VOLUME 74, NUMBER 10 PH YS ICAL REVIEW LETTERS 6 MARCH 1995 Observation of Excited Superdeformed Bands in 3 Ce and Evidence for Identical Bands in the Mass 130 Region D. Santos, ' J. Gizon, ' C. Foin, ' J. Genevey, ' A. Gizon, ' M. Jozsa, ' J. A. Pinston, ' C. W. Beausang, S. A. Forbes, P. J. Nolan, E. S. Paul, A. T. Semple, J. N. Wilson, R. M. Clark, K. Hauschild, 3 R. Wadsworth, - J. Simpson, B.M. Nyako, L. Zolnai, W. Klamra, N. El Aouad, and J. Dudek Recherche Scientifique, Universite Joseph Fourier, F 38026 -Grenoble, France 20liver Lodge Laboratory, University of Liverpool, Liverpool, L69 3BX, United Kingdom 'Department of Physics, University of York, Heslington, York YOI 5DD, United Kingdom M/'A4 4AD, United Kingdom 'Institute of Nuclear Research, H 4001 D-ebrecen, Hungary 6Manne Siegbahn Institute of Physics, S 10405 -Stockholm, Sweden Recherche Scientifique, Universite Louis Pasteur, F 67037 Stra-sbourg, France (Received 28 June 1994) Two excited superdeformed (SD) bands have been observed in "2Ce using the Eurogam gamma- ray spectrometer. Possible configurations are proposed in terms of particle-hole excitation from a theoretical analysis based on the cranking approximation with the Woods-Saxon deformed potential. From relationships between y-ray energies of SD bands in " Ce and "'Ce, the existence of identical bands and approximately quantized alignments is established in the mass 130 region. PACS numbers: 21.10. Re, 23.20.Lv, 27.60.+j The first collective band associated with large prolate deformation was discovered in '32Ce [1]. Later, superde- formed (SD) bands were found in A = 150 [2] and A = 190 [3] mass regions. These strongly deformed high- spin structures are usually associated with secondary min- ima in the potential energy surfaces at high angular mo- mentum which, in the mass 130 region, correspond to a quadrupole deformation P2 = 0.40, deduced from mean- lifetime measurements [4]. In the A = 150 and 190 nuclei, the deformations are somewhat larger with Pq = 0.45 — 0. 6. These systematic shape differences can be attributed to the pseudo-SU(3) symmetry of the nuclear field [5], which implies that, in nuclei around ' Ce, the SD bands result mainly from the effects of i]3/2 neutron intruders which lower the P2 = 0. 40 SD minimum to the yrast position at relatively low spins [6, 7]. Another special property of nuclei around ' Ce is the relatively high population of the SD structures. Indeed, the intensity of the SD bands in the A = 130 mass region can reach 5% — 10% of the 2+ ~ 0+ transition in the corresponding reaction channel while it is only about 1% — 2% for the higher-mass regions. It was therefore particularly striking that, prior to the present experiments with the new generation of large y-ray detector arrays, no excited SD band had been identified in the A = 130 nuclei while numerous such bands were found in the other regions. A further difference between SD nuclei in the A = 150 and 190 regions and those around A = 130 was the absence of identical bands in the latter. The present Letter reports on the observation of two excited SD bands in ' Ce. In parallel to our investigation, a single excited SD band has recently been found in the isotone ' "Nd [8]. In this Letter we also report on the first evidence of "identical" SD bands in the mass 130 region. The nucleus '32Ce was produced in the 'ooMo( S, 4n) reaction at the Nuclear Structure Facility at Daresbury. A 155 MeV 36S beam was used to bombard a self-supporting 'ooMo target of 625 pg/c mt2hickness. The y rays were detected by 42 Compton-suppressed detectors of the Eu- rogam (phase I) array. Only events with unsuppressed fold greater than or equal to 7, corresponding to a sup- pressed fold distribution peaked between 3 and 4, were reg- istered. A total of 7 X 108 events, 84% with suppressed fold ) 3, were recorded. Several methods were employed for data analysis. A systematic search for SD correlations was mainly carried out on conditioned matrices. Special algorithms [9] were used for setting gates on both SD tran- sitions and known transitions deexciting normal deformed (ND) states. An analysis has been performed to assign the new band to ' Ce, whereby we require m SD transition energies (m = 2, 3) and n known ND transition energies (n = 1, 2) simultaneously in a list of transitions (i.e. , m n = 2-1, 2-2, 3-1). In this way the newly observed SD lines survived only when they were in coincidence with the n lines in ' Ce. Event by event single gates were used for relative intensity determinations of the different bands to avoid distortions in the unfolding coincidences from mul- tiplicity differences. The yrast SD band, denoted "~Ce(yr), was populated with an intensity of 5.5% relative to the yield in the Ce channel. This band has been extended towards higher spins by two additional transitions (2. 115 and 1708 0031-9007/95/74(10)/1708(4)$06. 00 1995 The American Physical Society