The dates reported in this list are for geologic and archaeologic samples only. During the interval since our last date list (R, 1966, v 8, p 498-506) most of our measurements have been on samples of sea water. These will be reported separately at a later time. The methods used are essentially those reported previously (R, 1963, v 5, p 80-81) but with the following notable changes and additions: We now prepare our methane counting gas as described in Buddemeier et al (1970). Our IL membrane counter has since been augmented by 3 additional counters. Two of these are IL quartz proportional counters inside geiger anticoincidence shields. Operating pressures are ca 1.5 to 4atm. Backgrounds of these 2 counters are in the neighborhood of 1.8 and 3cpm and the net counting rate of NBS oxalic acid ranges from 7 to 18.7cpm, depending on the pressure. The third counter (“minicounter”) is rather special: .IL quartz proportional counter inside a methane proportional anticoincidence counter. Sample and anticoincidence counting gases are introduced simultaneously with a differential pressure that never exceeds a few cm Hg. The sample filling side is constructed so as to minimize dead volume; over 80% of the sample gas is inside the active volume of the 14C counter. The range of filling pressures which are possible is ca 1 to 4atm.
University of Washington Dates IV