Quasiparticle Configurations Research Articles

Half-Lives of Low-Lying Isomeric States in 169Ta

Two low-lying isomeric states in 169Ta have been identified via 159Tb(16O, 6nγ)169Ta reaction. Their half-lives are measured to be 28 ± 5 ns for the 9/2- level and 17 ± 4 ns for the 5/2- level by using the delayed γ-γ coincidence method. These two isomeric states are considered to be the bandheads with 9/2-[514] and 1/2-[541] configurations, respectively. Possible neutron quasiparticle configuration for the ground state of 169W is discussed.

Lifetimes of low-lying states in125,127La measured by the recoil distance method

Lifetimes of low-lying states in {sup 125,127}La nuclei were measured using the recoil distance method. The nuclei were produced by the {sup 94}Mo({sup 35}Cl,2p2n) and {sup 112}Cd({sup 19}F,4n) reactions, respectively. Experimental results were described in the framework of the core quasiparticle coupling model. It was found that the observed bands can be reasonably well described as {pi}g{sub 7/2}, {pi}g{sub 9/2}, and {pi}h{sub 11/2} quasiparticle configurations coupled to elongated ({beta}{sub 2}{approx}0.28) triaxial cores. No evidence for a rapid change of the nuclear shape in the {pi}h{sub 11/2} band in {sup 127}La is seen in our data. {copyright} {ital 1997} {ital The American Physical Society}

Interactions between a multitude of rotational bands in well deformed odd nuclei: A new method for spin and parity assignment

Using the ( 18O,5n) 163Er reaction a multitude of rotational bands have been established with firm spin and parity assignments in 163Er. In 17 out of 24 band crossings E2 cross-band transitions have been observed. The interaction strength varies between ∼ 1 and ∼ 50 keV with many of the values in the range 10–15 keV. These interactions sample a variety of the lowest (multi) -quasiparticle configurations. For some bands, in particular those with high K-values, the configurations can be established rather well. Quite complicated changes in the wavefunctions must occur at these crossings, and to explain the observed interaction strengths coupling to various vibrational degrees of freedom, in addition to possible residual neutron-proton interactions, may be needed.

Rotational and vibrational states in 115Te

High-spin states of the 115Te were studied by in-beam spectroscopy with the 89Y (29Si, p2n) fusion-evaporation reaction at a beam energy of 108 MeV. γ−γ coincidence and γ−γ angular correlation analyses were employed for determining the level scheme of 115Te. We have identified two vibrational-like bands built on the νh11/2 and νg7/2 quasiparticle states and the noncollective oblate states from the full alignment of quasiparticle configurations. In addition, a regular ΔI = 2 sequence with positive-parity was found for the first time in odd-A Te nuclei. This sequence is interpreted as a deformed structure resulting from three-quasiparticle alignment having the [π(g7/2, h11/2) ⊗ ν(h11/2)] configuration. Calculations of total Routhian surfaces and cranked shell model were performed and were used for assigning quasiparticle configurations to the states in 115Te.

High-spin states and band structures in182Pt

Excited states in {sup 182}Pt have been studied via the heavy-ion reactions {sup 170}Yb({sup 16}O,4n), {sup 162}Dy({sup 24}Mg,4n), and {sup 163}Dy({sup 24}Mg,5n). {gamma}-ray coincidence measurements were performed with arrays of HPGe detectors at the McMaster University Tandem Accelerator Laboratory ({sup 16}O-induced reaction) and the Institut de Physique Nucl{acute e}aire, Orsay ({sup 24}Mg-induced reactions). The ground-state rotational band has been extended to I=26{h_bar}, and six new band structures have been identified and assigned quasiparticle configurations. The {gamma}-vibrational band and the band built upon the first excited 0{sup +} state have also been extended. Properties of the rotational bands are compared with cranked-shell-model and total-Routhian-surface calculations. Evidence concerning shape coexistence at low spin and band crossings at high spin is discussed. {copyright} {ital 1997} {ital The American Physical Society}

