Linear attenuation coefficient and buildup factor of MCP-96 alloy for dose accuracy, beam collimation, and radiation protection.

The linear attenuation coefficients and buildup factor of MCP-96 alloy were determined for (60)Co, (54)Mn, and (137)Cs gamma emitters and a NaI detector. The thickness of the MCP-96 attenuator was varied from 1 to 4 cm. A collimated beam of gamma rays was allowed to pass through various thicknesses of the MCP-96 alloy. The attenuated beam was detected by a NaI detector, and data were recorded by a multichannel analyzer. The run was repeated without the collimator for broad-beam geometry. For each run, the attenuated beam intensity was normalized by the intensity of the unattenuated incident beam obtained by removing the attenuators. Linear attenuation coefficients were determined by plotting of the intensity of the collimated beam against the attenuator thickness. For every thickness of the alloy, the ratio of the attenuated to the unattenuated beam was found to be higher in broad-beam geometry as compared to the same ratio in narrow-beam geometry. We used the difference in these ratios in broad and narrow-beam geometries to calculate the buildup factor. The buildup factor was found to increase with beam energy and attenuator thickness. Variation in the source-to-detector distance gave a lower value of the buildup factor for a small and a large distance and a higher value for an intermediate distance. The buildup factor was found to be greater than 1 in all cases. We conclude that the buildup factor must be calculated and incorporated for dose correction and precision when the MCP-96 alloy is used for tissue compensation or radiation shielding and protection purposes.