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 molecules in the 2+ charge state after passage through both single and double 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 single 4.4 mu g/cm(2) foil correspond to a surviving fraction in the 2 + charge state of less than 6 x 10(-10). No statistically significant molecular survival was observed for pairs of stripping foils with a combined thickness of 4.0-4.6 mu g/cm(2), with an upper limit on surviving molecular 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 than adequate discrimination for the analysis of biomedical samples labeled at or above contemporary C-14. A low energy system using a double-foil stripper may be potentially useful for radiocarbon dating.