Precision and accuracy of Al-26 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 performe d with Al-26/Al-27 isotope ratio measurements via AMS with the Vienna Envir onmental 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 obtaine d using either Al-metal or Al2O3 samples but inconsistencies of different A l standards were found. An independent Al standard was produced by irradiat ing Al-metal samples with a high neutron fluence measuring the Al-26 activi ty 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 v ery good agreement between the activity and the AMS measurement was obtaine d, normalizing the AMS results with Al standards used at Purdue and Munich. (C) 2000 Elsevier Science B.V. All rights reserved.