Comparison of 41Ca analysis on 0.5 MV and 5 MV-AMS systems

A comparative study was made between the compact AMS system at the PSI/ETH Laboratory of Ion Beam Physics in Zurich with 0.5 MV terminal voltage and the 5 MV-AMS system at the Scottish Universities Environmental Research Centre (SUERC), Glasgow. Overall 34 urinary samples with 41Ca/40Ca ratios in the range from 4 x 10-11 to 3 x 10-10 were processed to CaF2 and aliquots of the same material were measured on both instruments. Measurements on the compact AMS system were performed in charge state 3+ achieving a transmission of 4% at 1.7 MeV beam energy. Under these conditions a suppression of the interference 41K is virtually impossible. However, samples with an excess of potassium can be identified by a shift of the 41Ca/41K peak in the ΔE -E histogram of the gas ionization detector employed and a criterion for data rejection can be defined. An overall precision of ∼4% and a 41Ca/40Ca background level of 5 x 10-12 have been reached. For studies with higher demands on the detection limit AMS systems like the one at SUERC are attractive: in charge state 5+ and using a gas stripper beam energy of 27 MeV, a transmission of 5%, a 41K suppression factor of ∼500 and a 41Ca/40Ca background level of 3 x 10-14 are achieved. We demonstrate that both systems are well suited for large-scale 41Ca biomedical applications.