Spectroscopy of high-spin states in 211,212,213Fr

The level structures of ²¹¹Fr, ²¹²Fr and ²¹³Fr have been observed to high spins, ~ 28 /kh, (and excitation energies ~ 8 MeV) using a variety of γ-ray spectroscopic techniques. The structure of these nuclides is discussed in terms of couplings of single-particle states through empirical shell-model calculations. Good agreement with experiment is obtained. In ²¹²Fr and ²¹³Fr core-excited configurations are required to explain the properties of the highest states. A number of long-lived states were observed in each nucleus some of which decay by enhanced E3 transitions. The E3 transition strengths are discussed.     

On the ferromagnetism of high-spin states

It is established on the basis of the idea of strong interaction within the unit cell that ferromagnetic instability is possible in a system with hopping between d-electron states of atoms that are in high-spin states and form a bcc lattice. The phase diagram of the existence of ferromagnetic ordering as a function of the degree of filling of the d shell is constructed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 275–280 (25 August 1998)     

Properties of unbound high-spin states in27Al

Selectively excited high-spin states in²⁷Al have been located by the reaction¹²C(¹⁶O,p)²⁷Al. The excitation functions of these states have been measured at incident energiesE _cm=18.7 to 30.1 MeV at intervals of 150 keV. They exhibit maxima of presumably non-statistical origin. At four different energies the subsequent decay of the²⁷Al states has been studied by detecting the final heavy recoils with the Munich recoil spectrometer in coincidence with the proton emitted in the first stage of the reaction. Using this new method branching ratios of theγ-, α-, andn-decay have been measured. Based on angular correlation arguments spins up to 27/2? have been determined within the experimental accuracy of 1–2?. The observations suggest a superdeformed shape of²⁷Al at least in some of the states.     

Lifetime study of high-spin states in 104,105In

In the neutron deficient isotopes _104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and still fair agreement for most measured B(M1) and B(E2) values. Received: 30 June 1998     

Two proton high-spin excitations and dipole bands in192Hg

The¹⁹²Hg nucleus was populated in the¹⁶⁰Gd(³⁶S, 4n) reaction at a beam energy of E=159 MeV. Emittedγ-rays were detected with the EUROGAM array comprising 43 Compton-suppressed large volume Ge detectors. The level scheme of¹⁹²Hg has been extended up to an excitation energy of E=10.4 MeV and spin I=34 ?. Two new structures, made of competing ΔI=1 and ΔI=2 transitions have been observed and their connexions with the low-lying levels established. Their lowest levels are located at 6.304 MeV and 6.879 MeV excitation energy. The experimental results are compared with mean-field HF+BCS calculations. It is proposed that the new structures originate from deformation-aligned quasi-proton excitations π(i_13/2 * h_9/2)_K=11 andπ (h_9/2) _K=8 ² , coupled to rotation-aligned quasi-neutron ν(i_13/2)ⁿ and quasi-proton π(h_11/2)² excitations.     

Concerning high-spin negative parity states in 20Ne

Unambiguous spin and parity assignment have been made from angular correlation measurements to states in ²⁰Ne at 15.18 MeV (6⁺) and 17.40 MeV (9^?). Our results are in disagreement with an earlier 9^? assignment to the 15.18 MeV state. The 17.40 MeV state is assigned to the K = 2^? rotational band based on the 2^? state at 4.97 meV.     

A weak coupling model for high-spin states

Weak coupling of a rotating core and an odd particle is used to explain the appearance of pure rotational bands, as well as decoupled aligned state bands by simple geometrical properties.     

g-Factors of high-spin states in the g- and s-bands

The phenomenon of the crossing of the g-band with the s-band is described by using the 0- and 2-quasiparticle cranked Hartree-Fock-Bogoliubov approximations with the number projection. The energy spectra and the gyromagnetic ratios of the g- and s-bands of¹⁶²Er are calculated.The author is also indebted to Dr. M. Wakai for his cooperative and stimulating discussions.     

A microscopic classification of high-spin states in 56Fe

A large-scale shell-model calculation on ⁵⁶Fe including positive parity states with spins up to J = 15 shows that several states in the yrast region may be of a particular nature. These states can be locd in groups of which the gamma decay and quadrupole moments show a collective behaviour. The signature of each group is the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ hole structure. This structure is coupled to a definite J_hole and T_hole with the spin J_hole being as large as possible. The level density above the yrast region turns out to be largely independent of J.     

