Evaluation of scattered radiation in a calibration range using exposure rate energy spectra

ISO standard 4037 specifies that for calibrating protection level dosimeters, scattered radiation should contribute less than 5% of the exposure. In previous work, the authors reported the results of an MCNP analysis of the shadow shield technique that was performed for a calibration range with a ¹³⁷Cs irradiator. This paper examines the energy distribution of the photons contributing to the exposure percent scatter (S%) and the detailed origin of the scatter that originates in the irradiator. In summary, it reports that: 1) the majority of S% is due to photons with energies that are significantly below the source energy, 2) a significant percentage of S% is due to photons that scatter within the source and source capsule walls, and 3) S% due to scatter within the irradiator is even more significant than previously reported.