Measurement of 10Be in air filters using BeF− ions from BaBeF4

AMS 10Be measurements in air filter samples have been carried out using targets of BaBeF4 and by injecting BeF− ions. As there is little interference from 10B due to the instability of BF−, it was possible to directly count 10Be2+ ions at 2 MV tandem voltage for the measurements. Due to the undesirable hydroscopic nature of BeF2 targets, we describe the preparation procedure for BaBeF4 as an alternate final compound, which was found to have 100% efficiency for precipitating beryllium. The low (⩽10 nA) BeF− current from the IsoTrace 834 SIMS type source was adequate for measuring 10Be in these air filters, which were exposed to 18,000 m3 air during the sampling process. The direct measurement of 7Be and possibly 10Be from the same sample preparation, appears to be quite feasible using BeF3- ions. The production efficiency for BeF3- from BaBeF4 is 5–10 times that of BeF− and is closer to that of BeO− from BeO targets. A potential beryllium carrier-free sample preparation method of producing BeF2 by co-precipitation with a fixed quantity of CaF2, is also discussed.