Analysis of level structure and monopole effects in Ca isotopes

Understanding the properties of nuclei near the double magic nucleus ⁴⁰Ca is crucial for both nuclear theory and experiments. In this study, Ca isotopes were investigated using an extended pairing-plus-quadrupole model with monopole corrections. The negative-parity states of ⁴⁴Ca were coupled with the intruder orbital \(g_{9/2}\) at 4 MeV. The values of \(E_{4+}\)/\(E_{2+}\) agree well with experimental trend from ⁴²Ca to ⁵⁰Ca, considering monopole effects between \(\nu f_{7/2}\) and \(\nu p_{3/2}\)(\(\nu f_{5/2}\)). This monopole effect, determined from data of ⁴⁸Ca and ⁵⁰Ca, supports the proposed new nuclear magic number \(N = 34\) by predicting a high-energy \(2^{+}\) state in ⁵⁴Ca.