High-spin states in odd-odd 168Lu

High-spin states in the odd-odd ¹⁶⁸Lu nucleus, populated in the ¹⁵⁴Sm(¹⁹F,5n) reaction at a beam energy of 96 MeV, were investigated using in-beam γ-ray spectroscopy techniques. The BC neutron crossing in the yrast band, based on πg _7/2[404]7/2⁺⊗νi _13/2[642]5/2⁺ configuration, occurs at ħω= 0.31 MeV. The two side bands, based on πh _11/2[514]9/2⁻⊗νi _13/2[642]5/2⁺ and πh _9/2[541]1/2⁻⊗νi _13/2[642]5/2⁺ configurations, show anomalous signature-splitting and signature-inversion in the first one, to occur at ħω= 0.24 MeV. A moderately delayed BC-crossing is anticipated in the second one. Received: 15 June 1998 / Revised version: 11 January 1999     

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 πh _9/2 ⊗ νi _13/2 configuration with oblate deformation has been established for ¹⁸⁸Tl. Based on the structure systematics of the oblate πh _9/2 ⊗ νi _13/2 bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in ¹⁸⁸Tl. The πh _9/2 ⊗ νi _13/2 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.     

Observation of intermediate bands feeding the positive-parity yrast band in 155Gd

High-spin states of ¹⁵⁵Gd were populated by using the ¹⁵⁴Sm(α,3nγ)¹⁵⁵Gd reaction at E _α= 33 MeV. γ-γ coincidence, E _γ singles, excitation function, and the DCO ratios were measured. we have identified three intermediate bands with ΔI= 2 feeding the positive yrast band. The bands are interpreted as such candidate bands that are mixed with the negative-parity ground state band. This observation can provide a plausible explanation for unusually large population of the positive-parity yrast band observed in a recent Coulomb excitation. Received: 2 November 1999     

Shape co-existence and structural evolution of the yrast band in 157Yb

The high-spin states of ¹⁵⁷Yb have been studied via the ¹⁴⁴Sm(¹⁶O, 3n) reaction at ¹⁶O energy of 90 MeV using techniques of in-beam γ-ray spectroscopy. Measurement of γ-γ-t coincidences was performed with 11 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, the level scheme for ¹⁵⁷Yb was established. The shape co-existence and structural evolution of the νi _13/2 band with increasing angular momentum in ¹⁵⁷Yb have been discussed. The systematics of the νi _13/2 bands in the N = 87 odd-A isotones have been compared. Received: 7 January 2002 / Accepted: 10 April 2002     

Yrast band spectroscopy of155Gd and157Dy

The yrast bands of¹⁵⁵Gd and¹⁵⁷Dy have been observed to high spins (I～25–40). The systematic properties of the N=91 isotones with particular reference to the second i_13/2 neutron and first h_11/2 proton alignments are discussed.     

Observation of signature inversion in odd-odd 178Ir

High spin states in ¹⁷⁸Ir have been studied via the ¹⁵²Sm(³¹P, 5nγ)¹⁷⁸Ir reaction through excitation functions, X-γ and γ-γ-t coincidence measurements. According to the band structure characteristics and the measured intraband B(M1)/B(E2) ratios, two rotational bands are identified and assigned to be associated with the πh _9/2⊗νi _13/2 and πh _11/2⊗νi _13/2 configurations, respectively. Both bands show the signature inversion feature. Received: 23 March 2000 / Accepted: 31 July 2000     

High-spin states in 160Lu

High-spin states of ¹⁶⁰Lu have been studied through the ¹⁴⁴Sm( ¹⁹F, 3n) reaction. The previously known πh _11/2⊗υi _13/2 yrast band is extended from I ^π = 21^- to 25^- and a four quasiparticle band with configuration πh _11/2[523]7/2 ^-⊗υh _9/2[521]3/2 ^-⊗ (υi _13/2)² is reported. Received: 21 May 2001 / Accepted: 19 July 2001     

Search for decoupled bands in Odd-Odd 174Re

An effort has been made to search for the decoupled bands in odd-odd ¹⁷⁴Re via the ¹⁵⁹Tb(²⁰Ne,5n γ)¹⁷⁴Re reaction through excitation functions, K x-γ and γ-γ coincidence measurements. The doubly decoupled band and the semidecoupled one have been found in this work. Their quasiparticle configurations are proposed to be π1/2⁻[541] ⊗ν1/2⁻[521] and π1/2⁻[541] ⊗νi _13/2, respectively, according to the characteristics of band structures in this mass region. Another band with strongly coupled character is also reported. Received: 23 November 1999 / Revised version: 5 January 2000     

High-spin states of rotational bands built upon νi13/2 in 166Lu

High-Spin states of odd-odd ¹⁶⁶Lu were populated using the ¹³⁹La(³⁰Si,3nγ)¹⁶⁶Lu at a beam energy of 120 MeV. Twelve new γ-rays were placed on top of the previously known two rotational bands built upon πg _7/2⊗νi _13/2 and πh _11/2⊗νi _13/2. Extending high-spin states up to 21⁺ and 25⁻ for each band, we have observed the onset of band crossing near ħω _c ≈ 0.35 MeV. The band crossing frequency of the yrast πh _11/2⊗νi _13/2 band is consistent with the neutron BC band crossing observed in lighter odd-odd Lu isotopes.     

Shape co-existence and structural evolution of thevi13/2 band in157Yb

The high-spin states of¹⁵⁷Yb have been studied via the reaction of¹⁴⁴Sm(¹⁶O, 3n) at¹⁶O energy of 90 MeV using techniques of in-beam γ-ray spectroscopy. Measurement of γ-γ-t coincidences was performed with 11 BGO(AC)HPGe detectors. Based on the γ-γ coincidence relationships and the measured results of γ-ray anisotropies and DCO ratios, the level scheme for¹⁵⁷Yb was established. The shape co-existence and structural evolution of thevi_13/2 band with increasing angular momentum in¹⁵⁷Yb have been discussed. The systematics of thevi_13/2 bands in theN=87 odd-A isotones have been compared.     

High-spin states and signature inversion in odd-odd182Au

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.     

Recoil distance half-life measurements of the excited states in 145Sm

A recoil distance method was used to measure half-lives of the excited states of ₁₄₅Sm. The reaction used was ₁₃₉La(₁₀B, 4n)₁₄₅Sm. A plunger system was used. Half-lives were determined for two excited states for the first time. The yrast 27/2₊ state was found to have a half-life of 1.1 ± 0.2 ns corresponding to the retardation of 3.1 × 10₋₄ comparing with the single particle estimate of M1. The excitation energy of this state was well reproduced by the shell model calculation having a mixed configuration of [π{h^11/2(g^7/2)₋₂ (d^5/2)₋₁}¹⁰⁻, νf^7/2] + [π{h^11/2(g^7/2)₋₁}⁹⁻,νh^9/2]. Another retarded E1 transition was also found in a decay of a 21/2₊ state. Its retardation was 1.6 × 10₋₄ comparing with the single particle value. Received: 9 September 1997 / Revised version: 12 June 1998     

Signature inversion in πi13/2⊗νi13/2 structure in 178Ir

High-spin states in ¹⁷⁸Ir were investigated by means of in-beam γ-ray spectroscopy techniques using the multidetector array GASP. Excited states of ¹⁷⁸Ir were populated through the ¹⁵⁹Tb(²⁴Mg, 5n) fusion-evaporation reaction at E(²⁴ Mg) = 131-141 MeV. Several rotational bands were observed. Among them, the πi _13/2⊗νi _13/2 structure has been identified up to spin 36 ?. This band exhibits an anomalous signature splitting and a signature inversion around spin 25 ?. Received: 13 December 2000 / Accepted: 11 April 2001     

High-spin states in odd-odd 168Lu

High-spin states of odd-odd ¹⁶⁸Lu were observed up to 18ħ for the first time using the ¹⁵⁹Tb(¹³C, 4nγ)¹⁶⁸Lu reaction at E _13C= 58.5 MeV. γ-γ coincidence, E _γ singles, excitation function, and the DCO ratios were measured. Two rotational bands with signature splitting were populated, among which the lower-energy band is identified as π 7/2⁺[404] ⊗ν 5/2⁺[642] in view of alignment and energy systematics. Received: 27 October 1997     

Configuration assignments and decay of 126La high-spin bands

High spin states of ¹²⁶La have been populated using the reaction ¹¹⁶Sn+¹⁴N at 68 MeV. γ-rays and conversion electrons were detected with the GAREL array. Multipolarities of the lowest-lying in-band dipole transitions have been determined from the deduced internal conversion coefficients. Experimental B(M1)/B(E2) ratios have been derived for the bands and compared with calculated values using the D?nau-Frauendorf geometrical model. Configurations are proposed for the bands comparing them with cranked shell model calculations and on the basis of the measured B(M1)/B(E2) ratios. The β-decay of ¹²⁶La has also been revisited. The population of the ¹²⁶Ba levels gives a probable spin value of five for the decaying high-spin ¹²⁶La state with T _1/2≈ 64 s which may indicate a signature inversion in the πh_11/2νh_11/2 band. Received: 12 October 1999     

Rotational structures in the 125Cs nucleus

The collective band structures of the ¹²⁵Cs nucleus have been investigated by in-beam γ-ray spectroscopic techniques following the ¹¹⁰Pd ( ¹⁹F, 4n) reaction at 75MeV. The previously known level scheme, with rotational bands built on πg_7/2, πg_9/2 and πh_11/2 orbitals, has been extended and evolves into bands involving rotationally aligned ν(h_11/2)² and π(h_11/2)² quasiparticles. A strongly coupled band has been reassigned a high-K πh_11/2 ⊗ νg_7/2 ⊗ νh_11/2 three-quasiparticle configuration and a new side band likely to be its chiral partner has been identified. Configurations assigned to various bands are discussed in the framework of Principal/Tilted Axis Cranking (PAC/TAC) model calculations.     

Spectroscopy of 112Pd using heavy-ion-induced fission

High-spin states in ¹¹²Pd were studied using prompt γ-ray spectroscopy with Gammasphere following heavy-ion-induced fission in the reaction ¹⁸O + ²⁰⁸Pb at 91 MeV. A new 8⁺ level at 2638 keV was discovered with transitions connecting it to the yrast band and the quasi-gamma band. The three, now established, closely spaced 8⁺ states indicate a mixing between the ground-state band, s-band, and quasi-gamma band. Several high-spin structures with likely negative parity have been extended to higher spin and it is proposed that they are based on the νh _11/2(g _7/2 d _5/2) and νh _11/2(s _1/2 d _3/2) configurations. Received: 28 November 2000 / Accepted: 8 February 2001     

The structure of 99Ru from (α,3n) reaction

The results of in-beam investigations of excited states of ⁹⁹Ru using the ⁹⁸Mo(α,3n) reaction are presented. Angular distributions of γ–rays and γ–γ coincidences have been measured. Excited states have been identified up to an energy of E = 5603 keV and spin of I^π= 31/2⁻. Mean lifetimes τ have been determined using the DSA method for eleven levels. Aligned angular momenta are discussed and the probable (νh _11/2) origin of a backbending at frequency about 0.5 MeV was confirmed. The possible role of (νd _5/2) alignment at frequencies above 0.5 MeV was pointed out. Received: 13 January 1999 / Revised version: 26 March 1999     

Rotational bands in the doubly odd 130Cs nucleus

The band structures built on the 5^- isomeric state ( T _1/2 = 3.46 m) in the doubly odd ¹³⁰Cs nucleus have been established up to I = 24? via the ¹²⁴Sn(¹¹B, 5n)¹³⁰Cs reaction. The previously observed bands based on the πh _11/2⊗νh _11/2, πg _7/2⊗νh _11/2 and πd _5/2⊗νh _11/2 configurations and a positive-parity side band with multiple connections to the α = 0 signature partner of the yrast πh _11/2⊗νh _11/2 band have been extended to higher spins. A new band based on the πh _11/2⊗νg _7/2 configuration is observed. The yrast πh _11/2⊗νh _11/2 band exhibits anomalous signature splitting whose magnitude decreases up to spin 15 and then increases without restoring the normal signature splitting. Received: 20 February 2001 / Accepted: 9 May 2001     

Rotational structures in 123Cs

High-spin states in ¹²³Cs, populated via the ¹⁰⁰Mo ( ²⁸Si, p4n) fusion-evaporation reaction at E _lab = 130 MeV, have been investigated employing in-beam γ-ray spectroscopic techniques. Rotational bands, built on πg _7/2, πg _9/2 and the unique-parity πh _11/2 orbitals, have been extended and evolve into bands involving rotationally aligned ν(h _11/2)² and π(h _11/2)² quasiparticles. A three-quasiparticle band based on the high-K πh _11/2 ⊗ νg _7/2 ⊗ νh _11/2 configuration has also been observed. Total Routhian Surface (TRS) calculations have been used to predict the nuclear shape parameters ( β₂, β₄, γ) for the various assigned configurations. The assigned configurations have been discussed in the framework of a microscopic theory based on the deformed Hartree-Fock (HF) and angular-momentum projection techniques.