Eur. Phys. J. A 4, 9–10 (1999) T HE EUROPEAN P HYSICAL JOURNAL A c  Springer-Verlag 1999 Short note A new high-spin isomer in 145 Sm K. Jessen 1 , W. Andrejtscheff 1,3 , M. Bergstr¨ om 2 , P. von Brentano 1 , A. Dewald 1 , B. Herskind 2 , H. Meise 1 , C. Schumacher 1 , G. Sletten 2 , O. Stuch 1 , D. Weißhaar 1 , I. Wiedenh¨ over 1 , J. Wrzesinski 2 1 Institut f¨ ur Kernphysik, Universt¨at zu K¨ oln, Z¨ ulpicher Straße 77, D–50937 K¨oln, Germany, e-mail: ian@ikp.Uni-Koeln.DE 2 Niels Bohr Institute, University of Copenhagen, DK–4000 Roskilde, Denmark 3 Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, BG–1784 Sofia, Bulgaria Received: 23 October 1998 Communicated by B. Povh Abstract. A new high-spin isomer in 145 Sm was observed by in-beam γ-ray spectroscopy with the reaction 122 Sn( 27 Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined to be Ex = 11147 keV, and using the generalized centroid-shift method its half-life was found to be T 1/2 = (7.4 ± 1.0) ns. PACS. 21.10.Tg Lifetimes – 25.70.Gh Compound nucleus – 27.60.+j 90 ≤ A ≤ 149 In the late seventies, Døssing et al. predicted the existence of yrast isomers in the A ≈ 150 region [1], and experiments provided first data on excitation energies and half-lives of such isomers. Later on, the accompanying decay schemes were reported. The most prominent of these isomers were observed in N = 83 isotones at excitation energies of 8–9 MeV with half-lives of 0.01–1 μs, but isomers at higher energies were also reported, e.g. in 149 Tb [2] and 151 Er [3]. Recently, Odahara et al. extended the level scheme of 145 Sm to the part above the μs isomer [4,5], which made the search for ns isomers at very high spins possible for this nucleus. In the 122 Sn( 27 Al,3np) reaction, the nucleus 145 Sm was produced at a beam energy of 127 MeV at the Niels Bohr Institute’s Tandem Accelerator Laboratory in Roskilde. The target consisted of a 1.5 mg/cm 2 tin foil enriched to 95.8% on a 10 mg/cm 2 181 Ta backing. A total of 6.8 × 10 8 γ –γ -coincidence events were registered with the Nord- ball detector array. The 60-segment BaF 2 inner ball of this spectrometer, surrounded by 20 HPGe detectors, sup- plies a precise time reference signal given by the BaF 2 element firing first. For any γ –γ -coincidence event, time differences between this reference and the Ge signals were recorded. The off-line analysis of time-related γ -ray spectra pro- vided evidence for the delay of a 1195 keV line (Fig. 1), that was observed in our data. Setting a gate on this tran- sition in our γ –γ -coincidence matrix revealed a clean spec- trum. The observed lines in this spectrum unambigously assign the 1195 keV transition to the 145 Sm high-spin level scheme, which lies above the μs isomer at 8786 keV exci- Fig. 1. Cut outs of a prompt and two delayed spectra. The line at 1195 keV becomes more intense for more delayed times of detection. Other delayed lines originate from known isomers tation energyas reported by Odahara et al. [5]. A second transition (1188 keV) belonging to this part of the 145 Sm level scheme turned out to be prompt and therefore pro- vided evidence for a new high-spin isomer in the ns range. In order to separate the required data from other exit channels well, we sorted three gated energy-time matrices with gates at 270, 1188, and 1195 keV, containing 9.5×10 5 , 1.3 × 10 5 , and 1.4 × 10 5 events, respectively.