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4.3 Nuclear Structure and Dynamics
steps will be the synthesis of elements with Z ≥ 119,
requiring beams heavier than 48 Ca, such as 50 Ti, which
is a technical challenge.
Due to the low production cross-sections, understanding
of the nuclear reaction mechanism is essential
for successful synthesis of SHE. Therefore, investigations
of the reaction dynamics are being pursued by studying
in detail fusion-evaporation, fusion-fission and quasifission
excitation functions with specific emphasis on the
deformation and the mass ratio of the reaction partners.
Recent theoretical studies demonstrate that nuclear
transfer reactions may be a unique approach to produce
neutron-rich isotopes of SHE, that are, in near future, not
reachable by any other means. Complementary physical
and chemical methods to separate and to study such
nuclei will be developed.
Stringent tests for the various nuclear models used in
predicting properties of SHE come from detailed spectroscopic
studies of nuclei as close as possible to the
SHE region. Research programmes carried out at JYFL,
GSI and GANIL study transfermium nuclei in the region
of 254 No close to the N = 152 deformed sub-shell gap.
These nuclei are the heaviest for which detailed in-beam
and decay spectroscopy can be performed by employing
modern gamma-ray spectroscopic and tagging techniques.
The deformed nature of these nuclei is confirmed
by the observation of rotational bands. Non-yrast and
K-isomeric states have recently been studied following
pioneering work at JYFL, yielding crucial information for
comparison to the predictions of various theories. New
instruments that allow the simultaneous detection of
conversion electrons and gamma-rays are under construction
to reach even higher sensitivity.
Systematic trends of nuclear binding energies, shell
structure and atomic properties are obtained with mass
and laser spectroscopy. The first accurate mass measurements
of transfermium nuclei ( 252-254 No, 255 Lr) were
performed at SHIPTRAP at GSI employing the novel
hybrid technology of gas stopping after in-flight separation.
Developments to carefully probe still heavier
nuclei with production rates approaching one atom per
day are in progress. Using similar approaches, studies
of isotopes of elements up to Z = 108 and of complex
atomic structures by means of laser spectroscopy are
envisaged.
The location of SHE shell closures can be probed by
measuring fission times of produced compound nuclei.
Evidence for components with longer fission lifetimes
in Z = 120 and Z = 124 compound nuclei was found in an
experiment at GANIL using crystal blocking techniques.
Developments for more precise fission time measurements
are in progress.
Relativistic effects, prominent for the inner electrons
of high-Z elements, affect the electronic structure of the
outer shells, thus influencing the chemical properties of
SHE. Therefore, these may deviate from the systematic
ordering in Mendeleev’s table. While chemical studies of
SHE represent an extraordinary experimental challenge,
they provide excellent tests for modern relativistic quantum
theory. Present experiments have reached elements
up to Hs and element Cn, and will be extended into the
element 114 region and beyond. Studies of new types
of SHE chemical compounds such as metal-organic
ones, formed after pre-separation in a recoil separator
like TASCA, will open up a completely new field of SHE
chemistry, which yields insights into detailed atomic
structure, thus being complementary to spectroscopic
methods.
New neutron-rich isotopes of SHE, possibly produced
in transfer reactions, may provide important information
on r-process nucleosynthesis in the region of the
heaviest elements. Half-life and fission data yield input
for recycling of synthesized material into the mediumheavy
abundance peaks.
The success of the programme outlined above
depends on the availability of high-intensity stableion
beams and the development of high-power targets
and innovative separators. In addition, it is important to
have access to the region where decay chains from 48 Ca
induced reactions with actinide targets end. The plan
within SPIRAL2 is to use the high-intensity stable and
neutron-rich beams while at GSI a dedicated cw-linac is
proposed as important milestones in this direction.
4.3.5 Collective Properties
Collective response of nuclei
The nuclear collective responses reveal information on
the bulk properties of nuclei and nuclear matter. This
response is characterized by the giant resonances of
various multipolarities with most of the strength well
above the particle separation energy. It is of particular
interest to study the collective strength in short-lived
nuclei because of the implications in nuclear and astrophysical
phenomenology (e.g., nuclear compressibility,
asymmetry energy in the nuclear equation of state, deformation
and damping mechanisms, and spin modes).
Additional dipole strength observed at low excitation
energy close to the particle-separation threshold in
neutron-rich nuclei has been associated with a vibration
of excess neutrons (neutron skin) against an isospinsaturated
core (an example for the unstable 68 Ni nucleus
is shown in Figure 5). Coulomb inelastic excitation and
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