Detecting Beryllium-10 from exotic decays by Accelerator Mass Spectrometry (AMS)

The one-neutron halo-nucleus ¹¹Be decays via beta-minus to the stable nucleus ¹¹B (t_1/2=13.76 s). In rare cases a subsequent emission of a proton leads to the unstable nucleus ¹⁰Be. Theoretical calculations predict a branching ratio of this rare decay channel of below 10^-7. With the capability of AMS in measuring ultra-low isotopic ratios (¹⁰Be/⁹Be < 10^-15) the branching ratio of beta-delayed proton decay to ¹⁰Be could be measured for the first time.
A beam of ¹¹Be ions was produced at the radioactive ion beam facility ISOLDE at CERN. After mass separation the ions were implanted in Cu targets. These targets containing the produced ¹⁰Be were spiked with low-level ⁹Be and in the form of BeO chemically prepared as AMS targets at HZDR. The resulting ¹⁰Be/⁹Be ratios were determined via AMS at the VERA laboratory of the University of Vienna. With the known quantity of added ⁹Be the amount of implanted ¹⁰Be was calculated. Due to the low expected branching ratio and the resulting low number of implanted ¹⁰Be atoms a high efficiency paired with a low background of the ⁹Be carrier material was necessary.
To further widen the spectrum of radionuclides measureable by AMS and lowering the detection limits for similar nuclear physics research, we are planning to implement an optical filtering method for selective suppression of isobars by laser photodetachment (LISEL) at the 6 MV tandem accelerator at HZDR.