A method for background correction in 10Be detection: evaluation of indirect isobaric interference by 7Be generated at the entrance window of a gas counter

Dr Yuki Matsushi1, Dr Hiroyuki Matsuzaki2

1Kyoto Univ, Gokasho, Uji, Japan, 2The University of Tokyo, Yayoi, Bunkyo-ku, Japan

This report presents a method of background correction for isobaric interference by 10B in 10Be accelerator mass spectrometry with 4.8 MV terminal voltage and 10Be3+ ion counting at Micro Analysis Laboratory, Tandem Accelerator, The University of Tokyo. The detector used here is a gas counter with an absorber cell (5 cm in length) filled with 12 kPa of N2 gas, which is separated by a Havar foil of 5.6 μm in thickness at the entrance and 3.0 μm-thick polypropylene film at the outlet. Signals of injected 10Be3+ were detected by two anode plates aligned in the main ionization chamber filled with of 6 kPa of flowing P-10 gas (90% Ar and 10% CH4), to plot the events on a 2D spectrum of loss and residual energies. By this configuration, tail of 10B signals can be clearly separated from the 10Be events, but the counts are enhanced by interposition of 7Be generated from reaction of 1H(10B, 7Be)4He due to hydrogen attached on the surface of the entrance Havar window. As the number of 7Be events should be proportional to the counts of 4He and/or 10B events, we can evaluate the interference via a statistical analysis for correlations between counting data for the multiple regions of interest on the 2D spectra. Here we propose a procedure for accurate background correction and demonstrate the validation using standards, chemical blanks, and natural samples with different 10Be/9Be isotopic ratios.


A geomorphologist using TCN.

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