Monte-Carlo simulation of photon transport in a heterogeneous phantom

Monte Carlo simulation studies have been undertaken to study the transport of uranium L X-rays and the 241Am 59.5-keV gamma photon in a heterogeneous mathematical phantom. The phantom transmission function is found to be expressible in the form f = α1esup-α2(μsub(s)xsub(s)+μsub(L)xsub(L)) for transport through soft tissue and lung, respectively. For Pu counting in the front position, α1 = 0.21 +- 0.03 and α2 = 1.42 +- 0.09 while for Am counting α1 = 0.48 +- 0.06 and α2 = 2.36 +- 0.16. For rear counting of Pu, α1 = 0.24 +- 0.03 and α2 = 1.55 +- 0.06, while for rear counting of Am, α1 = 0.40 +- 0.05 and α2 = 2.10 +- 0.16. The Monte-Carlo method predicts an effective soft tissue thickness (ESTT) of 5.2 +- 0.9 cm for the mathematical phantom, in excellent agreement with an average ESTT of 5.0 +- 1.0 cm calculated from previous 51Cr-103Pd experiments using human volunteers. These results are also utilized to predict phoswich calibration factors and to predict the L X-ray line shape for the phoswich detector. (author)