Eur. Phys. J. A (2004) 22: 391-395
https://doi.org/10.1140/epja/i2004-10063-3

Medium-spin excitations of the neutron-rich ⁸⁴Se isotope: Possible decrease in energy of the N = 50 neutron-core excitation

¹ CSNSM, IN2P3-CNRS/Université Paris-Sud, 91405, Orsay, France
² IReS, IN2P3-CNRS/Université Louis Pasteur, 67037, Strasbourg Cedex 2, France
³ IPNL, IN2P3-CNRS/Université Claude Bernard, 69622, Villeurbanne Cedex, France
⁴ INRNE, BAS, 1784, Sofia, Bulgaria
⁵ CEA/Saclay, DSM/DAPNIA/SPhN, 91191, Gif-sur-Yvette Cedex, France
⁶ JINR, Joliot-Curie 6, 141980, Dubna, Moscow region, Russia

Received: 23 February 2004
Accepted: 5 August 2004
Published online: 18 November 2004

Abstract

The ⁸⁴Se nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Medium-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 4.9MeV excitation energy and spin I ∼ 7ℏ. Its structure is interpreted by analogy with those of the stable heavier isotones. The evolution of the energy of the N = 50 neutron-core excitation is discussed as a function of the proton number.