Screening of external ¹³⁷Cs hotspots using standing type whole body monitor and quantification of internal...

While whole body counters are employed in in-vivo measurements of internal contamination due to high energy photon emitters, the presence of external contamination can interfere with quantification of activity burden. The present study demonstrated a methodology for screening of ¹³⁷Cs external hotspots using Quick Scan Whole Body Monitor (QSWBM) for routine monitoring of radiation workers. In case of accidental scenarios involving broader level of external contamination, estimation of internal contamination using in-vitro method is also discussed here. A set of five ratios (R-values) based on net count rates in QSWBM detectors for anterior and posterior counting corresponding to external contamination as well as internal contamination were evaluated using computational phantoms and FLUKA code. The study demonstrated that implementing two ratios - R_D (the ratio of net count rates in upper and lower detectors in anterior counting) and R_AP (the ratio of net count rates in anterior and posterior counting) - can effectively screen variety of external hotspot scenarios involving ¹³⁷Cs using QSWBM. If persistent and broader external contamination is expected as in case of accidental scenarios, in-vitro method using urine samples and gamma spectrometry can be implemented for quick and reliable estimation of internal contamination. HPGe based detection system was calibrated for 75 mL and 250 mL bottle geometry for accurate measurement of activity excretion rate. Minimum Detectable Activity (MDA) values for this method showed that excretion rate that can lead to Committed Effective Dose (CED) < 1 mSv can be quantified even up to 10 days since intake.