CA-41 MEASUREMENTS AT THE ZURICH AMS FACILITY

With a half-life of (104 +/- 5) kyr, which lies between the one of C-1 4 and Cl-36, Ca-41 is of interest for studies of the irradiation histo ry of extraterrestrial materials. The determination of Ca-41 by activi ty measurement is not easy because it purely decays via electron captu re with K-X-rays of 3.3-3.6 keV. A better way to measure the Ca-41 con tent is to use accelerator mass spectrometry (AMS). Our main goal is t o study the production cross-sections of Ca-41 and to analyze samples of extraterrestrial material. In order to obtain absolute Ca-41/Ca-40 ratios a new standard reference material has been produced by irradiat ing (CaCO3)-Ca-40 in the DIDO reactor of KFA Julich and measuring the Ca-41 activity with liquid scintillation spectroscopy at the PTB. As t he use of Ca-3(-) ions minimizes the K-41 background CaH2 targets have been produced. For the AMS measurements of Ca-41 the first attempts w ith our tandem accelerator with only 6 MV are shown. A high-intensity ion source and final identification with the dE/dx technique and a tim e-of-flight measurement has been used. At the present status of the ex periment blank values of Ca-41/Ca-40 ratios of 10(-13) have been reach ed, just limited by the detection efficiency.