Low-spin Signature Inversion Research Articles

Rotational band properties of173W

High-spin states in ${}^{173}$W have been studied using the ${}^{150}$Nd(${}^{28}\text{Si},5n$)${}^{173}$W reaction at beam energies of 135 and 140 MeV. The previously known bands associated with the $7/{2}^{+}[633]$, $5/{2}^{\ensuremath{-}}[512]$, and $1/{2}^{\ensuremath{-}}[521]$ configurations are extended significantly, and the unfavored signature branch of the $1/{2}^{\ensuremath{-}}[521]$ band is established for the first time. The band properties, such as level spacings, band-crossing frequencies, alignment gains, and signature splittings, are discussed with an emphasis on the low-spin signature inversion observed in the $5/{2}^{\ensuremath{-}}[512]$ band. By comparing the experimental $B(M1)/B(E2)$ ratios with the theoretical values, we conclude that the configuration of the $5/{2}^{\ensuremath{-}}[512]$ band is quite pure at low spins without appreciable admixture of the $5/{2}^{\ensuremath{-}}[523]$ orbit, in conflict with the particle rotor model calculated results.

Signature inversion in the 7/2−[503] band of 185Pt

High-spin states in 185Pt have been investigated using the 173Yb(16O, 4n) reaction at a beam energy of 90 MeV. The 7/2−[503] band in 185Pt is revised, and particularly the intra-band B(M1)/B(E2) ratios are deduced experimentally. Low-spin signature inversion is revealed in the 7/2−[503] band. The signature inversion can be interpreted if we assume configuration change in this band from the 7/2−[503] orbital to the 7/2−[514] orbital with increasing spin, which is supported by comparing the measured B(M1)/B(E2) ratios with the theoretical values from the semi-classical Dönau and Frauendorf approach.

High-spin states of odd-odd nuclei in the [formula omitted] mass region

Efforts have been made in our group to study the band structure of odd-odd nuclei in the A ∼ 170 mass region. We aimed at providing new data of high-spin states and searching for the low-spin signature inversion in the 2-qp bands built on the π h 9 / 2 ⊗ ν i 13 / 2 and π i 13 / 2 ⊗ ν i 13 / 2 configurations. In this talk, main results of our work will be summarized, and some systematic features of signature inversion discussed. The spin and parity assignments for the π i 13 / 2 ⊗ ν i 13 / 2 band in 184Au could be regarded as firm providing a good example for systematic and theoretical investigations.

Identification of a New Band and Its Signature Inversion in174Re

High spin states in 174Re are investigated via the152Sm(27Al,5nγ)174Re reaction and γ−γ coincidencerelationships are analysed carefully. A new band is identified due toits spectroscopic connection with the knownπ1/2−[541]⊗ν1/2−[521] band. This band is proposedto be the ground-state band built on the π1/2−[541]⊗ν5/2−[512] configuration in view of the low-lying intrinsic statesin the neighbouring odd-mass nuclei. It is of particular interestingthat the new band exhibits a phenomenon of low-spin signature inversion,providing a new situation for theoretical investigations.

SEARCH FOR SIGNATURE INVERSION IN THE πi13/2 ⊗ νi13/2 BANDS IN 182,184,186Au

Search for low-spin signature inversion in the πi13/2 ⊗ νi13/2 bands in odd-odd 182,184,186 Au has been conducted through the standard in-beam γ-spectroscopy techniques. The experiments for 182 Au and 186 Au have been performed in the Japan Atomic Energy Agency (JAEA) via the 152 Sm (35 Cl ,5 n )182 Au and 172 Yb (19 F ,5 n )186 Au reactions, respectively. A study of 184 Au has been made using a multi-detector array GASP in LNL, Italy, via the 159 Tb (29 Si ,4 n )184 Au reaction. The πi13/2 ⊗ νi13/2 bands in these three nuclei have been identified and extended up to high-spin states. In particular, the inter-band connection between the πi13/2 ⊗ νi13/2 band and the ground-state band in 184 Au has been established, leading to a firm spin-and-parity assignment for the πi13/2 ⊗ νi13/2 band. The low-spin signature inversion is found in the πi13/2 ⊗ νi13/2 bands in 182,184,186 Au according to our spin-assignment and the signature crossing observed at high-spin states.

