Quadrupole and octupole collectivity in light Po isotopes

The level structure of¹⁹⁶Po has been studied using a¹⁶⁰Dy(⁴⁰Ar, 4n) reaction and a recoil-catcher technique to reduce fission. The results showed a sharp drop off in the first (2⁺) and (4⁺) energies relative to systematics implying an abrupt increase in the quadrupole collectivity at N=112. In addition, second (2⁺) and(4⁺) states were identified at 859 and 1388 keV, respectively, suggesting the discovery of a 4p2h deformed band in Po isotopes which is related to known 2p2h proton bands in several Pb isotopes. A prompt¹⁸³W(²⁰Ne, 5n@#@) experiment located similar second 2⁺ and 4⁺ states at 1039 and 1483 keV in¹⁹⁸Po providing corroboration and extended information on the properties of the new Po deformed bands. A measured halflife of 850 (90) ns for the 2491 keV (11^?) state in¹⁹⁶Po implied collective E3 contributions to the extractedB (@#@ E3; 11^?→8⁺)=27(5) W.u.     

The subshell closure at N = 56 and the deformation of neutron-rich isotopes from Ge to Zr

The microscopic energy density method is applied to the study of nuclei with N ? 50 and Z = 32?40. The experimental Subshell effect at N = 56, which is not found in many previous works about this region, is well reproduced by the present self-consistent calculation. The existence of strongly deformed prolate isotopes of Zr and Sr for N ? 60 is also explained. A wide region of oblate shapes is predicted for N ? 60 and Z ? 36. The results also support the interpretation of low-energy isomers in the shape transition region as shape isomers.     

Enhanced collectivity in Ni

The neutron-rich nucleus ⁷⁴Ni was studied with inverse-kinematics inelastic proton scattering using a ⁷⁴Ni radioactive beam incident on a liquid hydrogen target at a center-of-mass energy of 80 MeV. From the measured de-excitation γ rays, the population of the first 2⁺ state was quantified. The angle-integrated excitation cross section was determined to be 14(4) mb. A deformation length of δ=1.04(16) fm$\delta =1.04(16)\text{fm}$ was extracted in comparison with distorted wave theory, which suggests that the enhancement of collectivity established for ⁷⁰Ni continues up to ⁷⁴Ni. A comparison with results of shell model and quasi-particle random phase approximation calculations indicates that the magic character of Z=28$Z=28$ or N=50$N=50$ is weakened in ⁷⁴Ni.     

High-K isomers as probes of octupole collectivity in heavy nuclei

The influence of the octupole deformation on the structure of high-K isomeric states in the region of heavy even–even actinide nuclei is studied through a reflection asymmetric deformed shell model (DSM). Two-quasiparticle states with high-K values are constructed by taking into account the pairing effect through a DSM + BCS procedure with constant pairing interaction. The behaviour of two-quasiparticle energies and magnetic dipole moments of Kπ=⁶⁺$K^{\pi }=6^{+}$, ⁶⁻$6^{-}$ and ⁸⁻$8^{-}$ configurations, applicable to mass numbers in the range A=234–252$A=234\text{–}252$, was examined over a wide range of quadrupole and octupole deformations. A pronounced sensitivity of the magnetic moments to the octupole deformation is found. The result suggests a possibly important role for high-K isomers in determining the degree of octupole deformation in heavy actinide nuclei.     

Influence of a strong proton-neutron interaction on mass 100 nuclei and properties of the octupole two-phonon multiplet in96Zr

Experimental evidence, which suggests a strong proton-neutron interaction giving rise to deformation and influencing the deformation properties of mass 100 nuclei, is reviewed, as is the large variation in the interaction strength for N=59 isotones and for coexisting states of 46≤Z≤54 isotones. Properties of the recently discovered octupole two-phonon multiplet in⁹⁶Zr are presented, compared to spdf-boson IBM calculations, and consequences of its fragmentation are discussed.     

Two-neutrino double β decay of96Zr to excited 2+ state of96Mo

The two-neutrino double beta decay of⁹⁶Zr isotope for 0⁺ → 2⁺ transition has been studied in the PHFB model. In our earlier work, the reliability of the intrinsic wave functions of⁹⁶Zr and⁹⁶Mo isotopes has been established by obtaining an overall agreement between a number of theoretically calculated spectroscopic properties as well as half-lives of 2vββ decay for 0⁺ → 0⁺ transition and the available experimental data. In the present work, the half-life of 2vββ decay for 0⁺ ar 2⁺ transition T ₁ ^2/2v (0⁺ →²⁺) has been calculated using the same set of intrinsic wave functions.     

Enhanced quadrupole collectivity at N = 40: the case of neutron-rich Fe isotopes

The transition rates for the 2(1)+ states in (62,64,66)Fe were studied using the recoil distance Doppler-shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell-model calculations with a new effective interaction developed for the fpgd valence space.     

New limits on the double beta decay half-lives of 94Zr, 96Zr, 116Cd and 124Sn

Searches have been made for the double beta decays of ^{94, 96}Zr, ¹¹⁶Cd, and ¹²⁴Sn to excited states in their daughter nuclei. No evidence of any of these decays was found, and lower limits on the half-lives against such decays have been established to be 10¹⁸–10¹⁹ yr. In addition, the single beta decay half-life of ⁹⁶Zr has been established to be ⩾1.4×10¹⁸ yr.     

