Total absorption spectroscopy of the $\beta$ decay of ${}^{76}\mathrm{Ga}$

The $\beta$ decay of ${}^{76}\mathrm{Ga}$ was studied using the technique of total absorption spectroscopy for the first time. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) detector. The extracted $\beta$-decay feeding intensity distribution and Gamow-Teller transition strength distribution are compared to shell-model calculations to help constrain nuclear matrix elements relevant to the neutrinoless double-$\beta$ decay of ${}^{76}\mathrm{Ge}$.

Figure 1

The TAS spectrum of SuN for the $\beta$ decay of ${}^{76}\mathrm{Ga}$ in singles (green, dashed line), normalized room background (blue, dotted line), and with a coincidence requirement with the silicon surface barrier detector (black, solid line). The energies of prominent sum peaks are labeled in the coincidence spectrum. There is also a label for the $Q$ value for the $\beta$ decay of ${}^{76}\mathrm{Ga}$ at 6916.2(2.0) keV [35].

Figure 2

Comparison of experimental (black, solid line) and simulated (red, dashed-dotted line) spectra using the existing decay scheme [37] to illustrate the discrepancy with the measurements reported in the present work. The spectra are (a) the TAS spectrum, (b) sum-of-segments spectrum, and (c) multiplicity spectrum. All three spectra were created with an energy threshold of 80 keV applied to each SuN segment. There is a label for $Q$ value in the TAS spectrum for the $\beta$ decay of ${}^{76}\mathrm{Ga}$ at 6916.2(2.0) keV [35].

Figure 3

The experimental decay curve for the $\beta$ decay of ${}^{76}\mathrm{Ga}$ (black, solid line) and the exponential fit from 0 to 300 s (red, dashed line). The extracted half-life is 30.6(3) s. The inset show the history of measurements of the half-life of ${}^{76}\mathrm{Ga}$.

Figure 4

Comparison of experimental (black, solid line) and simulated (red, dash-dotted line) spectra after fitting all three spectra simultaneously with the decay scheme modifications for (a) the TAS spectrum, (b) sum-of-segments spectrum, and (c) multiplicity spectrum. This is an example of one of the different fitting conditions with a specific energy calibration and binning. All three spectra were created with an energy threshold of 80 keV applied to each SuN segment. There is a label for $Q$ value in the TAS spectrum for the $\beta$ decay of ${}^{76}\mathrm{Ga}$ at 6916.2(2.0) keV [35].

Figure 5

Cumulative $\beta$-decay feeding intensity of ${}^{76}\mathrm{Ga}$ as a function of excitation energy in the daughter nucleus ${}^{76}\mathrm{Ge}$ for the present work (blue, solid line, with uncertainty in light-blue shading) and calculations with different Hamiltonians and different assumptions of the spin and parity of the ground state of ${}^{76}\mathrm{Ga}$. Panel (a) contains calculations using the $\mathit{jj}44\mathrm{b}$ Hamiltonian and panel (b) contains calculations using the JUN45 Hamiltonian. The half-lives from the present work and theoretical calculations are in parentheses. For the present work, the blue solid line is the cumulative average intensity, and the lower (upper) bound of the light-blue uncertainty band is the cumulative minimum (maximum) intensity. See text for an explanation of why the $2^{-}$ calculation and the present work are identical at relatively low excitation energy.

Figure 6

Same as Fig. 5, but for cumulative $B$(GT). The inset shows a closeup view of the low-excitation energy region.