Counting efficiencies of standing-type whole body counter using age-dependent BOMAB and voxel phantoms for Indian...

Partially shielded systems, such as the Quick Scan Whole Body Counter (QSWBC), are used to assess internal contamination from fission and activation products in the human body. In the present study, the geometry of the QSWBC was numerically modelled using the FLUKA code. The computational model was validated by comparing the simulated and experimental counting efficiencies (CEs) for the adult BOttle Mannequin ABsorption (BOMAB) phantom. Age-dependent Indian voxel phantoms were constructed from ICRP male adult and paediatric reference voxel phantoms (1-year, 5-year, 10-year and 15-year). This was done by rescaling to the height and weight of the corresponding BOMAB phantoms representing the Indian population. Monte Carlo simulations were carried out in FLUKA to estimate the CEs for ⁵⁷Co (122 keV), ¹³³Ba (356 keV), ¹³⁷Cs (662 keV), ¹³⁴Cs (795 keV), ⁶⁰Co (1173 & 1332 keV) and ⁴⁰K (1460 keV), using both age-dependent BOMAB and Indian voxel phantoms. The results highlight notable differences between the CEs of BOMAB and Indian voxel phantoms. In adults, Indian voxel phantoms showed CEs up to 68 % higher than those of the BOMAB phantoms at lower energies, which can be attributed to reduced self-attenuation and closer proximity between the source and detector. Linear regression analysis was performed to derive mathematical equations with strong correlations (R² > 0.9) for estimating individualized, body size-dependent CEs based on the body build index (BBI). The CEs were observed to decrease with increasing BBI across all energies for both phantoms. The CEs, initially increased with photon energy due to full energy deposition from photo electric effect but subsequently decreased due to reduced energy deposition. The results also indicated that CEs decline with age, with the highest efficiencies observed in 1-year-olds. These findings highlight the importance of using voxel phantoms and BBI-based CEs to enhance the accuracy of internal dose assessments for occupational workers as well as members of the general public.