Nuclear mean-square charge radii of63,64,66,68−82Ga nuclei: No anomalous behavior atN=32

Abstract

Collinear laser spectroscopy was performed on the 63,64,66,68−82 Ga isotopes with neutron numbers from N = 32 to N = 51. These measurements were carried out at the ISOLDE radioactive ion beam facility at CERN. Here we present the nuclear mean-square charge radii extracted from the isotope shifts and, for the lighter isotopes, new spin and moment values. New ground-state nuclear spin and moments were extracted from the hyperfine spectra of 63,70 Ga, measured on an atomic transition in the neutral atom. The ground-state spin of 63 Ga is determined to be I = 3/2. Analysis of the trend in the change in mean-square charge radii of the gallium isotopes demonstrates that there is no evidence of anomalous charge radii behavior in gallium in the region of N = 32.

Collinear laser spectroscopy at ISOLDE: new methods and highlights

“…A decrease in the radii is seen towards N=28 and a steep increase is observed when crossing the N=28 shell gap. No signature for a shell closure at N=32 is seen for Ca and K. Taken from [48,54,60,64,68]. (b) Radii relative to the N=30 value for each isotopic chain: the radii follow a remarkable similar increase beyond N=28, highlighting the sudden onset of deformation in the Mn radii beyond N=36.…”

“…could also be induced by the fact that this is a gap between orbits with opposite parity, thus requiring at least two neutron excitations to mix into the normal wave function and thus leading to a more pure 68 Ni configuration (it has E 2 2 1 > + ( ) MeV). The magnetic and quadrupole moments of the Cu isotopes around 69 Cu suggest also a 'magic' behaviour for 69 Cu, but as for the excitation energies and transition probabilities this can also be understood as mostly due to the parity change [47,63].…”

Laser spectroscopy of radioactive isotopes: Role and limitations of accurate isotope-shift calculations

“…Using the measured IS δν 71,69 = +40(4) MHz [62], the calculated atomic factors [F 417 = +400(60) MHz/fm 2 , M 417 = −431(170) GHz amu] yield a difference in radius of δ r 2 71,69 = −0.34 fm 2 , significantly larger than the nonoptical data. Of the two factors, the field factor appears to stabilize more readily than the mass shift factor.…”

“…Isotope shift measurements have recently been performed for gallium [62] and copper [61] isotopes. These studies were motivated by the reordering of the nuclear energy levels among the neutron-rich isotopes that occur due to the monopole component of the nucleon-nucleon force [28].…”

“…For gallium, IS measurements were performed for isotopes in the range 63−82 Ga [62]. Mean-square charge radii measurements had only previously been made for the stable 69,71 Ga isotopes using muonic atoms, yielding δ r 2 71,69 = −0.12(2) fm 2 [54].…”