Nuclear Spins and Moments of Ga Isotopes Reveal Sudden Structural Changes betweenN=40andN=50

Abstract

Collinear laser spectroscopy was performed on Ga (Z ¼ 31) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes (N ¼ 36-50 Nuclear structure has for some time been described by the single-particle (SP) states of nucleons in the shell model. The evolution and reordering of these levels along isotopic chains is explored at radioactive ion beam facilities to provide information on the nature of the nucleonnucleon interaction. Key to these studies is the determination of the value of the nuclear spin of each state, which provides a means of level identification. Whereas the spin may sometimes be inferred from nuclear decay and -spectroscopy data, laser spectroscopy [1,2] permits a measurement of the nuclear spin, in addition to the state's magnetic dipole and electric quadrupole moments. The latter two observables are very sensitive to the wave function and thus to the SP shell evolution. The sensitivity of the laser technique has been critically enhanced using bunched beams from a gas-filled linear rf quadrupole known as an ion beam cooler [3]. In this Letter we report the application of ISCOOL [4]-an ion beam cooler recently installed at ISOLDE-for collinear laser spectroscopy on Ga isotopes from stable to the magic N ¼ 50 shell gap, located 15 isotopes away from stability. For the first time g.s. spins have been measured, revealing sudden changes not observed in earlier experiments.The Ga isotopes have three protons outside the Z ¼ 28 shell gap. In a normal shell-model ordering, the three protons would occupy the p 3=2 level, leading to a g.s. spin I ¼ 3=2 for all odd-A Ga isotopes. However, in the Cu isotones with two protons fewer, it has been demonstrated that the proton SP ordering changes when neutrons start occupying the g 9=2 orbital around N ¼ 40 [5][6][7][8][9][10][11][12][13][14][15]. An inversion of the p 3=2 and f 5=2 SP levels was established recently in 75 Cu at N ¼ 46 [11], where the 5=2 À g.s. is near degenerate with a 3=2 À and 1=2 À state [11]. In this Letter we establish the g.s. spins and structure of the odd-A Ga isotopes from N ¼ 36 up to the N ¼ 50 shell closure, and we investigate the systematics of the 1=2 À , 3=2 À and 5=2 À levels.Fission fragments were produced in a thick UC x target (45 g=cm 2 ) using 1.4 GeV protons at an average current of $2 A. A proton-neutron converter [16] was used to suppress the Rb production. The Ga yield was selectively enhanced by a factor of 100 using the Resonant Ionization Laser-Ion Source [17], extracted and accelerated to 30 keV and mass selected. The ions were cooled and bunched by the newly-installed ISCOOL [4] and delivered to the collinear laser spectroscopy setup [18]. The ion beam was

Coulomb excitation ofGa73

“…4) does not show any broadening of the peak, indicating that the transition is either monoenergetic or that the energy difference is too small to cause any peak asymmetry. Also the population of a level with an energy of 1395.1 (12) No coincidence between the 218-and 433-keV γ rays is observed, which is due to the relatively small 433-keV γ branch in the decay of the 651-keV state [10]. Based on the limited number of 452-199-keV coincidences observed in the top spectrum, less than one 433-218-keV coincidence count is expected in the lower spectrum.…”

“…Recently, a collinear laser spectroscopy measurement confirmed the assumption of a 3/2 − ground state in all odd-A gallium isotopes, except for 73 Ga 42 and 81 Ga 50 , where the spin and parity of the ground states were found to be 1/2 − and 5/2 − , respectively [12]. A combination of the results from previous experiments opens the possibility of a 1/2 − , 3/2 − ground-state doublet in 73 Ga.…”

Shell-model study on event rates of lightest supersymmetric particles scattering offKr83andTePirinen1, Srivastava2, Suhonen3 et al. 2016Phys. Rev. D132130View full textAdd to dashboardCite

“…The calculations have been performed with a recently available effective interaction, jj44b, by Brown and Lisetskiy [42], and shell-model code NuShellX [43]. The single-particle energies employed in conjunction with the jj44b interaction are −9.6566, −9.2859, −8.2695, and −5.8944 MeV for the 1p 3=2 , 0f 5=2 , 1p 1=2 , 0g 9=2 orbitals, respectively.…”

gA -driven shapes of electron spectra of forbidden β decays in the nuclear shell model

“…pf g 9/2 shell: the jj44b interaction developed by Brown and Lisetskiy for the 0f 5/2 − 1p − 0g 9/2 model space (see endnote on Ref. [28] of [42]) was used for the calculation of the 87 Rb(3/2 − ) → 87 Sr(9/2 + ) transition. For the decays of the A = 94-99 nuclei, the effective interaction of Gloeckner [43] in the model space spanning the π 1p 1/2 , π 0g 9/2 , ν2s 1/2 , and 2d 5/2 was used.…”