Perspectives of Nuclear Physics in Europe - European Science ...

An improvement in the precision of the measurements
is also required. This necessary development can be
achieved in relatively small laboratories where a well
focused and stable beam is available. In addition, the
expertise gained can be crucial for further applications
with radioactive beams, which until now are characterized
by much lower intensities.
To improve the synergy between the existing facilities
it is recommended that NuPECC helps to coordinate
an active network between the European small scale
facilities, not only on the user side but also on the level
of technology development. From these coordinated
efforts large scale facilities can benefit as well.
Ultimately the key to obtaining the highest quality
data, and to be able to measure the weakest reaction
rates, is the beam intensity. The ECOS (European
Collaboration on Stable ion beams) study revealed the
needs for, and described the strategy to deliver, a dedicated
high intensity stable beam facility equipped with
the latest detection and target technique. The provision
of such a facility in Europe, either as a greenfields construction
or as a major upgrade to an existing facility,
would provide a major boost for nuclear astrophysics
measurements. This includes direct measurements,
indirect measurements, and the production of unstable
nuclei along with measuring their masses in storage
rings and traps.
Radioactive Beam facilities
In hot, dense explosive nuclear astrophysical environments,
nuclear reaction rates involving radioactive nuclei
become important. RIB facilities will play an essential
role in determining key properties and reaction rates
of nuclei influencing the energy generation and path of
nucleosynthesis in these processes.
ISOL RIB facilities offer the means by which key
explosive nuclear astrophysical reactions can be directly
measured in the laboratory. These measurements are
particularly important for explosive astrophysical environments
involving proton-rich species, such as Novae
and X-ray bursters where rates can be dominated by
a few isolated resonances. Pioneering work has been
done in Europe at Louvain-la-Neuve and in Canada at
TRIUMF/ISAC, were reaction rates were directly measured
using radioactive beams. It is essential that the
forthcoming generation of ISOL RIB facilities, including
SPIRAL2, HIE ISOLDE and SPES, and in the longer term
EURISOL, provide intense, pure beams of low energy (a
few hundred keV/u to a few MeV/u) near stability protonrich
nuclei for such direct measurements. The low energy
capability is uniquely important for nuclear astrophysics
experiments and it is important that the design of the
accelerators in these facilities are capable of this. There
is currently a limited capacity for these measurements
in Europe and indeed worldwide, due to beam intensity
limitations for certain key elemental and isotopic species.
In general, measuring these reactions will require
accompanying high efficiency, high granularity, charge
particle and γ-ray detection systems. High efficiency
recoil mass separators with high beam suppression
will be required for radiative capture reactions such as
(p,γ) and (α,γ). In some cases direct measurements will
not be feasible, e.g., (n,γ) reactions important for nonequilibrium
phases in the r-process in supernovae. Here
one can use (d,p) transfer reactions with ISOL RIBs at
~10 MeV/u as surrogates to identify – and to determine
spectroscopic factors of – key resonances using a high
acceptance spectrometer, such as VAMOS, to tag the
nucleus of interest. An analogous approach can be used
for measuring (p,γ) reactions on proton-rich nuclei for
very low energy resonances with extremely low capture
cross-sections.
At the high energy FAIR in-flight RIB facility, photodisintegration
studies of (γ,p) and (γ,n) reactions using the
R3B system will also be able to probe important capture
reaction processes. A very exciting recent development
at GSI has been the use of decelerated beams in the
ESR storage ring to measure the 96 Ru(p,γ) reaction for the
astrophysical p-process close to the astrophysical burning
energy regime. This approach could be extended to
RIBs to open up a whole new vista of measurements on
unstable p-process nuclei using the planned new storage
ring (NESR) at FAIR. Future facilities will provide for the
first time access to a whole swath of r-process nuclei,
where it will be important to measure static properties
such as the mass, half-life and decay branches of these
rare nuclei using channel selection devices such as the
super FRS. Such measurements are vital to address the
astrophysical origins of the heavy elements. Similarly,
such information will be important for nuclei located
in the upper reaches of the astrophysical rp-process.
Reaction studies using the high energy beams from
FAIR with the R3B, EXL and ELISE systems will offer
important insights into the nuclear equation-of-state
which will impact on our understating of the structure of
neutron stars. For example, giant resonances are sensitive
to the nuclear compressibility, and their variation
with isospin can be studied on the NESR using the EXL
system. Matter distribution measurements from elastic
p-scattering can be complemented by charge radii
measurements on RIBs using the ELISE e-ring system
to extract neutron skin thicknesses – a key parameter
for determining the thickness of the crust in neutron
stars and also relevant to derive optical potentials for
the calculation of reaction cross sections.
In addition to the uncertainties affecting the neutron
capture rates, weak interaction properties also suffer
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