Ca-41 measurements on the 1 MV AMS facility at the Centro Nacional de Aceleradores (CNA, Spain)

Abstract

We present a detailed study of the performance parameters for 41Ca measurements at the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) in Seville.

Mixing CaF2 with Ag, we get stable (40CaF3)− currents between 50 and 100 nA. Transmission of the 2+ state in the He stripper is 41%, while optical transmission in the HE sector is typically higher than 95%. At low energies we cannot separate 41Ca from the isobar 41K at the detector, but the interference is reduced by using (41CaF3)− ions. The remaining contribution is corrected by measurement of the other stable isotope of potassium, 39K, to estimate this interference (K-correction). After this correction, we reach a 41Ca/40Ca background level between 5 × 10−12 and 8 × 10−12, making possible measurements of 41Ca/40Ca ratios higher than 4 × 10−11. Intercomparisons with the 0.6 MV AMS system at ETH Zurich show a quite good correlation.