Role of the second barrier upon mass division in the spontaneous fission of the heaviest elements
- University of California, Lawrence Livermore National Laboratory, Livermore, California (United States)
In the region where theorists had earlier predicted the disappearance of the outer fission barrier or its dropping below the ground state, the mass and total kinetic-energy distributions from spontaneous fission of [sup 252]No, [sup 254]No, [sup 256][104], and [sup 258][104] have been measured. The results, in combination with earlier measurements for [sup 256]No, [sup 258]No, and [sup 262]No, show a sharp transition from the asymmetrical mass division in [sup 256]No to the symmetrical mass division for [sup 258]No and [sup 262]No. Conversely, all isotopes of element 104, including [sup 260][104], appear to yield broadly symmetrical mass distributions. The total kinetic energies around 200 MeV for the 104 isotopes indicate the fission by the low-energy mode of bimodal fission. Based on the hypothesis that the second barrier is responsible for the asymmetrical mass distributions, and when it disappears, for symmetrical ones, these observations for the isotopes of element 104 are in agreement with the 1976 calculations of the heights of the second fission barrier relative to the ground state. Some recent calculations of static potential-energy surfaces and of barrier heights deduced from half lives for spontaneous fission indicate that the second barrier is from 0 to 2.9 MeV above the ground state for the No and 104 isotopes. However, shape degrees of freedom have been limited in these calculations; therefore, they fail to provide realistic heights for the outer fission barrier. For the few cases where higher-order asymmetrical deformations are included, this barrier height is well below the ground state and, for these nuclides, symmetrical mass division only is observed. Without more extensive calculations of potential-energy surfaces for comparison with the findings, a firm conclusion about the role of the second barrier upon mass division in fission is impossible to obtain.
- OSTI ID:
- 6972171
- Journal Information:
- Physics of Atomic Nuclei (English Translation); (United States), Journal Name: Physics of Atomic Nuclei (English Translation); (United States) Vol. 57:7; ISSN 1063-7788; ISSN PANUEO
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
663590 -- Nuclear Mass Ranges-- A=220 & Above-- (1992-)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ALPHA DECAY RADIOISOTOPES
BETA DECAY RADIOISOTOPES
DECAY
DEFORMATION
DEGREES OF FREEDOM
DISTRIBUTION
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
ENERGY
ENERGY LEVELS
EVEN-EVEN NUCLEI
FISSION
FISSION BARRIER
GROUND STATES
HEAVY NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
KINETIC ENERGY
MASS DISTRIBUTION
MILLISEC LIVING RADIOISOTOPES
NOBELIUM 252
NOBELIUM 254
NOBELIUM 256
NOBELIUM 258
NOBELIUM 262
NOBELIUM ISOTOPES
NUCLEAR DECAY
NUCLEAR POTENTIAL
NUCLEAR REACTIONS
NUCLEI
POTENTIALS
RADIOISOTOPES
SEC
SECONDS LIVING RADIOISOTOPES
SPATIAL DISTRIBUTION
SPONTANEOUS FISSION
SPONTANEOUS FISSION RADIOISOTOPES
TRANS 104 ELEMENTS
TRANSPLUTONIUM ELEMENTS
TRANSURANIUM ELEMENTS