Computation of Gamma Buildup Factors and Heavy Ions Penetrating Depths in Clay Composite Materials Using Phy-X/PSD, EXABCal and SRIM Codes

Abstract

Most investigations of the gamma-shielding abilities of materials are often based on the Beer-Lambert law including recent studies on clay-polyethylene composites. The findings are usually silent on the secondary radiation effects that commonly occur due to photon buildup, known as Energy Absorption Buildup Factor (EABF) and Exposure Buildup Factor (EBF). In this work, the computation of EABF and EBF in the region of energy 0.015–15 MeV at different penetration depths or mean free paths up to 40 mfp—and simulation of 100 keV of Cs and Sr ion-penetration profiles of clay–polyethylene composites (A–G) containing 0–30 wt% low density polyethylene (LPDE)—was carried out. The buildup factors computation was performed using Phy-X/PSD and EXABCal codes, and the ion-penetrating profile was studied using a Monte Carlo simulation code called Stopping and Range of Ions in Matter (SRIM). The EABF and EBF values are functions of the photon energy and the penetration depth. In the region of intermediate energy, the EABF and EBF values are higher for each of the samples. For a given mfp, the peak value of either EBF or EABF of each sample increases with LDPE wt% in the clay matrix. The projected range of both Cs and Sr ions in the samples decreased with increasing sample bulk densities, with Cs having a higher projected range than Sr in all the samples. The Cs and Sr ions have the lowest respective projected ranges in sample A (of bulk density 2.03 g·cm−3; 0 wt% of LDPE), while the highest projected ranges were recorded in sample G (of bulk density 1.34 g·cm−3; with 30 wt% of LDPE), respectively. This study reaffirmed the suitability of clay composite for gamma-ray shielding applications; however, it may not yet be ready to be used as a backfill material to mitigate the migration of fission products present in radioactive nuclear wastes.