High-spin structure in ${}^{40}$K

High-spin states of ${}^{40}$K have been populated in the fusion-evaporation reaction ${}^{12}$C(${}^{30}$Si,$np$)${}^{40}$K and studied by means of $\gamma$-ray spectroscopy techniques using one triple-cluster detector of the Advanced Gamma Tracking Array at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. Several states with excitation energy up to 8 MeV and spin up to ${10}^{-}$ have been discovered. These states are discussed in terms of $J=3$ and $T=0$ neutron-proton hole pairs. Shell-model calculations in a large model space have shown good agreement with the experimental data for most of the energy levels. The evolution of the structure of this nucleus is here studied as a function of excitation energy and angular momentum.

Figure 1

Total projection of the $\gamma \gamma$-coincidence spectrum. Known yrast transitions in ${}^{40}\text{K}$ are labeled.

Figure 2

Level scheme of ${}^{40}\text{K}$ as obtained in this work (left) and level scheme obtained from shell-model calculations (right). Information from this work is indicated with red (gray). The width of the arrows corresponds to the intensity of the $\gamma$ rays. For the positive-parity states, the assigned configurations in the weak-coupling basis are also shown.

Figure 3

Summed $\gamma \gamma$-coincidence spectrum measured with a 13-mg/cm${}^2$-thick stopper foil of ${}^{58}\text{Ni}$ placed at a distance of $2.1$ mm from the target, without applying any Doppler correction. The spectrum is a sum of spectra gated on the 892- and the 1651-keV transitions.

Figure 4

Background-subtracted $\gamma \gamma$ spectra for some transitions in ${}^{40}\text{K}$. The spectra have been obtained by requiring a coincidence relationship with the $\gamma$ transition reported above the spectrum.

Figure 5

Summed $\gamma \gamma$-coincidence spectrum for all transitions listed in Table 1 in the energy ranges 0–1100 keV (a), 900–2100 keV (b), and 1900–3100 keV (c). The transitions at 1651 and 1823 keV were excluded from the gating conditions because similar energies are present in the ${}^{38}\text{Ar}$ decay scheme. The low-energy tail of the 892- and 1651-keV peaks are due to the 1.09-ns isomer of the $7_1^{+}$ state.