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.     

An angular momentum expansion of energy and structure of high spin states

A new angular momentum expansion of level energies of ground-state band of even-even nuclei has been obtained which is found to converge rapidly even for the most back-bending nuclei. Attempts have been made to interpret the parameters and calculate them microscopically. It is found that nuclear structure in the forward bending region is quite different compared to that in the back-bending region.     

Deformed states of high spin in42Ca

The⁴²Ca levels at 4,715 and 6,633 keV excitation energy have been investigated using the³⁹ K(α,pγ reaction atE _α=14 and 15 MeV. From particle-γ-ray angular correlations the spin assignmentsJ(4,715)=6, 4 andJ(6,633)=8, 6, 4 have been obtained. Lifetime measurements using the Doppler-shift attenuation method yieldedτ (4,715)=120±46 fs andτ(6,633)=52±21 fs. Both levels have positive parity and decay by enhancedE2 transitions. They are interpreted as theJ ^π=6⁺ and 8⁺ members, respectively, of theK ^π=0⁺ rotational band which has theE _x =1,837, 2,423 and 3,250 keV states as further members. The enhancement of inbandE2 transitions is 50 _?16 ⁺³⁵ W.u. (6→4) and 63 W.u. (8→6) respectively. The intrinsic quadrupole moments which have been derived on the basis of the coexistence model, areQ ₀=1.13?0.16/+0.37b(8→6) andQ ₀=1.36±0.25b(6→4), respectively. TheJ ^π=10⁺ member of the rotational band has possibly been observed as a level at 8,856±5 keV excitation energy.     

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.     

The gamma decay of high spin states of39K

First will be exhibited, for the stationary case, a connection between the probability, to find a particle in the region of interaction, and the derivative of the scattering phase shift for the momentum. From the idea, that in stationary scattering a resonance is linked with an appreciable increase of this probability, one obtains new and quantitative criteria for the behavior ofδ _l(k). For instance, the nonresonant behavior can be characterised by the condition 2k dδ _l(k)/dk<1. The maximum of probability for the particle to be in the region of interaction, is considered in accordance with the criterium of maximal change of the phase shift, as a function ofk. This characterises the location of the resonance. Wigner's lower limit fordδ _l (k)/dk allows to formulate a resonance condition directly for the cross section. Furthermore will be discussed some connections with the pole approximations of theS-matrix and the “collision lifetime” of Smith.     

Particle-hole states at high spin in 150Dy

The level scheme of the nucleus ¹⁵⁰Dy up to spin around 40 was obtained using the reaction ¹¹⁴Cd(⁴⁰Ar, 4n). Above spins 20 to 22 — the highest obtainable from the valence nucleons — the breaking of the ¹⁴⁶Gd pproton and neutron cores occurs in separate parallel cascades.     

First identification of high spin states in160Lu

High spin states of¹²⁸La have been investigated by means ofγ ray spectroscopy. Although two level schemes were reported prior to the present study, those schemes were different at excitation energies near the band head. A new level scheme has been obtained for the detailed discussion of signature dependence.     

First observation of high spin states in90Tc

High spin states in⁹⁰Tc have been studied via the⁵⁸Ni (³⁵Cl, 2pn) ⁹⁰Tc reaction at beam energy of 124 MeV. Twenty-six newγ-rays were observed, a new level scheme was established and spins were assigned. Two band-like structures were established up to about 20? with an excitation energy of 6–7 MeV. The band (B) shows collective characteristic at high spin. We suggest it to be of a quasi-particle configurationπg_9/2?vf _5/2.     

