

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