Spontaneous fission properties of sup 258 Fm, sup 259 Md, sup 260 Md, sup 258 No, and sup 260 (104): Bimodal fission

Journal Article · Tue Aug 01 04:00:00 EDT 1989 · Physical Review (Section) C: Nuclear Physics; (USA)

DOI:https://doi.org/10.1103/PhysRevC.40.770· OSTI ID:5665444

Hulet, E K; Wild, J F; Dougan, R J; Lougheed, R W; Landrum, J H; Dougan, A D; Baisden, P A; Henderson, C M; Dupzyk, R J ^[1]; Hahn, R L ^[2]; others, and

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1. University of California, Lawrence Livermore National Laboratory, Livermore, California 94551 (US)
2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830

We have measured the mass and kinetic-energy distributions from the spontaneous fission of {sup 258}Fm, {sup 258}No, {sup 259}Md, {sup 260}Md, and {sup 260}(104). All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property bimodal fission.'' Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have been advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in {sup 132}Sn.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5665444
• Journal Information: Physical Review (Section) C: Nuclear Physics; (USA), Journal Name: Physical Review (Section) C: Nuclear Physics; (USA) Vol. 40:2; ISSN 0556-2813; ISSN PRVCA
• Country of Publication: United States
• Language: English

Related Subjects

652020* -- Nuclear Properties & Reactions
A=220 & above
Experimental
653006 -- Nuclear Theory-- Spontaneous & Induced Fission
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
COINCIDENCE SPECTROMETRY
COUPLING
DECAY
ENERGY
ENERGY SPECTRA
EVEN-EVEN NUCLEI
FERMIUM 258
FERMIUM ISOTOPES
FISSION
FISSION FRAGMENTS
HALF-LIFE
HARTREE-FOCK METHOD
HEAVY NUCLEI
INTERMEDIATE COUPLING
INTERMEDIATE MASS NUCLEI
ISOTOPES
KINETIC ENERGY
L-S COUPLING
LIQUID DROP MODEL
MASS SPECTRA
MATHEMATICAL MODELS
MENDELEVIUM 259
MENDELEVIUM 260
MENDELEVIUM ISOTOPES
MICROSEC LIVING RADIOISOTOPES
MINUTES LIVING RADIOISOTOPES
NOBELIUM 258
NOBELIUM ISOTOPES
NUCLEAR DECAY
NUCLEAR FRAGMENTS
NUCLEAR MODELS
NUCLEAR REACTIONS
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
Q-VALUE
RADIOISOTOPES
SHELL MODELS
SPECTRA
SPONTANEOUS FISSION
TIN 132
TIN ISOTOPES