High spin states in73Se observed by the reaction70Ge(α,nγ)

⁷³Se has been investigated by the reaction⁷⁰Ge(α, nγ). Gamma excitation functions (E _α=10–16 MeV), gamma angular distributions (E _α=18 MeV) and gamma-gamma coincidences (E _α=15 MeV)) have been taken. A level scheme has been established, spins and partities have been assigned. States of a rotational band on the 151.2 keV (5/2^?) state and an anomalous band have been identified. Nuclear Reaction⁷⁰Ge(α,nγ)E _α=15 and 18 MeV; measuredE _γ,I _γ,γ-γ-coin.,γ-angular distribution,γ-excitation function.⁷³Se deduced levels,J, π. Enriched target, Ge(Li).     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

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.     

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.     

Electrical manipulation and measurement of spin properties of quantum spin Hall edge states

We study the effects of a gate-controlled Rashba spin-orbit coupling to quantum spin Hall edge states in HgTe quantum wells. A uniform Rashba coupling can be employed in tuning the spin orientation of the edge states while preserving the time-reversal symmetry. We introduce a sample geometry where the Rashba coupling can be used in probing helicity by purely electrical means without requiring spin detection, application of magnetic materials or magnetic fields. In the considered setup a tilt of the spin orientation with respect to the normal of the sample leads to a reduction in the two-terminal conductance with current-voltage characteristics and temperature dependence typical of Luttinger liquid constrictions.     

On the lifetime of excited states of frustration model of spin glasses

An analysis of the low energy excited states of the ± J model of Ising spins on a square lattice is developped in terms of clustering of solidary spins. Two types of clusters are exhibited : entropic and pinned clusters regarding the occurence of potential barriers in the relaxation. The mean reversal time of these clusters is determined and interpreted as one dimensional random walk in phase space. The size dependence of this mean reversal time varies as n² (n denoting the number of spins in the cluster) or $\text{n}{}^2\text{x exp(?}\text{ΔE}\text{k}{}_{\mathrm{B}}\text{T}\text{)}$ where ΔE is the potential barrier, instead of n in the case of ferromagnetic Ising model.     

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.     

Band structures in73Se

Excited states of⁷³Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the⁷⁰Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2⁺ band is likely to correspond to an oblate deformation while the 5/2⁺ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2⁺. The 3/2^? band is a strongly coupled band built on the [301] 3/2^} configuration.Nuclear reactions:⁷⁰Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE _γ,I _γ,σ(E _γ,θ),γγ-coin, linear polarization, DSA,γ(t).⁷⁵Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors.     

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.     

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.     

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.     

High spin states in75Se populated by the72Ge(α,n) and73Ge(α, 2n) reaction

The⁷²Ge(α, n)⁷⁵Se and⁷³Ge(α, 2n)⁷⁵Se reactions have been studied at bombarding energies of 15 MeV and 22.5 MeV respectively using Ge(Li)-detectors.γ-singles spectra,γ-γ-coincidences,γ-angular distributions and excitation functions have been taken. A level scheme has been constructed, which contains a stretched spin and a normal rotational band. Nuclear reactions⁷²Ge(α, n)⁷⁵Se,⁷³Ge(α, 2n)⁷⁵Se; measuredE _γ ,I _γ ,γ-γ-coincidences,γ-angular distribution,γ-excitation function.⁷⁵Se deduced levels,J, π, γ-multipolarity. Enriched target, Ge(Li).     

Optical spin injection and spin lifetime in Ge heterostructures

We demonstrate optical orientation in Ge/SiGe quantum wells and study their spin properties. The ultrafast electron transfer from the center of the Brillouin zone to its edge allows us to achieve high spin polarizations and to resolve the spin dynamics of holes and electrons. The circular polarization degree of the direct gap photoluminescence exceeds the theoretical bulk limit, yielding ～37% and ～85% for transitions with heavy and light holes states, respectively. The spin lifetime of holes at the top of the valence band is estimated to be ～0.5 ps and it is governed by transitions between light and heavy hole states. Electrons at the bottom of the conduction band, on the other hand, have a spin lifetime that exceeds 5?ns below 150?K. Theoretical analysis of the spin relaxation indicates that phonon-induced intervalley scattering dictates the spin lifetime of electrons.     

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.