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

Abstract

This report presents a procedure for background correction of indirect isobaric interference by 10B in accelerator mass spectrometry of cosmogenic 10Be. A gas counter with an absorber cell for 10B is used as a detector. Injected ions are detected by two anode plates aligned in the main ionization chamber to plot the signals on a two-dimensional spectrum of loss and residual energies. Using this configuration, the tail of 10B events that manage to pass through the absorber cell can be separated from the 10Be events, but the total counts in the 10Be region are increased by 7Be generated from the reaction of 10B(1H,4He)7Be due to hydrogen attached on the surface of the entrance window of the absorber cell. Since the number of 7Be events are proportional to the counts of 4He events, we can evaluate the interference via statistical analyses for correlations between counting data for multiple regions of interest on the two-dimensional spectra. This correction results in an increase in uncertainty for the counting statistics, but improves the accuracy of the maximum likelihood value of the 10Be/9Be isotopic ratios.