Effect of non-uniform distribution of radioactivity in human body on measurements using HPGe detector based scanning bed whole body counter

Abstract

In-vivo monitoring of radiation workers for high energy photon emitters is carried out using whole body counters. These are calibrated using standard radioactive sources uniformly distributed in BOMAB phantom. In the case of inhalation intake of Type S compounds, radioactivity is retained in lungs for a long time resulting in non-uniform distribution. In this paper, the effect of non-uniform distribution of activity in human body is studied on the direct measurement using shadow shield bed whole body counter (SSBWBC) with BOMAB and LLNL phantoms. First, the system was calibrated with known amount of ¹³³Ba, ¹³⁷Cs, ⁶⁰Co and ⁴⁰K uniformly distributed in water filled BOMAB phantom. Then, the system was calibrated with known amount of ¹⁵²Eu and ²⁴¹Am uniformly distributed in the lungs of LLNL phantom. The multiple gamma energies of radionuclides were used to determine the counting efficiencies for uniformly distributed activity in whole body as well as in the lungs. The study shows when uniform distribution of radionuclides in the whole body is assumed but activity is confined in the lungs only, measured activity is overestimated by 15 to 20 %. This results in similar overestimation in intake and CED.