Development of a gas counter for AMS measurement of 10Be and 26Al of cosmic spherules

Abstract

A gas counter suited for 10Be- and 26Al-AMS was newly developed at MALT (Micro Analysis Laboratory, Tandem accelerator, Research Center for Nuclear Science and Technology, University of Tokyo). This countermeasures not only the residual energy ( E r) of the incoming ion, but also its energy loss (Δ E) in the medium of the counter. Using this new counter, some improvements were made in 10Be- and 26Al-AMS measurements, with respect to the conventional detector system at MALT in which only E r is obtained by a solid state detector (SSD) set after a passive absorber. 10Be is more clearly separated from 10B in the two-dimensional E r– ΔE spectrum. However, the continuous background which is suspected to be 7Be produced by the reaction 10B(p, α) 7Be at the entrance of the absorber could not be clearly separated. This limits the isobar suppression factor for 10Be-AMS at MALT now. In the case of 26Al measurements, 17O 2+, coming together with 26Al 3+ into the detector, could be clearly separated. Consequently, the background level was well lowered in both cases, 10Be and 26Al. Now, 10Be and 26Al in cosmic spherules which were difficult to measure by the conventional detector system can be measured at MALT.