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Anisotropy Factors for a 252Cf Source

K. G. Veinot, J. S. Bogard

Nuclear Technology / Volume 168 / Number 2 / November 2009 / Pages 364-368

Neutron Measurements / Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (Part 2) / Radiation Protection /

A new 252Cf source has been procured for use at the Dosimetry Applications and Research facility at the Oak Ridge National Laboratory (ORNL). This source was encapsulated by the Californium Facility at ORNL; however, the encapsulation differs from previous designs designated as SR-Cf-100. The new encapsulation, designated SR-Cf-3000, has a similar cylindrical radius to the previous generation but is 1.6 cm longer. Since the encapsulation geometries differ, the amount of internal scattering of neutrons will also differ, leading to changes in anisotropy factors between the two designs. Additionally, the different encapsulations will affect the absorbed dose and dose equivalent delivered per neutron emitted by the source since both the quantity and energy distribution of the emitted neutrons will vary with irradiation angle. This work presents the fluence anisotropy factors for the SR-Cf-3000 series encapsulation as well as absorbed dose and dose equivalent values calculated for various angles of irradiation. The fluence anisotropy factors were found to range from a maximum of 1.037 to a minimum of 0.641 for irradiation angles perpendicular and parallel to the source axis, respectively. Anisotropy in absorbed dose varied from a maximum of 1.033 to a minimum of 0.676 while anisotropy of dose equivalent varied from 1.035 to 0.657. Anisotropy in the region most commonly used was found to be +3.2% for absorbed dose and +3.3% for dose equivalent, and these effects should be included when performing dosimeter irradiations.

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