Single-particle structure at $N=29$: The structure of ${}^{47}\mathrm{Ar}$ and first spectroscopy of ${}^{45}\mathrm{S}$

Comprehensive spectroscopy of the $N=29$ nucleus ${}^{47}\mathrm{Ar}$ is presented, based on two complementary direct reaction mechanisms: one-neutron pickup onto ${}^{46}\mathrm{Ar}$ projectiles and one-proton removal from the $1^{-}$ ground state of ${}^{48}\mathrm{K}$. The results are compared with shell-model calculations that use the state-of-the-art SDPF-U and SDPF-MU effective interactions. Also, from the ${}^9\mathrm{Be}({}^{46}\mathrm{Cl},{}^{45}\mathrm{S}+\gamma )X$ one-proton-removal reaction, we report the first $\gamma$-ray transitions observed from ${}^{45}\mathrm{S}$. By using comparisons with shell-model calculations, and from the observed intensities and energy sums, we propose a first tentative level scheme for ${}^{45}\mathrm{S}$.

Figure 1

Particle identification spectra for the one-proton-removal reactions to (a) ${}^{47}\mathrm{Ar}$ and (b) ${}^{45}\mathrm{S}$ used to determine the inclusive cross sections. The most intense structure in each spectrum is the hydrogen-like charge state of the projectile beam.

Figure 2

Event-by-event Doppler-reconstructed $\gamma$-ray spectra of ${}^{47}\mathrm{Ar}$: (a) as detected with GRETINA following ${}^{12}\mathrm{C}({}^{46}\mathrm{Ar},{}^{47}\mathrm{Ar}+\gamma )X$ one-neutron pickup ($v/c=0.337$) using nearest-neighbor addback, and (b) one-proton removal ${}^9\mathrm{Be}({}^{48}\mathrm{K},{}^{47}\mathrm{Ar}+\gamma )X$ with $\gamma$-ray spectroscopy using SeGA ($v/c=0.4$). The inset to panel (a) shows a coincidence spectrum with a software gate applied on the 1231 keV line indicating that the 515, 1016, and 1231 keV transitions are in coincidence.

Figure 3

Level scheme of ${}^{47}\mathrm{Ar}$ as observed in (a) one-neutron pickup and (b) one-proton removal. Levels and transitions indicated in black were observed to be populated with the respective reaction, levels and transitions marked in gray are known but were not observed in the respective reaction. The complementarity of the two reactions is apparent. Only the 1130 keV $1/2^{-}$ state [18] could not be accessed in the presented measurements.

Figure 4

One-neutron pickup partial cross sections to excited final states (a) as measured in the experiment, and as calculated following Sec. 2, with the (b) SDPF-U and (c) SDPF-MU SM spectroscopic factors.

Figure 5

One-proton-removal partial cross sections to ${}^{47}\mathrm{Ar}$ final states (a) as measured in the experiment, and as calculated following Sec. 2 with (b) SDPF-U and (c) SDPF-MU shell-model spectroscopic factors. The shell-model calculations use the wave function of the lowest-lying $1^{-}$ state, although this is not the ground state in either shell-model calculation. The $J^{\pi }=1^{-}$ spin assignment was determined from laser spectroscopy [29].

Figure 6

Event-by-event Doppler-reconstructed $\gamma$-ray spectrum of ${}^{45}\mathrm{S}$ following population of the nucleus in the ${}^9\mathrm{Be}({}^{46}\mathrm{Cl},{}^{45}\mathrm{S}+\gamma )X$ one-proton-removal reaction ($v/c=0.393$). The inset shows a tentative level scheme based on energy sums, intensity arguments, and comparison with shell-model calculations (see text).

Figure 7

SDPF-U shell-model level scheme of ${}^{45}\mathrm{S}$. The widths of the lines representing energy levels are proportional to the calculated partial cross section for the ${}^9\mathrm{Be}({}^{46}\mathrm{Cl},{}^{45}\mathrm{S})X$ one-proton-removal reaction, taking the wave function of the lowest $1^{-}$ state as the ground state of ${}^{46}\mathrm{Cl}$ (see text and Table 3). Only states predicted to be populated with more than 0.2 mb cross section are shown and only transitions with a branching ratio of 10% or higher are drawn.