Nuclear-structure studies of exotic nuclei with MINIBALL (Vol. 49, No. 2)

The MINIBALL spectrometer comprises 24 six-fold segmented, encapsulated high-purity germanium crystals. It was specially designed for highest g-ray detection efficiency which is advantageous for low-intensity radioactive ion beams. (picture courtesy CERN)

Investigations of exotic nuclei at the ISOLDE facility of CERN are pursued with reaccelerated radioactive ion beams by means of high-resolution g-ray spectroscopy. The experimental programme covers a range of topics, which are addressed with beams ranging from neutron-rich magnesium isotopes up to heavy radium isotopes. The nuclear-structure and nuclear-reaction studies provide important insights into collective properties and single particle excitations. The most important outcomes of these measurements include: discoveries of rare nuclear shapes like octupole deformation in the actinide region; the coexistence of different intrinsic nuclear shapes at low excitation energy, and within a very narrow energy range in strontium and mercury isotopes, for which nuclear shell model investigations yielded considerable discrepancies from theory when extrapolated from known stable nuclei; and the remarkable behaviour of exotic neutron-rich nuclei with the “magic” number of 20 neutrons and in the vicinity of semi-magic chains of Ni- and Sn isotopes. The article summarized results obtained with the REX-ISOLDE facility which is the precursor of the newly inaugurated HIE-ISOLDE accelerator at CERN. The new installation allows the in-beam spectroscopy programme to be continued with higher secondary-beam intensity, higher beam energy and better beam quality. The first results have been obtained after commissioning of the super-conducting accelerator.

P. A. Butler, J. Cederkall and P. Reiter, Nuclear-structure studies of exotic nuclei with MINIBALL, J. Phys. G: Nucl. Part. Phys. 44, 044012 (2017)