Merging of the island of inversion at N=40 and N=50

We performed a quantitative study of the nuclei with proton numbers from Z = 20 (Ca) to Z = 28 (Ni) and neutron numbers ranging from N = 38 to 52 using the realistic shell model, which merged the descriptions of nuclei around N = 40 and N = 50 within an extended model space. The 2+1 excitation energy (E(2+1 )) is calculated for neutron-rich Cr, Fe, and Ni isotopes. The results suggest that the islands of inversion at N = 40 and N = 50 merge around the Cr chain, and the N = 50 island of inversion is located below 78Ni. To demonstrate the prediction of the N = 50 island of inversion, we calculated and compared the E(2+1 ), B(E2; 0+ 1 -> 2+1 ), effective single-particle energies (ESPEs), the probability of particle-hole excitation, and the average occupations in the N = 40 and N = 50 isotones. Similar parabolic trends of E(2+1 ) and B(E2; 0+ 1 -> 2+1 ) in the N = 40 and 50 isotones are obtained. The calculated ESPEs give that the N = 40 and N = 50 shell gaps both increase with the variation of proton number from Z = 20 (Ca) to Z = 28 (Ni). However, our calculations indicate that different particle-hole excitations dominate in the ground states of the N = 40 and N = 50 islands of inversion, with 2p2h and 4p4h configurations being prominent in N = 40 isotones, whereas 2p2h excitations are most important in the N = 50 isotones. Furthermore, large occupations of the intruder quadrupole partner orbitals are also obtained in N = 40 and N = 50 isotones in our realistic shell model calculations. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

Automated summary

We conducted a quantitative study on nuclei with proton numbers ranging from Z = 20 (Ca) to Z = 28 (Ni) and neutron numbers from N = 38 to 52 using a realistic shell model. The results indicate that the islands of inversion at N = 40 and N = 50 merge around the Cr chain, with the N = 50 island of inversion located below 78Ni. Our calculations demonstrate the existence of the N = 50 island of inversion through various measurements and comparisons. The study also reveals different dominant particle-hole excitations in the ground states of the N = 40 and N = 50 islands of inversion.