Two-quasiparticle bands in72Br

High spin states in the doubly odd nucleus⁷²Br were investigated via the reaction⁵⁸Ni(¹⁶O,pn) at 52–65 MeV beam energy. A multi-element detector system consisting of ten Compton supressed Ge detectors (OSIRIS) and two NE213 neutron detectors was used to establish the yrast bands up to 5 MeV excitation energy and probable spins of 15⁺ resp. 14^?. The lifetimes of 12 states and lifetime limits of four states were measured with the recoil distance method, among them four 0.5–3.1 ns isomers. Doppler broadened line shapes obtained in an additionalγγ-coincidence experiment via the reaction⁴⁰Ca(³⁶Ar, 3pn) at 125 MeV revealed further lifetimes and (very short) side feeding times. Three rotational bands were established with deformation parameters ¦β ₂¦≈0.3 and moment of inertia parameters \(\tilde f\) /? ²=36 MeV^?1 (K ^ρ=1^?) resp. 23 MeV^?1; their quasi-particle configurations are being discussed.     

Lifetimes in73Se

Lifetimes of 8 levels in⁷³Se have been measured by the recoil distance Doppler shift technique via the reaction⁶⁰Ni(¹⁶O, 2pn)⁷³Se. Energies of negative and positive parity states as well asE 2 transition strengths are compared with theoretical values obtained from a symmetric rotor plus particle model and a triaxial rotor model.     

Identification and structure of high spin particle-hole states in89Mo

Particle-γ andγ-coincidences of the reaction⁵⁸Ni(³⁶Ar, 4pn)⁸⁹Mo have been used to gain more information about high spin states in⁸⁹Mo and to establish the yrast sequence up to 7.6 MeV excitation energy and probable spin 37/2 ?. Spins and parities were assigned on the basis of DCO-ratios measured with the OSIRIS spectrometer and a large volume Ge detector placed at 162° to the beam. Furthermore, aγ-ray angular distribution experiment was carried out using the reaction⁵⁸Ni(³⁵Cl, 3pn)⁸⁹Mo. As in the neighboring isotopes⁸⁸Mo and⁹⁰Mo, the positive-parity high-spin states can be grouped into shell model multiplets characterized by increasing seniorities of proton particles and neutron holes in the 1g_9/2 shell. The negative-parity states can be explained with one nucleon moving in thep _1/2 orbit. The energies and wave functions of these states have been deduced by means of the shell model code RITSSCHIL. The 2584 keV (21/2⁺) is an isomeric state the mean life of which has been estimated from delayedγγ-coincidences.     

Collective and two-particle excitations in78Se

Excited states in⁷⁸Se have been studied up to spin (12)? at about 5.8 MeV in the⁷⁶Ge(α, 2n) reaction using in-beamγ-ray spectroscopy. Mean lifetimes could be determined for 27 of the 33 levels observed by applying Doppler shift and pulsed-beam timing methods. According to theB(E2) values most of the levels have been grouped into collective bands. Irregularities in the level spacings of the yrast band above spin 6? are interpreted to be due to the interaction of the ground state band withg _9/2 two-proton and two-neutron excitations. The mutual mixing of these configurations is reflected by strongM 1 transitions between the mixed states. The interaction strengths between the configurations involved have been estimated from three-band mixing calculations.     

High spin states in the transitional nucleus88Mo

The reaction⁵⁸Ni(³⁶Ar,α qρ)⁸⁸Mo has been studied at 145 MeV beam energy. A detector array consisting of the OSIRIS spectrometer, four charged-particleΔE detectors and seven NE213 neutron detectors has been used to meaure the gamma radiation inγγ- and particle-γγ-coincidence mode. The level scheme of⁸⁸Mo has been extended up to 11.6 MeV excitation energy and probable spin 23?; some 70 transitions and 40 levels have been identified. Spin assignments have been proposed on the basis of measured DCO ratios. Hartree Fock cranking calculations of the Total Routhians and shell model calculations of the high spin states are presented which imply near-sphericity of the yrast line up to the highest spins found. A classification of the high spin states according to their leading seniority is proposed.     

Structure of high spin states in83Y

We report on the first in-beam study of high spin levels in⁸³Y which were established up to 9.0 MeV excitation energy and probable spin of 41/2⁺ resp. 27/2^? by means of the reaction⁵⁸Ni(²⁸Si, 3p). Ten lifetimes and six lifetime limits in the 10^?12–10^?9 s range were determined in two recoil distance Doppler shift experiments. The positive parity yrast states form ag _9/2 Coriolis decoupled band with partial alignment, near-rigid rotor moment of inertia and deformationβ ₂=0.29. The negative parity yrast band has very similar collective properties; it shows a pronounced band crossing at rotational frequency ?ω≈0.40 MeV which we associate with twoquasiparticleg _9/2 proton alignment. At 2.56 MeV excitation, a second ΔI=1 band starting with 17/2^? was found. On the basis of the similarity to⁸⁵Y and the very weakE2 decay of this state, we suggest that this band has (3qp) configuration with an alignedg _9/2 neutron pair. The lifetimes of the lowest 2⁺ and 4⁺ state in⁸⁴Zr populated in the reaction⁵⁸Ni (²⁸Si, 2p) were determined to be τ(2)=17.8(11) ps resp. τ(4)=3.5(4) ps.     

