Decay of excited nuclei produced in {sup 78,82}Kr+{sup 40}Ca reactions at 5.5 MeV/nucleon
- Grand Accelerateur National d'Ions Lourds (GANIL), CEA/DSM-CNRS/IN2P3, Boulevard H. Becquerel, F-14076, Caen (France)
- Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
- Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', I-80126, Napoli (Italy)
- Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation)
- IPHC, IN2P3-CNRS, F-67037, Strasbourg Cedex 2 (France)
- INFN, Sezione di Firenze, I-50125 Firenze (Italy)
- IPNO, IN2P3-CNRS and Universite Paris-Sud 11, F-91406, Orsay Cedex (France)
- LPC, IN2P3-CNRS, ENSICAEN and Universite, F-14050, Caen Cedex (France)
- CEA, IRFU, SPhN, CEA/Saclay, F-91191, Gif-sur-Yvette Cedex (France)
Decay modes of excited nuclei are investigated in {sup 78,82}Kr+{sup 40}Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the 4{pi} INDRA array. Kinetic-energy spectra and angular distributions of fragments with atomic number 3 {<=}Z{<=} 28 indicate a high degree of relaxation and are compatible with a fissionlike phenomenon. Persistence of structure effects is evidenced from elemental cross sections ({sigma}{sub Z}) as well as a strong odd-even staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross section of the {sup 78}Kr+{sup 40}Ca reaction is slightly higher than the one measured in the {sup 82}Kr+{sup 40}Ca reaction. The fissionlike component is larger by {approx}25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to Z = 14 in their ground states as well as excited states does not account for the main features of {sigma}{sub Z}. For both reactions, the transition-state formalism reasonably reproduces the Z distribution of the fragments with charge 12 {<=}Z{<=} 28. However, this model strongly overestimates the light-fragment cross sections and does not explain the o-e-s of the yields for 6 {<=}Z{<=} 10. The shape of the whole Z distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition among evaporation, fusion-fission, and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 {<=}Z{<=} 22 could signal a mechanism in addition to the capture process.
- OSTI ID:
- 21502490
- Journal Information:
- Physical Review. C, Nuclear Physics, Vol. 83, Issue 5; Other Information: DOI: 10.1103/PhysRevC.83.054619; (c) 2011 American Institute of Physics; ISSN 0556-2813
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANGULAR DISTRIBUTION
ASYMMETRY
ATOMIC NUMBER
CALCIUM 40 REACTIONS
CAPTURE
CROSS SECTIONS
EMISSION
EXCITATION
EXCITED STATES
FISSION
FORECASTING
GROUND STATES
KINETIC ENERGY
KRYPTON 78 TARGET
KRYPTON 82 TARGET
MEV RANGE 01-10
NUCLEAR DECAY
NUCLEAR FRAGMENTS
QUASI-FISSION
RELAXATION
DECAY
DISTRIBUTION
ENERGY
ENERGY LEVELS
ENERGY RANGE
ENERGY-LEVEL TRANSITIONS
HEAVY ION REACTIONS
MEV RANGE
NUCLEAR REACTIONS
TARGETS