NeuLAND - FAIR

heavy neutron-rich nuclei [Bro-00], [Hor-01]. A first attempt to extract the parameters
describing the neutron-proton asymmetry part of the equation of state for nuclear matter
from the measured low-lying dipole strength has been made by Kliemkiewicz et al.
[Kli-07] and by Carbone et al. [Car-10]. Experimental data concerning the collective response
of exotic nuclei including the giant resonances and the pygmy dipole strength are
still rather scarce. The existing dipole strength measurements suffer from an insufficient
response of the detector system.
From the experimental point of view, there are several challenges to deal with. The
heavy-ion induced electromagnetic excitation process requires high beam energies which
in turn put high demands on the detection systems. The combination of a largeacceptance
superconducting dipole with large field integral, a highly granular calorimeterlike
photon detector together with a high-efficiency and high-resolution detection of
neutrons make the R 3 B setup an ideal facility to study the collective response of exotic
nuclei.
The neutron detector has to be optimized for high detection efficiency and acceptance in
the beam-energy region from 200 to 1000 AMeV. A variation of beam energy is necessary
to disentangle dipole and quadrupole contributions to the excitation cross section. The
lower energy of 200 AMeV will be used to study giant monopole resonances in neutronrich
nuclei which are related to the incompressibility of asymmetric nuclear matter. We
will use alpha scattering in inverse kinematics in an active He gas target which will be
developed for these measurements. For heavy nuclei, like Pb, the beam energies around
1 AGeV are necessary to allow for fully stripped ion beams. It is mandatory to apply
a magnetic analysis for an identification of the fragments using a tracking system. So
far, this has not been possible due to the limitations of the present detection devices.
The improved resolution of NeuLAND will make a high-resolution detection of neutrons
possible even at a laboratory energy of 1 AGeV.
The kinetic energy of neutrons evaporated from collective states in the continuum follows
usually a Maxwellian distribution with a maximum at approximately 1 to 2 MeV.
An angular acceptance which allows detection of up to about 5 MeV kinetic energy is
required to cover the full distribution. This requirement is met by the ±80 mrad acceptance
defined by the gap of the dipole magnet and will be covered by the neutron
detector. The envisaged position and time resolution of 1.5 cm and 150 ps for NeuLAND
will result in an excitation energy resolution of about 100 keV at an excitation energy
of 1 MeV above the threshold (or 1 MeV kinetic energy of the neutron) for a 600 AMeV
beam at a distance fulfilling the full-acceptance criterium. At 1 AGeV, the detector can
be placed further away while providing the same acceptance and about the same energy
resolution.
The high intensities of radioactive beams provided by the Super-FRS at FAIR will
push the frontier towards more neutron-rich systems. In such nuclei, the effects of
asymmetry are magnified and the electromagnetic response of the nucleus reflects these
isospin-related changes. The Pygmy resonance is one example, but also the dipole and
quadrupole response as a whole change. The neutron-rich medium-mass nuclei which can
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