Measurements of 10Be and 26Al in some meteorites with internal beam monitor method

Abstract

Using the technique of “internal beam monitor method”, 26Al measurement of accelerator mass spectrometry with a low terminal voltage has been developed at the University of Tokyo tandem accelerator. Negative ion mixtures of 26Al − and 10B 16O − beams were accelerated with terminal voltages as low as 2.5 MV, and separated into a “main beam” ( 26Al 3+, 10 MeV) and a “monitoring beam” ( 16O 2+) by the magnet. The 26Al 27Al ratio was obtained by the simultaneous measurements of 26Al 3+ and 16O 2+, and measurement of negative ion current ratio ( 10B 16O − 27Al − ). The reproducibility in this method was found to be better than 7% by the measurements of a series of standard samples of 10 −9 to 10 −12 in 26Al 27Al ratio. The sensitivity was estimated to be about 1 × 10 −13. Using this technique, 26Al and 10Be in meteorites were measured. Preliminary results were obtained in four iron meteorites and in the metal phase and the whole rock of two chondrites. The 26Al 10Be activity ratios in Odessa, Henbury, Grant, ALH762, Peace River (Metal) and Bruderheim (Metal) meteorites were found to be 0.52, 0.67, 0.58, 0.68, 1.17 and 1.15, respectively.