Onset Of Nuclear Deformation Research Articles

High-precision mass measurement of neutron-rich 96Kr

While the nuclear deformation in the region around Z = 40 and N = 60 has been studied in great detail, the possible onset of nuclear deformation in the isotopic chain of krypton (Z = 36) is still a subject of controversy. Here, we present a high-precision mass measurement of the neutron-rich nuclide 96Kr, as measured by the Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) at TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN). A statistical method, based on a hyper-exponentially modified Gaussian, has been employed to model the data. As such, the uncertainty introduced by overlapping peaks from beam contaminants was reduced and the mass excess of 96Kr determined to be -53097(57)keV. The capability of the method has been confirmed with measurements of the stable isotopic pair 40Ar/40Ca, in which a relative accuracy Δm/m of 3.5 ⋅ 10− 8 and a mass resolving power of more than 400000 were achieved.

Single-particle and collective excitations inNi62

{\bf Background:} Level sequences of rotational character have been observed in several nuclei in the $A=60$ mass region. The importance of the deformation-driving $\pi f_{7/2}$ and $\nu g_{9/2}$ orbitals on the onset of nuclear deformation is stressed.\\ {\bf Purpose:} A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich $^{62}$Ni isotope. \\ {\bf Method:} The $^{26}$Mg($^{48}$Ca,2$\alpha$4$n\gamma$)$^{62}$Ni complex reaction at beam energies between 275 and 320~MeV was utilized. Reaction products were identified in mass ($A$) and charge ($Z$) with the Fragment Mass Analyzer (FMA) and $\gamma$ rays were detected with the Gammasphere array. \\ {\bf Results:} Two collective bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. \\ {\bf Conclusions:} Based on Cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the $A=60$ mass region, the two rotational bands are understood as being associated with configurations involving multiple $f_{7/2}$ protons and $g_{9/2}$ neutrons, driving the nucleus to sizable prolate deformation.

Low-frequencyKπ=0+modes in deformed neutron-rich nuclei: Pairing- and β-vibrational modes of neutrons

Low-frequency K{sup {pi}}=0{sup +} states in deformed neutron-rich nuclei are investigated by means of the quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov formalism in the coordinate space. We have obtained the very strongly collective K{sup {pi}}=0{sup +} modes not only in neutron-rich Mg isotope but also in Cr and Fe isotopes in N=40 region, where the onset of nuclear deformation has been discussed. It is found that the spatially extended structure of neutron quasiparticle wave functions around the Fermi level brings about a striking enhancement of the transition strengths. It is also found that the fluctuation of the pairing field plays an important role in generating coherence among two-quasiparticle excitations of neutron.

Collinear laser spectroscopy of radioisotopes of zirconium

Isotope shifts and hyperfine structures have been measured for radioisotopes of ionic zirconium using on-line laser spectroscopy at the IGISOL facility in Jyväskylä, where the installation of an ion beam cooler/buncher has significantly improved the experimental sensitivity. Measurements have been made on all the neutron-deficient isotopes from 87Zr to 90Zr, including the isomers 87m,89mZr, and the neutron-rich isotopes from 96Zr to 102Zr. The change in mean square charge radii between the isotopes and the nuclear moments of the odd isotopes have been extracted. The data show a sudden increase in the mean square charge radius at mass A = 100, consistent with an onset of nuclear deformation which has been observed in the gamma ray spectroscopy of isotope chains in this region of the nuclear chart.

Further evaluation of the fitted Nilsson parameters in the A

Systematic potential-energy-surface (PES) and cranked-shell-model (CSM) calculations have been performed for nuclei in the A\ensuremath{\approxeq}120--140 mass region using the newly fitted Nilsson potential (\ensuremath{\kappa},\ensuremath{\mu}) parameters. The roles of the ${\mathit{h}}_{11/2}$ quasiparticles in the onset of nuclear deformation and rotational alignment are explored. The PES calculations predict prolate-oblate energy-difference curves for several odd-proton nuclei which suggest the coexistence of oblate and prolate ${\mathit{h}}_{11/2}$ single quasiproton states. A major conclusion of this work is that the newly fitted Nilsson potential (\ensuremath{\kappa},\ensuremath{\mu}) parameter sets result in calculated rotational band-crossing frequencies that are in good agreement with experimental proton alignment in addition to reproducing the bandhead energies of odd-Z nuclei in this mass region.