Rotational bands in73Br: The disappearance of shape coexistence in72Se

By means of the reaction⁴⁰Ca (³⁶Ar, 3p), the band structure of⁷³Br connected with the g9/2 single-particle proton orbit has been investigated up to I^π=33/2⁺. In contrast to the core spectrum in⁷²Se, which is dominated by the coexistance of different shapes, the nucleus⁷³Br features rotational bands with slowly increasing moments of inertia. Their deformation β₂=0.40(2) has been deduced from recoil distanc lifetime measurements.     

Lifetimes of unresolved transitions from very high spin states in nuclei nearN=82

Average lifetimes of unresolved transitions deexciting very high spin states populated in²⁸Si(^{136, 129}Xe,xn)^164? x, 157?xEr reactions have been determined by a Doppler shift attenuation method. We find that the yrast bump region between 1.0 and 1.6 MeV contains a majority of strongly collectiveE2 transitions with very short lifetimes (a few tens of fsec) in the well deformed nuclei around¹⁵⁹Er and, with less certainty, almost comparably short lifetimes in the more spherical nuclei around¹⁵²Er. In the high energy region of 2.0–3.2 MeV we observe transitions which depopulate longer lived states in the nuclei nearN=82 than in the well deformed systems.     

Deformations and shape changes in81Y

High spin states in⁸¹Y up to the probable 33/2⁺ and 29/2^? yrast states have been measured via the reaction⁵⁸Ni(²⁸Si,αp, using the Cologne tandem accelerator. Directional correlations of oriented nuclei were determined and the level scheme was extended with lifetimes measured by means of DSA and recoil distance techniques. Reduced transition strengths inferred from lifetimes were consistent with the results of Hartree-Fock-Bogolyubov calculations, which predict a nearly axially symmetric deformation ofβ ₂≈0.37 for theπ=+ band. Predictions reveal an alignment driving the system to a smaller and triaxial deformation withβ ₂=0.23 andγ=?30°, although the data show this crossing to be somewhat delayed. Particle-rotor calculations for the one-quasiparticle bands corroborate the predictions of deformation parameters based on the cranking model.     

Lifetime measurements of the high spin yrast states in128Ce

Lifetime measurements of the high spin states in the yrast band of¹²⁸Ce were performed using the Doppler shift attenuation method in connection with the reaction¹⁰⁰Ru(³²S, 2p2n)¹²⁸Ce at incident energy of 141 MeV. In the vicinity of the band crossing, the previously reported anomalously highB(E2) value was not observed. The gross behavior of the normalized transition strength is approximate to symmetric rotor. It is confirmed that the trend of increase in collectivity with decreasing neutron number, which was indicated in the previous studies on^130,132,134Ce, continues in¹²⁸Ce. The value of quadrupole deformation parameterβ ₂ deduced from the measured lifetimes is in good agreement with the theoretical calculation using a cranking model based on a non-axially deformed Woods-Saxon potential.     

High spin bands in120Xe

High spin states in¹²⁰Xe were populated in the reaction¹⁰⁶Cd(¹⁸O, 4n) at a bombarding. energy of 90 MeV and the subsequent de- excitation was studied using γ- ray spectroscopic methods. New levels and several. spin and parity. assignments were established. The yrast band was observed up to theK ^π=22⁺state with two band crossins athw _c=0.39MeV and 0.45Mev Negative parity levels and a new positive parity band were also identified.     

The ground stateM1 strength in40Ca

The M1 gamma decay strengths of the ground state transitions of the 1⁺,T=1 states of⁴⁰Ca at 9.86 MeV and 10.32 MeV have been measured using the reaction³⁹K(p,γ)⁴⁰Ca. The measured ground state gamma decay widths of these levels are 1.06±0.15 eV and 5.8±0.8 eV respectively. These relatively large M1 strengths can be explained by a shell model calculation incorporating excited core configurations.     

The level scheme of91Nb from the reaction90Zr (p, γ)91Nb

The level scheme of⁹¹Nb has been investigated with the reaction⁹⁰Zr(p, γ)⁹¹Nb. Proton energies between 3.0 and 7.2 MeV were used. The γ spectra were taken with Ge(Li) detectors. Primary γ transitions to 36 excited states of⁹¹Nb up to 3.8 MeV excitation energy and many secondary γ transitions from the decay of those states were observed, leading to an extension of the known level scheme. The proton binding energy for⁹¹Nb was determined as (5167± 5) keV. Eleven γ transitions in⁹⁰Zr, part of them new, from the competing reaction⁹⁰Zr(p, p′ γ) were also observed.     

Excited states of154Nd studied through the decay of154Pr

Excited states in the neutron-rich doubly-odd nucleus⁷⁸As have been identified for the first time by proton-γ and γ-γ coincidence measurements via the⁷⁶Ge(α, pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5⁽⁺⁾ to (10⁺) states are ascribed to the (πg _9/2?νg _9/2) intruder two-quasiparticle configuration with some collective components in the 9⁽⁺⁾ and (10⁺) states.     

