41Ca measurements at the Zurich AMS facility

Abstract

With a half-life of (104±5) kyr, which lies between the one of 14C and 36Cl, 41Ca is of interest for studies of the irradiation history of extraterrestrial materials. The determination of 41Ca by activity measurement is not easy because it purely decays via electron capture with K-X-rays of 3.3–3.6 keV. A better way to measure the 41Ca content is to use accelerator mass spectrometry (AMS). Our main goal is to study the production cross-sections of 41Ca and to analyze samples of extraterrestrial material. In order to obtain absolute 41Ca 40Ca ratios a new standard reference material has been produced by irradiating 40CaCO 3 in the DIDO reactor of KFA Jülich and measuring the 41Ca activity with liquid scintillation spectroscopy at the PTB. As the use of CaH 3 − ions minimizes the 41K background CaH 2 targets have been produced. For the AMS measurements of 41Ca the first attempts with our tandem accelerator with only 6 MV are shown. A high-intensity ion source and final identification with the dE dx technique and a time-of-flight measurement has been used. At the present status of the experiment blank values of 41Ca 40Ca ratios of 10 −13 have been reached, just limited by the detection efficiency.