Collective structures in doubly odd120I

High spin states in the doubly odd ${}^{120}\mathrm{I}$ nucleus have been investigated through in-beam gamma-ray spectroscopy following the ${}^{108}{\mathrm{P}\mathrm{d}+}^{16}\mathrm{O}$ and ${}^{114}{\mathrm{C}\mathrm{d}+}^{11}\mathrm{B}$ fusion-evaporation reactions. A new \ensuremath{\Delta}I=1 collective band, based on the \ensuremath{\pi}${\mathrm{g}}_{7/2}$\ensuremath{\bigotimes}\ensuremath{\upsilon}${\mathrm{h}}_{11/2}$ quasiparticle configuration, has been identified. This band exhibits energy staggering in the odd-even spin states and is found to be intense as compared to the earlier known \ensuremath{\pi}${\mathrm{g}}_{9/2}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\bigotimes}\ensuremath{\upsilon}${\mathrm{h}}_{11/2}$ nonstaggered band. A loss in collectivity is observed at the ${\mathrm{I}}^{\mathrm{\ensuremath{\pi}}}$${=(23}^{\mathrm{\ensuremath{-}}}$) state, implying an abrupt band termination.

M1bands and intruder bands in113In

High spin states in ${}^{113}$In have been established up to 6.2 MeV in excitation energy and to a tentative spin of (43/2${}^{\ensuremath{-}})$ through the reaction ${}^{110}$Pd${(}^{7}$Li, ${4n)}^{113}$In at a beam energy of 40 MeV. In-beam measurements involved $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences, angular distribution of emitted gamma rays, and directional correlation of oriented states. $M$1 bands consisting of $\ensuremath{\Delta}I=1$ dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei. Two intruder bands based on the $\ensuremath{\pi}{h}_{11/2}$ orbital and $\ensuremath{\pi}{g}_{7/2}$ orbital have been observed. Results of the total Routhian surface and cranked shell model calculations are compared with the experimental data. Alignment features of the intruder bands in the $N=62$ and 64 isotones are discussed.

Pi h11/2 intruder and pi g9/2-1 strongly coupled bands in 115Sb.

High spin states have been populated in $^{115}\mathrm{Sb}$ with the reaction $^{100}\mathrm{Mo}$${(}^{19}$F,4n${)}^{115}$Sb at a beam energy of 82 MeV. Two intruder rotational bands (\ensuremath{\Delta}I=2) extending to spins 43/${2}^{\mathrm{\ensuremath{-}}}$ and 51/${2}^{\mathrm{\ensuremath{-}}}$ have been observed. The extracted relative B(E2) value supports the nearly diabatic nature of these two bands. The transition energies in these two bands are nearly similar and the bands have a relative spin alignment of 4\ensuremath{\Elzxh} at low frequencies. The bands have been interpreted to be based on the \ensuremath{\pi}${\mathit{h}}_{11/2}$ orbital coupled to the deformed 2p-2h states of the $^{114}\mathrm{Sn}$ core. Possible quasiparticle configurations for the excited negative parity band are discussed and it is suggested that this band is based on aligned ${\mathit{h}}_{11/2}$ neutrons, the yrare extension of which is observed diabatically down to very low spin values. Two strongly coupled (\ensuremath{\Delta}I=1) rotational bands involving the (\ensuremath{\pi}${\mathit{g}}_{9/2}$${)}^{\mathrm{\ensuremath{-}}1}$ configuration have been observed, of which the known strongly coupled band has been extended from 23/${2}^{+}$ to 37/${2}^{+}$ in spin and the extracted B(M1;I\ensuremath{\rightarrow}I-1)/B(E2;I\ensuremath{\rightarrow}I-2) values for this band are compared with the D\"onau-Frauendorf formula. Alignment features due to the ${\mathit{h}}_{11/2}$ neutrons in the observed bands are compared with the core nucleus $^{114}\mathrm{Sn}$ and cranked shell model calculations. Equilibrium deformations for a range of odd Sb isotopes have been calculated with various intrinsic proton configurations. \textcopyright{} 1996 The American Physical Society.

