44 of the two counting systems available for use consisted of four diodes, pre- amlifiers and amplifiers routed through a router-mixer to each of four 128channel quadrants of a 512-channel multichannel analyzer (MCA). The MCA cea ee ee Fare ag ney tn --rery was dumped ‘nto beth typewriter (digitzl) and graphical (analog) outputs after typical counting periods of 800 minutes. gzin was adjusted to 10 KeV/channel. c7 KeV or better. The detector amplifier The resolution of the diodes (FHI) was Background count rates in the four diodes used for plutonium and uranium analysis were 0-8 counts/&00 minutes under each of the observed alpha peaks. Background count rates in the four diodes used for polontum analysis were typically 5 counts/800 minutes/peak. The absolute disintegration rate of the isotopes of plutonium, uranium and 2105, in the plated samples was determined hy computing the ratio of the count rate observed for each isotope to the count rate for a secondary Standard of known disintegration rate; corrections were made for background count rate, alpha particle branching ratios, and any impurities in the radiochenical spikes. The disintegration rate of the secondary standards of plutonium was ea: Getermined by similar calibrations with a standard the AEC Health and Safety Laboratories (HASL). 236 Pu solution supplied by The reliability of the pluto- nium calibration was verified by the agreement between the concentrations of plutonium found by this laboratory and these found by other laboratories in @ subsequent interlaboratory standard 23942405, solution supplied hy the Lawrence Livermore Laboratory. In addition, the 239+2405 and 2385, concen- trations measured by this laboratory in seaweed and sediment samples supplied ty the International Atomic Energy Agency were also in close agreement to those recommended by the IAEA. are Shown in Table 6. The results of both these intercalibrations