Rotational Inertia of Nuclei

Deleplanque, M. A.; Körner, H. J.; Kluge, H.; Macchiavelli, A. O.; Bendjaballah, N.; Diamond, R.M.; Stephens, F. S.

doi:10.1103/physrevlett.50.409

Cited by 38 publications

(11 citation statements)

References 7 publications

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“…At 260 MeV the limit is reached, and the additional 10 MeV only pumps more energy into the compound nucleus. From the measured one-dimensional spectra the value of the dynamical moment of inertia ᑣ ͑2͒ eff was deduced making use of the relation H͑E g ͒͞f͑E g ͒ ᑣ ͑2͒ eff ͞4h 2 discussed in [13,14]. In this expression, H͑E g ͒ is the number of E2 transitions at E g in the spectrum normalized to the number of counts in the transition connecting the 2 1 to the 0 1 state and corrected for the feeding f͑E g ͒.…”

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confidence: 99%

UnresolvedγRays in114Te: Mass Dependence of Rotational Damping

et al. 1999

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Unresolved g rays of 114 Te sorted into one-and two-dimensional spectra were studied. The reaction 64 Ni͑E beam 230 270 MeV͒ 1 54 Cr was used and the g rays were detected with the EUROBALL array. The effective moment of inertia for the quasicontinuum was found to be almost constant for I ͑20 40͒h, in contrast with the decreasing behavior of the terminating yrast band. A comparative analysis with the nucleus 164 Yb is presented and the results from a fluctuation analysis were compared with cranked shell model calculations. The comparison shows consistency in the scaling of the rotational damping width with mass number.PACS numbers: 21.10. Re, 21.60.Ka, 23.20.Lv, 27.60. + j The understanding of rotational motion in thermally excited nuclei is one of the central issues in nuclear structure and more in general in the study of effects beyond mean field. Until now, convincing evidence of collective damped rotation has been obtained for the mass region A ഠ 160. The overall features of quasicontinuum spectra have been well described with the rotational damping model calculations in which the mean-field rotational bands of the cranked shell model are mixed by the residual two-body interaction [1]. In the original formulation of rotational damping [2], schematic estimates for the scaling of the mixing process of mean-field bands with mass number were derived. The energy U 0 relative to the yrast line, at which the damping (mixing) sets in, depends on the level density and on the strength of the residual interaction, and is predicted to vary with mass number U 0~A 22͞3 . The rotational damping width G rot , expressing the width of the quadrupole transition strength distribution, is proportional to the statistical dispersion of the rotational frequency of cranked shell model n-particle-n-hole states. For G rot the scaling is expected to follow the relation G rotĨ A 25͞2 e 21 , where I, A, and e are the spin, mass number, and deformation, respectively. Experiments have earlier confirmed the prediction of U 0 ഠ 0.7 MeV for the onset of damping in rare-earth nuclei [3]. However, the damping width G rot appears to be a quantity not easily accessible in experiments [4]. Experimentally, its variation with mass number for normally deformed nuclei has never been investigated. On the other hand, a detailed test of effects beyond mean field such as the rotational damping mechanism is also relevant in view of the analogy discussed in Ref.[5] with nuclear magnetic resonance. To determine the validity of the relation given above, one needs to compare nuclei with a similar deformation, but with different masses; good examples are nuclei with A ഠ 160 and A ഠ 110 for which a factor of 2 difference in the damping width is expected.Some evidence of collective rotation in the quasicontinuum in nuclei with A 110 120, characterized by spherical shapes at low spins, was found two decades ago in experiments made with scintillator detectors [6]. More recent discrete spectroscopy studies made with multigermanium detector arrays have identified di...

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UnresolvedγRays in114Te: Mass Dependence of Rotational Damping

et al. 1999

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“…The overall shape from the simulation can be improved further by including an expected increase in proton alignment at high rotational frequencies. 15 However, the inclusion of gradually increasing alignment affects the extracted values of r rot and U 0 little, and is included in the estimated errors. For the first time it has been possible to reproduce the general features of the quasicontinuum and determine both the average spreading width and the critical excitation energy at which damping sets in.…”

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Determination of the Spreading Width for the Collective Transition Strength at Finite Temperature

Jc¹,

Gb²,

Herskind³

et al. 1985

Phys. Rev. Lett.

