Evaluation of scatter contribution from shielding materials used in scatter measurements for calibration range...

The contribution of scatter from the shielding material used in scatter measurements at the Ohio Emergency Management Agency was evaluated. This was accomplished by comparing physical measurements with results generated by detectors modeled in the Monte Carlo shielding code, MCNP4B. The high purity germanium (HPGe) detector model was improved by using radiographs to more accurately represent the detector geometry, including a model of the lithium-contact transition region, and considering the effects of the non-uniform electric field in the germanium crystal. Photons scattered from the shielding material were found to contribute 4.25% of the total scatter recorded by the HPGe detector (thus contributing only 0.26% of the total dose) at a point 5 m from a 1.35 GBq (36.4 mCi) 137Cs source.