High-spin Level Structure Research Articles

First observation of high-spin states in the N = 83 nucleus 142Pr

High-spin states of the N = 83 nucleus 142Pr have been observed for the first time using the 138Ba(7Li, 3n) reaction at a beam energy of 38 MeV. A total of 40 new transitions and 22 new levels have been identified, leading to a considerable extension of the level scheme of 142Pr. The experimental level structures of 142Pr are compared with its neighboring N = 83 isotones 144Pm and 146Eu. Shell model calculations employing the jj56pna interaction reproduce the experimental findings and provide guidance in the interpretation of the observed high-spin level structures.

High-spin level structure and Ground-state phase transition in the odd-mass 103−109Rh isotopes in the framework of exactly solvable sdg interacting boson–fermion model

In this article, the negative-parity states in the odd-mass Rh103−109 isotopes in terms of the sd and sdg interacting-boson fermion models were studied. The transitional interacting boson–fermion model Hamiltonians in sd and sdg-IBFM versions based on affine SU(1,1) Lie Algebra were employed to describe the evolution from the spherical to deformed gamma unstable shapes along with the chain of Rh isotopes. In this method, sdg-IBFM Hamiltonian, which is a three level pairing Hamiltonian was determined easily via the exactly solvable method. Some observables of the shape phase transitions such as energy levels, the two neutron separation energies, signature splitting of the γ-vibrational band, the α-decay and double β−-decay energies were calculated and examined for these isotopes. The present calculation correctly reproduces the spherical to gamma-soft phase transition in the Rh isotopes. Some comparisons were made with sd-IBFM.

Reinvestigation of octupole bands in neutron-rich 141Xe

High-spin level structures in neutron-rich 141Xe nucleus have been reinvestigated by measuring the triple fold and four-fold γ coincidence data obtained in the spontaneous fission of 252Cf. Several new levels and transitions are identified. The previously proposed octupole bands have been significatively updated and expanded. The systematic characteristics of the octupole deformation and octupole correlations are discussed. Reflection asymmetric shell model calculations for the octupole bands of 141Xe are in good agreement with the experimental data.

High-spin states in the semimagic nucleusY89and neutron-core excitations in theN=50isotones

The semimagic nucleus $^{89}\mathrm{Y}$ has been investigated using the $^{82}\mathrm{Se}(^{11}\mathrm{B},4n)$ reaction at beam energies of 48 and 52 MeV. More than 24 new transitions have been identified, leading to a considerable extension of the level structures of $^{89}\mathrm{Y}$. The experimental results are compared with the large-basis shell model calculations. They show that cross-shell neutron excitations play a pivotal role in high-spin level structures of $^{89}\mathrm{Y}$. The systematic features of neutron-core excitations in the $N=50$ isotones are also discussed.

Erratum: High-spin states and level structure inRb84[Phys. Rev. C 82, 014306 (2010)

Erratum: High-spin states and level structure in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi mathvariant="normal">Rb</mml:mi><mml:mprescripts /><mml:none /><mml:mn>84</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>[Phys. Rev. C 82, 014306 (2010)

High-spin level structures of the near-spherical nuclei91,92Zr

High-spin level structures of the near-spherical nuclei ${}^{91,92}$Zr have been reinvestigated via the ${}^{82}$Se(${}^{13}$C, $xn$) $(x=4,3)$ reactions at a beam energy of 44 MeV. By the use of in-beam spectroscopic methods, 13 new transitions belonging to ${}^{91}$Zr and 19 to ${}^{92}$Zr have been observed and the level schemes of ${}^{91,92}$Zr have been extended up to ${E}_{x}\ensuremath{\approx}$ 11 MeV excitation energy. The newly constructed level schemes are characterized by the ${}^{88}$Sr core breaking, and the proton ${p}_{3/2}\text{\ensuremath{-}}{p}_{1/2}$ energy gap in ${}^{92}$Zr is obviously reduced compared with ${}^{91}$Zr when one more neutron goes into the $({d}_{5/2}/{g}_{7/2})$ orbital.

High-spin level structure of the semi-magic nucleusNb91

The high-spin level structure of the semi-magic nucleus $^{91}\mathrm{Nb}$ has been investigated via the ${}^{82}$Se(${}^{14}$N,$5n$)$^{91}\mathrm{Nb}$ reaction at a beam energy of 60 MeV. Based on these experimental results, a new level scheme is established that modifies and extends earlier schemes. Shell-model calculations have been carried out to interpret the level structure of $^{91}\mathrm{Nb}$. The calculated results show that the inclusion of neutron particle-hole excitation across the $N=50$ shell gap is essential to adequately describe states above $I=(21/2\phantom{\rule{0.16em}{0ex}}--\phantom{\rule{0.16em}{0ex}}23/2)\ensuremath{\hbar}$, with excitation energies above $\ensuremath{\sim}$6.0 MeV.

