Enhanced beam currents with co-precipitated niobium as a matrix for AMS measurements of 10Be

When dealing with small amounts of 10Be, it is challenging to achieve the good performance in the ion source that is needed to enable a reliable AMS measurement. We have co-precipitated beryllium with dissolved NbCl5, using a range of mixing ratios, to establish an optimal and practical procedure. 9Be16O− beam currents for co-precipitated samples of 9Be-Nb are often higher, but show a slower rise than for samples either co-precipitated or mixed with silver. However, while the Ag sample currents soon deteriorate, Nb sample currents stay high for an extended time, leading to higher measuring performance and better statistics. Although co-precipitated Be-Nb mixtures do not reach such high beam currents as BeO mechanically mixed with Nb powder, we prefer co-precipitation as it provides enough material for handling and an additional mixing step is avoided. We recommend use of NbCl5 as an alternative to AgNO3 on account of the much lower boron association of niobium compared to silver. No critical limit in the matrix:Be mixing ratio was observed, but we note a steady decline of maximum currents reached with increasing mixing ratio.