Counting efficiencies of shadow shield whole body counter for adult and paediatric reference computational phantoms

Shadow Shield Whole Body Counter (SSWBC) is used to estimate internal dose of radiation workers due to the intake of fission and activation products. The SSWBC geometry was numerically modelled in FLUKA code. The computational model was validated by comparing the experimental and simulated counting efficiencies (CEs), also known as response, using Bhabha Atomic Research Centre (BARC) reference BOttle Mannequin Absorption (BOMAB) phantom. Monte Carlo simulations were carried out in FLUKA to estimate the response for High Energy Photon emitters (HEPs, E_γ > 200 keV) using adult and paediatric (new-born, 1-year, 5-year, 10-year and 15-year) reference computational phantoms for male and female provided by International Commission on Radiation Protection. The scanning geometry of the system was simulated, scoring energy deposition in a NaI(Tl) detector at 15 static locations along the bed's length. The final response was calculated by averaging the detector responses at 15 static locations obtained from the simulations. The results highlight that the gender-averaged response at 300 keV for 5-year-olds is ∼20% higher than that for adults. For 15-year-olds and adults, female phantoms have 2.4% and 3.8% higher responses than males at 300 keV and, 3.2% and 1.1% higher responses at 1400 keV. From new-born to 10-year response is similar for both genders. The results also highlight that for any age group, response increases up to few detector locations and then it falls sharply. At any energy, the detector location for peak response is different for various age groups. These results will be useful for realistic assessment of HEPs in members of the public during any nuclear or radiological emergency scenarios.