cc ctal. Te is epticzsil; coupled ro seven, 7.5 om diameter iew background magnetically shielded, photomultiplier tubes. The signal output from each photomultiplier tube is connected in parallel and the combined output routed to ‘a preamplifier/amplifier and 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). 2. Calibration Analysis of 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) indicated the need to calibrate for 40% 6045 and 13765, The present system was calibrated in 1978 using an Anderson REMCAL phantom (co 63) and in 1979 using a BOMAB bottle phantom. Each radionuclide was introduced into the phantom's organs in an amount equivalent to the fraction in organ of reference of that in total body as defined by the ICRP in Publication 2 (ICRP 59). Under conditions of continuous exposure where equilibrium has been reached these fractions are correct. This is achieved for the nuclide 405, The nu- clides 606, and 13766 are in non-equilibrium throughout the exposure and post ex- posure intervals. Cesium is taken up principally in cells with 80% to muscle and 8% to bone (SP 68) where the mean residence times are both 160 days. This implies a nearly uniform distribution of the nuclide throughout the whole body. Thus, with 88% of the uptake spread throughout the body with a long halftime and with the remaining 12% of the uptake in the extracellular fluid, which retains