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The experimentally observed structure of the E2 transitions in the quasicontinuum for 168 Yb is analyzed. The valley ridge structure along the E y i = E y 2 diagonal in y-energy correlation spectra has been reproduced by a model simulation in which a spreading of the rotational decay strength r rot is introduced in regions of nuclear excitation energy U > UQ where the density of bands with slightly differing moments of inertia and alignment is high. The values of r rot and U 0 vary from 75 to 110 keV and from 1.25 to 1.0 MeV, respectively, in the energy range 780 < E y < 1160 keV.PACS numbers: 23.20.Lv, 21.lO.Pc

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“…a decrease of pair correlations and deformation changes, and has been observed in most nuclei in the rare earth region. A moreAnteresting result, however, is the decrease of J(c 2} at high frequencies which is clearly observed as a widening of the f~egtral valley in the correlation matrices for the ~'Te + 4~a and I~SSm + 22-Ne systems (in which 162Hf and ~~176 respectively, are populated pl:e.cLominarktly), but seems to be present also in the 144Sm + ZONe and ~48Sm + 20Ne cases (leading mainly to 160Hf and ~U~Hf, respectively) 9 Experimental evidence for a decrease of j~L);" at high frequencies has been reported some time ago for Er and Yb isotopes (4)(5)(6), but the results were somewhat tentative due to the weak valley-ridge structure observed with NaI(T1) detectors in these cases. The decrease in j~,)t~ has been interpreted as evidence for an alignment of quasiparticle spins at high rotational frequencies (4)(5)(6).…”

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E ?-E ? correlation studies of light-mass Hf isotopes

Theine

Blume

Hübel

et al. 1989

Z. Physik A - Atomic Nuclei

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Abstract:Gamma-ray energy correlations have been measured for several reactions leading to lightmass Hf isotopes with 160 -~ A ~ 166. The correlation spectra show ridge-valley structures up to high rotational frequencies from which a drop in j(2) o is deduced at high frequencies. This drop suggests that a large portion of the angular momentum is generated by aligning particles. It may also be explained by the theoretically predicted triaxial states with large deformation.The~-ray spectra emitted by evaporation residues produced in compound nucleus reactions consist of both, discrete lines and an unresolved part, the quasi-continuum. Since the limit for the observation of discrete lines is reached at a spin of about 40 15 in most well deformed nuclei, information on higher-spin states has to be extracted from quasicontinuum spectra. A powerful tool to determine nuclear properties in the high-spin region from continuum spectra is the analysis of E~f-E x` correlations (1).In the first Ey-Ea~ correlation studies NaI(TI) detectors were used (1). They have good photo absorption efficiencies and the correction for uncorrelated events can be made quite reliably. On the other hand, their energy resolution is rather poor which causes problems in the analysis of the correlation spectra. In particular, it is difficult to separate discrete line features from the ridge-valley structures produced by the unresolved bands. More recently, Compton-suppressed Ge detectors were employed which show peak to Compton ratios comparable to those of NaI(TI) detectors, but have much better energy resolution. In this work we report on an investigation of the E~;-E~, correlations in 1-60-]66-Hf using multidetector arrays of CSS. From the ridge-valley stru~yres we deduce dynamical moments of inertia J~J up to high rotational frequencies. This investigation is part of the work to study the high-spin discrete level structure of the light-mass Hf isotopes.High-spin states in the liKht Hf isotopes were populated in 144'148Sm + 20'22Ne and 126Te + 40Ca compound reactions and in-beam bY-ray coincidences were measured with the OSIRIS array at the VICKSI accelerator of the HMI Berlin (2) and with the HERA array at the 88" cyclotron of the LBL Berkeley {3}. In all exReriments stacks of two or three thin (-500, pg/em ~} meta]lj~ foils of tb~enriched isotopes (t~r 96,5%; 14nSm: 95 %; JZbTe: 98%) were used as targets. The reaction products were allowed to recoil into vacuum and the y-rays emitted by the recoiling nuclei were fully Dopplersh i fted.In the off-line analysis the coincidences were sorted into EK1 -EK 2 matrices with an energy resolution of 4 keV/cSannel. No reaction channel selection could be applied, but in all cases the 4n-channel was dominant -in particular at high spins. In the correlation matrices a correction for the uncorrelated events has to be applied. We followed the approach by Andersen et al. (I) to subtract the uncorrelated events (COR-method). In order to distinguish the continuum ridges from effects caused by discrete lines or ...

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Rotational Inertia of Nuclei

Cited by 38 publications

References 7 publications

UnresolvedγRays in114Te: Mass Dependence of Rotational Damping

UnresolvedγRays in114Te: Mass Dependence of Rotational Damping

Determination of the Spreading Width for the Collective Transition Strength at Finite Temperature

E ?-E ? correlation studies of light-mass Hf isotopes

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