The MINIBALL target chamber at CERN-ISOLDE

Researchers from University of Jyväskylä investigate the structure of mercury nuclei at CERN

New information on the nuclear shapes of even-even isotopes of mercury with mass numbers 182-188 has been obtained in experiments at CERN-ISOLDE. The new data which have been obtained help to understand the structure and dynamics of the atomic nucleus, a quantum many-body system.

In these mercury isotopes, the nuclear ground state has an oblate deformation (a sphere squashed at the poles, like the earth). However, with only a small change in excitation energy, the shape of the nucleus changes. These nuclear states are so close in energy, that one can speak of shape coexistence and mixing of nuclear states. Observation of this type of quantum-mechanical phenomenon is extremely difficult, but the experimental instrumentation at the CERN-ISOLDE laboratory has enabled detailed measurements to be made.

To perform the studies, short-lived, neutron-deficient isotopes of mercury have been created and accelerated to about 10% of the speed of light. This Radioactive Ion Beam, as it is known, is used to strike a stationary, thin target foil. In the reaction the beam is excited and the electromagnetic and particle radiation is observed with position-sensitive detectors. From the energy and angular correlation data, one can draw conclusions about the structure of the nucleus.

Studies based on work from University of Jyväskylä Accelerator Laboratory

Physicists from the University of Jyväskylä took part in the experiments and in the interpretation of the results, which were published in Physical Review Letters. The research is part of a wider program of study, in which a substantial number of experiments have been carried out at the Accelerator Laboratory of the University of Jyväskylä. The earlier experiments in Jyväskylä opened new research directions and formed the basis for the studies carried out in CERN.

The subscription of Finland to CERN is funded via the Academy of Finland, and the Academy has also funded research in this program through grants to University of Jyväskylä docent Tuomas Grahn and Academy Research Fellow Janne Pakarinen. Finland is a member of the CERN-ISOLDE collaboration, and participation is funded through the Helsinki Institute of Physics (HIP) Nuclear Matter Program.

Further Information:

http://dx.doi.org/10.1103/PhysRevLett.112.162701

Academy Research Fellow Janne Pakarinen, janne.pakarinen@jyu.fi, p.040 805 4900
University Lecturer, Docent Tuomas Grahn, tuomas.grahn@jyu.fi, p. 040 805 4516