. sample was prepared in which a Project 6.4 ion chamber was sealed and immersed in a l-gal polyethylene bottle containing radioactive washdown water diluted sufficiently with dilute acid to give an activity within the operating range of the detector. The ionization decay data are given in Table 5.3 and are plotted in Fig. 5.3, Survey meter readings at the time indicated background within the shielding to be about 5 to 19 per cent of the room reading as measured at station 73A (Project 6.4 ion chamber), In general, the main background source was above the chambers; however, at + 7 hr the background increased rapidly due to higher cone centrations of activity in the sea about the ship, With the background source being mainly from the hull, station 73A readings would be more affected than those of the sample since it was much nearer the hull, Accordingly, from + 7 to + 16 hr, 5 per cent of 73A was used as a backeground correction instead of 10 per cent as was used for all other readings. 4 new chamber was set up at USNRDL to continue the decay after return of the YAG's, The data for + 120 to + 150 days gave a decay of Tr teode . The high-counting samples as well as background on the YAG 39 proved to be in the severe coincidence loss region of the geiger tube, Before disembarking, two of the decay samples were utilized as split samples to determine the coincidence corrections at the operating counting rates, The readings are given in Table 5.4 along with the standard and background reading, Rb for the holder. The backzround readings show that attempts to keep the planchet holder clean were unsuccessful, Howe ever using the ratios for shelves 3, 4, and 5, and the background readings it was possible to calculate the true background, The observed reading was the sum of the plate contamination plus the background, or J Ry = Bra Ry (5.1) in which a” is the y to x shelf ratio, B the background, and R, the contamination as read on shelf x. Values calculated by use of Eq. 5.1 are given in Table 5,5, The average value of B, 532 c/m, checks well with the value, 531 c/m, when a heavy Al absorber was interposed be- tween the holder and the tube, The coincidence loss for the GM counter was calculated, from, RO = R + R2p, + RT + RAT+... (5.2) in which R is the observed count, the T's are constants and R° is the corrected count, The constants T,, Tg and T3 were determined from the aplit sample data. Thus, for any set of split samples, the corrected total count was, Re° s R,° + Ro® - B (5.3) after substitution for the corrected counts from Eq. 5.2, there resulted, RytRy-Ry-B = (Ry?By?) + (ay-RyRy” )Tgt(Ry*-Ry4-RQ")T3 108 (5.4)