Quenching of spectroscopic factors for proton removal in oxygen isotopes

We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes (14,16,22,24,28)O with a chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.     

Nuclear deformations in the pairing-plus-quadrupole model (II). Discussion of validity of the model

This paper attempts to choose the parameters of the pairing-plus-quadrupole model as realistically as possible. A correction is introduced to take into account the different numbers of neutrons and protons. An expression is given for the deformation energy of a nucleus with an arbitrary two-body interaction. Then the pairing-plus-quadrupole matrix elements are compared with those of more realistic interactions, and it is decided to keep only matrix elements between states of two adjacent oscillator shells. An argument is given to determine a priori the strength of the quadrupole force, and various corrections to this are discussed. No similar argument is found for the pairing force. Residual effects of the remaining oscillator shells are included in an approximate fashion. Comparison with previous work along these lines is presented.     

Quadrupole moments of neutron isomers in Sm isotopes

The quadrupole moments of the neutron isomers in^140,142Sm were determined by measuring the quadrupole interaction of Sm in Gd using single crystals. The moment for the 10⁺ isomer in¹⁴⁰Sm was determined to be ¦Q¦=167(48) fm² and for the 7^? isomer in¹⁴²Sm ¦Q¦=112(27) fm². The quadrupole moments are a measure for a deformation which turned out to be very similar to the deformation found for corresponding proton isomers in Gd isotones.     

Survey of ground state neutron spectroscopic factors from Li to Cr isotopes

The ground state neutron spectroscopic factors for 80 nuclei ranging in Z from 3 to 24 have been extracted by analyzing the past measurements of the angular distributions from (d, p) and (p, d) reactions. We demonstrate an approach that provides systematic and consistent values with minimum assumptions. For the 61 nuclei that have been described by large-basis shell-model calculations, most experimental spectroscopic factors are reproduced to within 20%.     

Proton orbit sizes of the isotopes of tin

Root-mean square radii of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{and 2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ in the isotopes of tin with A = 112, 116, 118, 120 and 124 have been determined from a DWBA analysis of crosssection data from the sub-Coulomb (t, α) reaction. The differential cross sections for the (t, α) reaction were measured at lab angles in the range from 60° to 160° for triton energies in the range from 4.75 MeV to 5.25 MeV. Spectroscopic factors of the populated states were obtained from a sum rule analysis of published proton stripping and pickup reactions on the isotopes of tin. The measured orbit sizes are compared with the results of Hartree-Fock calculations and the systematic features of the asymptotic proton wave functions are discussed.     

Electric monopole transitions and isotope shift of nuclear radii of even Sm isotopes in the interacting boson model

The interacting boson model has been used to calculate the isotope shift in^146–154Sm isotopes. Fitted model parameters have been used for calculation of the monopole strength parameters (EO) and the branching ratios X(EO/E2) for^150–154Sm. Consideration of the effective proton boson number as it reflects the Z=64 subshell closure, is shown to be insignificant in the present calculation.     

Shape evolution for Sm isotopes in relativistic mean-field theory

The evolution of shape from the spherical to the axially deformed shapes in the Sm isotopes is investigated microscopically in relativistic mean-field theory. The microscopic and self-consistent quadrupole deformation constrained relativistic mean-field calculations show a clear shape change for the even-even Sm isotopes with N = 82-96. The potential surfaces for ¹⁴⁸Sm, ¹⁵⁰Sm and ¹⁵²Sm are found to be relatively flat, which may be the possible critical-point nuclei. By examining the single-particle spectra and nearest-neighbor spacing distribution of the single-particle levels, one finds that the single-particle levels in ¹⁴⁸Sm , ¹⁵⁰Sm, and ¹⁵²Sm distribute more uniformly.     

