Sub-nanosecond Half-life Measurement of the Yrast I π =5 - State in the N =78 Nucleus 136 58 Ce using Fast-timing Coincident Gamma-ray Spectroscopy T. Alharbi, 1, 2 P.H. Regan, 1, 3, ∗ N. M˘ arginean, 4 Zs. Podoly´ ak, 1 A. Bajoga, 1 R. Britton, 1 D. Bucurescu, 4 D. Deleanu, 4 D. Filipescu, 4 D. Ghit˘ a, 4 T. Glodariu, 4 C. Mihai, 4 K. Mulholland, 5 R. M˘ arginean, 4 A. Negret, 4 C.R. Nita, 4 Z. Patel, 1 O.J. Roberts, 6 L. Stroe, 4 T. Sava, 4 C. Townsley, 1 and N.V. Zamfir 4 1 Department of Physics, University of Surrey, Guildford, GU2 7XH, UK 2 Department of Physics, Faculty of Science in Zulfi, Almajmaah University, P.O. Box 1712, 11932, Saudi Arabia 3 National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK 4 Horia Hulubei - National Institute for Physics and Nuclear Engineering (IFIN-HH), Bucharest, Romania 5 School of Engineering, University of the West of Scotland, High Street, Paisley PA1 2BE, UK 6 School of Computing Engineering and Mathematics, University of Brighton, Brighton, BN2 4GJ, UK We report on the measurement of the half-life of the yrast I π =5 - state in the transitional nucleus 136 Ce using a combined HPGe-LaBr3(Ce) scintillator gamma-ray detection array. The measured value for the E1 decay is approximately half a nanosecond, which corresponds to an E1 decay strength of approximately 2×10 -6 Wu. This value is in line with single-particle type E1 decays in this mass region and suggests no sign of additional K-hindrance associated with axially symmetric quadrupole deformations observed for lighter cerium isotopes. I. INTRODUCTION The measurement of low-lying electric dipole decay strengths in Cerium nuclei can be used as a guide as to the influence of both single particle spherical configurations in heavier Cerium isotopes approaching the N =82 shell closure [1] and the development of collective behaviour as- sociated with quadrupole deformed structures in lighter Ce isotopes [2–5]. A low-lying, I π =5 - states has been identified in 138 Ce 80 , with a suggested structure based on mixed neutron (d -1 3/2 ⊗ h -1 11/2 ) and (s -1 1/2 ⊗ h -1 11/2 ) con- figurations [1, 6]. The N =78 isotone 136 Ce, shows more of a transitional-type behaviour at higher spins [7], but also exhibits a low-lying I π =5 - state at just below 2 MeV excitation energy. Decays from negative parity states to the states in the ground state configuration in lighter cerium isotopes have been demonstrated to ex- hibit significant additional decay hindrances associated with conservation of the K-quantum number in axially deformed nuclei [2, 8, 9]. This short conference paper presents preliminary results on the measurement of the half-life of the yrast I π =5 - state in the transitional nucleus 136 Ce and compares the extracted E1 transition strength with recent results in the neighboring N =80 * Corresponding author: p.regan@surrey.ac.uk isotone 138 Ce. The measurement was performed using the coincident fast-timing spectroscopy technique with a mixed Ge-LaBr 3 gamma-ray detection array. II. EXPERIMENTAL DETAILS, DATA ANALYSIS AND RESULTS Excited states in the N =78 nucleus, 136 Ce were popu- lated through the 124 Sn( 16 O,4n ) fusion-evaporation reac- tion at an incident beam energy of 67 MeV. The exper- iment was performed at the IFIN Tandem Accelerator Laboratory at Magurele, Bucharest, Romania. An iso- topically enriched 124 Sn target of thickness 3.4 mg/cm 2 on Au 13 mg/cm 2 backing to stop the recoiling nuclei, was used together with a continuous DC beam over a period of 4 days. The typical on-target beam current of was approximately 10 pnA throughout the duration of the experiment. The production cross section for the 124 Sn( 16 O,4n ) 136 Ce reaction was estimated using the pace4 code [10] to be ∼400 mb. Gamma-rays were detected by the rosphere array which, in this experiment, comprised 14 high-purity ger- manium detectors (HPGe) and 11 LaBr 3 (Ce) scintilla- tor detectors [11] for gamma-ray detections. Each of the HPGe detectors were surrounded by active Compton sup- pression shields. The HPGe detectors were placed at dif- ferent angles; (six) at backward angles of -37 ◦ and -70 ◦ , Available online at www.sciencedirect.com Nuclear Data Sheets 120 (2014) 59–61 0090-3752/© 2014 Elsevier Inc. All rights reserved. www.elsevier.com/locate/nds http://dx.doi.org/10.1016/j.nds.2014.07.006