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Calculations of anisotropy factors for radionuclide neutron sources due to scattering from source encapsulation and support structures

Tsujimura, Norio   ; Yoshida, Tadayoshi ; Momose, Takumaro  

The authors developed a model calculating angular neutron fluence distributions for radionuclide neutron sources which are heavily encapsulated or surrounded with some source support structures such as a source holder and a source movement system. These structures cause a highly anisotropic neutron fluence distribution, and hence it should be properly corrected for calibration of neutron measuring instruments. The calculations were made for two types of widely used neutron sources, $$^{241}$$Am-Be and $$^{252}$$Cf, by a combination of the in-house code simulating $$^{9}$$Be($$alpha$$,n) reactions and the Monte Carlo code MCNP4C. As a result, anisotropy factors in the direction perpendicular to the source capsule axis for bare neutron sources were evaluated to be 1.012, 1.030 and 1.035 for $$^{252}$$Cf in a standard Amersham X1 capsule, $$^{241}$$Am-Be in a X3 capsule and $$^{241}$$Am-Be in a X4 capsule, respectively. These values are in reasonable agreements with published data. In contrast, anisotropy factors for these neutron sources including support structures increased by approximately 10% due to scattering of neutrons.

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Category:Environmental Sciences

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