High-spin states in189Hg

High-spin levels in¹⁸⁹Hg have been populated via the¹⁷⁵Lu(¹⁹F, 5n) reaction. A rotation-aligned band built on a 13/2⁺ state originating from theνi _13/2 subshell is identified which is interpreted within the framework of “quasiparticle+rotor” models. A negative parity band built on a 21/2^? state which can be accounted for by a three quasi-particle state is also observed.     

IBFA description of high-spin positive-parity states in Rh isotopes

Properties of the odd-mass Rh isotopes are investigated in the framework of the interacting boson-fermion approximation (IBFA) model in which the odd proton movea in the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ orbitals. Lifetimes of some high-spin positive-parity states in ⁹⁹Rh obtained by the recoil-distance method with the ⁸⁸Sr(¹⁴N, 3n) reaction are also reported. Calculated excitation energies and electromagnetic properties of the high-spin positive-parity states are compared with experiment and an acceptable agreement is obtained.     

g Factors for high-spin states of238U

Calculations of the g-factor and the moment of inertia J for high-spin states of²³⁸U are performed using the model which is based on the cranking Hartree-Fock-Bogolyubov (CHFB) theory. Importance of the state-dependent pairing force on 3(ω²) is investigated.     

Shell model high-spin states in 67 151 Ho84

In an in-beam study of ₆₇ ¹⁵¹ Ho₈₄ we have established its high-spin states up to 10 MeV and have suggested spin assignments up to (49/2) at 6.2 MeV. The main decay-cascade proceeds through the yrast states of the h³ _11/2f² _7/2 and h³ _11/2f_7/2h_9/2 5-particle configurations, which are predicted with good accuracy in parameter-free shell-model calculations. States with one proton in d_3/2, or involving i_13/2 or f_7/2×3^– excitations were also identified.     

Search for missing predicted high-spin states in28Si

New shell model calculations have predicted several high-spin (I ^π=5⁺ and 6⁺) levels in²⁸Si near 10 MeV excitation energy which are missing from or ambiguous in existing experimental studies. Angular distributions, linear polarizations and Doppler-shifts ofγ-rays have been measured for theγ-decay of theE _p=1,911 and 2,073 KeV resonances of the²⁷Al(p, γ) reaction in an attempt to discover these missing states or confirm the discrepancies between experiment and theory. The excitation energies and spin-parities of the resonances were determined as 13,424.4±0.2 keV,I ^π=5⁺ and 13,582.3±0.5 keV,I ^π=6⁺. States populated in theγ-decay of these resonances were assigned spins and parities as follows: 11,777 keV,I ^π=5⁺; 11,331 keV,I ^π=6⁺; 10,417 keV,I ^π=5⁺; 9,417 keV,I ^π=4⁺ and 8,945 keV,I ^π=5⁺. On the basis ofγ-ray transition rates T=1 is assigned to the 13,424 keV level and T=0 to the 10,417 and 11,777 keV levels. With the new data excellent agreement is achieved between the experimental spectrum of²⁸Si and the new shell model predictions. These data provide evidence for aK ^π=3⁺ rotational band comprised by the 6,276, 6,889, 8,945 and 11,331 keV levels. This band emerges also from the shell model wave functions as do theK ^π=0⁺ bands based on the ground state and the 6,691 keV state.     

Reduced transition probabilities for high-spin states in 232Th

The lifetimes and reduced transition probabilities for spins 6⁺ ? 18⁺ in the ground-state rotational band of ²³²Th have been measured by recoil-distance, Doppler-broadened lineshape, and multiple Coulomb excitation methods using ⁸⁴Kr and ¹³⁶Xe projectiles. Within the limits of experimental uncertainty, transition probabilities from all of the methods are consistent with those of a good rotor for spins 6⁺ ? 18⁺. The descrepancy with the prediction of simple β-band mixing and centrifugal stretching models is discussed.     

Structure change of 156Yb at high-spin states

High-spin states of 156Yb have been studied via the 144Sm(16O,4n)156Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. The characteristics of the negative-parity sequence above the 25- state may related to the excitation from the nucleon in the Z = 64, N = 82 core. The E-GOS curve for the positive-parity yrast sequence in 156Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. The Cranked Woods-Saxon-Strutinsky calculations by means of Total-Routhian-Surface (TRS) methods has been made to understand this structure change.