Nuclear moments of the low-lying isomeric 1+ state of 34Al: Investigation on the neutron 1p1h excitation across N = 20 in the island of inversion

An experimental view on shape coexistence in nuclei

“…The ground-state β 2 deformation of 79 Zn, estimated from its measured spectroscopic quadrupole moment [184], is equal to 0.15 (2), which is consistent with the values of 0.15(2) and 0.14(2) obtained from the measured B(E2; 2 + 1 → 0 + 1 ) values in 78 Zn and 80 Zn, respectively [186]. If the measured isomer shift is entirely attributed to an increase of deformation, it leads to an estimate of β 2 ≈ 0.22 for the isomer [184].…”

“…A very different g factor obtained for the low-lying 1 + isomer in 34 Al led to its association with a 1p − 1h intruder configuration [78]. The absolute value of the quadrupole moment of this state is about 50% larger than that of the normal-order ground state in 32 Al [78], evidencing an enhanced deformation due to the particle-hole excitation across the N = 20 shell gap. Based on β-γ and β-γ-γ coincidences observed in the β decay of 34 Mg, the 1 + isomer was shown to be located only 47 keV above the normal-order ground state in 34 Al, which identifies 34 Al as a crossing point of the normal-order and intruder configurations [79].…”

“…A large g factor of the ground state in 34 Al was interpreted as resulting from an important 2p − 2h intruder admixture to the normal-order configuration [77]. A very different g factor obtained for the low-lying 1 + isomer in 34 Al led to its association with a 1p − 1h intruder configuration [78]. The absolute value of the quadrupole moment of this state is about 50% larger than that of the normal-order ground state in 32 Al [78], evidencing an enhanced deformation due to the particle-hole excitation across the N = 20 shell gap.…”

“…The first and most direct evidence for shape coexistence in the immediate vicinity of 78 Ni was obtained through the measurement of a large isomer shift for the 1/2 + isomer in 79 Zn [184]. The excitation energy of this isomer was determined in a 78 Zn(d, p) 79 Zn study to be 1.10(15) MeV [185].…”

Mass measurements of neutron-rich isotopes near N=20 by in-trap decay with the ISOLTRAP spectrometer

“…The ground states of [31][32][33][34] Mg and 30,31 Ne were shown to be highly dominated by intruder configurations [7][8][9][10]. [31][32][33][34] Al isotopes, supposed to be transition isotopes between the spherical Z = 14 and the deformed Z = 12, were also studied in detail by decay spectroscopy [11], β-NMR [12][13][14][15], and mass measurements [5,16]. A unique feature of the S 2n values resulting from mass measurements was observed at N = 21 where the Al and Mg curves cross (see Fig.…”