AECD -3446 -22- COUNTING A, Equipment and Operation. A major change from previous years in counting arrangement was made for the 1949 samples, Whereas in earlier years samples had been counted with an end window GM counter, all samples in 1949 were counted in an internal counting chamber continuously flushed with methane. The differences are that in the new arrangement, (1) the counter is more sensitive and hence alpha as well as weak beta can be counted; (2) the geometry is greater, 50 percent as compared to 18 percent; and (3) the chamber can hold a larger plate, up to 2 inches as comparedto 1-1/2 inches, and thereby accommodates an 80 percent larger sample without increasing sample thickness. Stainless steel plates 2 were two of Radiation Counter Laboratory's Nucleometers - Mark 9, Model 3 with a continuous-flow internal counting chamber - Mark 12, Model 1, Operating at a voltage of 4500 volts for one counter and 4700 volts for the other, alpha, beta, and gamma were counted in 1949 whereas in previous years alpha and some soft beta were not counted due to absorption by air and window. Although some alpha counts of the samples were made in the propor- tional range of the counter (3100 volts) and in some instances significant alpha counts were found, the results were not recorded because the ash thickness (4+ 0.7 mg/ cm?) was too great for complete alpha counting, It is intended that a separation of the ash on the plates will be run and then a record of the alpha activity reported later as an appendix to this report. _ Ashing of samples commencedat the Applied Fisheries Laboratory in midSeptember, 1949, and continued off and on until the end of the counting period. ini Difficulty in obtaining 2-inch stainless steel plates of ,005-inch thickness slowed az down the ashing process and necessitated extra handling and storage of the ash. f Counting of samples was delayed until arrival and testing of the Nucleometers had been completed. Practically all of the samples were counted between December, 1949, and March, 1950. A shorter counting period would have been more desirable in that decay between time of making the first and last count does not make the samples exactly comparable. However, since the time elapsed from the Bikini -