High-spin states and signature inversion in 78Br.

High-spin states in {sup 78}Br have been studied up to an excitation energy of approximately 6 MeV and a spin of 17{h_bar} using the {sup 70}Zn({sup 11}B,3{ital n}){sup 78}Br reaction at a beam energy of 45 MeV. The properties of the observed rotational bands, including moments of inertia, signature splitting, and signature inversion, are discussed within the context of the cranked shell model. It is shown that cranked-shell-model calculations are able to reproduce the experimentally observed signature inversion in the positive-parity yrast bands in the odd-odd isotopes {sup 74,76,78}Br, which permits the assignments of quasiparticle configurations to these bands. {copyright} {ital 1996 The American Physical Society.}

High spin bands in 102Pd

The nucleus 102Pd has been studied using 148 MeV 34S ions impinging on 76Ge. The γ-rays were detected with the Nordball array and the light charged particles with a 4π charged particle detector system. Rotational bands have been extended using γ-ray yields, γγ coincidences and angular correlation information. Calculated spin diabatic surfaces were used for assigning quasiparticle configurations to the bands. The (+,0) high spin band extending to 26+ may be explained by a π(g92)2 ⊗ ν(“g72”)2 quasiparticle configuration. The protons are predicted to align first. The negative parity bands are suggested to be built on ν (“g72”h112) evolving to π(g92)2 ⊗ ν(“g72”h112) at the highest spins.

Multiple dipole bands at prolate shapes in 136Nd and their description through the projected shell model.

Five bands dominated by strong {ital M}1 transitions have been observed in the {sup 136}Nd nucleus. Two of them consist of only dipole transitions, whereas the other three show also weak crossover transitions. The bands have been firmly connected to lower-spin states. Theoretical calculations using the projected shell model suggest quasiparticle configurations involving two protons and two neutrons for the four lowest-lying bands. {copyright} {ital 1996 The American Physical Society.}

First observation of yrast band in odd-odd 162Lu

High spin states of the odd-odd 162Lu nucleus have been studied via 147Sm(19F,4nγ)162Lu reaction at 95 MeV beam energy. Level scheme for yrast band based on π[h11/2]υ[i13/2] quasiparticle configuration was established up to Iπ=(23−) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in 162Lu is larger than that in the 160Tm nucleus.

Signature Inversion of Yrast Band in Odd-Odd 162Lu Nucleus

High spin states of the odd-odd 162Lu nucleus have been studied via 147 Sm(19F, 4nγ) reaction at 95 MeV beam energy. Level scheme for yrast band based on π[h11/2]ν[i13/2] quasiparticle configuration was established up to Iπ = (23-) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in 162 Lu is larger than that in 160 Tm nucleus.

Spectroscopy in the second well of the 148Gd nucleus: Two quasiparticle and collective excitations.

Six superdeformed (SD) bands have been observed in the nucleus {sup 148}Gd using the {gamma}-spectrometer GASP. The structure of the observed SD bands is discussed within the concept of cranked-Strutinsky-type calculations including pairing interaction. For the configuration assignments two different parametrizations of the Woods-Saxon potential are compared. Five of the observed SD bands are described in terms of quasiparticle configurations, whereas one is suggested to have vibrational-like structure. From this data a {Delta}{ital I}=2 staggering in the rotational spectrum of the yrast SD band also has been observed. {copyright} {ital 1996 The American Physical Society.}

Collective states in 129La

Low-spin states of the odd-proton nucleus 129 La have been investigated by means of in-beam γ-ray spectroscopy. Many new low-lying levels have been established. Of special interest are three new negative-parity bands which are identified as the unfavored yrast- and the favored and unfavored yrare-bands based on a π h 11 2 quasiparticle configuration. The negative-parity states are discussed within the framework of the rigid triaxial rotor plus particle model (RTRP) considering excitation energies, branching and multipole mixing ratios. We are able to establish a value of γ ≈ 16° for the triaxial deformation parameter for 129 La.

