A rotational band of nineteen transitions with a moment of inertia 3$ nA of 84£ 2 MeV" 1 has been observed in 152 Dy. The band feeds into the oblate yrast states between 19" and 25" and it is proposed that the lowest member of the band has a spin of 22 + and thus the band extends up to 6Qfr. It is identified as the yrast superdeformed band and its intensity accounts for the whole of the ridge structure seen previously in continuum E y -E r correlations.PACS numbers: 21.10. Re, 23.20.Lv, 27.70.+q The nucleusDy has been extensively studied and three different structures have been identified. The low-spin yrast levels have a pseudovibrational structure 1 which develops into a low-deformation (fi = 0.15) prolate rotational band 2 extending up to 40fr. This band, in the spin region between SR and 38£, lies between 0.5 and 1.5 MeV above the yrast states which have a weak oblate structure formed by particles in equatorial orbits. 3 " 5 At higher spins the y-ray continuum is dominated by a collective E2 bump. 6 Part of this bump has been shown to arise from superdeformed (/J^O^) bands from the existence of ridges with a moment of inertia3 (2) = (85 ±2)H 2 MeV" 1 in E y 'Ey correlation spectra. 7,8 In this Letter we present data showing a discrete-line rotational band extending over nineteen transitions from 602 to 1449 keV with an almost constant energy separation of 47 keV which corresponds to the superdeformed moment of inertia. The major -y-ray decay deexciting the band feeds into the yrast oblate structure between the 19"" and 25"" states and then proceeds via the 60-ns 17 + isomer. Additionally 25% of the decay intensity bypasses this isomer. We propose that the decay process from the bottom of the band is essentially statistical, involving several transitions, and we assign the spin at the bottom of the band to be 22£, thus establishing the spin at the top of the band to be 60fr. This is the first observation of a discrete-line superdeformed band and it extends the spin at which discrete states have been seen from about 46* (e.g., 158 Er, Tj0m etaL 9 ) to 60T.The experiment was carried out on the tandem accelerator at the Daresbury Laboratory using the TES-SAS spectrometer, which consists of a 50-element bismuth germanate (BGO) crystal ball similar to that used in TESSA2 10 with twelve escape-suppressed germanium detectors. 11 The states in 152 Dy were populated by the reaction 108 Pd( 48 Ca,4>7) at 205 MeV with a target consisting of two 500-/ig-cm~2 self-supporting foils isotopically enriched at 95% in 108 Pd. A 15-mgcm" 2 gold catcher foil was positioned 5 cm downstream of the targets such that it was outside the focus of the germanium detectors but within the full detection efficiency of the BGO ball. A total of over 150 million double (Ge-Ge) coincidences were recorded together with the sum energy and number of hits (fold) in the BGO ball. The time difference between the BGO ball and the second-coincidence germanium detector was recorded and enabled most of the neutron-induced events in the germanium detec...

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A y-ray spectraswpic study of the high spin states of the nucleus ' 5' Dy has been performed using the reaction '0RPd(dsCa,4n)'"Dy at a bombarding energy of 205 MeV. Gamma rays were detected using the TESSA) multi-detector array. A set of discrete-line States forming a rotational band has been observed in the data and has been shown to extend up to a spin of around 6Ofi and an excitation energy of about 30MeV. The y-ray energy data is consistent with dynamic moment of inertia P of (85 f 3)h2 MeV-', indicating a large quadrupole deformation. A measurement of the collectivity of the band has been made using the Doppler Shift attenuation method, with the data for the lower spin states yielding a qlladrupole moment of e,,= (J813)e b. This is in excellent agreement with the calculated value of 17.6 e b for a superdeformed shape with a major-to-minor axis ratio of 2 : l . The data for the dynamic moment of inertia are consistent with the calculated high-j configuration for the superdeformed band, and the variation of 9' ' ' with frequency is reproduced by both cranked Nilssan and Woods-Saxon models. The intensity pattern for the band indicates that the superdeformed states are populated with an anomalously high intensity at spins close to the fission limit, suggesting that there is some enhanced population mechanism. The hand is observed to de-excite suddenly at around I = 26h, although the linking transitions between these States and the yrast States have not been Observed. Evidence is presented for the existence of non-yrast superdeformed bands in the p r a y continuum.The intensity of these bands is measured and compared with the results of Monte Carlo simulations. NUCLEAR REACnONS "Pd("Ca,4n) E ("Ca) = 205 MeV; measured E,, I,, y-y coincidence and angular correlations. '''Dy; deduced levels, decays; assigned E,, J and n. Superdeformed band; quadrupole moment. *licmscopic structure, comparison with Nilssan and Woods-Saxon models. Feeding mechanisms. Comparison with results of Monte Carlo simulations.

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