Short-Lived DREAMS of Be-7

Short-Lived DREAMS of Be-7

Rugel, G.; Merchel, S.; Scharf, A.; Querfeld, R.; Steinhauser, G.; Tiessen, C.

Routine AMS (Accelerator Mass Spectrometry) nuclide half-lives range from a few thousand to a few million years. In contrast to this, we measured short-lived ⁷Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1]. The possibly troublesome isobar ⁷Li in mass spectrometry is easily separated by passing an additional silicon nitride foil as it does not exist in charge state 4+. The ⁷Be-sample data has been normalized to a proton-activated normalization material (produced by ⁷Li(p,n)⁷Be) that was measured by 𝛾-counting and chemically processed by adding stable ⁹Be carrier to BeO (⁷Be/⁹Be ≈ 10¹²).

This way, at DREAMS ⁷Be could be quantified as low as of 90 mBq, which is a challenge for conventional 𝛾-counting in a timely manner. Additionally, the measurement of ⁷Be and ¹⁰Be (T1/2 = 1.387 Ma) within the same sample is advantageous for investigating the production, transport, and deposition of atmospherically produced ⁷¹⁰Be [2]. Combined with a very good blank ratio of 5 × 10¹⁶ ⁷Be/⁹Be (corresponding to 0.8 mBq), it allows rainwater samples as small as 10 ml to be prepared with simple and fast chemistry (< 7 h for a batch of ten samples) and measured with AMS (< 11 h for a batch of ten samples) [3,4].

DREAMS [1,5] is part of the HZDR Ion Beam Center, a large-scale user facility, where external users apply for free AMS measurements of ⁷Be and other radionuclides (¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, ¹²⁹I,…) via a proposal system.

Acknow.: Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the production and 𝛾-counting of the ⁷Be normalization material. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We would like to thank the DREAMS operator team for their assistance with AMS measurements. Funding by a DAAD RISE-Pro Grant (HZDR-PH-456) is highly appreciated.

[1] Rugel, G., et al.: The first four years of the AMS-facility DREAMS: Status and developments for more accurate radionuclide data. Nucl. Instr. Meth. Phys. Res. B (2016) Issue 370, pp. 94-100. [2] Smith, A.M., et al.: A new capability for ANTARES: ⁷Be by AMS for ice samples. Nucl. Instr. Meth. Phys. Res. B (2013) Issue 294, pp. 59-66. [3] Querfeld, R., et al.: Low-cost production of a beryllium-7 tracer from rainwater and purification: preliminary results. J. Radioanal. Nucl. Chem. (2017) Issue 314, pp. 521-527. [4] Tiessen, C., et al.: Optimising accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rain samples. J. Radioanal. Nucl. Chem. (in preparation). [5]

Keywords: AMS; radionuclide

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