Decay of three-particle high spin states in85Y

High spin states in⁸⁵Y have been excited in the reaction⁷²Ge(¹⁶O,p2n) at 48–60 MeV beam energy. From measurements ofnγ andγγ coincidences, excitation functions and angular distributions, the high spin spectrum of⁸⁵Y has been established up to 5.4 MeV excitation energy and spinI≦29/2. Lifetimes or limits of lifetimes have been determined for 14 levels via the recoil distance and Doppler shift attenuation method. Theg _9/2 decoupled proton band is found to backbend atI ^π=17/2⁺ as also seen in the reduction of the 17/2⁺→13/2⁺ and 21/2⁺→17/2⁺ E2 transition strengths. The lowest (3qp) positive parity band has predominantly aν ² g _9/2×πg _9/2 structure. The observed negative parity yrast states in the spin range 15/2^?≦I≦29/2^? are most probably of (g _9/2)² ×(f _5/2,p _1/2) (3qp) nature as suggested by a comparison of the⁸⁴Sr and⁸⁵Y level structures and electromagnetic transition strengths.     

Hartree-Fock theory of nuclear deformations and high spin states

A brief review of the Hartree-Fock approximation to nuclear shapes and nuclear spectra is presented. Various aspects of rotation-alignment effect and high spin states are illustrated in the Hartree-Fock model.     

Statistical theory of hot nuclei and high spin states

The hot rotating compound systems formed in heavy ion collisions are studied using the statistical theory with a view to determine the spin and temperature dependence of nuclear shapes. Shape transitions are observed for these systems at particular spin values. The neutron and proton separation energies for heavier high spin systems have been evaluated. Results are presented for ₇₀ ¹⁷⁰ Yb and ₇₈ ¹⁹⁴ Pt.     

Spectroscopy and lifetime measurement of high spin states in 73Se

The nucleus ⁷³ Se was studied by the reaction ⁵¹ V(²⁸ Si,αpn)⁷³ Se. The level scheme extended upto $\frac{{41}} {2}\bar h $ in both +ve and ?ve parity bands with 10 new transitions placed in the level scheme. Lifetimes of 17 high spin states measured by DSAM. The transitional quadrupole moment is found to drop down after the band crossing suggesting a less deformed configuration. At the band crossing region, Q _t increases suddenly in both +ve and ?ve parity bands. It is argued that the +ve parity band is a decoupled band.     

Nuclear deformations in 186Hg from lifetime measurements

Using the recoil-distance Doppler-shift method, we have measured the half-lives of the 2⁺, 4⁺, 6⁺ and 8⁺ states in ¹⁸⁶Hg following the reaction ¹⁷⁰Yb(²⁰Ne, 4n) ¹⁸⁶Hg. We find a strong enhancement of the 6⁺→4⁺ transition probability, B(E2, 6⁺→4⁺)=1.9±0.8 e²b², over the 2⁺→0⁺ value, B(E2, 2⁺→0⁺)=0.28±0.05 e²b². These results indicate that ¹⁸⁶Hg makes an angular-momentum-induced transition from nearly spherical to strongly deformed shapes.     

Quenched magnetic transitions from high spin states in light nuclei

Recent investigations of stretchedM 6 transitions in thes-d shell have uncovered the unexpected systematic trend that isoscalarM 6 transitions are two to three times more retarded than the isovector ones. We present the result of a microscopic calculation analyzing the different mechanisms usually invoked in the formation of the quenching and suggest that an additional argument based on the difference in structure between isoscalar and isovector transition densities may be playing a predominant role in explaining the data.     

Transition to non-collective states at high spin in 124Xe

Excited states in ¹²⁴Xe were populated in the reaction ⁸²Se(⁴⁸Ca, 6n)¹²⁴Xe and γ -ray coincidence relationships were measured with the Gammasphere spectrometer. Two new bands are observed and several of the previously known bands are extended in the high- as well as in the low-spin region. Two irregular high-spin structures are also added. The irregularities are a fingerprint of a transition from collective to non-collective behaviour. Configuration assignments to the new structures are proposed on the basis of systematics and by comparing experimental properties with calculations within the framework of the cranking model.     

Electromagnetic properties of high spin states in158Dy and164Dy

We present calculations of electromagnetic properties of¹⁵⁸Dy and¹⁶⁴Dy based on the solution of the self-consistent cranking model and approximate angular momentum projection technique developed earlier. The calculated values compare fairly well with the existing experimental data.