Analysis of signal characteristics and influencing factors of self-powered gamma detector for reactor

Self-powered gamma detector (SPGD) can be used for monitoring the gamma flux in the reactor core. This study establishes a Monte Carlo simulation model of SPGD with a focus on the space charge effect in the insulator and the current contribution from the collector. To evaluate candidate emitter materials, simulations are performed under the Very High Temperature Reactor (VHTR) spectrum. The results show that SPGDs using lead (Pb) and bismuth (Bi) as emitters achieve a gamma signal proportion exceeding 99%. Additionally, the effects of emitter diameter, insulator thickness, and collector thickness on gamma sensitivity are analyzed. Experimental validation is conducted using a cobalt-60 source on a zirconium-type SPGD and a rhodium-type self-powered neutron detector (SPND), yielding relative deviations between the simulated and experimental gamma sensitivities of -4.55% and -9.45%. Thus, the proposed model can be used for the sensitivity prediction of SPGD and the analysis of gamma background current in SPND.