Quadruplet spectroscopy in the region of strong nuclear octupole correlations

Experimental evidence from the spectroscopy of¹⁵⁵Gd and¹⁵³Sm for the theoretically predicted quadruplet band structure, with band parity sequences (+––+) and (–++–), is examined.We wish to thank Dr. R. Piepenbring for illuminating discussions on the differences between octupole correlations in the actinides and in the rare earths. These investigations were supported by the National Science Foundation under contract number PHYS9-06613 with the Florida State University.     

A quantum parity-conserving study on octupole deformation in the light-actinide region

Based on a constrained Hartree-Fock plus BCS calculation with Gogny forces, we construct the collective hamiltonian (GCM+mean field and ATDHF+cranking approach) with the quadrupole and octupole deformations as coordinates. We calculate the 0⁺, 1⁻ splitting as well as the E1 and E3 transition probabilities for ²²²Ra. The agreement with experimental results is very good.     

Structure of even-even actinides in the interacting boson model and the N = 152 subshell closure

We show that a wide range of deformed actinides can be described in terms of an interacting boson model hamiltonian with three parameters, two of them [including the coefficient of the only SU(3) symmetry breaking term] remaining almost constant over the whole region. In addition to ground γ₁ and β₁ spectra, B(E2:0_g⁺ → 2_g⁺) values are well reproduced with no extra adjustable parameters for nuclei with 136⩽N⩽146, while for nuclei beyond N = 146 an effective boson number has to be considered in order to fit the observed in the B(E2:0⁺_g → 2⁺_g) values, which is due to the presensce of a subshell closure at N = 152. The sensitive dependence of the B(E2:0_g⁺→2_g⁺) values on the effective boson numbers is emphasized. β₁ → ground and β₁ → ground transitions are fitted by breaking the SU(3) symmetry of the E2 transition operator.     

Strange-quark collectivity of the φ-meson at RHIC

Based on A Multi-Phase Transport (AMPT) model, the elliptic flow v₂ of φ-mesons which is reconstructed from K ⁺ K ^- at the Relativistic Heavy-Ion Collider (RHIC) energy has been studied. The results show that the reconstructed v₂ of the φ-meson can keep the earlier information before φ decays and it seems to obey the number of constituent-quark scaling as other mesons and baryons. This result indicates that the φ v₂ mostly reflects the parton level collectivity developed during the early stage of the collisions and the strange and light up/down quarks have similar collectivity properties before the hadronization.     

The collectivity in the yrast band of100Zr: the half-life of the 4 1 + state

The half-lives of the 2⁺ and 4⁺ levels of the yrast band in¹⁰⁰Zr have been determined to be 0.54(4) ns and 37(4) ps, respectively, at the fission-product separator JOSEF, in a β^?- γ- γ coincidence experiment which exploited the fast timing properties of plastic and BaF₂ detectors. The half- life of the 4₁ ⁺ state corresponds to an intrinsic quadrupole moment of ¦Q₀¦=3.14(17)b which confirms the strongly deformed nature, in a way independent of the configuration mixing in the ground state. The value of t_1/2(2₁ ⁺) corroborates a recently published value. There is evidence for a decrease of ¦Q₀¦ with increasing spin in the yrast bands of the N=60 isotones⁹⁸Sr and¹⁰⁰Zr.     

Multipolarity of some transitions in the96Zr(p,n γ e)96Nb reaction

The conversion electron andγ-ray spectra of the⁹⁶Zr(p, n γ)⁹⁶Nb reaction were measured with Ge(Li) and superconducting magnet transporter Si(Li) spectrometers respectively, at 4MeV bombarding proton energy. The multipolarities of some transitions were determined and conclusions were drawn on the spins and parities of the excited states of⁹⁶Nb.     

L 2 andL 3 subshell fluorescence and Coster-Kronig yields forZ=96 from the decay of249Cf

TheL ₂ andL ₃ subshell fluorescence and Coster-Kronig yields forZ=96 have been measured by theK-L x-ray coincidence method with high resolution Si(Li) and Ge(Li) x-ray detectors. The results ν₂=0.650±0.036, ω₂=0.552±0.032, ω₃=0.515±0.034, andf ₂₃=0.188±0.019 agree fairly well with theory. New measurements of theL x-ray singles spectra of²⁴⁴Cm and²³⁸Pu with a high resolution Si(Li) detector permitted reevaluation of the values of ω₂ andf ₂₃ forZ=92 and 94 reported by Byrneet al. The revised values atZ=92 are ω₂=0.529±0.035 andf ₂₃=0.23±0.12, and atZ=94, ω₂=0.523±0.023 andf ₂₃=0.24±0.08. These revised values are in much better agreement with theory and with current experiments.     

Incipient octupole and 26-pole deformation in the mass region 220 < A < 230

The increase in calculated binding energies of nuclides in the mass region 220<A<230 due to varying the 2⁶-pole deformation parameter is found to be ∽1.0 MeV. The implications of this finding for octupole deformation are discussed.