Optimization design of a detector for neutron fluence rate measurement

A novel neutron detector mainly applied for neutron fluence rate measurement in neutron radiation filed is given in this paper. The performance of the detector was optimized by MCNP-4C code. A type SP9 ³He proportional counter was placed in the center of this spherical detector, 50 air guides were regularly positioned along the radical of the spherical moderator, and two pitchblende layers were introduced into the detector. The optimal parameters of the detector were as following: 19 cm in diameter, 10 mm diameter of air guides, a 7 mm thick inner pitchblende layer in inner radius of 41 mm with a ²³⁵U concentration of 3%, and a 10 mm thick outer pitchblende layer in inner radius of 84 mm with a ²³⁵U concentration of 7%. The results show that the relative energy response varies from 0.70 to 1.65 and the deviation of the angel independence response is less than 15% in the range from thermal to 20 MeV. (authors)