High-spin level structure of the doubly odd nucleus104Ag

The high-spin level structure of the doubly odd nucleus ${}^{104}$Ag has been investigated via the ${}^{97}$Mo(${}^{11}$B, 4n)${}^{104}$Ag reaction at a beam energy of 50 MeV. The newly established level scheme includes lower-lying two-quasiparticle states and several higher-lying bands. Two positive-parity bands associated with the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{d}_{5/2}$ and $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{7/2}$ configurations are extended significantly. Based on the comparison with the analogous structures in neighboring nuclei and the features of nuclear chirality, the negative parity bands are suggested as candidate chiral doublet bands with the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration.

Identification of a New Four-Quasiparticle State in Odd-Odd 186Au

The high-spin level structure of 186Au is re-investigated by means of in-beam γ-ray spectroscopy via the 172Yb(19F, 5nγ)186Au reaction. The oblate bands previously reported are revised and extended to higher-spin states. A new Iπ = (20+) excited state has been identified and assigned to the πh−111/2 ⊗ νi−213/2h−19/2 configuration. The total Routhian surface and cranked shell model calculations suggest that the πh−111/2 ⊗ νi−213/2h−19/2 band in 186Au has a non-axial deformation.

In-beam gamma spectroscopy of 73As nucleus

The high spin level structure of 73As nucleus is studied by populating the nucleus in 64Ni(12C,p2n)73As reaction. Level scheme is revised significantly. Positive parity sequence is extended up to 33/2+ and a negative parity side band is identified and extended up to high spins 37/2−. In addition about 15 new energy levels and a total of about 25 new gamma transitions were placed in the level scheme.

High-spin states inAu188: Further evidence for nonaxial shape

The high-spin level structure of $^{188}\mathrm{Au}$ has been investigated via the $^{173}\mathrm{Yb}$($^{19}\mathrm{F}$,$4n$$\ensuremath{\gamma}$) reaction at beam energies of 86 and 90 MeV. The previously reported level scheme has been modified and extended significantly. A new ${I}^{\ensuremath{\pi}}={20}^{+}$ state associated with $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}{h}_{9/2}^{\ensuremath{-}1}$ configuration and two new rotational bands, one of which is built on the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ configuration, have been identified. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around $^{188}\mathrm{Au}$ for the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ bands in odd-odd Au isotopes. Evidence for $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}1}$ structure of nonaxial shape with $\ensuremath{\gamma}&lt;\ensuremath{-}{70}^{\ifmmode^\circ\else\textdegree\fi{}}$ has been obtained by comparison with total Routhian surface and cranked-shell-model calculations.

High-spin states inNb96,97

The high-spin level structures of the {sup 96,97}Nb isotopes have been studied. The isotopes were produced in the fission of the compound systems formed in two heavy-ion-induced reactions, {sup 24}Mg (134.5 MeV) + {sup 173}Yb and {sup 23}Na (129 MeV) + {sup 176}Yb. Gamma-ray spectroscopy was accomplished with the Gammasphere array. High-spin states are observed for the first time in both isotopes with excitation energies up to 5.2 and 6.6 MeV in {sup 96,97}Nb, respectively. The coupling of the odd proton occupying the g{sub 9/2} orbital to the yrast states in the subshell closure nucleus of {sup 96}Zr can account for the first excited states of {sup 97}Nb. A comparison with the first excited states in {sup 95}Zr is also attempted. The addition of a neutron hole in {sup 96}Nb results in a much more fragmented level scheme.

A New High-Spin Level Scheme of 128I

High-spin states in the odd-odd nucleus 128I are investigated via the 124Sn(7Li,3n)128I reaction at 28 and 32 MeV beam energies. A new level scheme of 128I is established up to high-spin states at Iπ = 16, including 48 levels and 72 γ transitions. The present level scheme is largely different from the one in a recent publication due to identification of several doublet and triplet γ transitions and their proper placements in the level scheme. The high-spin level structure exhibits no obvious collective properties and is possibly associated with two and multi-quasiparticle configurations.

High-spin level structure inMo94,95

High-spin level structures of $^{94,95}\mathrm{Mo}$ have been reinvestigated via the $^{16}\mathrm{O}(^{82}\mathrm{Se},\mathit{xn}\ensuremath{\gamma})^{94,95}\mathrm{Mo}(x=4,3)$ reactions at $E(^{82}\mathrm{Se})=460$ MeV. The previously reported level schemes of these two nuclei have been largely modified up to \ensuremath{\sim}11 MeV in excitation energy due to identifications of some important linking transitions. Shell-model calculations have been made in the model space of $\ensuremath{\pi}({p}_{1/2},{g}_{9/2},{d}_{5/2}){}^{4}$ and $\ensuremath{\nu}({d}_{5/2},{s}_{1/2},{d}_{3/2},{g}_{7/2},{h}_{11/2}){}^{2(3)}$ and compared with the modified level schemes. The structures of the newly assigned high-spin states in $^{94,95}\mathrm{Mo}$ have been discussed.