Paramagnetic relaxation of Er in an Er single crystal

The paramagnetic relaxation of Er in an Er single crystal was measured atT≫TN and compared to the relaxation of Er ions in a polycrystalline Pb host. The results indicate an enhancement of at most 50% of the f-conduction electron exchange interaction in Er, as expected for highly ionic f-orbitals. The ratio of the quadrupole moments of the154Er(Iπ=11−) and the155Er(Iπ=13/2+) isomers was measured to be 1.18(3) indicating onset of nuclear deformation at N=87.

Systematics of ground-state quadrupole moments of odd-Adeformed nuclei determined with muonicMx rays

The ground-state quadrupole moments of $^{151}\mathrm{Eu}$, $^{153}\mathrm{Eu}$, $^{159}\mathrm{Tb}$, $^{163}\mathrm{Dy}$, $^{167}\mathrm{Er}$, $^{177}\mathrm{Hf}$, $^{179}\mathrm{Hf}$, $^{191}\mathrm{Ir}$, and $^{193}\mathrm{Ir}$ were determined by measuring the quadrupole hyperfine-splitting energies of muonic $M$ x rays. The results are $Q=0.903(10)e$ b for $^{151}\mathrm{Eu}$, $Q=2.412(21) e$ b for $^{153}\mathrm{Eu}$, $Q=1.432(8) e$ b for $^{159}\mathrm{Tb}$, $Q=2.648(21) e$ b for $^{163}\mathrm{Dy}$, $Q=3,565(29) e$ b for $^{167}\mathrm{Er}$, $Q=3.365(29) e$ b for $^{177}\mathrm{Hf}$, $Q=3.793(33) e$ b for $^{179}\mathrm{Hf}$, $Q=0.816(9) e$ b for $^{191}\mathrm{Ir}$, and $Q=0.751(9) e$ b for $^{193}\mathrm{Ir}$. The present quadrupole moments, compared with values obtained from electronic-atom hyperfine measurements, show that the Sternheimer correction factors used in the rare-earth electronic-atom analysis are unreliable. Systematics of deformation parameters ${\ensuremath{\beta}}_{2}$ calculated from the present quadrupole moments for odd-$A$ nuclei, and from $B(E2)$ values of Coulomb excitation measurements for even-$A$ nuclei, also indicate that the largest deformation change so far known exists between $^{151}\mathrm{Eu}$ and $^{153}\mathrm{Eu}$. Except at the onset of nuclear deformation, the deformation parameters of the odd-$A$ nuclei are quite consistent with those of the even-$A$ neighbors.

The neutron-rich barium isotopes

The nuclei 142Ba, 144Ba and 146Ba (Z=56) have been studied using the technique of gamma-gamma angular correlations. The activities were produced using the on-line fission product mass separator OSTIS at the Institut Laue-Langevin. Spins have been assigned to most of the low-lying levels in these isotopes and multipole mixing ratios have been deduced. On the basis of coincidence data new information has been included in the decay schemes. The onset of nuclear deformation has been identified in these nuclei and found to occur between N=86 and N=88, which is two neutrons earlier than might be expected by comparison with the well known transitional nuclei in the Z=60 and 64 region. The current data are used to test the ability of the simplest form of the interacting boson model to describe this new transitional region.

(t,p)-reaction studies of the transitional nuclei- 150Nd and 152Nd

The 0 + states observed in the reactions 148Nd(t, p) 150Nd and 150Nd(t, p) 152Nd are reported and discussed. Their properties suggest significant differences between the samarium and neodymium at the onset of nuclear deformation.

The Mass Effect Corresponding to the Onset of Nuclear Deformation in the RegionN∼90

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