Precision and accuracy of 26Al measurements at VERA

An accurate determination of the Al-27(n,2n)Al-26 excitation function near threshold was carried out. The detection of the produced Al-26 was performed with Al-26/Al-27 isotope ratio measurements via AMS with the Vienna Environmental Research Accelerator (VERA). To this end systematic investigations of Al-metal and Al-oxide samples were performed and several standards were systematically investigated. No difference in the AMS results were obtained using either Al-metal or Al2O3 samples but inconsistencies of different Al standards were found. An independent Al standard was produced by irradiating Al-metal samples with a high neutron fluence measuring the Al-26 activity with a Ge-diode. The resulting Al-26/Al-27 ratio could then be directly compared with the results from an AMS measurement on the same material. A very good agreement between the activity and the AMS measurement was obtained, normalizing the AMS results with Al standards used at Purdue and Munich. (C) 2000 Elsevier Science B.V. All rights reserved.