First measurement of proton decay from a transfer reaction to ${}^{21}\mathrm{Na}$

Decay protons from excited states in ${}^{21}\mathrm{Na}$ populated through a previously reported ${}^{24}\mathrm{Mg}(p,\alpha ){}^{21}\mathrm{Na}$ transfer reaction [Cha et al., Phys. Rev. C 96, 025810 (2017)] were analyzed to extract the proton branching ratios of the energy levels. By utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched ${}^{24}\mathrm{Mg}$ solid targets, the decay protons were detected in coincidence with $\alpha$ particles from the $(p,\alpha )$ reaction using a silicon strip detector array. Proton decay branching ratios of several ${}^{21}\mathrm{Na}$ levels were deduced for the $p0$ and $p1$ decay channels to the ground and first excited states in ${}^{20}\mathrm{Ne}$, respectively.

Figure 1

A schematic diagram of the experimental setup for the ${}^{24}\mathrm{Mg}(p,\alpha ){}^{21}\mathrm{Na}^{*}\left(p\right){}^{20}\mathrm{Ne}^{*}$ measurement is shown.

Figure 2

Particle identification (energy loss vs total energy) plot obtained at ${\theta }_{\text{lab}}=23.6^{\circ }$ from the $p+{}^{24}\mathrm{Mg}$ reaction. Events falling in the gates (I) and (II) are identified as the $\alpha$ particles and protons, respectively.

Figure 3

The decay proton energy versus coincident $\alpha$-particle energy plot is shown for all identified events. Events falling in the red, blue, and green gates are associated with the ground state ($p0$), the first excited state ($p1$), and the second excited state ($p2$) of ${}^{20}\mathrm{Ne}$, respectively.

Figure 4

(a) ${}^{21}\mathrm{Na}$ excitation energy spectrum obtained from the ${}^{24}\mathrm{Mg}(p,\alpha ){}^{21}\mathrm{Na}$ reaction measurement [8]. Identified levels are labeled with their excitation energies. All energies are in MeV. (b) Spectra gated on decay proton coincidences. The spectra gated on the $p0$, $p1$, and $p2$ groups of Fig. 3 are shown as red dashed, blue dotted, and green solid lines, respectively.

Figure 5

Normalized intensity of proton decays from the 5.825-MeV level as a function of relative angle for the $p0$ (black solid line) and $p1$ (blue dotted line) channels in panel (a). Similarly, the empirical intensities for the 6.594- and 6.879-MeV levels are shown as a black solid line in panels (b) and (c), respectively. The calculated distributions assuming isotropic and anisotropic decay are shown as red dashed and green dotted lines, respectively.

Figure 6

Proton energy spectra are shown as black solid lines for the coincident events falling in the $p0$ (a) and $p1$ (b) gates. Several apparent peaks associated with ${}^{21}\mathrm{Na}$ levels are labeled with their excitation energies in MeV. Expected proton energy spectra are also shown in the figure as red dotted lines.