EVALUATION OF GAMMA-RAY AND NEUTRON FLUXES IN A NEUTRON IRRADIATOR USED FOR RAD-HARD ELECTRONIC COMPONENTS TESTING

An irradiator with four Am-Be neutron sources (activity 111 GBq each) was used for testing electronic RAD-HARD components developed for space application [1]. For this goal, an essential requirement to be met is the knowledge with sufficient precision of neutron and gamma-ray fluxes in the irradiation channel where the components are put for the test. For this goal, an experimental measurement activity was started to validate also Monte Carlo simulation results, obtained with application of MCNP5 code. As regards gamma-ray flux, we considered separately two gamma-ray contributions: the first one, at 60 keV energy, associated with the decay of the 241Am, and the second one, at 2.2 MeV, due to the radiative capture of neutrons in the biological shield (water) surrounding the neutron sources. Experimental measurements were realized with TLD700 dosimeters in two different configurations: TLD “naked” to measure the dose of the total gamma irradiation field, and TLD put inside a lead shield to determine (for difference) 60 keV gamma-ray contribution. The dimensions of used dosimeters, very small, allowed an accurate dose behaviour determination. For the TLD calibration, we exposed them to well-know doses values at the 60Co irradiator named IGS3, situated in the Department of the University of Palermo. As regards the evaluation of the neutron radiation field, experimental measurements were realized both by neutron activation with gold foils (nude and cadmium covered) and with thermoluminescent dosimeters (TLD600 and TLD700). Results have been compared with the ones obtained by a Monte Carlo (MCNP) simulation performed adopting a model of the irradiator previously validated [2]. The comparison between the experimental data and those obtained performing a Monte Carlo simulation allowed the determination of both neutron (thermal) and gamma field in several points inside the irradiation channel and, in particular, in those positions more used to the realization of irradiation tests. [1] S.G. Cappello, C. Pace, A. Parlato, S. Rizzo, E.TOMARCHIO: “ Gamma-ray irradiation tests of CMOS sensors used in imaging techniques”, Nuclear Technology & Radiation Protection 29 (2014), pp. S14-S19. [2] P. Buffa, S. Rizzo, E. TOMARCHIO: “A Monte Carlo-aided design of a modular 241Am-Be neutron irradiator”, Nuclear Technology & Radiation Protection XXVIII, No.3 (2013), pp. 265-272.