Comparison of two JAERI phantoms and the problems discovered

During the course of an intercomparison exercise it was possible to compare two JAERI phantoms with each other by using a multi-energy photon emitting lung set (241Am/152Eu). One belonged to the IAEA (Vienna), the other belonged to the Human Monitoring Laboratory (Ottawa). The intercomparison of the phantoms showed that they were statistically distinct from each other, although the differences were small. The counting efficiencies varied from each other by about 4% at 17 keV and 2% at photon energies above 17 keV. It was concluded that these difference were either due to small variations of chest wall thickness during the manufacturing process or positioning errors. The intercomparison also revealed a serious problem with one of the overlay plates of the HML's phantom. The adipose mass fraction of the overlay plate was found to be much greater (approximately 40%) than the manufacturer's stated value (10%).