D. Fink, R. Middleton, J. Klein, P. Sharma, University of Rochester

Nuclear Instruments and Methods 47 (1990) 79-96

We describe in detail methods and techniques we have developed to measure 41 Ca/40Cu ratios to a sensitivity of 6 x 10^-16 using our FN tandem accelerator. The major steps involved were (1) adoption of 41CaH3 negative ions to reduce 41K (41K/40Ca _ 5 x 10^-13); (2) production of typically 5 mu A of 40CaH3 ions from calcium hydride in a high-intensity source: (3) refinement of a technique to efficiently convert CaO samples, as small as 15 mg, into CaH2: (4) implementation of a high resolution velocity selector to remove interferring 40Ca and 42Ca ions and (5) use of a multi-anode gas ionization detector to provide excellent discrimination of 41Ca from the remaining background ions. The system performs admirably, enabling measurements with +- 5% reproducibility on extraterrestrial samples. such as meteorites and lunar rocks. In addition, we have also carried out the first measurements. without pro-enrichment, of 41Ca in terrestrial rockss and bones. From these measurements, we conclude that radiocalcium dating of bones will most likely not develop into a viable dating technique. The 41Ca concentrations in modern bones are not only disappointingly low and quite close to our sensitivity limit. but show a marked variability. On the other hand, the study of 41Ca in extraterrestrial samples offers much promise as a means of determining terrestrial ages and pre-atmospheric sizes of meteorites, and of investigating the average solar cosmic ray flux during the past 300000 years.