Electric monopole transitions: What they can tell us about nuclear structure Page: 4 of 13
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internal conversion or internal-pair formation). The EO strength parameter is
conventionally quoted in units of p2x103.
EO Strength and Shape Coexistence
One of the earliest clear-cut examples of shape coexistence was provided by the
neutron deficient even-even Hg isotopes5), several of which are depicted in fig. 1.
The ground-state band of these isotopes is based on a proton 2h configuration, while
the deformed excited band is based on a proton 2p-4h configuration which arises
from the excitation of a proton-pair into the intruder h9/2 orbital. In addition to the
electric monopole transitions between the 0+ states in these nuclei, the EO strength is
enhanced for the AI=0, I0 transitions between the shape coexisting configurations.
This is a common feature identified with shape coexistence. The lifetimes of the oz
states in these isotopes are difficult to measure because they fall in the picosecond
range and have no y-ray branching to the 2* state. However, recent measurements6)
have yielded half-lives of 204"5' ps and 72 ps which correspond to p2(EO) x 103
values of 7.732 and >32 for 188Hg and 186Hg, respectively. Additionally, the mixing
of the bands in 188Hg (1%), when computed using the experimental6) p2(EO) and a
deformation of s=0.25 for the 02 band, is consistent with the mixing obtained using
the experimental6) p2(EO) and an experimental value7) for A<r2>.
2+,a 6 0+ 375
6* 116 2' 1208
4+ 1081' 4+ 1005
4+ 808 2+ 88
2 4 2+ 413
0+ 0 "z0+ 0
186 Hg 188 Hg
p2 x 10
Fig. 1. Weakly deformed (0;) and strongly deformed (0z) bands in several even-
even Hg isotopes (see ref. 5 for complete details). The p2 values (units p2 x 103) are
taken from ref. 6.
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Zganjar, E.F. & Wood, J.L. Electric monopole transitions: What they can tell us about nuclear structure, article, July 2, 1997; Baton Rouge, Louisiana. (digital.library.unt.edu/ark:/67531/metadc710996/m1/4/: accessed February 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.