The following list of dates is compiled from samples prepared and catalogued since publication of our last date list (R, 1975, v 17, p 99-111). The counting equipment and operating procedures are the same. Ages are quoted with a 1σ counting error which includes statistical variation of the sample count as well as for background and standard, using ad 1950 as the reference year and 95% NBS oxalic acid for 14C dating as the standard. The half-life value used is 5570 years.

The following radiocarbon measurements are a partial list of geologic samples from S Florida dated during the summer of 1975. The technique used is liquid scintillation counting of wholly synthesized benzene as indicated in R, v 16, p 402-408 and R, v 18, p 210-220. Dates are calculated using a 14C half-life of 5568 yr and errors are reported as one standard deviation. Before conversion, shell material was etched with HCl to remove all soft or powdery material. All wood and peat samples were treated with NaOH.

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.

This list comprises age measurements carried out from 1973 to 1974 In dating the samples reported here as well as in calculating their ages, the same equipment and methods were used as previously described (R, 19/3, v 15, p 586–591; 1974, v 16, p 388–394).

Measurements have continued with the same proportional counter system, pretreatment procedure, methane preparation and measurement, and calculation, as described previously (R, 1970, v 12, p 298-318). Uncertainties quoted are single standard deviations originating from standard, sample, background counting rates and half-life. No 13C/12C ratios were measured.

The following list of dates are selected from geologic and archaeologic samples measured in early 1975. The technique employed is liquid scintillation counting of wholly synthesized benzene as described by Noakes et al (1965) and discussed in R, v 16, p 402–408. Errors are reported as one standard deviation.

Procedures and equipment of the laboratory have been described in previous date lists. Lake cores and marls are treated with acid only, wood, charcoal, and peat samples with dilute NaOH and dilute H3PO4 (unless indicated otherwise) before conversion to methane which is used as counting gas.

This list of radiocarbon age measurements is for the period 1972–1974. Most of the samples are of archaeologic interest. The pretreatments of samples used are basically those described by Ralph and Michael (1971). All samples were converted to methane using the method developed by Fairhall, Schell, and Takashima (1961) and counted in .5L counting tubes at 2 to 4atm of pressure. The WSU Radiocarbon Laboratory has been relocated to the basement of Dana Hall (three stories) and additional shielding has been added. The backgrounds of the counting tubes are .90 counts/min and have an atmospheric pressure dependence of –.035 counts/min/cm Hg.