Welcome to the description of our experimental
methods
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.
History
The first collinear experiments
of the
The first measurements at CERN
were devoted to Ba and Yt isotopes. In 1986 a new, sensitive detection scheme
was proposed: collisional ionization It was shown to be successful on Kr
isotopes (NIMB17,354). One year later a first publication appeared devoted to
measurements on 11Li, performed with beta-NMR combined with optical pumping in
a collinear configuration (PLB197,311). In 1988 a new non-optical detection
method was developed and used on Sr at COLLAPS (PRL60,25). A report on a
successful application of resonance ionization on a fast Yt beam came in 1991
(JPB,24,4831). In 1995, the group reported on a collinear experiment using
collisional ionization and alpha-detection (ENAM95Proc.,133). Then, in
1998-2001 experiments on Ne were performed, which used a
collinear-anticollinear configuration to calibrate the acceleration voltage. Since
2002, successful experiments on Li and Mg isotopes have been in the center of
our activities. And soon, Cu isotopes will be investigated …
On the following COLLAPS pages
you can find more details about our experimental techniques:
- The
first - and oldest - method is the detection of the fluorescence light emitted
by the excited atoms, well known as "classical collinear laser
spectroscopy".
All
the other methods are based on the principle of optical pumping:
-Detection
of the optical resonance by making use of the change in the population of
states with big differences in ionization energy - the reionization method
-Detection of the population change by observing the change in nuclear polarization with the ß-NMR technique.
Information about ISOLDE can be accessed at www.cern.ch/isolde.
Last
modified: 05-05-2006, by MK