High-spin states in doubly odd 114I.

High-spin states have been identified in doubly odd $^{114}\mathrm{I}$ produced in the $^{60}\mathrm{Ni}$${(}^{58}$Ni,3pn\ensuremath{\gamma}) reaction. Two rotational band structures have been observed. One band exhibits no signature splitting, while the second exhibits a large signature splitting. These bands are interpreted in terms of \ensuremath{\pi}${\mathit{g}}_{9/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${\mathit{h}}_{11/2}$ and \ensuremath{\pi}${\mathit{g}}_{7/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${\mathit{h}}_{11/2}$ quasiparticle configurations, respectively.

Rotational bands near theZ=50 closed shell:Sb51111

Rotational states have been identified in $_{51}^{111}\mathrm{Sb}$ for the first time. Three decoupled (\ensuremath{\Delta}I=2) bands extending to over 1 MeV in rotational frequency have been observed. At the highest frequencies, the ${\mathit{scrJ}}^{(2)}$ moments of inertia for these three bands are seen to decrease steadily to unexpectedly low values; this is interpreted as evidence for a novel form of band termination. One of these bands is interpreted as being based on the \ensuremath{\pi}${\mathit{h}}_{11/2}$ orbital coupled to a deformed [(\ensuremath{\pi}${\mathit{g}}_{9/2}$${)}^{\mathrm{\ensuremath{-}}2}$\ensuremath{\bigotimes}(\ensuremath{\pi}${\mathit{g}}_{7/2}$)${]}_{0+}$ state of the $_{50}^{110}\mathrm{Sn}$ core. The interaction strength for the alignment of a pair of ${\mathit{h}}_{11/2}$ neutrons has been extracted and compared with calculations. Two possible quasiparticle configurations are discussed for the other decoupled bands. Two strongly coupled (\ensuremath{\Delta}I=1) bands have been identified and both shown to involve the [(\ensuremath{\pi}${\mathit{g}}_{9/2}$${)}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\bigotimes}(\ensuremath{\pi}${\mathit{g}}_{7/2}$${)}^{2}$] configuration. A large number of spherical states have also been observed, which can be explained on the basis of valence protons coupled to spherical states in the $^{110}\mathrm{Sn}$ core.

High-spin bands in 105Ag

The nucleus 105Ag has been studied using 162–173 MeV 37Cl ions impinging on 76Ge. The γ-rays were detected with the Nordball array and the light charged particles with a 4π charged-particle detector system. Rotational bands have been established using γ-ray yields, γγ-coincidences and angular-correlation information. Calculations of spin diabatic surfaces are used for assigning quasiparticle configurations to the bands. A high-spin band extending to (67/2) may be explained by five-quasiparticle configurations with moderate deformation or with a highly deformed structure involving πh 11/2 and ν(h 11/2) 2 orbitals.

High-spin states in 109,111Cd and 107Pd

The nuclei 107Pd, 109Cd and 111Cd have been studied using proton-, 13C- and 18O-induced reactions. Fourteen bands were observed in 109Cd and the yrast cascade was extended to I π = ( 51 2 −) . Two of the bands consist of δI = 1 transitions. In 107Pd the present level scheme includes three bands, while in 111Cd with much lower reaction cross section only the yrast cascade was observed. Experimental routhians and aligned angular momenta as well as B(M1)/ B(E2) ratios were extracted and used, together with the predictions of TRS and CSM calculations, to assign quasiparticle configurations to the bands. In several bands, the neutron h 11 2 alignment was observed and the alignment frequency was found to be sensitive to the deformation and to the neutron number. Shape change effects are discussed.

Collective bands in 106Ag and 107Ag

The nuclei 106Ag and 107Ag have been studied using 80 MeV 17O ions impinging on 94Zr. The γ- rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using γ-ray yields, γγ coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands.