New states and γ-transitions in 209Bi observed in the (3He, d*γγ)-subcoulomb-reaction

High-spin states in ¹⁴³Pm have been investigated via the ¹²⁸Te(¹⁹F,4nγ)¹⁴³Pm reaction using techniques of in-beam γ-spectroscopy. γ-ray singles, γ-γ coincidences, γ-ray anisotropies and DCO ratios have been measured. Based on these measurements, the level scheme of ¹⁴³Pm has been extended up to an excitation energy of 10535.4 keV, including 48 new γ-rays deexciting 28 new levels. The yrast levels in ¹⁴³Pm can be understood qualitatively in the framework of a weak-coupling model. Received: 10 July 2000 / Accepted: 12 October 2000     

Coulomb energy differences between isobaric analogue states in 70Br and 70Se

Gamma ray transitions de-exciting states in the N = Z nucleus ⁷⁰Br have been identified for the first time using the GASP and EUROBALL arrays coupled with ancillary detectors. The level scheme of ⁷⁰Br has been established by means of particle-gated γ-γ and γ-γ-γ coincidences. The Coulomb energy differences between isobaric analogue states in ⁷⁰Br and ⁷⁰Se show a deviation from the expected behaviour which could be related to dripline effects. Received: 18 July 2001 / Accepted: 25 September 2001     

High-spin states in the 96Tc nucleus

High-spin states in the ⁹⁶Tc nucleus have been studied with the reactions ⁸²Se(¹⁹F,5nγ) at 68 MeV and Zn(³⁶S,αpxn) at 130 MeV. Two γ-ray cascades (irregular bandlike structures) have been observed up to an excitation energy of about 10 MeV and spin 21-22?. Received: 19 January 2001 / Accepted: 30 March 2001     

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     

Study of the N = 50 major shell effect toward 78Ni at PARRNe⋆

The γ-ray de-excitations following the β-decay of ⁸³Ga and the β-n decay of ⁸⁴Ga have been studied. The radioactive species were produced using the PARRNe on-line mass-separator installed at the IPN Orsay Tandem accelerator. Two γ-lines were attributed to ⁸³Ge with the aid of β-γ and γ-γ coincidences. The Z identification of the γ-lines was provided by time analysis of a buid-up/decay cycle. The excited levels of ⁸³Ge can be explained by the coupling of the single neutron state ν2d _5/2 to the first 2⁺ excitation of the ⁸²Ge core.     

Identification of Rotational Band in Doubly Odd 170Ta

High spin states in ¹⁷⁰Ta have been studied via ¹⁵⁹Tb(¹⁶O,5nγ)¹⁷⁰Ta reaction through excitation functions, K X-γ and γ-γ-t coincidence measurements. Three rotational bands have been identified among which one coupled band and an unfavored δI=2 E2 transition sequence are newly found in this work. The possible quasiparticle configurations of these bands are discussed. Received: 7 November 1997     

Microsecond isomers in 187Tl and 188Pb

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between ¹⁵⁵Gd and ³⁶Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the ¹⁵⁹Tb(³²S, 4n) reaction the γ-decay of isomeric levels in ¹⁸⁷Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in ¹⁸⁸Pb was also observed and its lifetime was measured as 1150 ± 30 ns, and limits of 20–600 ns were placed on the meanlife of an isomer conjectured in ¹⁸⁷Pb. Received: 20 August 1999     

Fragment dependence of high energy γ-ray emission in the spontaneous fission of 252Cf

The high energy γ-ray emission accompanying the spontaneous fission of ²⁵²Cf has been measured in coincidence with individual fission fragments selected by discrete γ-ray transitions. The enhancement of the γ-ray emission probability in the energy range E_γ= 3–8 MeV has been observed for the fission fragments in the region of nearly symmetric mass splitting, confirming results reported in previous investigations. The γ-γ coincidence technique employed in the present work clearly demonstrate that the major contribution to this enhancement is caused by the fission channels where one fragment is near to the N= 82 or Z= 50 shell closures. The high energy γ-ray emission probability does not show any significant dependence on the number of neutrons emitted in the fission process, supporting the hypothesis that high energy γ-rays are mainly emitted from the fragments after the neutron evaporation. Received: 22 December 1998     

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 levels in 147Tb

The high-spin states of ¹⁴⁷Tb have been studied with regard to their spins. The data were obtained by in-beam γ-ray spectroscopy using the reaction ¹²⁰Sn(³¹P,4n)¹⁴⁷Tb at 152 MeV performed at the Osiris spectrometer in Berlin. We obtained multipole mixing ratios for 60 transitions, and level spins up to 67/2ħ are introduced. Received: 30 March 1998     

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     

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     

Signature inversion in the yrare band of <Superscript>119</Superscript>Xe

Excited states of the ¹¹⁹Xe nucleus have been studied by using in-beam γ-ray spectroscopy with the ¹⁰⁷Ag ( ¹⁶O, p3n) ¹¹⁹Xe fusion-evaporation reaction at a beam energy of 85 MeV. The level scheme of ¹¹⁹Xe has been derived from γ-γ coincidence and γ-γ angular correlation analyses. We have, for the first time, established the second negative-parity favored and unfavored states built on the 11/2^- state, namely the yrare rotational bands in ¹¹⁹Xe. In contrast to the behavior of the yrast bands where the favored states are lying lower in energy, the yrare favored states were observed to lie above the unfavored band. Such a signature inversion in ¹¹⁹Xe is changed to be normal at I = 12?. Received: 8 January 2002 / Accepted: 18 April 2002     

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     

Low-spin states of doubly odd 182Au

Low-lying states in the odd-odd light gold isotope ¹⁸²Au have been populated by the β⁺/EC decay of the ¹⁸²Hg nuclei. Level energies, spin and parity values were determined using on-line γ-ray and e^- spectroscopy measurements. No isomeric state with a long half-life was found in the ¹⁸²Au nucleus. Spin and parity I ^π = 2⁺ can be very likely assigned to the ¹⁸²Au ground state. Received: 19 December 2000 / Accepted: 28 February 2001     

Intruder states in even-even neutron-rich Pd isotopes

The decays of ¹¹²Rh ^g and ¹¹²Rh ^m obtained as on-line mass separated fission products have been investigated by standard β and γ spectroscopic techniques and γ-γ angular correlations. Low-lying 0⁺ and 2⁺ states are identified in the daughter nucleus ¹¹²Pd. Systematics suggests the existence of an intruder band which is the lowest in ¹¹⁰Pd, i.e. two neutrons before the midshell. Received:13 March 1998     

Decay of 1.643 h <Superscript>95</Superscript>Ru and its daughter's level structure

The decay of ⁹⁵Ru has been investigated by means of γ-ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo( α, n) ⁹⁵Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of ⁹⁵Tc is discussed in the framework of the projected shell model.     

High-spin isomers in 183Os

High-spin states in ¹⁸³Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I ^π= ((43/2)⁻) and (43/2)⁺ have been identified at excitation energies of E _x = 5.068 and 5.168 MeV. The half-lives are determined as T _1/2= 27 ± 3 and 24 ± 2 ns. Received: 22 December 1997     

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     

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