Calcium-41 Concentration in Terrestrial Materials: Prospects for Dating of Pleistocene Samples

Abstract

Calcium-41 has been suggested as a new tool for radiometric dating in the range of 10(5) to 10(6) years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10(-14) and 3 x 10(-15) were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.

41Ca Concentrations in Modern Bone and Their Implications for Dating

“…We have made the first measurements without pre-enrichment of 41Ca in terrestrial rock and bone samples using accelerator mass spectrometry. Although the results in tufa deposits from Egypt are in good agreement with the saturation value of 8 x 1015 predicted by Raisbeck and Yiou (1979), the average 41Ca:40Ca ratio of 2x1015 (range: 0.6 to 4.2x1015) that we measure in modern bone is an order of magnitude lower than that obtained previously by Henning, et al (1987) on a cow bone that was measured using AMS following isotope enrichment. The low value and the variability (more than a factor of seven) of the 4 Ca:40Ca ratio in modern bone make the possibility of dating bones using 41Ca unlikely.…”

Single-atom detection of calcium isotopes by atom-trap trace analysis

“…Because there are no interferences from other elements ATTA has the potential to also detect the long-lived isotope 41 Ca at its natural abundance level of 10 −14 [5]. This would open the possibility to perform radio-calcium dating with 41 Ca, which has a half-life of 10 5 years [5,6]. Furthermore, 41 Ca could be used as a tracer to directly monitor the bone loss and retention rates of human subjects in both research and diagnosis of osteoporosis [7].…”

“…In a recent experiment one million year old groundwater from the Nubian Aquifer (Egypt) has been dated using ATTA, by detecting very small traces of 81 Kr [4]. Because there are no interferences from other elements ATTA has the potential to also detect the long-lived isotope 41 Ca at its natural abundance level of 10 −14 [5]. This would open the possibility to perform radio-calcium dating with 41 Ca, which has a half-life of 10 5 years [5,6].…”

Radiocarbon dating coming of age

“…In fact, atom counting is not dependent on the half-life, and therefore allows one to measure longlived radioisotopes which could not be detected at natural abundances with decay counting. An example is cosmogenic 41 Ca (t 1/2 = 104,000 yr), which was studied with AMS in a variety of applications [21,22].…”