Experimental investigation of the destruction of 1 MeV 12CH2 molecules in single and double stripping foils

Abstract

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 14C was observed for a single foil with thickness 4.4 μg/cm2. 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 μg/cm2 foil correspond to a surviving fraction in the 2+ charge state of less than 6 × 10−10. No statistically significant molecular survival was observed for pairs of stripping foils with a combined thickness of 4.0–4.6 μg/cm2, 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 14C 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 14C. A low energy system using a double-foil stripper may be potentially useful for radiocarbon dating.