Semi-decoupled Bands Research Articles

Decoupled and semi-decoupled bands in Hg197 and Hg199

The structure of decoupled positive-parity and semidecoupled negative-parity bands up to high spin in $^{197,199}\mathrm{Hg}$ has been studied using multinucleon transfer reactions with the Gammasphere array. A positive-parity band in $^{199}\mathrm{Hg}$ with the ${(\ensuremath{\nu}{i}_{13/2})}^{3}$ decoupled configuration that deexcites to levels in the negative-parity sequences is newly established. The semidecoupled sequences in both isotopes are extended to higher spin. Rotation-aligned angular momenta and crossing frequencies determined from experiment are in fair agreement with those from cranking calculations. A transition from oblate collective rotation at low spin to triaxial noncollective shapes at high spin is indicated.

Decoupled and semi-decoupled bands in Hg 197 and Hg 199

Decoupled and semi-decoupled bands in Hg 197 and Hg 199

Publisher's Note: Semi-decoupled band and other high-spin band structures in Pt188 [Phys. Rev. C 96 , 014315 (2017)

Publisher's Note: Semi-decoupled band and other high-spin band structures in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Pt</mml:mi><mml:mprescripts /><mml:none /><mml:mn>188</mml:mn></mml:mmultiscripts></mml:math> [Phys. Rev. C <b>96</b> , 014315 (2017)

Semi-decoupled band and other high-spin band structures in Pt188

High-spin states in the $^{188}\mathrm{Pt}$ nucleus have been investigated employing the $^{174}\mathrm{Yb}(^{18}\mathrm{O},4n)^{188}\mathrm{Pt}$ reaction. The level scheme has been significantly extended with the addition of several new $\ensuremath{\gamma}$ rays. The Indian National Gamma Array (INGA) spectrometer consisting of eighteen clover Ge detectors facilitated angular correlation and linear polarization measurements for spin-parity assignment of levels. The ${I}^{\ensuremath{\pi}}={5}^{\ensuremath{-}}$ semi-decoupled band has been investigated in detail, and the long-standing ambiguity regarding the correct ordering of associated $\ensuremath{\gamma}$ rays is now removed with the new observation of transitions linking the even-spin levels to the odd-spin ones. A weak, $\mathrm{\ensuremath{\Delta}}I=2$ sequence of $\ensuremath{\gamma}$ rays with alignment and moment of inertia similar to the yrast, even-spin, rotation-aligned neutron ${i}_{13/2}$ band has been newly observed. Cranking calculations suggest that this new odd-spin sequence arises from the excitation of a valence quasineutron to the next ${i}_{13/2}$ level.

Observation of a new rotational band in 104Nb nucleus

The high spin states in neutron-rich 104Nb have been investigated from study of prompt γ-rays in spontaneous fission of 252Cf with the Gammasphere detector array. A new rotational band has been identified for the first time. This band is proposed as a semi-decoupled band based on the configuration γ5/2−[303]Λν1/2−[541].

First identification of a collective band in the odd-oddNb104nucleus

The higher spin levels in neutron-rich $^{104}\mathrm{Nb}$ have been investigated from a study of the prompt \ensuremath{\gamma} rays in spontaneous fission of $^{252}\mathrm{Cf}$ with the Gammasphere detector array. A new collective band has been identified for the first time. This band is proposed as a semidecoupled band based on the configuration $\ensuremath{\pi}5/{2}^{\ensuremath{-}}[303]\ensuremath{\bigotimes}\ensuremath{\nu}1/{2}^{\ensuremath{-}}[541]$. The other structural characteristics are discussed.

Signature inversion in the semidecoupled $\pi h_{9/2} \otimes \nu i_{13/2}$ band of the odd-odd nucleus 172 Lu

High-spin states in the odd-odd nucleus 172Lu have been populated in a 170Er(7Li,5n) reaction at 51 MeV and the emitted $\gamma$ -radiation was detected with the GASP array. A new semidecoupled band with the proposed $\pi 1/2^-[541] \otimes \nu 7/2^ + [633]$ configuration has been established exhibiting a signature inversion. A systematic study of the signature inversion in odd-odd nuclei of the rare-earth region is presented. The variation of the inversion spin remains nearly constant for nuclei with the same N-Z, increases with N for an isotopic chain and decreases with Z for an isotonic chain. On the basis of the systematics a change of the spins by $1\hbar$ is proposed for the semidecoupled bands in 180Re, 182,184Ir and 184,186Au.

