Research at GSI & FAIR: Electromagnetic dissociation of Radioactive Nuclei
Radioactive Nuclei decay into more stable nuclei. They can either be produced in reactions where at rather low energies near the reaction partner's Coulomb barrier, or they can be made by projectile fission or fragmentation at higher energies, i.e., at velocities approaching the velocity of light, c. The second method has the advantage to allow a fast transport of the beams of the radioactive nuclei to a second reaction site before they decay. The picture on the right hand side shows the number of protons Z versus the number of neutrons N for the known nuclei. The yellow area comprises examined isotopes with known lifetimes. Among these are also the stable nuclei, or with long lifetimes, in black. The brown area on the left, proton-rich side represents nuclei created in photon-induced processes, while the brown field on the neutron-rich side to the right contains isotopes created in capture processes in neutron-rich environments. The region of possibly synthesisable nuclei extends both to the proton-rich as well as the neutron-rich side.
The interest in the dissociation of radioactive nuclei is related to the original production of all the chemical elements in cosmic scenarios, which in many cases has to encompass radioactive nuclides. As the 'element cooking' , the nucleosynthesis - which usually happens inside massive stars - is enhanced in hot and thus photon rich environments, the simultaneous photo-dissociation has to be regarded. Actually, its cross-section is linked to the radiative capture by the rule of detailed balance which gives a second motivation for its measurement. Theoretical calculations of this cross-section are unreliable, as, up to now, the standard model of nuclear structure - the Nuclear Shell Model - has only been tested in regions close to the valley of stability in the nuclear chart. When leaving this region of stable nuclei new phenomena are expected and new insights into the complex nuclear many-body problem should be obtainable.
These experiments have not been done up to now as beams of radioactive nuclei are only available since new accelerators, which are suited to produce them in sufficient quantities with high beam intensities and energies, have been built. Furthermore, the experimental methods to identify and to study the decay characteristics of radioactive nuclei has been steadily improved and new techniques with superior detection efficiencies and resolutions are being developed. A large number of radioactive nuclei with neutron excess can be produced in the fission of Th or U by real photons. The group develops new detection concepts for particles emerging in reactions with radioactive beams, especially focusing on neutron detectors for the R3B setup at the future FAIR facility.
Efforts at HZDR
To learn more about our technical contribution to FAIR, please go to the detector technology page instead. The nuclear physics group is involved in design and prototyping of the NeuLAND detector for 0.2 - 1 GeV neutrons. NeuLAND is a part of the R3B (Reactions with Relativistic Radioactive Beams) experiment at FAIR.
Recent and Current Experimental Activities:
- Coulomb dissociation of B-8 and the Solar Neutrino Flux at the KaoS spectrometer at GSI
- Coulomb dissociation of unstable Mo-isotopes at the LAND setup at GSI
- Nuclear multifragmentation at the fragment separator at GSI
- Coulomb dissociation of neutron rich nuclei
These experiments are carried out in close collaboration with international groups.