Calculating photon buildup factors in determining the γ-ray shielding effectiveness of some materials susceptible to be used for the conception of neutrons and γ-ray shielding

Abstract

We report γ−ray shielding effectiveness of eight selected shielding materials susceptible to be used for the conception of γ−ray and fast neutrons absorbers has been investigated. Four of the selected materials were polyethylene composites, the first one is doped with 7.5% Lithium (Lithium7.5%-Polyethylene), the second one is doped with 8.97% boron (Borated8.97%-Polyethylene), the third one is doped with 5.45% boron (Borated5.45%-Polyethylene), and the fourth one contains high hydrogen content as well as 0.9% by weight boron namely Self Extinguishing Borated Polythylene. The other four considered materials are FlexiBoron, High Temperature Boron Silicone, Polykast Dry Mix, and Field castable Heat Resistant shielding. These materials have been selected in fact because they contain iron (Fe), zinc (Zn), Strontium (Sr) and Manganese (Mn) which heavy elements and considered as good absorbers of γ−radiation and also because they contain hydrogen which is considered as the furthermost active moderator as well as boron which is an extremely appropriate absorber of thermal neutrons. The study has been conducted by determining the γ−ray energy absorption buildup factors (EABF) as well as the exposure buildup factors (EBF). The evaluation of the buildup factors has been determined by employing the five parameters geometric progression (G-P) fitting approximation and taking into account the reference standard database (1991-ANSI/ANS-6.4.3). This determination has been carried out using a photon energy varying from 0.015 to 15 MeV with a permeation depth until 40 mean free paths. By investigating on the reliance of EABF and EBF on the incident photon energy, chemical arrangement, and permeation depth, a deeply comparison between the obtained values of EABF and EBF has been performed. By inspecting the obtained values of EABF and EBF established for the first time, our numerical simulations allow to conclude that among the selected shielding materials, Field castable Heat Resistant shielding and 5.45% Borated Polyethylene provide the lower buildup factors at lower energies (<1.5 MeV for EABF, <2 MeV for EBF), suggesting thereby their candidacy to serve as potential shielding materials against γ−radiation in this energy range. The results of the present investigation therefore shed light on selectivity of the appropriate shielding material as well as the determination of the optimum thickness of the shielding material subject of having superior neutrons shielding ability.

Keywords

• Shielding materials
• G-P fitting approximation
• Energy absorption buildup factor
• Exposure buildup factor