UCLA Radiocarbon Dates IX

Abstract

The measurements reported have been carried out during the first half of 1968 in the Isotope Laboratory of the Institute of Geophysics and Planetary Physics as a continuation of the UCLA date lists I through VIII. Samples were analyzed as CO₂-gas at close to one atm in a 7.5 L proportional counter with three energy channels described in earlier publication. Radiocarbon ages have been calculated for uniformity on the basis of a 5568 yr half-life in accord with a recommendation by the Sixth International C¹⁴and H³Dating Conference, June 1965, in Pullman, Washington. The standard for the contemporary biosphere remains as 95% of the count rate of NBS oxalic acid for radiocarbon laboratories. Background determinations have been based on CO₂obtained from marble. The error listed is always at least a one-sigma statistical counting error. In critical cases C¹³/C¹²isotope ratio measurements were made to correct the dates for fractionation. All samples were subjected to accepted NaOH, HCl or other special chemical pretreatments discussed below depending on the individual case to exclude contamination.