SLIDE 39 Whole-body counter. The detector chosen for field use by Brookhaven personnel was a 28 cm diameter, 10 cm thick, sodium ifodide thallium activated scintillation crystal NaI(Tl). It is optically coupled to three low background magnetically shielded photomltiplier tubes connected in parallel through a summing box with the combined output routed to an amplifier and then to a microprocessor-based computer and pulse height analyzer (PHA). The PHA data is stored on a magnetic discette, and results are analyzed in the field and at BNL using a matrix reduction, minimization of the sum of squares techniques. 207 The gamma emitting nuclides observed have been 657n, 137 G6 60G5 and Bi. Additionally, naturally occurring K is present in normal amounts. A typical counting time is 15 minutes and a typical minimum detection limit is 100 Bq (3 nCi). The whole-body counting system is currently standarized against a human like phantom.