14C ages of 10 Yamato and Allan Hills meteorites

Carbon was extracted from 1g samples of ten Antarctic chondrites, using stepwise heating. The evolved CO_2 was collected at 1000℃, melt and remelt. The ^C concentrations were measured at the Isotrace AMS facility and were compared with the zero-age ^C concentration of the Bruderheim (L6) chondrite. The Allan Hills meteorite ALH-77231 (L6) yielded a terrestrial age, not corrected for in situ production, of 30ka. The uncorrected terrestrial ages of the 9 Yamato meteorites Y-74014 (H6), Y-74097 (Dio), Y-74191 (L3), Y-75271 (L5), Y-790448 (LL3), Y-791500 (H3), Y-791630 (L4), Y-791717 (C3) and Y-74647 (H5) showed a wide range from 500a to 30ka

The IAEA 14C Intercomparison Exercise 1990

As a follow-up to the meeting of experts convened at the International Atomic Energy Agency (IAEA) in February 1989, and the International 14C Workshop held in Glasgow in September 1989, the 14C Quality Assurance Program was formulated. In a joint effort of several radiocarbon teams and IAEA staff, we have prepared a set of five new intercomparison materials. These are natural materials frequently used by radiocarbon laboratories. The materials were distributed to 137 laboratories in May 1990. In February 1991, a meeting of experts was convened in Vienna to evaluate the results, to determine the radiocarbon activity of the five samples expressed in % Modern (pMC) terms and to define the 13C/12C ratio, and to make recommendations on further use of these materials. We present here the results of the exercise and the agreed consensus values for each of the five materials and discuss the different analyses that were undertaken.

An attempt to detect stable N- ions from a sputter ion source and some implications of the results for the design of tandems for ultra-sensitive carbon analysis

The present paper discusses an experiment, using a Middleton sputter ion source, where a sensitive search was made for 14N- ions in the presence of an intense carbon beam. It was found that negative nitrogen ions, capable of withstanding acceleration fields of 1.5 MV/m, were not produced in detectable intensities. The paper also points out some design requirements of tandem facilities that must be satisfied if full advantage is to be taken of this negative result to permit the measurement of very weak 14C beams