DOI 10.1140/epja/i2002-10005-1 Eur. Phys. J. A 14, 137–146 (2002) T HE EUROPEAN P HYSICAL JOURNAL A c  Societ` a Italiana di Fisica Springer-Verlag 2002 High-resolution in-beam particle spectroscopy —New results on prompt proton emission from 58 Cu D. Rudolph 1, a , D.G. Sarantites 2 , C. Andreoiu 1 , C. Fahlander 1 , D.P. Balamuth 3 , R.J. Charity 2 , M. Devlin 2, b , J. Eberth 4 , A. Galindo-Uribarri 5 , P.A. Hausladen 3, c , D. Seweryniak 6 , L.G. Sobotka 2 , and Th. Steinhardt 4 1 Department of Physics, Lund University, S-22100 Lund, Sweden 2 Chemistry Department, Washington University, St. Louis, MO 63130, USA 3 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA 4 Institut f¨ ur Kernphysik, Universit¨at zu K¨ oln, D-50937 K¨ oln, Germany 5 Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 6 Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA Received: 11 March 2002 / Revised version: 4 April 2002 Communicated by D. Schwalm Abstract. Prompt proton decay lines in 58 Cu have been studied by means of high-resolution in-beam particle-γ coincidence spectroscopy using the gammasphere Ge-detector array in conjunction with a dedicated set of ancillary detectors including four ΔE-E silicon-strip telescopes. High-spin states in 58 Cu have been populated via the heavy-ion fusion-evaporation reaction 28 Si( 36 Ar, 1α1p1n) at 148 MeV beam energy. The full-width at half maximum for the proton peak could be reduced significantly compared to earlier experiments. The results indicate that only one prompt proton decay branch exists in the decay-out of the well-deformed band of 58 Cu. PACS. 23.20.Lv Gamma transitions and level energies – 23.50.+z Decay by proton emission – 27.40.+z 39 ≤ A ≤ 58 1 Introduction In proton-rich nuclei in the vicinity of 56 Ni a new nuclear decay mode called prompt particle emission has been es- tablished during recent years. The first case of prompt proton emission from excited high-spin states in the well- deformed second minimum of the nuclear potential into spherical daughter states had been identified in 58 Cu [1]. In the following, additional prompt proton decays have been found in 56 Ni [2] and 59 Cu [3, 4], and a case of prompt α-particle emission has been observed in 58 Ni [5]. The decay mode is called “prompt”, because the for- mation of the residual nucleus, the γ -decay of the rota- tional band in the second minimum, the particle emis- sion, and finally the γ -decay in the daughter nucleus are observed in “prompt” coincidence in thin-target in-beam fusion-evaporation experiments, which have a typical ob- servation time window of less than three nanoseconds. Thereafter, the recoiling nuclei have left both the focus of a e-mail: Dirk.Rudolph@kosufy.lu.se b Present address: LANSCE-3, Los Alamos National Labo- ratory, Los Alamos, NM 87545, USA. c Present address: Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. the Ge-detector array and the charged-particle detection system surrounding the target position. The particle de- cays compete with the conventional γ -decay-out, and they may be viewed as self-regulated two-dimensional quantum tunneling processes: The problem is two dimensional, be- cause the initial states are prolate deformed with a long- to-short axis ratio of about 1.5:1 (see, e.g., refs. [1, 6]). The process is self-regulated, because the emission of the parti- cles induces a drastic rearrangement of the nuclear mean- field potential, since the final states are spherical or even slightly oblate deformed. In fact, the shape change associ- ated with the decay mode seems to cause major problems in the theoretical description of the process, though pro- ton decay rates from spherical-to-spherical or deformed- to-deformed states are well understood based on signif- icant recent advances in the theoretical modelling (see, e.g., refs. [7–11] and references therein). In turn, the exper- imental knowledge concerning the prompt proton decays has been increased systematically following the first obser- vation of the decay mode [1]. The focus has been on 58 Cu, where spins and parities of the initial and final state could be assigned [6,12] and lifetimes of γ - and proton-decaying states have been measured in the decay-out regime of the rotational band [6, 13].