Eur. Phys. J. A (2020) 56: 290
https://doi.org/10.1140/epja/s10050-020-00294-7

Regular Article – Experimental Physics

Signature of a possible -cluster state in doubly-magic Ni

¹ KVI-CART, University of Groningen, NL-9747 AA, Groningen, The Netherlands
² GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
³ Department of Physics, Konan University, 658-8501, Kobe, Japan
⁴ LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, Caen, France
⁵ GANIL, CEA/DRF-CNRS/IN2P3, Bvd Henri Becquerel, 14076, Caen, France
⁶ Universidade de Santiago de Compostela, 15706, Santiago de Compostela, Spain
⁷ Research Center for Nuclear Physics, Osaka University, 567-0047, Osaka, Japan
⁸ Physics Department, University of Notre Dame, 46556, Notre Dame, IN, USA
⁹ IJCLab, Université Paris-Saclay, CNRS/IN2P3, 91405, Orsay Cedex, France
¹⁰ Institute of Nuclear Research (ATOMKI), P.O. Box 51, 4001, Debrecen, Hungary
¹¹ G.N. Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 144980, Moscow oblast, Russia
¹² National Research Nuclear Center, Moscow Engineering Physics Institute, Kashirskoe sh. 31, 115409, Moscow, Russia
¹³ Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342, Kraków, Poland
¹⁴ Instituut voor Kern- en Stralingsfysica, KU Leuven, 3001, Leuven, Belgium
¹⁵ IPN Orsay, Université Paris Sud, IN2P3-CNRS, 91406, Orsay Cedex, France
¹⁶ Irfu, CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
¹⁷ SCK CEN, Boeretang 200, 2400, Mol, Belgium
¹⁸ Indian Institute of Technology (Indian School of Mines), 826004, Dhanbad, Jharkhand, India

^a s.bagchi@gsi.de

Received: 28 April 2020
Accepted: 28 October 2020
Published online: 12 November 2020

Abstract

An inelastic -scattering experiment on the unstable , doubly-magic Ni nucleus was performed in inverse kinematics at an incident energy of 50 A.MeV at GANIL. High multiplicity for -particle emission was observed within the limited phase-space of the experimental setup. This observation cannot be explained by means of the statistical-decay model. The ideal classical gas model at kT = 0.4 MeV reproduces fairly well the experimental momentum distribution and the observed multiplicity of particles corresponds to an excitation energy around 96 MeV. The method of distributed -decay ensembles is in agreement with the experimental results if we assume that the -gas state in Ni exists at around   MeV. These results suggest that there may exist an exotic state consisting of many particles at the excitation energy of  MeV.