Determination Of Shielding Effectiveness Of Some Selected Materials Available In Lesotho Using Mcnp Code

ABSTRACT In this study, the Monte Carlo N-particle simulation code MCNPX-2.6.0 was used to determine the shielding effectiveness of clay, wood and sandstone. This was done by determining the transmission of 60Co gamma and X-rays with energies 60 keV, 120 keV and 300 keV through wood, clay and sandstone. The transport computations were done for slab shield, computing half-value layers (HVLs), tenth-value layers (TVLs), buildup factors, and attenuation coefficients (both linear and mass attenuation coefficients). Plaque, point and cylindrical source geometries were considered. The materials of thickness ranging from 0 to 50 cm with an increment of 5 cm were irradiated by each source geometry. The transmitted photon flux ranges from 69.4 % for wood down to 14.3 % while from 48.3 % down to 0.65 % and 46.8 % down to 0.48 % for clay and sandstone respectively. Wood buildup factors for 60Co were found to be lower (1.28 to 2.5) compared to (2.2 to 9.84) for both clay and sandstone. The associated linear attenuation coefficients (LACs) were within 3.8E10-02 to 9.5E-02 cm-1 for the three materials. Similarly, for x-ray sources. The effectiveness of the three materials, comparing with the results of lead, performing cost-benefit analysis using average prices in Lesotho based on thicknesses was very economical. The transmission of x-rays ranges from 76 % for wood down to 6 % for higher energy x-rays (300 keV), from 69 % down to 1 % for 120 keV and from 65 % down to 0.5 % for 60 keV. For clay and sandstone, the transmission ranges from within 87- 89 % down to ≈ 0 % for 300 keV, 79-80 % also down to ≈ 0 % for 120 keV and 61- 63 % down to ≈ 0 % for 60 keV. For lower energy x-rays, the computed buildup factors ranged from 1.20 to 34 for the three materials whiles from 1.16 to 25 for higher energy x-rays. The associated LACs for lower energy (9.12E-2 ) to higher energy x-rays (5.57E-02 cm-1 ) for wood whiles the results for clay and sandstone were within the range 5.4E-01 to 5.7E-01 cm-1 . The cost-benefit analysis done on three materials using assumed monetary values (based on average prices in Lesotho) controlled by the thickness and volume of the materials for same area of 81 m2 (9 m x 9 m), indicated the positive benefit B for three materials; $4,395 for wood with 0.91 m thickness and 73.71 m3 volume, $3,730.8 for clay with 0.46 m thickness and 34.83 m3 volume and $4,233 for sandstone with thickness of 0.43 and 37.26 m3 volume with the benefit based replacement of lead with assumed cost of $10,000.