TRIGA-LASER

Collinear laser spectroscopy is an approved method for the determination of nuclear ground state and excited state properties of rare short lived radioactive isotopes. It allows for the assignation of the nuclear spin and the nucleus shape properties like the magnetic dipole and the electric quadrupole moment as well as the change in the mean square charge radius of the nucleus. These extracted parameters provide fundamental information on the structure of nuclei far off stability.

For access on the radioactive isotopes we started to set up a collinear laser spectroscopy experiment at the TRIGA research reactor at the University of Mainz. A uranium or californium target will be placed near the reactor core in a target chamber and receive a high neutron flux of about 10^11 neutrons/cm^2. The products of neutron induced fission will then be thermalized by buffer gas and transported to an ion source by a gas-jet system. The transport gas is interspersed with aerosol clusters to adsorb the fission products in the chamber which will then be guided through a small capillary to an ion source. There the light transport gas is removed and the fission products are ionized in order to form a radioactive ion beam.

TRIGA research reactor at the University of Mainz - click for bigger version -

After acceleration and mass separation the beam enters a switchyard and can then be sent to either a cryogenic penning trap or to our collinear spectroscopy setup.

The He Gas-Jet System - click for bigger version

To perform laser spectroscopy the ion beam is superimposed with the excitation laser by a deflection capacitor. The laser wavelength in the rest frame of the beam depends on the ion velocity (Doppler shift). Therefore the beam is decelerated by electrostatic lenses in order to tune this wavelength on resonance with the atomic transition. The whole resonance can be scanned by varying the deceleration voltage while keeping the laser on a fixed wavelength and is observed by fluorescence in optical detection region. An optional charge exchange cell allows for transformation of the fast ion beam into an atom beam in case that the ions wavelengths are not feasible for standard laser systems.

Superimposition of the ion beam with the excitation laser by a deflection capacitor - click for bigger version