FastM1 transitions in85Rb

Excited states in⁸⁵Rb have been studied via the⁸²Se(⁷Li, 4n) reaction by using in-beamγ-ray spectroscopy. On the basis of new experimental data on coincidence relations, angular distributions and linear polarizations of theγ-rays the yrast sequence has been extended up to a 33/2⁺ level at 7.1 MeV excitation energy. Using the DSA method mean lifetimes have been determined for 9 levels. Above the 21/2⁺ yrast state 5 fast M1 transitions withB (M 1) ≧0.3 W.u. have been identified. They are interpreted as transitions between recoupled states of the configuration πg_9/2ν(g_9/2) ₈₊ ^?2 or πg_9/2(f ₅ ² /?1p ₃ ^2?1 )₄₊ν(g_9/2) ₈₊ ^?2 .     

Heavy-ion in-beam studies of the nucleus87Nb

High spin states in the transitional nucleus⁸⁷Nb up to 14 MeV excitation have been established for the first time via the reactions⁴⁰Ca(⁵⁰Cr, 3p)⁸⁷Nb and⁵⁸Ni (³²S, 3p)⁸⁷Nb. The⁸⁷Nbγ-radiations have been identified throughγ-ray spectra taken in coincidence with the evaporation residues detected in the Daresbury recoil separator or with multiple proton emission. Gamma-gamma coincidences, DCO ratios,γ-ray angular distributions and lifetimes have been measured. A total of some 100 transitions have been placed into a level scheme comprising of sixty states. The one-quasiparticle (1qp) bands of either parity and several other band-like structures have been identified, some containing alignedg _9/2 nucleons. Moderately enhancedE2 in-band transitions of 13–48 W.u. as well as several weakE2 yrast transitions connecting bands with different quasiparticle numbers have been found. Similarities with respect to theN=46 isotones⁸³Rb,⁸⁴Sr,⁸⁵Y,⁸⁶Zr and⁸⁸Mo are discussed.     

First identification and shell model structure of92Rh

Excited states in theN=47 nucleus⁹²Rh were populated via the fusion evaporation reaction⁵⁸Ni(⁴⁰Ca,αpn)⁹²Rh at 180 MeV beam energy. A level scheme reaching up to about 7 MeV and probable spins of (19⁺) and (21^?) was established and interpreted with the shell model in the (p _1/2,g _9/2) model space.     

Measurement ofg-factors in160Yb by aγ-γ coincidence technique

Aγ-γ coincidence technique has been developed forg-factor measurements of short-lived nuclear states. The method involvesγ-detection in 4π geometry as well as transient magnetic fields and the recoil-distance technique. A first experiment was performed for the isotope¹⁶⁰Yb produced in the reaction⁶⁴Ni(¹⁰⁰Mo, 4n) at 430 MeV beam energy. The valueg=? 0.23(31) of the 14⁺ yrast state, which is compatible with zero, establishes thevi _13/2 quasiparticle structure to be responsible for the first backbend. A meang-factor for low spin states around the 4⁺ state,g=+0.48(26) was also derived as well as lifetimes for yrast states up toI ^π=8⁺.     

Quasi-free (p,pα) scattering on 24Mg, 28Si, 40Ca and 58Ni at 157 MeV

Sixfold energy spectra have been measured for the (p, pα) reaction at 157 MeV on ²⁴Mg, ²⁸Si, ⁴⁰Ca and ⁵⁸Ni around quasi-free kinematic conditions. For the three s-d shell nuclei the experiment covered a map ranging from 0 to 220 MeV/c in recoil momentum and from 0 to 20 MeV in excitation energy of the final nucleus. Recoil momentum distributions have been obtained for the 0⁺ ground state and the 2⁺ first excited state of ²⁰Ne, ²⁴Mg and ³⁶Ar, and also for the states around 4.4 MeV (mainly 4⁺) of ³⁶Ar. The a spectroscopic factors extracted by a DWIA analysis are about three times larger than those predicted by the SU(3) model; however, they agree quite well in relative magnitude for a number of cases. The disagreement in shape between experiment and theory observed at low recoil momentum for the 2⁺ states might result from another reaction mechanism. The cross sections for ⁵⁸Ni are about a factor often smaller than those for ⁴⁰Ca. The ⁵⁸Ni(p, pα)⁵⁴Fe reaction seems to lead mainly to excited states of the final nucleus.     

Energy levels of175Hf

The reaction¹⁷⁵Hf(d, t)¹⁷⁵Hf was studied using 12 MeV deuterons from the Florida State University super FN tandem Van de Graaff accelerator. The outgoing tritons were analyzed by means of a Browne-Buechner type broad range magnetic spectrograph. Twenty-four states in¹⁷⁵Hf have been identified and fifteen states have been given wave function assignments on the basis of the spectroscopy associated with rotational band structure in deformed odd-A nuclei. TheQ-value for the reaction was measured to be ?1925±8 keV.