Calibration of Hand-held Instruments for Whole Body Measurements of Caesium-137

The responses of eight hand-held instruments to 137 Cs internal contamination in people are determined. The caesium was presented in the form of a bottle manikin absorption (BOMAB) phantom filled with 137 Cs in solution. The phantom was assembled to represent the ICRP 23 Reference Man and five smaller configurations representing a 16, 14, 8, and 4 year old, and a 3 month old infant. Measurements were taken at 30 cm, 1 m, and 2 m above the surface of the part/s representing the chest with the phantom arranged horizontally. This corresponds to positioning the instrument at the abdominal end of the sternum in a human subject. Minimum detectable activity (MDA) values were calculated for whole body and lung measurements. The MDAs for whole body measurement of an adult at 30 cm ranged from 140 kBq to 2 MBq, but were ≈ 10 kBq for the three instruments with a region of interest (ROI) set up for the 137 Cs photopeak. Generally, MDAs decreased with decreasing age/size, with those for the 3 month old infant at about 55% of those for the adult. For lung measurements at 30 cm MDA values were about 70% of those for whole body. MDAs at 1 m were about 5x higher than at 30 cm, and at 2 m about 15x higher. Committed effective doses corresponding to the MDA values, 24 hours after intake of soluble 137 Cs, ranged from 2 to 30 mSv for an adult measured at 30 cm, or about 0.15 mSv when ROI facilities were used. Corresponding doses to children, 16 to 4 years of age, decreased with decreasing age, but those for the 3 month old infant were similar to those for the adult. Many of the instruments tested were readily capable of detecting 137 Cs activities in whole body, which correspond to a committed effective dose of 10 mSv, for intake by inhalation, 24 hours before measurement. The procedures and instruments described in this report could be used to rapidly monitor a large group of people for 137 Cs internal contamination. The results of this screening could be used to identify people for possible decorporation therapy.