We report the first direct measurement of the nuclear electron-capture (EC) decay $Q$ value of ${}^7\mathrm{Be}\to {}^7\mathrm{Li}$ via high-precision Penning trap mass spectrometry (PTMS). This was performed using the LEBIT Penning trap located at the National Superconducting Cyclotron Laboratory/Facility for Rare Isotope Beams (NSCL/FRIB) using the newly commissioned Batch-Mode Ion-Source (BMIS) to deliver the unstable ${}^7\mathrm{Be}^{+}$ samples. With a measured value of $Q_{EC}=861.963\left(23\right)$ keV, this result is three times more precise than any previous determination of this quantity. This improved precision and accuracy of the ${}^7\mathrm{Be}$ EC decay $Q$ value is critical for ongoing experiments that measure the recoiling nucleus in this system as a signature to search for beyond the Standard Model (BSM) neutrino physics using ${}^7\mathrm{Be}$-doped superconducting sensors. This experiment has extended LEBIT capabilities, using the first low-energy beam delivered by BMIS at FRIB for PTMS, as well as measuring the lightest-mass isotopes so far with LEBIT.

• Received 21 August 2023
• Accepted 22 January 2024

DOI:https://doi.org/10.1103/PhysRevC.109.L022501