Euroball III, a European γ-ray facility and superdeformation in Gd nuclei around A=146

Summarized are the main lines of investigations of new phenomena in nuclei under extreme circumstances close to the limit of stability for which the excitation energy, the angular momentum or the ratio of protons to neutrons take extreme values. It is emphasized that the most powerful means to carry out such experiments is the high precision γ-ray spectroscopy. Discussed are the main features of γ-ray detectors which have to be optimized as a photopeak efficiency, peak/total ratio, energy resolution, isolated hit probability. The Nordball spectrometer in the study of the superdeformed band in 143Eu is described. The Euroball project and the γ-detector array Euroball III to be used in the project experiments are discussed. The main advantages of Cluster detector, encapsulated Ge detector and BGO escape-suppression detector are outlined. To search for superdeformation in 144Gd an experiment at the γ-spectrometer GASP has been performed using the reaction 100Mo(48Ti,4n) at a beam energy 221 MeV. Using the Radford package, 14 coincident transition are identified and a double-gated coincidence spectrum of the resulting superdeformed band is obtained. The intensity of the superdeformed band was estimated to be ∼0.2% of the total population of the nucleus 144Gd. The weak population of the superdeformed band in 144Gd explain why it is not possible to detect it in the previous experiments. The three close lying transitions at ∼ 890 KeV indicate that the superdeformed band in 144 Gd undergoes a band crossing at a rotational frequency of ℎ ω=0.45 MeV. This is the first experimental observation of a crossing in a superdeformed band related to the alignment of a proton pair. An open question is the small intensity of the superdeformed band in 144 Gd. 14 figs., 36 refs. (orig.)