then to a microprocessor-based computer/pulse height analyzer (PHA). The PHA data is stored on a magnetic discette, and the results may be analyzed either in the field or at BNL using a matrix reduction, minimization of the sum of squares technique (TS 76). B. Calibration Analysis of NaIl(Tl) spectra by the matrix reduction technique requires that the computer library contain individual standards for each radionuclide that is expected in the field measurements and that the field measurements and standards be the same geometry. To accomplish this, a review of the previous whole body counting data (CO 75, CO 77) 6005 and 13706, indicated the need to calibrate for 405 The current system was calibrated using an Anderson REMCAL phantom (CO 63). Each radionuclide was introduced into the phantom's organs in an amount equivalent to the fraction of the total body concentration as defined by the ICRP in Publication 2 (ICRP 59). 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 radioac~ tive 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 nd subject and the standard phantom was positioned such that the central