Preparation of Ca-41 AMS standards

Absolute accelerator mass spectrometry (AMS) measurements require reliable standards for calibration. The Space Sciences Laboratory at the University of California, Berkeley, and the Center for Accelerator Mass Spectrometry a t Lawrence Livermore National Laboratory (LLNL) have prepared new Ca-41 AMS standards. The highly enriched (CaCO3)-Ca-41 was obtained from Oak Ridge N ational Laboratory. After purification of the CaCO3, the precise Ca-41/Ca r atio in the original material was determined by surface ionization mass spe ctrometry. The Ca-41 was sequentially diluted with natural Ca to obtain Ca- 41/Ca ratios of 1.155 x 10(-10) 9.755 x 10(-12) 5.139 x 10(-12) 1.095 x 10( -12) and 5.884 x 10(-13). A solution with a Ca-41/Ca ratio of 10(-6) was al so prepared for biomedical research. The solutions having Ca-41/Ca ratios b etween 10(-10) and 10(-12) were measured by AMS. Although the present blank level, 5 x 10(-14) Ca-41/Ca, was higher than anticipated, excellent linear ity was obtained from 6 x 10(-13) to 1.2 x 10(-10) Ca-41/Ca. (C) 2000 Elsev ier Science B.V. All rights reserved.