High-spin states in the proton-unbound nucleusRe161

Excited states in Re161 were populated using the Cd106(Ni58, p2n) reaction at a beam energy of 270 MeV, resulting in the first observation of γ rays emitted from this nucleus. The reaction products were separated from scattered beam and fission fragments by the gas-filled recoil separator RITU, and were implanted in the double-sided silicon strip detectors of the GREAT spectrometer. Prompt γ rays were detected by the JUROGAM Ge detector array and were assigned to Re161 based on α- and proton-decay tagging of the implanted reaction products. The near-yrast high-spin level structure, which was delineated to spins around 39/2, is discussed in the context of the total Routhian surface formalism. The level scheme is interpreted in terms of the alignment of h9/2/f7/2 neutrons at lower spins, followed by excitations involving the πh11/2 subshell at higher spins.Received 1 May 2006DOI:https://doi.org/10.1103/PhysRevC.74.024316©2006 American Physical Society

High-Spin States in Odd–Odd 140Pr Nucleus

High-spin level structure of doubly odd nucleus 140Pr has beeninvestigated via the 130Te(14N,4n)140Pr reactionat beam energies from 55 to 65 MeV. Measurements of γ-ray excitationfunctions, γ-ray singles and γ-γ-t coincidences wereperformed with twelve BGO(AC)HPGe detectors. The level scheme of140Pr, including 27 new levels and 42 new γ rays, has beenestablished for the first time. The level structure is compared withthose in the neighbouring odd–odd nuclei, and interpreted qualitatively.

Properties of theπi13∕2⊗νi13∕2band in odd-oddAu184

High-spin level structure in $^{184}\mathrm{Au}$ has been reinvestigated using the multidetector array of GASP via the $^{159}\mathrm{Tb}(^{29}\mathrm{Si},4\mathrm{n}\ensuremath{\gamma})^{184}\mathrm{Au}$ reaction at a beam energy of $140\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The ground-state band and the excited $\ensuremath{\pi}{i}_{13∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13∕2}$ 2-qp band have been extended up to lower and higher spin states. An upbend has been observed in the excited band at $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\sim}0.25\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and is interpreted as resulting from a pair of $\ensuremath{\pi}{h}_{9∕2}$ alignment. This low-frequency ${(\ensuremath{\pi}{h}_{9∕2})}^{2}$ alignment is supported by the measured $B(M1)∕B(E2)$ ratios and alignment properties in neighboring odd-$A$ nuclei. The linking transitions between the two bands and to the ground state have been established leading to a firm spin-and-parity assignment for the $\ensuremath{\pi}{i}_{13∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13∕2}$ band in $^{184}\mathrm{Au}$. This result provides strong evidence for the low-spin signature inversion in the $\ensuremath{\pi}{i}_{13∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13∕2}$ bands of odd-odd nuclei in the $A\ensuremath{\sim}180$ mass region.

Observation of magnetic rotation in odd-oddAg104

The high spin level structure of $^{104}\text{Ag}$ has been extended to ${I}^{\ensuremath{\pi}}={20}^{+}$ and excitation energy of $7.159\phantom{\rule{0.3em}{0ex}}\text{MeV}$ through the discrete line $\ensuremath{\gamma}$-ray spectroscopy. The negative parity ground state band has been confirmed and extended to ${I}^{\ensuremath{\pi}}={18}^{\ensuremath{-}}$. Two new nonyrast dipole bands, one with positive and the other with negative parity, have been observed. The parities of the two bands have been established through polarization directional correlation measurement of the feed-out transitions from these bands. The level lifetimes have been measured in the ground state band and the positive parity dipole band. The measured total angular momenta and the $B(M1)$ rates have been compared with the predictions of hybrid version of the tilted axis cranking. The $B(M1)$ rates have also been compared with the values obtained from D\onau's geometric formula. The tilted axis calculations give good overall agreement which suggests that all the three bands of $^{104}\text{Ag}$ exhibits magnetic rotation.

High-Spin States in the N = 50 Nucleus 88Sr

The excited states of 88Sr have been produced in the reaction16O(82Se,4p6n) and studied using in-beam γ spectroscopytechniques. Two high-spin level structures have been observed andestablished up to 8.5 MeV and 7.9 MeV excitation energy, respectively. Basedon the measurements of the directional correlations of γ-raysde-exciting oriented states and anisotropic factors of γ-rays, spinvalues of the excited states have been assigned up to the highest levelsobserved.

New insight in the level structure of 153Er

The high-spin level structure of the 153Er nucleus has been reinvestigated by in-beam γ-ray and electron spectroscopy with (14N,pxn) reaction. Excitation energies, spin and parity assignments are unambiguously established for the two lowest isomers T1/2≃ 380 ns and T1/2\simeq 10 ns. The characteristics of the third one (T1/2≃ 250 ns) at 5.2 MeV are still questionable but its main decay modes are better known. An extension of the level scheme is proposed up to 8.4 MeV.Experimental results have been discussed in terms of shell model multiplets and compared with the other structures observed in N=85 neighbouring nuclei.