Measurement of 26 Al for atmospheric and climate research and the potential of 26 Al/ 10 Be ratios M. Auer a, * , W. Kutschera a , A. Priller a , D. Wagenbach b , A. Wallner a , E.M. Wild a a Vienna Environmental Research Accelerator (VERA), Institut fu ¨ r Isotopenforschung und Kernphysik, Universita ¨ t Wien, 1090 A-Wien, Austria b Institut fu ¨ r Umweltphysik, Rupprecht-Karls-Universita ¨ t Heidelberg, 69120 D-Heidelberg, Germany Available online 12 March 2007 Abstract The measurement of the paired cosmogenic radionuclides 26 Al and 10 Be in environmental samples has potential applications in atmo- spheric and climate research. For this study, we report the first measurements of the 26 Al/ 10 Be atomic ratio in tropospheric aerosol sam- ples from sites in Europe and Antarctica performed at the Vienna Environmental Research Accelerator (VERA). These initial results show that the 26 Al/ 10 Be atomic ratio in tropospheric aerosols averages 1.78 · 10 À3 and does not vary significantly between the different locations. We also report results of systematic investigations of the ionization and detection efficiency which we performed to improve the measurement precision for 26 Al by AMS. Maximum detection efficiencies of up to 9 · 10 À4 (in units of 26 Al atoms detected/initial) were achieved for chemically pure Al 2 O 3 , while for atmospheric samples we reached efficiencies of up to 2.2 · 10 À4 . Ó 2007 Elsevier B.V. All rights reserved. PACS: 01.30.Cc; 07.75.+h; 92.60.Iv; 92.20.Td Keywords: Atmospheric 26 Al; 10 Be; Accelerator mass spectrometry 1. Introduction Among the long lived cosmogenic radionuclides in the atmosphere, 26 Al (t 1/2 = 0.708 ± 0.017 Ma [1]) has rarely been applied to atmospheric and climate studies to date [2,3]. On Earth, 26 Al is produced in the atmosphere by spallation of argon (atmospheric 26 Al) and is also produced in rock by spallation of silicon (terrestrial 26 Al). 26 Al pro- duced on the Earth’s surface is commonly accreted together with 26 Al from extraterrestrial material such as interplanetary dust (extraterrestrial 26 Al). While terrestrial and extraterrestrial 26 Al have been extensively investigated, data on atmospheric 26 Al are extremely sparse to date, although its potential use in atmospheric and climate research has been recognized [2,4] particularly when mea- sured in combination with 10 Be (The half-live of 10 Be is currently debated with values between 1.51 ± 0.06 [5] and 1.34 ± 0.07 Ma [6]). Atmospheric 10 Be and 26 Al are both produced and deposited in a similar way in the atmosphere. This similar- ity offers a range of applications for 26 Al, of which the most promising is dating of climate archives, in particular old ice relicts via the atomic 26 Al/ 10 Be ratio. If the archive remains a closed system after deposition, the 26 Al/ 10 Be ratio decreases over time due to the different half-lives of 10 Be and 26 Al, with an effective half-life of the 26 Al/ 10 Be ratio between 1.33 Ma for a 10 Be half-life of 1.51 Ma and 1.50 Ma for a 10 Be half-life of 1.34 Ma. Assuming a tempo- rally and spatially constant 26 Al/ 10 Be ratio in atmospheric deposition, it is possible to directly deduce the age of a sample, provided that the initial ratio is well known. The age range which can be addressed by this method is on the order of 1 Ma up to 5 Ma. Especially in ice, these older age ranges are not easily determined by other dating methods. In order to apply 26 Al in atmospheric research, its sources and transport in the atmosphere have to be well 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.305 * Corresponding author. Tel.: +43 1 4277 51712; fax: +43 1 4277 9517. E-mail address: matthias.auer@univie.ac.at (M. Auer). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 259 (2007) 595–599 NIM B Beam Interactions with Materials & Atoms