Measurement of ¹⁰Be in 1,000- and 5,000-year-old Antarctic ice

Abstract

MEASUREMENT of radionuclides by nuclear accelerator spec-trometry may lead to wider application of measurement of long-lived cosmogenic isotopes to archeological, geophysical and astrophysical problems (see ref. 1 for further details of the technique). We previously² discussed the prospects for the isotope ¹⁰Be and reported the successful measurement of this isotope using both the internal2 and the external³ ion sources of the Grenoble cyclotron. ¹⁰Be (half life = 1.5 × 10⁶yr; ref. 4) is formed by the interaction of cosmic rays with the Earth's atmosphere, and then precipitated out into various geophysical reservoirs such as marine sediments and polar ice⁵. The ¹⁰Be profile in these reservoirs can thus be used to search for evidence of historical variations in parameters (geomagnetic field, solar modulation, primary cosmic ray intensity) which influence the deposition rate. We report here the use of the accelerator technique for the determination of ¹⁰Be concentrations in samples of Antarctic ice believed to be about 1, 000 and 5, 000 yr old. The only published measurement for ¹⁰Be in polar deposits is that of McCorkell et al.⁶ who made their measurement on a sample extracted from 1.2 × 10⁶ l of Greenland ice. The present measurements were made on samples from 10 l. We believe this difference is indicative of the tremendous potential that is offered by the accelerator technique.