Figure 1

Part of the nuclear chart showing the most neutron-rich nuclei known to exist out to $Z=18$. Highlighted are ${}^{48}\mathrm{Ca}$ (primary beam), ${}^{48}\mathrm{K}$ and ${}^{46}\mathrm{Cl}$ (secondary beams), and ${}^{48}\mathrm{Ar}$ and ${}^{46}\mathrm{S}$ (respective final reaction residues). For comparison, the observation of ${}^{44}\mathrm{Si}$ [9], ${}^{40}\mathrm{Mg}$, ${}^{42}\mathrm{Al}$, and possibly ${}^{43}\mathrm{Al}$ [19] was achieved only in 2007.Reuse & Permissions

Figure 2

Particle-identification spectrum for the reaction residues produced in ${}^9\mathrm{Be}({}^{48}\mathrm{K},{}^{48}\mathrm{Ar})X$ at $85.7\mathrm{MeV}/\mathrm{u}$ midtarget energy. The energy loss measured in the S800 ionization chamber is plotted versus the ion’s time of flight. ${}^{48}\mathrm{Ar}$ can be unambiguously separated from other projectilelike fragmentation residues produced in the reaction ${}^{48}\mathrm{K}+{}^9\mathrm{Be}$.Reuse & Permissions

Figure 3

Parallel momentum distribution of the ${}^{48}\mathrm{K}^{18+}$ ions (a) and the reaction product ${}^{48}\mathrm{Ar}$ (c) relative to $18.353\mathrm{GeV}/c$. (b) and (d) show the reconstructed scattering angle. The ${}^{48}\mathrm{K}^{18+}$ ions were not subject to a nuclear reaction, and the spectra show the effect of the ${}^9\mathrm{Be}$-induced nucleon-exchange reaction relative to the unreacted ${}^{48}\mathrm{K}^{18+}$ ions passing through the target. The measured longitudinal momentum distribution of ${}^{47}\mathrm{Ar}$ produced in the one-proton knockout from ${}^{48}\mathrm{K}$ under identical conditions is overlaid (blue dashed line).Reuse & Permissions

Figure 4

Event-by-event Doppler reconstructed $\gamma$-ray spectra detected in coincidence with ${}^{46}\mathrm{S}$ and ${}^{48}\mathrm{Ar}$. The 952(8) keV peak is attributed to the deexcitation of the $2_1^{+}$ state in ${}^{46}\mathrm{S}$. There is no evidence for peaks other than this transition. The two peaks observed at 1037 and 1706 keV for ${}^{48}\mathrm{Ar}$ are attributed to the $2_1^{+}\to 0_1^{+}$ and $4_1^{+}\to 2_1^{+}$ transitions, respectively, in agreement with a previous measurement [8].Reuse & Permissions

Figure 5

Measured energies of the first $2^{+}$ states in silicon, sulfur, and argon isotopes with neutron numbers $N=26$, 28, and 30 (a) compared to shell-model calculations. The calculation in (b) uses the SDPF-NR effective interaction [16]. The calculations for the silicon isotopes in (c) use the SDPF-NR2 interaction which is derived by reducing the $pf$ shell $J=0^{+}$ matrix element by 0.85. The results for sulfur and argon in (c) are obtained from a linear interpolation in terms of $Z$ between SDPF-NR ($Z=20$) and SDPF-NR2 ($Z=14$). The calculations for the silicon isotopes in (d) use the interaction SDPF-NR3 derived by additionally lowering the neutron $p_{3/2}$ and $p_{1/2}$ orbitals by 1 MeV. The results for sulfur and argon in (d) are obtained from a linear interpolation in terms of $Z$ between the SDPF-NR ($Z=20$) and the SDPF-NR3 ($Z=14$) interactions.Reuse & Permissions