Two-quasiparticle and collective excitations in transitional 108,110 Pd nuclei

High-spin states in 108,110Pd isotopes are studied by $\gamma$ -ray spectroscopy of heavy-ion-induced fission. The Pd isotopes are produced in the fission channel of the 31P + 176Yb reaction at beam energy 152 MeV. The prompt $\gamma$ -rays are detected with the EUROBALL4 multidetector array. The yrast states of 108,110Pd have been observed above the region of the first backbend. The level scheme of 108Pd was extended with a new negative-parity band. The yrast sequence in 110Pd is observed up to spin I = 14 + and negative-parity bands have also been identified. The backbending in these even-mass Pd isotopes is associated with the alignment of the neutron (h 11/2)2 pair. The negative-parity states arise from two neutron configurations $\nu h_{11/2} \otimes \nu g_{7/2}$ and $\nu h_{11/2} \otimes \nu d_{5/2}$ and they are interpreted in the frame of two-quasiparticle + rotor model as semidecoupled bands. The observed experimental staggering in the $\gamma$ -bands of 108,110Pd supports the theoretical predictions for $\gamma$ -instability of their shapes.

Rotational bands and signature inversion in odd-oddRe172

High-spin states in the odd-odd $^{172}\mathrm{Re}$ have been investigated via the $^{149}\mathrm{Sm}(^{27}\mathrm{Al},4n\ensuremath{\gamma})^{172}\mathrm{Re}$ reaction through excitation functions, $x\text{\ensuremath{-}}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements. A level scheme consisting of three rotational bands has been identified for the first time extending the high-spin studies of $A\ensuremath{\sim}160$ odd-odd nuclei to the currently lightest rhenium isotope. The three bands have been assigned to be built on the $\ensuremath{\pi}{h}_{11∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13∕2}$, $\ensuremath{\pi}{h}_{9∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13∕2}$, and $\ensuremath{\pi}1∕{2}^{\ensuremath{-}}[541]\ensuremath{\bigotimes}\ensuremath{\nu}1∕{2}^{\ensuremath{-}}[521]$ configurations according to their rotational properties in quasiparticle alignments, signature splitting, in-band $B(M1)∕B(E2)$ ratios, level spacing systematics, band crossing frequencies, as well as the existing knowledge in neighboring nuclei. Low-spin signature inversion has been confirmed in the first two bands due to the observation of signature crossing at high-spin states. The general features of inversion phenomenon in the semidecoupled bands are presented and discussed with reference to theoretical calculations of two quasiparticle plus rotor model including $p\text{\ensuremath{-}}n$ interactions.

Structure of the Semi-decoupled π 1/2[411] Band in OddProton Nucleus 169Ta

High spin states of the odd proton-nucleus 169Ta have beenpopulated in the reaction 155Gd(19F,5n) with beam energiesof 97 MeV. Rotational band based on d3/2 proton 1/2[411]Nilsson state has been pushed up to 39/2+ in the α = 1/2decay sequence. Its signature partner, the α = -1/2 decay sequence withfour link transitions has been established and 1/2[411] band in169Ta was reassigned to be a semi-decoupled band. Thesystematics of the signature splitting in the K = 1/2 bands in therear-earth region and the accidental degeneracy conclusion given by theangular projection shell model were discussed.

Signature Inversion of the Semi-decoupled Band in the Odd-OddNucleus 170Ta

The high-spin states of the odd-odd nucleus 170Ta have been studied bythe 155Gd (19F, 4n) 170Ta reaction at the beam energy of 97 MeV.The α = 1 sequence of the semi-decoupled band has been pushed tohigher-spin states and the signature inversion point was observed at19.5 ℏ. The results are compared with those of theneighbouring odd-odd nuclei.

Coincidence recoil-distance Doppler-shift lifetime measurements in128Ba

Mean lifetimes of 24 excited states in ${}^{128}\mathrm{Ba}$ populated via the ${}^{116}\mathrm{Cd}{(}^{16}\mathrm{O},4n)$ reaction at $E=76\mathrm{MeV}$ were measured by means of the recoil-distance Doppler-shift method in coincidence mode. A new version of the differential decay-curve method which takes into account the velocity distribution of the recoils and the effect of the Doppler-shift attenuation in the stopper was applied for the lifetime determination. The $B(E2)$ values in the ground-state band indicate a reduction of the transition strengths which may be partly explained by the O(6) limiting case of the interacting boson model or alternatively, by rotationally induced changes in the single-particle level structure at spins higher than ${I}^{\ensuremath{\pi}}{=4}^{+}.$ The general collective (or Frankfurt) model is found to describe well the intraband transition strengths in the quasi-\ensuremath{\gamma} band which also exhibit the features characteristic for a $K=2\ensuremath{\Elzxh}$ rotational band. However, none of the collective models applied can describe in a consistent way all observed properties of the low-lying collective states. The newly measured $B(E2,\stackrel{\ensuremath{\rightarrow}}{I}I\ensuremath{-}2)$ and $B(M1,\stackrel{\ensuremath{\rightarrow}}{I}I\ensuremath{-}1)$ transition strengths reconfirm the configuration $\ensuremath{\pi}{h}_{11/2}{d}_{5/2}$ of the negative-parity semidecoupled bands. The lowest levels of the higher-lying ``dipole'' band in ${}^{128}\mathrm{Ba},$ which is built on the high-K four-quasiparticle prolate configuration $(\ensuremath{\pi}{h}_{11/2}{d}_{5/2})\ensuremath{\bigotimes}(\ensuremath{\nu}{h}_{11/2}{g}_{7/2}),$ are studied.

