Collective Motions in A=100-112 Nuclei
J.H. Hamilton
a
, A.V. Ramayya
a
, J.K. Hwang
a
, S.J. Zhu
b
,
C. Goodin
a
, Y.X. Luo
a,c
, J.O. Rasmussen
c
, S. Frauendorf
d
and G.M. Ter-Akopian
e
a
Physics Department, Vanderbilt University, Nashville, TN 37235, USA
b
Physics Department, Tsinghua University, Beijing 100084, China
c
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
d
Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA
e
Flerov Laboratory for Nuclear Reactions, JINR, Dubna 141980, Russia
Abstract. With a very high statistics data set with 5.7x10
11
triple and higher fold γ coincidences
from the spontaneous fission of
252
Cf, a wealth of fascinating new collective motions in nuclei
with A=100-112 have been observed. Nothing was known previously about one- and two-
phonon γ-bands in odd-A nuclei. We discovered the first one-and two- phonon γ vibrational
bands in an odd N-even Z nucleus,
105
Mo. The energies of the one- and two- phonon bands in
104
Mo,
105
Mo,
106
Mo and
108
Mo were recently studied and are remarkably similar in energies. The
first chiral doublet bands in e-e nuclei were observed in triaxial
106,108
Mo and
110,112
Ru while such
chiral bands in
108
Ru are perturbed by its γ-soft shape. The experimental evidences, including our
recent angular correlation studies are presented along with what these new bands are telling us
about the evolving collective structures and deformation in this region.
Keywords: Collective motion,
252
Cf, γ-vibrational bands, Chiral bands.
PACS: 21.10.-k, 21.60.Ev, 25.85.Ca, 27.60.+j.
INTRODUCTION
Nuclei in general assume one of three shapes a) spherical b) near spherical, and c)
prolate deformed. The energy levels for even-even nuclei found in each of these cases
are illustrated in Fig. 1. Spherical shapes are found for nuclei which have spherical
double magic proton and neutron shells. The spherical magic numbers are 2, 8, 20, 50,
82, 126. Well removed from the magic number nuclei are well deformed with
deformation β
2
~0.25 where
2/)
13
(
13
2
RR
RR
+
−
≈
β
where R
3
is the long symmetry axis
and R
1
=R
2
are the short axis of the prolate nucleus. The energy levels in near spherical
nuclei are generated by one, two and three quadrupole phonon vibrations of their
shape. Deformed nuclei can have bands of levels built on rotational motion of their
ground states with energies E=
)1(
2
+
ℑ
II
=
where for the ground state of e-e nuclei I
π
= 2
+
, 4
+
, 6
+
, …. Deformed nuclei can also vibrate by pushing and pulling on the ends
of the nuclei, β vibration in Fig. 1, and on the sides, γ vibration, with rotational bands
95
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CP1280, Proceedings of the 2009 Joint Annual Conference of the National Society of Black Physicists
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