Enrichment of 1 4 CH 4 by Thermal Diffusion for Use in Radiocarbon Dating

By means of a thermal diffusion column the range of the radiocarbon dating method can be extended by about 20 000 years. In order to calculate suitable dimensions and operation conditions, a theory of nonlinear enrichment is derived. On the basis of a formula which describes the dependence of the enrichment factor on time and the characteristic values of the column, a concentric column of 11m length was constructed. The enrichment factors obtained for 13CH4 as a function of time (up to 400 h) and pressure (150 —1500 Torr) and for 14CH4 at 740 Torr and up to 1000 h are presented and discussed. A method is described to indirectly determine the enrichment factor in the stationary state and the characteristic time.