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4.3 Nuclear Structure and Dynamics
require long and stable beam conditions. A new facility
is currently under investigation for this purpose (ISOL@
MYRRHA).
The future with spin-oriented radioactive
beams at in-flight facilities
Complementary to the aforementioned laser studies
are the measurements of moments based on the use
of spin-oriented radioactive beams, produced in different
low (5-10 MeV/u), intermediate (10-100 MeV/u) and
high (0.1-1 GeV/u) energy reactions with intense primary
stable-ion beams. To maintain the reaction-induced
orientation during the in-flight selection process, fully
stripped secondary beams are needed. In the future,
at the super-FRS of FAIR intense high-energy beams
from U-fission and fragmentation will allow studies on
isomeric beams to be extended to the neutron-rich
A>100 region. For studies of ground-state moments,
spin-polarized fragment beams require an asymmetric
secondary beam selection, currently available at some
of the in-flight facilities. In the future, post-accelerated
radioactive beams up to 150 MeV/u from EURISOL
can be used for producing even more exotic polarized
fragment beams for moments studies of elements not
accessible by laser methods.
The future with relativistic
radioactive beams
Measurements of nuclear reaction cross sections at
relativistic energies (500-1000 MeV/u) allow for the matter
radii of unstable nuclei to be determined. Since matter
radii are directly related to the nuclear size, the measurement
of total interaction cross-sections is capable of
unravelling unusual nuclear structures, such as halos.
Moreover, from knowledge of both matter and charge
radii one can deduce the neutron skin thicknesses, e.g.
from optical isotope shift measurements. For nuclei of
A>30, the relation to EOS is discussed and important
constraints to the parameters of asymmetric nuclear
matter can be obtained.
Due to the different cross-section and energy dependence
of p-p and p-n interactions in nuclear reactions,
diffuseness and radius parameters for matter and charge
distributions can be determined from a Glauber-model
based analysis of interaction cross-sections, obtained
from different targets at different energies. Using relativistic
radioactive beams at SuperFRS of FAIR, skin
thicknesses can be deduced even for very weak beams
with rates down to ~0,1 ions per second, where optical
methods are not applicable. With higher intensities, more
detailed information on the radial charge and matter
distributions can be obtained by elastic and inelastic
scattering off light hadronic probes in inverse kinematics
in storage rings and by scattering off leptonic probes in
an electron-nucleus collider, as is planned in the ELISe
experiment at FAIR. As an example, Figure 9 shows the
proton density distributions in 46 Ar and the corresponding
form factors, according to different calculations. The
ELISE experiment will be able to distinguish whether the
predicted proton bubbles do really exist.
Nuclear masses
Figure 9. Top:
radial proton density
distributions of
46
Ar calculated with
different forces in
the HF-approach.
Bottom: angular
differential form
factors, which will
be obtained from
300 MeV electron
scattering off the
density distributions
from the top.
Nuclear masses directly probe the total binding energy of
nuclei and have always played a key role in experimental
and theoretical nuclear physics. Accurately known binding
energies serve to derive effective nuclear forces and to
fit the parameters of the interaction, in order to reproduce
not only nuclear masses, but also empirical saturation
properties of nuclear matter and neutron stars.
Together with beta-decay half-lives and reaction rates,
masses are important quantities for nuclear astrophysics
and the quantitative understanding of solar abundances,
energy- and neutron sources in quiescent and explosive
burning processes and also for constraining duration,
pathway and physical conditions of stellar nucleosynthesis.
Derived quantities, such as proton- and neutron-separation
energies and pairing-gap energies, often give
122 | Perspectives of Nuclear Physics in Europe – NuPECC Long Range Plan 2010