MAT science Week

Half-lives of routine accelerator mass spectrometry (AMS) nuclides typically range from thousands to millions of years. We measured short-lived $^{7}$Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1] as low as 90 mBq, which can be challenging for rapid $\gamma$-counting. Simultaneous determination of $^{7}$Be and $^{10}$Be (T$_{1/2}$ = 1.387 Ma) via AMS is advantageous for improved understanding of production, transport, and deposition of atmospherically produced $^{7,9,10}$Be [2]. Data was normalized to a $^{7}$Be sample produced via $^{7}$Li(p,n)$^{7}$Be, measured by $\gamma$-counting and chemically processed to BeO after adding low-level $^{9}$Be carrier ($^{7}$Be/$^{9}$Be $\approx 10{^{-12}}$). The isobar $^{7}$Li is completely eliminated by chemistry and the degrader foil technique (at detector $^{7}$Be$^{4+}$, 10.2 MeV, no $^{7}$Li$^{4+}$ possible). The blank ratio of $5\times 10{^{-16}}$ $^{7}$Be/$^{9}$Be (0.8 mBq) and simple and fast chemistry allows for the measurement of rainwater samples, collected in Germany, as small as 10 mL corresponding to a few times $10{^{-14}}$ $^{7}$Be/$^{9}$Be [3,4]. Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the $^{7}$Be normalization material. [1] G. Rugel et al., *NIMB* 370 (2016) 94. [2] A.M. Smith et al., *NIMB* 294 (2013) 59. [3] R. Querfeld et al., *JRNC* 314 (2017) 521. [4] C. Tiessen et al. *JRNC* (to be submitted).