Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers

Abstract

Collinear laser spectroscopy was performed on Zn (Z=30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N=33–49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-A neutron-rich nuclei up to N=50. Exactly one long-lived (>10 ms) isomeric state has been established in each ^69–79Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell–model calculations in the f₅pg₉ and fpg₉d₅ model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder I^π=1/2⁺ isomer in ⁷⁹Zn is reproduced only if the νs_1/2 orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction. The spin and moments of the low-lying isomeric state in ⁷³Zn suggest a strong onset of deformation at N=43, while the progression towards ⁷⁹Zn points to the stability of the =28 and =50 shell gaps, supporting the magicity of ⁷⁸Ni

Investigating the large deformation of the 5/2+ isomeric state in Zn73 : An indicator for triaxiality

“…In recent laser spectroscopy studies on neutron-rich Zn isotopes ( 69-79 Zn), several earlier observed isomeric states were identified in all odd-Zn isotopes, and spins and parities could be unambiguously assigned [19]. However, no evidence was seen for a long-lived (5.8 s) isomeric state in 73 Zn, which had been proposed to exist in 73 Zn, from a β-decay study on a cocktail beam of A = 73 isotopes [20].…”

“…Measurements of ground state properties from laser spectroscopy have also provided considerable nuclear structure information in this region [14][15][16][17][18][19]. With one proton above Z = 28, a study of Cu isotopes revealed a primarily single-particle nature and a weak "magic" behavior around N = 40 from the spins, moments, and charge radii, but also showed a nonnegligible contribution from NN correlations and cross-shell excitations [14,16,17].…”

“…With one proton above Z = 28, a study of Cu isotopes revealed a primarily single-particle nature and a weak "magic" behavior around N = 40 from the spins, moments, and charge radii, but also showed a nonnegligible contribution from NN correlations and cross-shell excitations [14,16,17]. In contrast, with two and three protons above Z = 28, the collective behavior above N > 40 is significantly enhanced in the Zn and Ga isotopic chains, as indicated by their measured quadrupole moments [15,19]. It was concluded in Ref.…”

“…It was concluded in Ref. [19] that Zn isotopes are considered + isomer peaks (b1) labeled with diamonds. In (3), the measurement period is extended to 100 ms (of ten 10 ms cycles), which reduces the isomeric count rate relative to the ground state (b2).…”

“…We also want to establish or to eliminate simultaneously the possible existence of an additional long-lived isomer, having a 5.8 s half-life. The magnetic and quadrupole moments of the 5/2 + isomeric state were reported in our prior work [19], where the results were compared to large scale shell model calculations with different effective interactions. Here we provide further analysis of the wave function of the isomeric state obtained through shell model calculations [23,24] with two effective interactions.…”