The following list comprises measurements made since those reported in NPL II and is complete to the end of

The following list comprises measurements made since those reported in NPL III and is complete to the end of November 1965.Ages are relative to A.D. 1950 and are calculated using a half-life of 5568 yr. The measurements, corrected for fractionation (quoted δC13 values are relative to the P.D.B. standard), are referred to 0.950 times the activity of the NBS oxalic acid as contemporary reference standard. The quoted uncertainty is one standard deviation derived from a proper combination of the parameter variances as described in detail in NPL III. These variances are those of the standard and background measurements over a rolling twenty week period, of the sample δC14 and δC13 measurements and of the de Vries effect (assumed to add an additional uncertainty equivalent to a standard deviation of 80 yr). Any uncertainty in the half-life has been excluded so that relative C14 ages may be correctly compared. Absolute age assessments, however, should be made using the accepted best value for the half-life and the appropriate uncertainty then included. If the net sample count rate is less than 4 times the standard error of the difference between the sample and background count rates, a lower limit to the age is reported corresponding to a net sample count rate of 4 times the standard error of this difference.

The following list comprises measurements made since those reported in Radiocarbon, 1969, v. 11, P. 130-136. No changes have been made in measurement technique or in the method of calculating the results described in Radiocarbon, 1965, v. 7, p. 156-161. It was necessary during 1968 to replace all the geiger counters used in the anti-coincidence rings, but the long term stability of background and standard count rates implicit in the use of a 20-week rolling mean has been maintained.Ages are given relative to A.D. 1950 and have been calculated using a half-life of 5568 yr. Measurements, corrected for fractionation relative to the P.D.B. standard, are referred to 0.950 times the activity of the NBS oxalic acid as contemporary reference standard. The quoted uncertainty is one standard deviation and includes an additional uncertainty, taken to be equivalent to a standard deviation of 80 yr, for the de Vries effect, but excludes the uncertainty of the half-life. Should a net sample count rate be less than 4 times the standard error of the difference between the sample and background count rates a lower limit to the age would be reported corresponding to a net sample count rate of 4 times the standard error of this difference.

No abstract

The following list comprises measurements made since those reported in NPL V.No changes have been made in measurement technique or in the method of calculating results described in NPL III.