Excited states and signature inversion inCs116

Excited states have been observed for the first time in the very neutron-deficient, odd-odd nucleus, ${}_{55}^{116}{\mathrm{Cs}}_{61}$. The assignment to $^{116}\mathrm{Cs}$ has been made by the detection of \ensuremath{\gamma} rays in coincidence with evaporated charged particles and with evaporation residues. The observed states form a rotational band which has been assigned to the $\ensuremath{\nu}({h}_{11/2}) \ensuremath{\bigotimes} \ensuremath{\pi}({h}_{11/2})$ configuration. Tentative spin assignments have been made on the basis of systematic comparisons with neighboring cesium isotopes. A low-spin signature inversion is observed in the band at a rotational frequency of about 0.23 MeV$/\ensuremath{\hbar}$. The observed signature inversions in the odd-odd $^{116\ensuremath{-}126}\mathrm{Cs}$ isotopes have been compared with the results of extended total Routhian surface calculations, in which signature inversion arises as a consequence of quadrupole-pairing correlations and triaxial deformation. As previously shown for some of the odd-odd $A\ensuremath{\simeq}120$ isotopes, the calculations reproduce the signature inversions reasonably well.

Properties of the πh9/2⊗νi13/2 Oblate Band in 188Tl

High spin states in 188Tl have been investigated via the157Gd(35Cl,4n) reaction at beam energy of 170 MeV. Arotational band built on the πh9/2⊗νi13/2configuration with oblate deformation has been established. Consideringthe similarity between the band structure observed in odd–odd Tl nuclei,spin values have been tentatively proposed for the new band in188Tl. The πh9/2⊗νi13/2 oblate band in188Tl shows low-spin signature inversion, and it can be interpretedqualitatively by the two quasiparticle plus rotor model including aJ-dependent p–n residual interaction.

Observation of a πh9/2 ⊗ νi13/2 oblate band in 188Tl

Excited states in 188Tl have been studied experimentally using the 157Gd (35Cl, 4n) reaction at a beam energy of 170MeV. A rotational band built on the πh9/2 ⊗ νi13/2 configuration with oblate deformation has been established for 188Tl. Based on the structure systematics of the oblate πh9/2 ⊗ νi13/2 bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in 188Tl. The πh9/2 ⊗ νi13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two-quasiparticle plus rotor model including a J-dependent p-n residual interaction.

Low-spin signature inversion in theπh9/2⊗νi13/2oblate band ofTl190

High-spin states in $^{190}\mathrm{Tl}$ have been studied experimentally by using the $^{160}\mathrm{Gd}$($^{35}\mathrm{Cl}$,5n) fusion-evaporation reaction at beam energies of 167 and 175 MeV. A rotational band built on the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ configuration with oblate deformation has been established for $^{190}\mathrm{Tl}$. Spin values are assigned by adopting the results from $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ decay work for $^{194}\mathrm{Bi}$ found in the literature. With the configuration and spin-parity assignments, the low-spin signature inversion has been revealed for the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ oblate band in $^{190}\mathrm{Tl}$. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ configuration. The low-spin signature inversion for the oblate $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ band can be interpreted by the two-quasiparticle-plus-rotor model including a J-dependent $p\ensuremath{-}n$ residual interaction.

First observation of low-spin signature inversion in the πh9/2 ⊗ νi13/2 oblate band

Excited states in 190Tl have been studied experimentally using the 160Gd(35Cl, 5n) reaction, and resulted in the identification of a strongly coupled band based on the πh9/2 ⊗ νi13/2 configuration with oblate deformation. Combining with the results from the previous α-decay of 194Bi, spin values have been proposed for the πh9/2 ⊗ νi13/2 oblate band in 190Tl. This oblate band shows low-spin signature inversion. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate πh9/2 ⊗ νi13/2 configuration.

Observation of signature inversion in the πh9/2Äνi13/2 oblate band

High-spin states in 190Tl have been studied via the 160Gd(35Cl, 5nγ) reaction. The level scheme, consisting of the πh9/2⊗vi13/2 oblate band and a cascade with character of single particle excitations, has been established. Spin values have been firmly assigned to the oblate band in 190Tl, resulting in low-spin signature inversion in the πh9/2⊗vi13/2 oblate band for the first time. Based on the similarity of the level structure in doubly odd Tl nuclei, spin values for the oblate bands in 192–200Tl should be re-assigned, and a consistent low-spin signature inversion has occurred in these oblate deformed nuclei. The low-spin signature inversion phenomena can be interpreted qualitatively by using the 2-quasiparticle plus rotor model including p-n residual interactions.

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.

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.

High-spin states and signature inversion in odd-odd 182Au

High-spin states in182Au have been produced and studied via the152Sm(35Cl,5nγ)182Au reaction. The level scheme consisting of the πh 9/2⊗νi 13/2 and πi 13/2⊗νi 13/2 bands has been established for the first time. The low spin signature inversion in both bands has been found. The observed signature inversion phenomena can be interpreted qualitatively using the pairing and deformation self-consistent cranked Wood-Saxon calculations.

Signature inversion phenomena in odd-odd 182Au

High-spin states in the odd-odd 182Au nucleus have been investigated using the 152Sm(35Cl, 5nγ)182Au reaction through X-γ and γ-γ-t coincidence measurements. Rotational bands based on the πh 9/2⊗νi 13/2 and πi 13/2⊗νi 13/2 configurations have been identified. It is found that the two bands show characteristics of low-spin signature inversion. The observed signature inversion can be well reproduced by pairing-deformation self-consistent cranking Woods-Saxon calculations.