Isotope shifts in Sm II and changes in mean-square nuclear charge radii of the stable even Sm isotopes

Isotope shifts have been measured in Sm II from which the shifts between pure configurations 4f ⁶ s and 4f ⁶5d can be determined. The specific mass shift for such a “transition” was estimated to be (?1±2)mK for a change of two neutrons. The values derived for the change in the nuclear charge distribution,δ〈r ²〉, are in good agreement with the results obtained from isotope shift measurements in Sm I (H. Brand et al.: J. Phys. B11, L99, 1978). The weighted mean values representing the best information onδ〈r ²〉 presently available are in fm²: [144, 148] 0.488(23); [148, 150] 0.285(14); [150, 152] 0.400(19); [152, 154] 0.217(11).     

Microscopic mean-field boson approach to the shape transition in Sm isotopes

The phase transition from spherical to deformed shape in nuclei ^146–156Sm is analyzed within the mean-field approximation applied to the Dyson boson image of the shell-model hamiltonian. No quasiparticle transformation is involved in the present approach and the Pauli principle in the physical boson subspace is approximately taken into account. The low-energy spectra, B(E2; 0₁⁺→ 2₁⁺) values and the corresponding transition densities are calculated. The results provide a reasonable explanation of the shape transition in the Sm isotopes. The role of bosons with different angular momenta is investigated and it is found that the g-bosons (J = 4) cannot be neglected in the transitional region. Comparison of the present results with those of other approaches is given as well.     

Nuclear deformations in the pairing-plus-quadrupole model (III). Static nuclear shapes in the rare-earth region

The potential energy of deformation (β, γ), is calculated with the pairing-plus-quadrupole model for nuclei with N=82–126, Z=50–82. There is a sudden onset of deformation in the N=86–90 region, and the static nuclear shape, the lowest minimum of the potential function, changes from spherical to prolate. The disappearance of deformation in the Z=74–80 region is more gradual, and the static shape changes from prolate to asymmetric to oblate to spherical. The energy of zero-point motion is calculated, and it is concluded that all the stable deformed shapes of the region are prolate. Proton and neutron energy gaps, intrinsic quadrupole moments, moments of inertia and gyromagnetic ratios of the doubly even nuclei of the rare-earth region are calculated and compared with the experimental data.     

Shell model Monte Carlo studies of N = Zpf-shell nuclei with pairing-plus-quadrupole Hamiltonian

We perform shell model Monte Carlo calculations of selected N = Z pf-shell nuclei with a schematic Hamiltonian containing isovector pairing and quadrupole-quadrupole interactions. Compared to realistic interactions, this Hamiltonian does not give rise to the SMMC “sign problem”, while at the same time resembles essential features of the realistic interactions. We study pairing correlations in the ground states of N = Z nuclei and investigate the thermal dependence of selected observables for the odd-odd nucleus ⁵⁴Co and the even-even nuclei ⁶⁰Zn and ⁶⁰Ni. Comparison of the present results to those with the realistic KB3 interaction indicates a transition with increasing temperature from a phase of isovector pairing dominance to one where isoscalar pairing correlations dominate. In addition, our results confirm the qualitative reliability of the procedure used to cure the sign problem in the SMMC calculations with realistic forces.     

Shape transitions in even Mo and Sm isotopes: Study in a new microscopic interacting boson model scheme

A simple dynamic procedure, based on the deformed Hartree-Fock solution of a nucleus, is presented to construct the IBM operators in microscopic basis. The parameters of these operators are evaluated by establishing a Marumori mapping from the truncated shell model space onto the boson space. The transitions from spherical to axial-rotor shape observed in the low-lying levels ofeven ^96–108Mo and^146–154Sm isotopes are reproduced qualitatively by applying this procedure with a fixed set of fermion input parameters to each chain. Variation of a few parameters in fermion space leads to quantitative agreement.     

133Sm和149Yb的β缓发质子衰变

利用⁴⁰Ca+⁹⁶Ru融合蒸发反应产生了近质子滴线核¹³³Sm, 配合氦喷嘴带传输系统采用“质子-γ”符合方法观测了它们的β缓发质子衰变, 其中包括半衰期、质子能谱、第二代子核低位态之间的γ跃迁, 并估计出衰变到第二代子核不同低位态的分支比. 通过统计理论拟合上述实验数据, 指认了¹³³Sm的自旋宇称的可能范围. 并用Woods-Saxon Strutinsky方法计算了限制组态的¹³³Sm的核势能面, 通过对比发现¹³³Sm的自旋宇称可能有两种成分:5/2⁺和1/2^－. 这一结果与2001年发表的¹³³Sm(EC+β⁺)衰变的简单衰变纲图是相容的. 此外用同一方法分析了2001年Eur. Phys.J.A12:1—4中发表的有关¹⁴⁹Yb的β缓发质子衰变实验数据, 由此指认了¹⁴⁹Yb的基态自旋宇称为1/2^－.     

