s2elum with a snort aalfcime (1.9 day), the source geometry wi'l rot be significantly affected with respect to an ingestion/excretion equilibrium of cesium within the body. 6004 is not distributed uniformly throughout the body with 20% of an oral intake being retained in the liver with a very long biological halftime and about 80% being cleared from the extracellular fluid to out of the body with a biological halftime of’ one day or less. Thus source geometry will be significantly effected with respect to ingestion/excretion equilibrium of cobalt within the body. To verify the activity in the phantom prior to use as a standard, an aliquot of the phantom solution was counted on a lithium drifted germanium detector which was calibrated with NBS standard sources. The phantom was then counted in a shadow shield whole body counter (WBC) (PA65). The whole body counting system consists of a stationary crystal and stationary bed. The counter detects radioactive material located principally in the thorax, so positioning of the phantom and the in vivo counting subjects must be as similar as possible. To facilitate reproducible counting geometries, each subject and the standard phantom was positioned such that the central axis of the crystal intersected the central axis of the body about 25 em below the sternal notch. The distance between the surface of the bed and the bottom of the detector is 32.4 cm. The total system efficiencies for 40, 606, and 1376, are listed in Table 8 as are typical minimum detection limits for these nuclides. In 1979, a shadow shield chair geometry replaced the shadow shield bed configuration. the past. The chair whole-body counter used the same electronics as in The system was calibrated using a Bomab bottle phantom. distributed activity concentrations of 40, calibration. 60 Uniformly Co and 1376, were used for system Verification of phantom activity was accomplished as previously