Neutron dosimetry with detectors of finite size. I. Theory.

Abstract

A theory for detector response in fields of fast neutrons has been developed. The theory is valid for convex detectors of all sizes exposed to isotropic fields of neutrons. In the theory the detector shape is characterized by distributions of chord lengths along which the neutron produced charged particles travel and deposit energy. Chord length distributions for charged particles generated in the surrounding medium (externals) and in the detector itself (internals) are presented for spheres, spheroids, cylinders and parallel plane geometries. The form on which the theory is written makes it possible to evaluate the theory with simplified assumptions, such as characterizing the detector with a single mean chord length for the external particles. Specifically, the response of ionization chambers has been considered, taking into account the energy dependence of the W-values for the different charged particles. In a following article (part II) the theory will be subjected to experimental test.