A search for novel β^--delayed proton decay in 11Be at NSCL

In 2014, the apparent transmutation of a ¹¹Be sample gathered at CERN-ISOLDE into ¹⁰Be was observed by applying the accelerator mass spectrometry (AMS) technique to the sample. The inferred β^--delayed proton branch was nearly two orders of magnitude greater than expected; however, in 2019, a direct measurement of the ¹¹Be(β^-p) decay at TRIUMF yielded a similarly large proton branch intensity. A series of new AMS measurements from 2020 observed ¹⁰Be production rates yielding a β^-p intensity upper limit that is inconsistent with both previous (AMS, direct) measurements. Contamination of the ¹¹Be sample by molecular ¹⁰BeH in the low-energy beam is a plausible explanation for the AMS measurement inconsistencies.

We present the analysis status of an independent search for direct detection of low-energy protons from ¹¹Be(β^-p) with the Gaseous Detector with Germanium Tagging (GADGET) at the NSCL. The search depends on the accurate modeling of the β^--delayed alpha-particle background in the region of interest, E<280 keV, which has been modeled using data from a previous β^- delayed alpha particle measurement as input to the AZURE2 R-matrix code and facilitated by gamma-particle coincidences in our own data.