DOI 10.1140/epja/i2002-10126-5 Eur. Phys. J. A 17, 1–5 (2003) T HE EUROPEAN P HYSICAL JOURNAL A Short Note Spectroscopy of the neutron-deficient nuclide 171 Pt T. B¨ack 1, a , B. Cederwall 1 , K. Lagergren 1 , R. Wyss 1 , A. Johnson 1 , P. Greenlees 2 , D. Jenkins 4 , P. Jones 2 , D.T. Joss 3, b , R. Julin 2 , S. Juutinen 2 , A. Keenan 2 , H. Kettunen 2 , P. Kuusiniemi 2 , M. Leino 2 , A.-P. Lepp¨ anen 2 , M. Muikku 5 , P. Nieminen 2 , J. Pakarinen 2 , P. Rahkila 2 , and J. Uusitalo 2 1 Department of Physics, Royal Institute of Technology, SE-10691 Stockholm, Sweden 2 Department of Physics, University of Jyv¨askyl¨a, P.O. Box 35, FIN-40351, Jyv¨askyl¨a, Finland 3 School of Chemistry and Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK 4 Oliver Lodge Laboratory, Department of Physics, University of Liverpool, Liverpool, L69 7ZE, UK 5 STUK - Radiation and Nuclear Safety Authority, P.O. Box 14, 00881 Helsinki, Finland Received: 5 December 2002 / Published online: 15 April 2003 – c  Societ` a Italiana di Fisica / Springer-Verlag 2003 Communicated by C. Signorini Abstract. A number of previously unobserved γ-rays emitted from the neutron-deficient nuclide 171 Pt have been identified using the recoil decay tagging technique. The level scheme has been updated using infor- mation from γ-γ coincidences and angular distribution measurements. To further confirm the assignments of the γ-rays to 171 Pt, the events were correlated with the alpha-decay of the daughter nucleus 167 Os. PACS. 23.20.Lv Gamma transitions and level energies – 27.70.+q 150 ≤ A ≤ 189 1 Introduction The region near the proton drip line around A = 170 has been an object of intense investigation in the last few years [1–11]. Studies have revealed a richness in phys- ical phenomena like shape coexistence and vibrational structures. The study of the lightest nuclides in the re- gion presents a difficult challenge. The production cross- sections in suitable fusion-evaporation reactions using sta- ble beams and targets lie in the μb or sub-μb region. Fur- thermore, these weakly populated nuclear species have to be detected and identified in an intense γ -ray background from fusion-evaporation channels closer to stability, fis- sion, transfer reactions, Coulomb excitation, etc., as well as radioactivity. The experimental access to excited states in this re- gion of the nuclear chart relies on the predominance of alpha (or proton) unstable ground- or low-lying excited states. The highly selective and efficient recoil decay tag- ging (RDT) technique [12,13] has thus provided a crucial experimental tool for structural studies of heavy neutron- deficient nuclei. In this method the characteristic particle decay energies are measured in a focal-plane detector of a a e-mail: back@nuclear.kth.se b Present address : CRLC, Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK. recoil mass filtering device and correlated with the prompt γ -rays detected near the target. The platinum isotopes exhibit collective bands which indicate underlying structural changes as the proton drip line is approached [1]. Near the stability line their ground states are characterised by near-oblate shapes with rather small quadrupole deformations. The yrast levels in the odd isotopes have been assigned to νi 13/2 configurations and have spacings very similar to the corresponding lev- els in the even isotopes, indicating a decoupling of the odd i 13/2 neutron from the core. This situation is drasti- cally changed as we approach the neutron mid-shell. Here (100 ≤ N ≤ 108), the similarity of level spacings is lost, pushing the lowest excited states for the odd isotopes up in energy relative to those in the even isotopes. This can be interpreted as a transition into a region of strongly cou- pled configurations, characterised by a prolate core and a high Ω-value for the odd i 13/2 particle. As we continue towards the proton drip line, the situation changes again. For N ≤ 98, a prolate band and a weakly deformed triax- ial band are predicted to coexist. Indeed, the ground-state bands of 176 Pt [14,15] and 174 Pt [16] show strongly per- turbed rotational patterns. When comparing the level energies of 171 Pt and 172 Pt [1] (N = 93 and N = 94), the pattern changes once again. Here, the similarity of level spacings between