This paper presents the evaluation of the geometry correction factor for calibration of Bonner sphere spectrometer (BSS) equipped with the 3He counter (typical SP9), based on Monte Carlo simulation. Using the MCNP4C code, geometry factors and effectiveness parameters (d) of a 800 polyethylene sphere (r = 10.16 cm) were calculated for 10 different energies and 3 various distances between the source and center of the sphere. The obtained results showed that the geometry factor increases with the distance, and the effectiveness parameter is independent of distance. Finally, for 200, 300, 500, 800 and 1200 spheres exposed to four different radio-isotopic neutron sources with various energy spectrums, the effectiveness parameters were determined, which it is worthy to consider d : d(r, E).

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