β-Decay Half-Lives of Neutron-Rich Sulfur to Potassium: Evolution of the N=32 and 34 Subshell Closures below Calcium

The half-lives of 24 isotopes ranging from sulfur to potassium were measured using the ZeroDegree Advanced Decay Station at the Radioactive Isotope Beam Factory, including six of the most neutron-rich-^{47}S, ^{48,49}Cl, ^{51,52}Ar, ^{55}K-for the first time, while the precision for ^{48}Ar and ^{53,54}K was significantly improved. Two prominent features are found: First, a half-life drop at ^{54}K_{35} relative to ^{52,53}K, supporting the persistence of the N=34 subshell closure in potassium with Z=19. Second, a high β-decay rate for ^{48}Cl_{31} compared to ^{47}Cl and ^{49}Cl, which can be explained by the critical role of the ν1p_{1/2} orbital in shell-model calculations. The present calculations indicate that the N=32 subshell gap in chlorine with Z=17 is slightly smaller than that in calcium (Z=20), and the significant excitation across the N=32 subshell in ^{48}Cl_{31} is mainly due to strong configuration mixing.