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

Abstract

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

Rotational damping in a multi-j shell particles-rotor model

“…The gamma-rays which are emitted from the above excited region can not be distinguished as discrete peaks, thus forming a quasi-continuum spectra. Experimentally rotational damping has been studied through the analysis of quasi-continuum spectra [3,4,5,6,7]. Recent experimental progress in high precision three-dimensional gamma-ray correlation measurements makes it possible to study various features of collective rotational motion in the regions of discrete rotational bands and damped rotational motion [8,9,10,11,12,13,14,15].…”

Pair transfer at high angular momenta

“…In the last part we have used the definition of the gap parameter fl, and introduced the pairing strength G. (6).…”

“…For a realistic evaluation of the pair transfer amplitudes in the CHFB and CRPA theories we shall use the hamiltonian and configuration space of One of the more attractive features of the hamiltonian (10) is the separability of the forces, which allows drastic simplifications in solving the CHFB equations (5)- (6). In the RPA case it reduces the diagonalization of a huge matrix to the simple problem of finding the zeroes of a determinant of dimensionality equal to the number of terms in expression (10).…”

Rotational damping motion in nuclei

“…At high angular momentum most of these gamma rays seem to be of rotational character (they correspond to stretched E2 transitions and their energies are roughly correlated with the spin). The study of the correlations of these gamma rays seems to indicate [1][2][3] that the nuclear rotational motion is damped at modest temperatures. The rotational damping causes each rotational state to emit, rather than a single gamma ray energy, one from a distribution of energies, with a full width at half maximum (FWHM), Frot-The existence of damping implies that a mixing of states is taking place.…”