UCLA Radiocarbon Dates IV

Abstract

The measurements reported in this list have been carried out in the Isotope Laboratory of the Institute of Geophysics and Planetary Physics during 1964. They are a continuation of the previously reported date lists UCLA I, II and III. The same counting procedure has been continued: CO₂ proportional counting at 1 atm of pressure in a 7.5 L counter with three energy channels. Dates have been calculated according to the recommendations of the Fifth Radiocarbon Conference, Cambridge, 1962, on the basis of a radiocarbon half-life of 5568 yr (Godwin, 1962). The modern standard for organic samples has been based on 95% of the count rate of NBS oxalic acid for radiocarbon laboratories. Background measurements are determined with CO₂ derived from marble. The ages of carbonate-containing substances such as shells and tufa have been calculated on the basis of estimates for the corresponding contemporary C¹⁴ activity (Broecker and Walton, 1959), as discussed in the respective sample descriptions. New methods of sample preparation are described in context with the date listings.