Superdeformed bands in the A∼130 region

Discovery, some typical features, origin, population and deexcitation of superdeformed bands (SD) are briefly reviewed. The last generation arrays are designed to study very weak amplitudes phenomena and they must have a large efficiency and large resolving power. Compared to the previous γ-ray spectrometers the new generation (EUROGAM and GASP already operating, GAMMASPHERE under construction, EUROBALL and TRIGAMM project) is characterized by a much greater number of Ge detectors and a total peak efficiency 10 or 20 times larger. The main characteristics of the new arrays: EUROGAM and GASP are given. The first observation of the SD bands in the 130 mass region based on two experiments is reported. The first nucleus studied is 132 Ce produced in the 100Mo(36S,4n) reaction at 155 MeV. The γ-rays were detected by 42 Ge detectors of EUROGAM 1. Two excited SD bands have been identified in 132 Ce. The first one is composed of 13 transitions of energies between 794 and 1687 KeV and another of 12 transitions between 947 and 1725 KeV. Another experiment has been performed using EUROGAM to search for excited SD bands in 133Pr produced by reaction 100Mo(37Cl,4n) at 155 MeV. Four SD bands have been discovered in 133Pr with transitions ranging from 0.8 to 1.6 MeV. The observation of identical SD bands in Ce and Pr isotopes and the decay out of the yrast SD bands in 133Nd and 135Nd are discussed. The new projects on other arrays of the third generation as EUROBALL, GAMMASPHERE, TRIGAM are briefly reviewed. It is emphasized that the use of new arrays will give the possibility to observe weaker amplitude phenomena like the hyperdeformation also predicted in the mass 130 region. 21 figs., 46 refs.(orig.)