Examination of the effect of counting geometry on 125I monitoring using MCNP

This paper theoretically investigates how the counting efficiencies of three selected detector (NaI) sizes are affected by neck-detector distance, detector misplacement, thickness of overlaying tissue, and size of the thyroid gland. The detector sizes were small, 2.54 cm diameter and 0.2 cm crystal thickness; medium, 7.62 cm diameter and 0.2 cm crystal thickness; large 30.48 cm diameter and 0.2 cm crystal thickness. The evaluations were determined using a Monte Carlo technique. The simulations show that the large detector minimizes the uncertainties for all problems except the thickness of overlaying tissue.