Radiocarbon dating with tandem electrostatic accelerators

The work to be described represents a collaboration among scientists from the University of Rochester, General Ionex Corporation and the University of Toronto. The cyclotron accelerator technique was used to directly detect 14C and other radioisotopes. The Rochester-General Ionex-Toronto group, which pioneered this new direct detection technique, has made most of the major contributions to this new technology as applied to tandem electrostatic accelerators. These include: 1. Establishing that 14N which differs in mass by only one part in 105 from 14C poses absolutely no background problem in direct 14C detection when a sputter source is used to produce negative ions. No 14N originating as a 14N- ion at the ion source has been detected with the Rochester tandem electrostatic accelerator; 2. Proving that dates back to approximately 70,000 years can be measured in the direct detection of 14C negative ions from carbon samples using a tandem electrostatic accelerator; 3. Establishing that an important molecular contaminant of mass 14, namely 12CH2, is sufficiently stable as a charge 2+ ion that tandem accelerators with terminal potentials of 1 MV or less are inadequate for radiocarbon dating; 4. Demonstrating that sample sizes of a few milligrams or less of carbon are sufficient to establish radiocarbon dates back to 50,000 years or so; 5. Demonstrating that the sensitivity for the new direct detection technique is better than one part in 1013 for the radioisotope 36Cl which is important for establishing million year chronologies for ground water; 6. Demonstrating that the direct radiocarbon detection technique is reproducible to an accuracy of 0.7% - 3% (corresponding to radiocarbon dating uncertainties of more or less 60 to more or less 250 years) with the ultimate limit set by 14C counting statistics. The author discusses these contributions and gives experimental data