Rotational bands in Odd-Odd 180Ir

High spin states in 180Ir have been studied via 154 Sm(31P,5nγ)180Ir reaction through excitation functions, X-γ and γ-γ-t coincidence measurements. Three rotational bands are identified including a doubly decoupled band, a semi-decoupled one, and a coupled structure up to (26+). The quasiparticle configurations associated with these bands are suggested according to in-band B(M1)/B(E2) ratios and band structures of neighboring odd-odd nuclei. Signature inversion in the semidecoupled band is discussed relying on systematics.

In-band M1 and E2 transition rates and collective structures in 128Ba

Subpicosecond mean lifetimes of eight excited states in 128Ba populated via the 96Zr( 36S,4n) reaction were measured by the Doppler-shift attenuation (DSA) technique using a line-shape analysis. The differential decay-curve method (DDCM) was applied for the lifetime determination. The B(E2) values in the yrast band indicate that the first band-crossing is with a proton S-band. The configuration πh 11 2 d 5 2 of the negative-parity semi-decoupled bands is confirmed by the measured B(E2, I → I − 2) and B(M1, I → I − 1) transition strengths. The higher-lying “dipole” band in 128Ba can be described as a high- K four-quasiparticle band built on the prolate configuration (πh 11 2 d 5 2 ) ⊗ (νh 11 2 g 7 2 ) .

Signature inversion in semi-decoupled bands: residual interaction between h9/2 protons and i13/2 neutrons [Phys. Lett. B 406 (1997) 193

Signature inversion in semi-decoupled bands: residual interaction between h9/2 protons and i13/2 neutrons [Phys. Lett. B 406 (1997) 193

Signature inversion in semi-decoupled bands: residual interaction between h protons and i neutrons

Abstract Semi-decoupled bands based on the πh 9 2 ⊗ vi 13 2 configuration are observed in 162 Tm, 164 Tm and 174 Ta. Spins assigned to these bands imply an inversion of the expected signature splitting, which is interpreted as being the result of a residual proton-neutron interaction.

Semidecoupled Band and Shape Driving Effect of the π½-[541] Orbital in 170Ta

High spin states in 170Ta have been studied via 159Tb(16O, 5nγ)170Ta reaction at 105 MeV beam energy. Three rotational bands have been observed among which one coupled band and an unfavored ΔI = 2 transition sequence of the semidecoupled band are identified in this work. The effects of the π½-[541] proton intruder orbital are qualitatively discussed.

Semidecoupled band structure in odd-odd 134La and 136Pr.

The level schemes of the isotones {sup 134}La and {sup 136}Pr were obtained with in-beam gamma spectroscopy techniques using fusion evaporation reactions with {sup 10}B, {sup 14}N, and {sup 16}O beams and enriched targets of {sup 126,128}Te and {sup 123}Sb. Rotational bands assigned to the {pi}{ital h}{sub 11/2}{direct product}{nu}{ital h}{sub 11/2} configuration were seen in both nuclei. Another band seen in {sup 136}Pr was tentatively assigned to the {pi}(413)5/2{direct product}{nu}{ital h}{sub 11/2} configuration. A beginning of a backbend seems to show up in this band.

Investigation of level energies and B(E2) values for rotation-aligned bands in Hg isotopes

High spin states in 191, 192, 193, 195, 197, 199Hg were investigated by observing γ-rays and conversion electrons in the compound reactions 192, 194, 198Pt(α, x n) and 192 Pt( 3 He, 4 n) . In 197Hg the decoupled band built on the 13 2 + state and the semi-decoupled negative-parity band are observed up to I π = 41 2 + and 33 2 − , respectively. A careful investigation of 199Hg revealed no new high spin states above the previously known levels with I π = 25 2 + and 31 2 −. Half-lives were determined for the 10 +, 7 −, 8 − and 16 − states in 192Hg, the if 33 2 + states in 191,193 Hg and the (frc states in 191, 193, 195, 197Hg. The systematics of the level energies and B(E2) values for the positive-parity ground and 13 2 + bands and the negative-parity semi-decoupled bands in 190–200Hg is discussed.

Decoupled two-quasiparticle bands and backbending in174W and172Hf

Negative parity sidebands have been observed to high spin in the N=100 isotones 174W and 172Hf. Their high and constant moment of inertial and decay characteristics, identify them as semi-decoupled bands, probably of a configuration involving a p3/2 or h9/2 neutron and an i13/2 neutron. The character of these bands is used to estimate the properties of the (i13/2)2 neutron band responsible for backbending and, through a two-band mixing calculation, the details of backbending.