Counting efficiency of whole-body monitoring system using BOMAB and ANSI/IAEA thyroid phantom due to internal contamination of super(131) I

In this study, the effect of Indian reference BOttle MAnnikin aBsorber (BOMAB) neck with axial cavity and American National Standards Institute (ANSI)/International Atomic Energy Agency (IAEA) thyroid phantom using pencil sources of 133Ba on counting efficiency (CE) is seen experimentally in static geometry for whole-body monitoring system comprising 10.16-cm diameter and 7.62-cm-thick NaI(Tl) detector. The CE estimated using the neck part of BOMAB phantom is 50.2 % lower in comparison with ANSI phantom. The simulation results are validated in static geometries with experimental CE and the differences are within 1.3 %. It is observed that CE for pencil source distribution is 3.97 % higher for 133Ba in comparison with CE of 131I source. In conclusion, the calibration of whole-body monitoring system for 131I should be carried out with ANSI/IAEA thyroid phantom, the neck-to-detector distance controlled or the CE corrected for this, and the CE should be corrected for OTT.