The silver activated Geiger counters are frequently used for measuring pulsed neutron fluxes especially in plasma focus devices. These counters basically utilize a Geiger-Mueller (GM) counter surrounded by a silver layer as an activation medium and also a polyethylene layer as a neutron moderator. Neutrons are slowed down in polyethylene prior to activating the silver layer. The neutron flux can be estimated through measuring the silver activity by Geiger-Mueller counter. In this paper, the construction of an activation counter is explained and the Monte Carlo MCNP4C code is used to calculate the calibration constant. Finally, the calculated calibration constant is compared with the measurement undertaken with an Am–Be neutron source, based on the saturation count rate method. The comparison represents a good agreement between simulation and experimental values of calibration constant. The Amir Kabir Plasma Focus (APF) device is used as a fast neutron source.

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