Projected shell model study of neutron-deficient 122Ce

The observed excited states of ¹²²Ce nucleus have been studied in the framework of projected shell model (PSM). The yrast band has been studied up to spin 26ħ. The first band crossing has been predicted above a rotational frequency of 0.4 MeV/ħ that corresponds to first backbending. The calculation reproduces the experimentally observed ground state band up to spin 14 ħ. The electromagnetic quantities, transition quadrupole moments and g-factors are predicted and there is a need to measure these quantities experimentally.     

Intrinsic and rotational states in 173Ta

High spin rotational levels in ¹⁷³Ta are populated in the ¹⁶⁵Ho(¹²C, 4n)¹⁷³Ta and ¹⁷⁵Lu(α, 6n)¹⁷³Ta reactions. The de-excitation γ-ray cascades are studied with Ge(Li) detectors. The rotational bands, which are built on the $\text{7}\text{2}$⁺(404), $\text{5}\text{2}$⁺(402), $\text{9}\text{2}$^?(514) and $\text{1}\text{2}$^?(541) intrinsic states, are identified up to high spin values. A state, interpreted as a three quasi-particle state with a probable spin of $\text{21}\text{2}$ is located at 1713 keV. Its half-life is about 100 ns. The behaviour of the moment of inertia of each rotational band versus the rotational frequency is compared with that of the doubly even core.     

Lifetime measurement of the ((11/2)−) isomer in 125Cs

A new rotational band has been observed in ¹⁶⁷Lu by ¹⁵²Sm (¹⁹F,4n)reaction at the HI-13 tandem accelerator of CIAE in Beijing. The high spin transition energies of the new band are almost identical to the triaxial superdeformed bands recently discovered in ¹⁶³Lu and ¹⁶⁵Lu. This new band is predicted as a triaxial superdeformed band by total routhian surface calculations. Received: 6 October 1997     

Properties of rotational excitations in odd mass Dy isotopes

The data on high-spin rotational states in¹⁵⁵Dy,¹⁵⁷Dy,¹⁵⁹Dy and¹⁶¹Dy are discussed within a model where a particle is coupled to a rotor with a variable moment of inertia. In this model there is often a definite improvement in the quality and stability of the fits to levels in the positive-parity band below spin 25/2 when the moment of inertia of the core exhibits a linear dependence on the square of the rotational angular velocity as compared to the situation where a linear dependence onI(I+1) is assumed. In the improved fits the empirical matrix elements of the Coriolis force exhibit a smooth and significant increase with decreasing moment of inertia. The rotational energies above spin 25/2 in the positive-parity band and above 19/2 in the 11/2^? [505] band are understood within the present theoretical model if the moment of inertia increases more rapidly than the linear trend established at lower spin. In the 11/2^? [505] band this increase follows rather closely the behaviour in the even nuclei whereas in the positive-parity band the curves are quite flat even beyond the point where the moment of inertia in the even nuclei exhibits a discontinuous or back-bending behaviour. The significance of this observation is discussed in the light of existing theories on nuclear moments of inertia.     

Seven and nine quasi-particleK-isomers in175Hf

NewK-isomers with very high spin (up to 57/2) have been found in¹⁷⁵Hf. This is the highest spin isomer seen in deformed nuclei and involves 9 quasi-particles. The predominant decay to the I=55/2 state in aK ^π=35/2^?, 5 quasi-particle rotational band further demonstrates the surprising breakdown of theK-selection rules, reported previously in neighbouring nuclei.     

Observation of back- and forwardbending in the182Os ground-state band

From a study of theγ-decay of high-spin states populated using the (α, 8n) reaction, the ground-state rotational band in¹⁸²Os has been established up to spin 20⁺. A plot of the moment of inertia as a function of the square of the rotational frequency for this ground-state band results in a back-and-forwardbending curve, indicating that an explanation in terms of pure Coriolis decoupling in thei _13/2 neutron orbital requires revision. The moment of inertia reaches a maximum of only 74% of the rigid rotor value.     

Suppression of band crossing in the neutron-rich nuclei 172, 173Yb due to the absence of a static pair field

High-spin states in the neutron-rich nuclei ^172,173Yb have been populated in a ¹⁷⁰Er(⁷Li,(p,d,t)xn) incomplete-fusion reaction and the emitted γ-radiation was detected with the GASP array. The signature partners of the 7/2⁺[633] rotational band of the odd-N ¹⁷³Yb isotope have been newly established and were observed up to spin values of (45/2⁺) and (43/2⁺), respectively. The ground-state band of the even-even nucleus ¹⁷²Yb has been observed up to a spin value of (22⁺). No band crossings were found in these bands. To explain this observation, it is proposed that the static pair field is absent, considering that the neutron odd-even mass differences reach for these nuclei very small values and that the band crossing is absent in cranked shell modell calculations without pairing. The results indicate, however, that strong dynamic correlations are still present.     

