A new capability for ANTARES: 7Be by AMS for ice samples

ANSTO, in collaboration with the Australian Antarctic Division (AAD) and the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), has an on-going program of 10Be (t½ = 1.39 × 106 a) concentration measurement in firn and ice at Law Dome, Antarctica. In recent years snow pit samples have also been measured for 7Be (t½ = 53.28 d) concentration as this isotope has the potential to give further insight into the transport and deposition of cosmogenic beryllium to Law Dome and so improve the use of 10Be as a proxy for solar activity. Early 7Be measurements were made by gamma-ray spectrometry (GRS) with typical counting times of 3 days. In 2010, we developed the capability for 7Be/9Be measurement on the 10 MV ANTARES (Australian National Tandem Accelerator for Applied Research) accelerator using carbon foil post-stripping of 7Be3+ to 7Be4+ to eliminate the 7Li isobar. We describe the method and explain the advantages of using accelerator mass spectrometry (AMS) over GRS for 7Be analysis.