COLLAPS is a small experiment located at the “isotope factory” ISOLDE at CERN. Its aim is the investigation of ground state properties of exotic, short lived nuclei, such as spins, electro-magnetic moments and charge radii.
All these observables contribute widely to our understanding of the nuclear force – they give valuable information about the coupling between nucleons, about symmetry of the nuclear wave-functions and thus about the symmetry of the nuclear interaction itself. In this way, for example, the discovery that the nuclei can possess a spectroscopic nuclear moment gave the decisive proof for the existence of non-central parts of the nucleon-nucleon force. Another example is the light halo nucleus 11Li, whose spin and magnetic moment have been measured for the first time by our group. These results confirmed the halo-structure, and excluded a stong deformation, which was also considered before. In the same way, in 2005, we determined the spin of 31Mg, which turns out to lie in an interesting region of “island of inversion.”
COLLAPS combines expertise in atomic and nuclear physics, because it mainly uses the hyperfine interaction to obtain information about nuclei by manipulating the atomic electrons. This is indicated already by its name: COLLAPS stands for COLlinear Laser Spectroscopy, i.e. we use the laser light to induce electron-transitions in atoms or ions, and from the hyperfine splitting (HFS) or isotope shifts (IS), we get the ground state properties of the nuclei. Presently, we also use another method: beta-NMR technique, which can give very precise values of the magnetic dipole moments and electric quadrupole moments.