A study on some models of neutron thermopiles

Abstract The neutron thermopiles studied at the Electronics Laboratory of C.N.E.N. are described and discussed as a tool for in-core measurements. Theoretical considerations permit the evaluation of the sensitivity of the instrument under various conditions of reactor power, neutron spectrum, sensitive material, filling gas, thermal insulation. Other characteristics such as time response and life are also considered. The perturbation introduced by the probe in the surrounding neutron flux is discussed as well. Experimental results, obtained by measurements from 27 mounts tested in a Triga reactor, are given. Among them are: the thermal neutron sensitivity, an effect of sensitivity decrease, a comparison of some identical probes, the gamma sensitivity, the flux perturbation, the intrinsic noise, the time response and the activation. It was possible to obtain watertight miniaturized probes, having a sensitivity of 1 × 10 −15 V/n · cm 2 · sec, 1 sec response time and a life of some hundreds h in 10 12 n/cm 2 · sec.