Identification of band structures in the 137La nucleus

High-spin states of ¹³⁷La have been investigated with the reaction ¹³⁰Te(¹¹B, 4n) at a beam energy of 50MeV. The level scheme of ¹³⁷La has been expanded with spin up to 33/2ℏ. Several new bands have been found in this nucleus. A band crossing in the band based on the 17/2^- level has been observed at a rotational frequency of ℏω ∼ 0.48MeV. From systematic comparison, this band crossing probably originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band ( γ ∼ -60^°).     

Ground-state rotational band in 181Ta

The ground-state rotational band in ¹⁸¹Ta has been observed up to a spin of $\text{21}\text{2}{}^{\mathrm{+}}$ using Coulomb excitation with ⁸⁴Kr ions. The nuclear lifetimes of the band members have been determined from the Doppler-broadened lineshapes of the de-excitation γ-rays, and the angular distributions of the γ-rays have been measured. It is found that the E2 transition rates from higher spin states $\text{(≧}\text{17}\text{2}{}^{\mathrm{+}}\text{)}$ are retarded relative to the rotational model predictions. A suggestion is made that this retardation may be due to the Coriolis antipairing effect.     

Band head spin assignment of superdeformed bands in 86Zr

Two parameter expressions for rotational spectra viz. variable moment of inertia (VMI), ab formula and three parameter Harris ω² expansion are used to assign the band head spins (I₀) of four rotational superdeformed bands in ⁸⁶Zr. The least-squares fitting method is employed to obtain the band head spins of these four bands in the A~80 mass region. Model parameters are extracted by fitting of intraband γ-ray energies, so as to obtain a minimum root-mean-square (rms) deviation between the calculated and the observed transition energies. The calculated transition energies are found to depend sensitively on the assigned spins. Whenever an accurate band head spin is assigned, the calculated transition energies are in agreement with the experimental transition energies. The dynamic moment of inertia is also extracted and its variation with rotational frequency is investigated. Since a better agreement of band head spin with experimental results is found using the VMI model, it is a more powerful tool than the ab formula and Harris ω² expansion.     

Sensitivity of Saturation Transfer Electron Spin Resonance Extended to Extremely Slow Mobility in Glassy Materials

A novel extension of the saturation transfer (ST) ESR technique that enables the determination of extremely long rotational correlation times of nitroxide spin labels up to values around 10⁴s is proposed. The method is based on the observation that the integral of ST-ESR spectra is sensitive to the spin–lattice relaxation time of the electron of the spin label, which in turn is directly dependent upon the rotational correlation time. The method is applied to the spin label TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) in glycerol. From the known viscosity data and the related rotational correlation times of the TEMPOL spin label in glycerol, the rotational correlation times of unknown samples can be determined. The method is especially applicable to systems with a very high viscosity, such as glassy materials. The method is applied to a 20 wt% glucose–water mixture in the glassy state, giving a value for the highest limiting rotational correlation time of about 10³s at a temperature of 45 K below the glass transition temperature of this system. This is an extension by six decades for the rotational correlation time, as compared to the current application of ST-ESR.     

High spin rotational states in 154Dy, 164Er And 162Yb

High spin rotational states in ¹⁵⁴Dy, ¹⁶⁴Er and ¹⁶²Yb have been investigated with (α, 4nγ) and (α, 6nγ) reactions. The ground state rotational bands have been identified up to spin 14 for ¹⁵⁴Dy and ¹⁶²Yb and spin 16 for ¹⁶⁴Er. Anomalous behaviour of the moment of inertia has been observed in ¹⁶⁴Er.     

Observation of superdeformed bands in194Hg

Two rotational bands, with energy spacings characteristic of superdeformed shapes, have been observed following bombardment of¹⁵⁰Nd with⁴⁸Ca. The more intensively populated band consists of 18 transitions and is assigned to¹⁹⁴Hg. The depopulation of this band occurs around spin 10. The second band, consisting of at least 16 transitions, was populated less strongly and is tentatively assigned to¹⁹⁴Hg also. The lowest level in this band is assigned spin 8. The energy differences between transitions for both bands decrease from ～40 keV at low rotational frequencies to ～30 keV at the highest observed frequencies. The moments of inertia of the bands are similar to those of the two previously observed superdeformed bands in^191,192Hg. The similarities and differences of the four known bands in the mercury region are discussed.     

