Isotopes, Inc. radiocarbon measurements, [Part] 1.

Abstract

Radiocarbon analyses have been performed at Isotopes, Inc. since 1957 using proportional-counting techniques. Carbon dioxide is employed as the counting gas at pressures up to 2 atmospheres. The counter presently in service is electrolytic Cu and has an active volume of just under 2 liters. It is shielded by 1 in. of Hg, a ring of 23 G-M counters operated in anti-coincidence with the sample counter, 4 in. of paraffin wax, and 18 in. of hot-rolled steel. A background of 9.2 counts/min. has been attained with this arrangement. Prior to use of the NBS oxalic-acid standard, the modern standard was 1885 pine wood. Age corrected to 1960, this wood had an activity of 94.0 + or - 1.9% of the NBS oxalic-acid standard. The NBS oxalic-acid standard is now being used as the modern value, and A (sub ox) X 0.95 is 23.3 counts/min. corrected to a standard temperature of 273 degrees K. Shell dates reported were calculated using the pine-wood standard, without correction for supposed fractionation of C isotopes.