The
EUROBALL IV detector, designed by a European collaboration including
researchers from six countries (Germany, Denmark, France, Italy, United
Kingdom and Sweden), is housed at the VIVITRON accelerator in Strasbourg.
Recent improvements to the detector are enabling physicists at the
CNRS Department of Nuclear and Particle Physics (IN2P3) to obtain
new results regarding the structure of "exotic" nuclei and
the behavior of "superdeformed" nuclei. Superdeformed nuclei
are shaped like rugby balls [or American footballs] due to their high-speed
rotation.
The
improved detector has a new internal calorimeter composed of 210 bismuth
germanate crystals which, along with the existing 239 germanium crystals
of the detector, forms a high efficiency array enabling scientists
to study very rare events.
The
group has observed rare deexcitation events and has studied series
of consecutive nuclei, enabling neutron pairing to be studied using
highly deformed neodymium isotopes. It has also studied continuum
spectra in lead and mercury and has observed octupole deformations,
which are now being sought in other nuclei. The effects of oscillations
in energy in superdeformed bands have also been confirmed in gadolinium
and terbium, possibly explained by the presence of a new symmetry.
The magnetic properties of superdeformed lead and mercury nuclei with
unpaired neutrons have also been studied.
"Exotic"
nuclei (nuclei containing very different numbers of protons and neutrons)
have been explored by combining the capacities of the EUROBALL IV
and those of other detectors. The structures of neutron-rich nuclei
with masses of about 100-120 have been observed for the first time,
and studies have also begun with proton-rich nuclei.
Other
experiments are probing pairing correlations not only between nucleons
of the same species but between proton and neutron in heavy nuclei
with identical numbers of protons and neutrons. Future experiments
will study hyperdeformed states predicted by theory but not yet experimentally
observed.
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