Calculation of anisotropy factors for radionuclide neutron sources

Tsujimura, Norio   ; Yoshida, Tadayoshi 

The authors developed a model for calculating the angular neutron fluence distributions for radionuclide neutron sources which are encapsulated in stainless steel capsules or surrounded by support structures as a source holder and a source movement system. These structures may cause an anisotropic neutron fluence distribution. This should be taken into account in the neutron-measuring instruments calibration procedure. The calculations were made for two types of widely used neutron sources, Am-Be and Cf, by combining an in-house code simulating the Be(,n) reactions and the Monte Carlo code MCNP-4C. As a result, anisotropy factors in the direction perpendicular to the source capsule axis for bare neutron sources were evaluated to be 1.012 for Cf in a standard Amersham X1 capsule, 1.030, 1.039 and 1.045 for Am-Be in a standard Amersham X3, X4 and X14 capsules, respectively. These values are in reasonable agreement with the published data.