Investigation of the potential ultralow Q -value β -decay candidates 89 Sr and 139 Ba using Penning trap mass spectrometry

Background: Ultralow $Q$-value $\ensuremath{\beta}$ decays are interesting processes to study with potential applications to nuclear $\ensuremath{\beta}$-decay theory and neutrino physics. While a number of potential ultralow $Q$-value $\ensuremath{\beta}$-decay candidates exist, improved mass measurements are necessary to determine which of these are energetically allowed.Purpose: To perform precise atomic mass measurements of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$. Use these new measurements along with the precisely known atomic masses of $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ and nuclear energy level data for $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$ to determine if there could be an ultralow $Q$-value decay branch in the $\ensuremath{\beta}$ decay of $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ or $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}$.Method: High-precision Penning trap mass spectrometry was used to determine the atomic mass of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$, from which $\ensuremath{\beta}$-decay $Q$ values for $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ were obtained.Results: The $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ and $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ values were measured to be ${Q}_{\mathrm{Sr}}=1502.20(0.35)$ keV and ${Q}_{\mathrm{Ba}}=2308.37(0.68)$ keV. These results were compared to energies of excited states in $^{89}\mathrm{Y}$ at 1507.4(0.1) keV, and in $^{139}\mathrm{La}$ at 2310(19) keV and 2313(1) keV to determine $Q$ values of $\ensuremath{-}5.20(0.37)$ keV for the potential ultralow $\ensuremath{\beta}$-decay branch of $^{89}\mathrm{Sr}$ and $\ensuremath{-}1.6(19.0)$ keV and $\ensuremath{-}4.6(1.2)$ keV for those of $^{139}\mathrm{Ba}$.Conclusion: The potential ultralow $Q$-value decay branch of $^{89}\mathrm{Sr}$ to the $^{89}\mathrm{Y}$ ($3/{2}^{\ensuremath{-}}$, 1507.4 keV) state is energetically forbidden and has been ruled out. The potential ultralow $Q$-value decay branch of $^{139}\mathrm{Ba}$ to the 2313 keV state in $^{139}\mathrm{La}$ with unknown ${J}^{\ensuremath{\pi}}$ has also been ruled out at the $4\ensuremath{\sigma}$ level, while more precise energy level data is needed for the $^{139}\mathrm{La}$ ($1/{2}^{+}$, 2310 keV) state to determine if an ultralow $Q$-value $\ensuremath{\beta}$-decay branch to this state is energetically allowed.