CERN Accelerating science

Low-energy Coulomb excitation provides a well-understood means of
exciting atomic nuclei and allows measuring electromagnetic moments that
can be directly related to the nuclear shape. The availability of radioactive
ion beams (RIBs) at energies near the Coulomb barrier has made it possible
to study shape coexistence in a variety of short-lived exotic nuclei. This
review presents a short overview of the methods related to multi-step
Coulomb excitation experiments, followed by a discussion of several
examples. The focus is on two mass regions where recent Coulomb excitation experiments have contributed to the quantitative understanding of
shape coexistence: nuclei with mass A » 70 near the N = Z line and nuclei
with A » 100 near neutron number N = 60. Experimental results are
summarized and their significance for understanding shape coexistence is
discussed. Experimental observables such as quadrupole moments and
electromagnetic transition strengths represent furthermore important
benchmarks for advancing theoretical nuclear structure models. With several new RIB facilities planned and under construction, Coulomb excitation
will remain to be an important tool to extend the studies of nuclear shapes
toward more exotic systems, and to obtain a more comprehensive and
quantitative understanding of shape coexistence.