Intensity of a weak 519-keV $\gamma$ ray following $\beta$ decay of the superallowed emitter ${}^{34}\mathrm{Ar}$ determined via the ${}^{33}\mathrm{S}$($p,\gamma$)${}^{34}\mathrm{Cl}$ reaction

The predominant branch in the $\beta$ decay of ${}^{34}\mathrm{Ar}$ is the superallowed $0^{+}\to 0^{+}$ transition to the ground state of ${}^{34}\mathrm{Cl}$. To determine its important branching ratio one must first establish the ratios for the competing Gamow-Teller branches based on the measured intensities of $\gamma$ rays subsequently emitted from the excited states they populate in ${}^{34}\mathrm{Cl}$. The strongest of these branches populates the $1^{+}$ state at 666 keV in ${}^{34}\mathrm{Cl}$, which has three possible $\gamma$-decay paths. We report here a measurement of the decay of this state, which we populated via resonant proton capture in the reaction ${}^{33}\mathrm{S}$($p,\gamma$)${}^{34}\mathrm{Cl}$. We find that the intensity of the 519-keV $\gamma$-ray path is 1.46(19)% relative to that of the 666-keV path. This result is critical to new precise measurements of the superallowed decay of ${}^{34}\mathrm{Ar}$.

Figure 1

Beta-decay scheme of ${}^{34}\mathrm{Ar}$, singling out the three possible $\gamma$-ray transitions from the 666-keV state. The 205-keV transition is shown by the dashed line because only an upper limit has been set on its intensity. The basic diagram is taken from Ref. [3]. Each level is labeled with its ($J^{\pi },T$) as well as its energy, expressed in keV, relative to the ${}^{34}\mathrm{Cl}$ ground state.

Figure 2

(a–c) Relevant portions of the $\gamma$-ray spectrum obtained in coincidence with a single gate set around the 5515-keV $\gamma$ ray, which populates the 666-keV level in ${}^{34}\mathrm{Cl}$. (d–f) The same portions are shown after subtraction of spectra obtained from “background” gates set on either side of the 5515-keV peak. Throughout, the energies (in keV) of the four possible deexcitation $\gamma$ rays are marked [as is that of the annihilation peak in (b)].