Proton magic even-even isotopes and giant halos of Ca isotopes with relativistic continuum Hartree-Bogoliubov theory

We study the proton magic O, Ca, Ni, Zr, Sn, and Pb isotope chains from the proton drip line to the neutron drip line with the relativistic continuum Hartree-Bogoliubov (RCHB) theory. Particulary, we study in detail the properties of even-even Ca isotopes due to the appearance of giant halos in neutron rich Ca nuclei near the neutron drip line. The RCHB theory is able to reproduce the experimental binding energiesE _b and two neutron separation energiesS _2n very well. The predicted neutron drip line nuclei are²⁸O,⁷²Ca,⁹⁸Ni,¹³⁶Zr,¹⁷⁶Sn, and²⁶⁶Pb. Halo and giant halo properties predicted in Ca isotopes withA>60 are investigated in detail through analysis of two neutron separation energies, nucleon density distributions, single particle energy levels, and the occupation probabilities of energy levels including continuum states. The spin-orbit splitting and the diffuseness of nuclear potential in these Ca isotopes, as well as the neighboring lighter isotopes in the drip line Ca region and find certain possibilities of giant halo nuclei in the Ne−Na−Mg drip line nuclei are also studied.     

Quenching of neutron spectroscopic factors of radioactive carbon isotopes with knockout reactions within a wide energy range

The quenching factors of one-neutron spectroscopic factors,which are ratios of theoretical to experimental one-neutron removal cross sections,are studied for the carbon isotopes ~(15-19)C,with ~(12)C and ~9Be targets within incident energies from around 50 to 900 MeV/nucleon.The resulting values of quenching factors do not show strong energy dependence within such an energy range.The average values of the these quenching factors agree well with the systematics in [J.A.Tostevin and A.Gade,Phys.Rev.C,90 057602(2014)],which was established for a large set of radioactive nuclei with different masses below 305 MeV/nucleon.     

On-line nuclear orientation of the deformed neutron-deficient Eu,Sm and Pm isotopes

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on^142m Eu,^141m Sm, and¹⁴¹Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes^{139, 138}Eu,^139m Sm, and¹³⁸Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for¹³⁸Eu appear to contradict the earlier πh_11/2⊗νh_11/2 ground-state configuration assignment.     

Quadrupole moments and nucleon excitation strengths in even-A Sm isotopes

We present a coherent coupled-channel analysis of 7 MeV neutron and 16 MeV proton elastic and inelastic scattering from ^{148, 152, 154}Sm. The optical potential and nuclear deformation parameters are determined so as to fit not only these elastic and inelastic scattering data but also the low-energy neutron scattering properties and the total cross sections over a wide energy range. This analysis provides evidence of the same excitation strengths for both projectiles in the case of ^{152, 154}Sm, and of a smaller excitation strength for the proton than for the neutron in case of ¹⁴⁸Sm. Moreover the quadrupole moments of these deformed optical potentials are in good agreement with those extracted from Coulomb excitation measurements and from nuclear matter distribution calculations.     

Even Zn isotopes in the cluster-vibration model

Even-A nuclear systems with two protons in the 28–50 valence shell (even Zn isotopes) are described in the cluster-vibration model. Energy spectra and electromagnetic properties are calculated and their qualitative features are discussed with emphasis on the coexistence between quasivibrational and quasirotational characteristics. The influence of possible cubic anharmonicities and of the presence of the$\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ configuration are investigated. For some states, pairing phonons are recognized as intrinsic building blocks created in the cluster-vibration model. The relation between this approach and recent shell-model calculations is discussed.