First high-resolution analysis of the 5ν3 band of nitrogen dioxide near 1.3 μm

The first high-resolution absorption spectrum of the 5ν₃ band of the ¹⁴N¹⁶O₂ molecule at 7766.071 cm^?1 was recorded by high sensitivity CW-Cavity Ring Down Spectroscopy between 7674 and 7795 cm^?1. The noise equivalent absorption of the recordings was α_min≈1×10^?10 cm^?1. The assignments involve energy levels of the (0,0,5) vibrational state with rotational quantum numbers up to K_a=9 and N=47. The set of the spin–rotation energy levels were reproduced within their experimental uncertainty using a theoretical model, which takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,5) vibrational state and those of the (0,2,4) dark state together with the electron spin–rotation resonances within the (0,0,5) and (0,2,4) states. Precise values were determined for the (0,0,5) vibrational energy rotational, spin-rotational constants and for the (0,2,4)?(0,0,5) coupling constants. In addition the (0,2,4) rotational and spin-rotational constants were estimated. Using these parameters and the value of the transition dipole moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 5ν₃ band was generated and is provided as Supplementary material.     

Nuclear structure and formation mechanism of heavy shell-stabilized nuclei

In a series of experiments, ⁴⁸Ca induced cold fusion reactions on Pb targets were employed to populate states in ^253,254No isotopes. The groundstate band of ²⁵⁴No is identified up to spin 20⁺. The deduced quadrupole deformation is β=0.27(2). Evidence for decays from a rotational band built on a 7/2[624] configuration was obtained in ²⁵³No. The initial angular momentum and excitation energy of ^253,254No residues, after neutron emission, was determined. States up to spin 22 ? and excitation energy of E ^*=8.5 MeV were observed. The data provide direct information on the fission barrier at high spins B _f ≥5 MeV, and on the shell-correction energy E _shell ^exp ≥4.1 MeV.     

High-spin states in 222Th

Levels to spin 16⁺ in the ground band and 17^? in the octupole band in ²²²Th have been identified using the reaction ²⁰⁸Pb(¹⁸O, 4n)²²²Th at 93 MeV. To suppress intense γ-ray background from fission a residue detector was built and operated in coincidence with the Ge(Li) and NaI(Tl) detectors. The apparent moment of inertia in the ground-state rotational band rises very rapidly with increasing spin, however, no indications of backbending were observed. The octupole band at low spin has an aligned angular momentum $\text{J ≈ 3}\text{h}\text{?}$ relative to the ground-state band. Strong cross-band E1 transitions competed with collective E2 transitions within each band. Analysis showed that the ratios $\text{B(}\text{E}\text{1)}\text{B(}\text{E}\text{2)}$ were within experimental uncertainty independent of both the spin and parity of the parent state.The average γ-ray multiplicity per cascade was measured for ²²²Th. The results were in reasonable agreement with the computer code ORNL-ALICE.     

High spin states in116Te

The high spin states in¹¹⁶Te were populated in the Ru(¹⁹F,p4n) reaction at E_lab=90MeV and the subsequent deexcitation was studied using the γ-ray spectroscopic techniques. Ninteen new transitions have been added to extend the level scheme. A ΔI=2 rotational band is identified for the first time in an even-A Tellurium nucleus.     

Hartree-Fock-Bogoliubov calculations of the rotational band of the very heavy 254No nucleus

We report on Hartree-Fock-Bogoliubov (HFB) calculations of the ground-state rotational band of the heavy nucleus ²⁵⁴No recently observed experimentally. The calculated quadrupole deformation is consistent with the experimental value of β = 0.27 and is almost constant over the whole band. We also reproduce fairly well the excitation spectra and moments of inertia of this isotope up to the maximal experimentally observed state of spin 20. The rather high stability of this nucleus against fission is illustrated by the deformation energy curve providing very high fission barriers at zero spin within the HFB and HFB plus Lipkin-Nogami formalisms. The variation of these barriers with increased angular velocities is also studied. Received: 23 November 2000 / Accepted: 24 October 2001     

Structure analysis of 159Sm and properties of odd-mass neutron-rich nuclei in mass-160 region

Recent fission experiment data provide interesting structure information for neutron-rich nuclei in the mass A ∼ 160 region. We apply the projected shell model to study the strongly-deformed, neutron-rich Sm isotopes. We perform calculations for rotational bands up to spin I = 20 (29/2) for even-even (odd-neutron) Sm isotopes, and analyze the band structure of low-lying states with quasiparticle excitations. Emphasis is given to rotational bands based on one-quasiparticle (1-qp) configurations in the odd-mass ¹⁵⁹Sm. The ¹⁵⁹Sm result is discussed together with those of the even-even isotopes ^158,160Sm. New bands in ¹⁵⁹Sm based on neutron 1-qp 1/2⁻ and 5/2⁺ configurations are predicted. Electromagnetic transition probabilities are discussed.