Evolution of nuclear shapes at high spins Page: 1 of 7
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? (Invited talk to be published in the proceedings of ACS Symposium on Recent
Advances in the Study of Nuclei off the Line of Stability, Chicago, Illinois,
September 8-1?, 1985.)
EVOLUTION OF NUCLEAR SHAPES AT HIGH SPINS dE85 018074
Noah R. Johnson
Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Outstanding progress has been made during the past ten years on an
understanding of the properties of nuclei excited into states of high angular
momentum. Much of the experimental progress has resulted from y-y coin-
cidence measurements utilizing complex detector arrays. Many of the proper-
ties of the yrast and near-yrast bands in nuclei revealed in these measure-
ments have become reasonably well explained by current theory. Both cranked
shell model (CSM) and cranked Hartree-Fock Bogoliubov (CHFB) calculations
have enjoyed considerable success in accounting for many aspects of high spin
behavior. However, for a detailed understanding of the structure of these
high spin states and for a stringent test of these models, it is necessary to
resort to measurements of their static and dynamic electromagnetic multipole
moments. During the past few years we at Oak Ridge have concentrated on stu-
dies of the latter quantity, the dynamic electric quadrupole (E2) moments
which are a direct reflection of the collective aspects of the nuclear wave
functions. For this, we have carried out Doppler-shift lifetime measurements
utilizing primarily the recoil-distance technique.
The nuclei with neutron number N *= 90 possess many interesting proper-
ties. These nuclei have very shallow minima in their potential energy sur-
faces, and thus, are very susceptible to deformation driving influences. It
is the evolution of nuclear shapes as a function of spin or rotational fre-
quency for these nuclei that has commanded much of our interest in the life-
time measurements to be discussed here. There is growing evidence that many
deformed nuclei which have prolate shapes in their ground states conform to
triaxial or oblate shapes at higher spins. Since the E2 matrix elements
along the yrast line are sensitive indicators of deformation changes, mea-
surements of lifetimes of these states to provide the matrix elements has
become the major avenue for tracing the evolving shape of a nucleus at high
spin. Of the several nuclei we have studied with N » 90, those to be dis-
cussed here are 160»161Yb [FEW82], [J0H82], [FEW82], [FEW85] and 158Er
[0SH84a], [0SH84b]. In addition, we will discuss briefly the preliminary,
but interesting and surprising results from our recent investigation of the
N = 98 nucleus, 172W [RA085]. bv»cc.pt»nc.otthit.mici.,tt*.
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Johnson, N.R. Evolution of nuclear shapes at high spins, article, January 1, 1985; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1067084/m1/1/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.