Signature inversion in the yrast band of164Ta

Excited states in Ta-164 were populated in the Nd-142(Al-27,5n)Ta-164 reaction and investigated using the AFRODITE spectrometer Arran. The yrast rotational decay sequence Lip to spin 21(-) is identified for the first time and assigned to the pi[514]9/2(-) x nu[660]1/2(+) configuration. A less intense. excited hand is also identified. Low-spin signature inversion is observed in the yrast band, and is compared with the extended total Routhian surface calculations. It is likely that quadrupole pairing plays a role in generating the anomalous signature splitting, but an additional mechanism apart front the assumed mean field and quadrupole pairing interaction may be required to account for the experimental data.

High-spin states in 166Lu

Five rotational bands with configurations {π7/2+[404] ⊗ν5/2+[642]} K = 6, {π9/2-[514] ⊗ν5/2+[642]} K = 7, {π1/2+[411] ⊗ν5/2+[642]} K = 2, {π1/2-[541] ⊗ν5/2+[642]} K = 2 and {π5/2+[402] ⊗ν5/2+[642]} K = 5 were populated through the 152Sm ( 19F, 5n) 166Lu reaction at a beam energy of 97MeV. The last three bands are identified in the present study. A phase change of level staggering is observed and low-spin signature inversion is suggested in the band {π1/2-[541] ⊗ν5/2+[642]} K=2. The inversion spin 17.5? (spin at inversion point) of this band fits well to the systematic variation trend of inversion spin, increasing with N and decreasing with Z, for the known π1/2-[541] ⊗νi13/2 bands observed in odd-odd deformed nuclei around A = 170.

High-spin states in odd-odd170Ta

High-spin states in ${}^{170}\mathrm{Ta}$ have been studied via ${}^{159}{\mathrm{T}\mathrm{b}(}^{16}\mathrm{O},5n\ensuremath{\gamma}{)}^{170}\mathrm{Ta}$ reaction through excitation functions, K x-\ensuremath{\gamma}, and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}\ensuremath{-}t$ coincidence measurements. Three rotational bands have been identified which consist of two strongly coupled bands and a semidecoupled one. The quasiparticle configurations of these bands and the interpretation of experimental results are discussed based on the existing knowledge of neighboring odd-mass and odd-odd nuclei and in the framework of the cranked-shell model. Low-spin signature inversion in the $\ensuremath{\pi}{9/2}^{\ensuremath{-}}[514]\ensuremath{\bigotimes}\ensuremath{\nu}{5/2}^{+}[642]$ and $\ensuremath{\pi}{1/2}^{\ensuremath{-}}[541]\ensuremath{\bigotimes}\ensuremath{\nu}{5/2}^{+}[642]$ bands are discussed. A delay (reduction) of the band-crossing frequency is observed in the $\ensuremath{\pi}{1/2}^{\ensuremath{-}}[541]\ensuremath{\bigotimes}\ensuremath{\nu}{5/2}^{+}[642]$ $(\ensuremath{\pi}{5/2}^{+}[402]\ensuremath{\bigotimes}\ensuremath{\nu}{5/2}^{+}[642])$ band. This configuration-dependent crossing frequency is discussed in comparison with the AB crossing frequencies in the related bands of neighboring odd-Z isotopes.

Observation of signature inversion in theν(h11/2)⊗π(h11/2)band of122Cs

High-spin states have been studied in ${}^{122}\mathrm{Cs}$ using the ${}^{94}\mathrm{Mo}{(}^{31}\mathrm{P},2pn)$ reaction. Two rotational bands have been observed to spins of 28 and $21 \ensuremath{\Elzxh}.$ The most intensely populated band has been reassigned to have the $\ensuremath{\nu}{(h}_{11/2})\ensuremath{\bigotimes}\ensuremath{\pi}{(h}_{11/2})$ configuration. A low-spin signature inversion is observed in this band between 19 and $20 \ensuremath{\Elzxh},$ consistent with the neighboring odd-odd cesium isotopes. Spectroscopic properties are discussed, including signature inversion of bands in $A\ensuremath{\simeq}120$ nuclei.

First observation of excited states in 118Cs: signature inversion in the band

Excited states have been observed for the first time in the very neutron-deficient odd-odd 55118Cs nucleus. A doubly-decoupled band based on the π(h112) ⊗ ν(h112) configuration has been identified to spins over 30 ħ. The band has been assigned to 118Cs using γ-recoil and γ-X-ray coincidences. A low-spin signature inversion is observed between 16 and 17 ħ. The band is discussed with respect to the systematics of signature inversion in odd-odd A ⋍ 120 nuclei.