Asymmetric Fission in the ⁷⁸Kr+⁴⁰Ca reactions at 5.5 MeV/nucleon

¹ Grand Accélérateur National d’Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Bvd H. Becquerel, 14076, Caen, France
² Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
³ Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, I-80126, Napoli, Italy
⁴ INFN, Sezione di Napoli, I-80126, Napoli, Italy
⁵ IPHC, IN2P3-CNRS and Université Strasbourg, F-67037, Strasbourg Cedex2, France
⁶ INFN, Sezione di Firenze, I-50125 Firenze, Italy
⁷ IPNO, IN2P3-CNRS and Université Paris-Sud 11, F-91406, Orsay Cedex, France
⁸ LPC, IN2P3-CNRS, ENSICAEN and Université, F-14050, Caen Cedex, France
⁹ CEA, IRFU, SPhN, CEA/Saclay, F-91191, Gif-sur-Yvette Cedex, France
¹⁰ INFN, LNL, I-35020 Legnaro (Padova) Italy
¹¹ INFN, Sezione di Bologna, I-40127 Bologna, Italy
¹² IPNL, IN2P3-CNRS et Université, F-69622, Villeurbanne Cedex, France
¹³ Laboratoire de Physique Nucléaire, Université de Laval, Québec, Canada
¹⁴ Dipartimento di Scienze Ambientali, Seconda UniversitÀ di Napoli, I-81100, Caserta, Italy

^a e-mail: wieleczko@ganil.fr

Abstract

The cross section, kinetic energy distribution and angular distribution of fragments with atomic number 3 ≤ Z ≤ 28 emitted in the reaction ⁷⁸Kr + ⁴⁰Ca at the bombarding energy of 5.5 MeV/nucleon and coincidence between light charged particles and fragments were measured by means of the 4π-INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong even-odd-staggering (o-es) is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations assuming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parameterization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.