Nuclear radii and momentum distributions

The discoveries of exotic forms of nuclei such as neutron and proton halos, neutron skins, and new magic numbers mostly originated from measurements of nuclear radii by the interaction-cross-section measurements and subsequent fragmentation measurements.

(i) Matter and proton radii:
The interaction cross section has been well established to be an efficient method to determine nucleon radii of unstable nuclei. It has been applied for elements up to argon. The nucleon density distributions have also been determined by the energy and the target dependences of the interaction cross section. Halo nuclei have been discovered in nuclei near the drip lines but the neutron drip line is reached only up to oxygen isotopes (Z=8) so far. Giant neutron halos including more than two neutrons are also predicted in heavier elements. It is of great importance to search for such a new structure in nuclei. Halos revealed a new quest on the coupling of continuum and discrete states. It prompted studies of nuclear theories to understand bound and unbound objects from first principles. The thickness of neutron skins is one of the sensitive ways to determine the equation of state (EOS) of asymmetric nuclear matter. The EOS for asymmetric nuclear matter is of upmost importance for understanding the stellar objects (such as neutron stars) and their dynamic changes (such as supernovae). Neutron skin thicknesses are mostly determined by combining the matter radii extracted from σI and the proton-distribution radii deduced from charge radii. For isotope chains, charge radii are mostly determined by laser spectroscopy methods, such as isotope shift measurements In case of isotopes where charge radii are difficult to determine by isotope shifts measurements, a nuclear charge changing cross section can provide a mean to determine the proton distribution radius.
Determination of proton distribution radii by nuclear charge changing cross section measurements is still under development but there have been several successes in light elements. A particular advantage of this method is that it can be applied for very short-lived and weak intensity nuclides and thus has the possibility to reach the most neutron-rich isotopes.
The Super FRS is the ideal instrument in the world to perform these cross section measurements due to the desired high energy coupled with the advantages of high mass resolution and transmission.

(ii) Momentum distribution of fragments:
The momentum distributions of fragments following one or two-nucleon removal was one of the early spectroscopic methods that gave knowledge on the wave function of the initial nucleus. It is of great importance to extend these studies to higher-mass regions in order to probe whether magic numbers 50, 82, 128 still persist and whether new magic numbers will appear. The advantage of the present method is that a very low intensity beam (~10/s) can be used for detailed spectroscopy. High-resolution momentum measurements are possible by applying the dispersion-matching mode.
The usage of R3B for this type of experiments is also under discussion, especially with γ-rays from excited states of the fragment observed in coincidence. While this has potential to provide a more detailed knowledge on the final states, it requires higher intensity beams. The large acceptance of the R3B-dipole magnet may have advantages, for example, for the detection of multi-particle final states.