EXPERIMENTAL INVESTIGATION OF THE DESTRUCTION OF 1 MEV (CH2)-C-12 MOLECULES IN SINGLE AND DOUBLE STRIPPING FOILS

We have performed experiments examining the destruction of mass-14 mol ecules in the 2+ charge state after passage through both single and do uble carbon stripping foils at 1 MeV. A background level of less than 2% of contemporary C-14 was observed for a single foil with thickness 4.4 mu g/cm(2). Significantly increased attenuation of 1 MeV molecular ions after passage through a pair of thin carbon stripping foils was demonstrated, as compared to a single carbon foil of comparable total thickness. The detected molecular counts after passage through a singl e 4.4 mu g/cm(2) foil correspond to a surviving fraction in the 2 + ch arge state of less than 6 x 10(-10). No statistically significant mole cular survival was observed for pairs of stripping foils with a combin ed thickness of 4.0-4.6 mu g/cm(2), with an upper limit on surviving m olecular fraction a factor of 15 lower than for the single foil. These results show that a low energy AMS system based on the detection of C -14 in the 2 + charge state after a foil stripper will provide more th an adequate discrimination for the analysis of biomedical samples labe led at or above contemporary C-14. A low energy system using a double- foil stripper may be potentially useful for radiocarbon dating.