Recently,
high-spin band structures in mass ∼100 and 130 regions have been
investigated quite vigorously due to observation of doublet band
structures, possibly originating from breaking of the chiral symmetry in
the intrinsic frame of reference
[1],
[2] and
[3]. A systematic study of the experimental features of
ΔI=1 doublet bands and their interpretation has been reviewed in Ref.
[4].
Earlier studies reported the observation of doublet band structures in
several odd–odd nuclei in the two mass regions that are based on
two-quasiparticle excitations
[5],
[6],
[7],
[8],
[9],
[10],
[11],
[12] and
[13].
It has been demonstrated using phenomenological approaches that for the
doublet band structures to arise from the restoration of chiral
symmetry breaking mechanism, two experimental criteria must be
fulfilled. First, the observation of two nearly degenerate
ΔI=1 bands and second the two bands having identical electromagnetic properties, i.e., similar
B(M1) and
B(E2)
values for in-band and inter-band transitions. Lifetime measurements of
doublet band structures in several nuclei revealed that the second
criterion is not fulfilled by many nuclei and the interpretation of
these bands as chiral partners is erroneous
[14],
[15] and
[16]. In particular, for the doublet bands in
134Pr that exhibit the best overall energy degeneracy, lifetime measurements revealed that
B(M1) values are, although, similar but
B(E2)
values of the main band are a factor of 2–3 larger than that of the
partner band and, therefore, the two bands cannot arise from the chiral
symmetry breaking
[17] and
[18].
