Evidence for bimodal fission in the heaviest elements

Conference · Sat Aug 01 04:00:00 EDT 1987

OSTI ID:6234408

Hulet, E K; Wild, J F; Lougheed, R W; Dougan, R J; Landrum, J H; Dougan, A D; Schaedel, M; Hahn, R L; Baisden, P A; Henderson, C M

We have measured the mass and kinetic-energy partitioning in the spontaneous fission of five heavy nuclides: /sup 258/Fm, /sup 259/Md, /sup 260/Md /sup 258/No, and /sup 260/(104). Each was produced by heavy-ion reactions with either /sup 248/Cm, /sup 249/Bk, or /sup 254/Es targets. Energies of correlated fragments from the isotopes with millisecond half lives, /sup 258/No and /sup 260/(104), were measured on-line by a special rotating-wheel instrument, while the others were determined off-line after mass separation. All fissioned with mass distributions that were symmetric. Total-kinetic-energy distributions peaked near either 200 or 235 MeV. Surprisingly, because only a single Gaussian energy distribution had been observed previously in actinide fission, these energy distributions were skewed upward or downward from the peak in each case, except for /sup 260/(104), indicating a composite of two energy distributions. We were able to fit accurately two Gaussian curves to the gross energy distributions from the four remaining nuclides. From the multiple TKE distributions and the shapes of the mass distributions, we conclude that there is a low-energy fission component with liquid-drop characteristics which is admixed with a much higher-energy component due to closed fragment shells. We now have further evidence for this conclusion from measurements of the neutron multiplicity in the spontaneous fission of /sup 260/Md. 25 refs., 9 figs.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6234408
• Report Number(s): UCRL-97089; CONF-870970-1; ON: DE87014553
• Country of Publication: United States
• Language: English

Related Subjects

652020* -- Nuclear Properties & Reactions
A=220 & above
Experimental
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
DATA
DECAY
DISTRIBUTION
ELEMENT 104 260
ELEMENT 104 ISOTOPES
ENERGY
ENERGY SPECTRA
EVEN-EVEN NUCLEI
EXPERIMENTAL DATA
FERMIUM 258
FERMIUM ISOTOPES
FISSION
HEAVY NUCLEI
INFORMATION
ISOTOPES
KINETIC ENERGY
MASS DISTRIBUTION
MENDELEVIUM 259
MENDELEVIUM 260
MENDELEVIUM ISOTOPES
MICROSEC LIVING RADIOISOTOPES
MILLISEC LIVING RADIOISOTOPES
NOBELIUM 258
NOBELIUM ISOTOPES
NUCLEAR REACTIONS
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
RADIOISOTOPES
SPATIAL DISTRIBUTION
SPECTRA
SPONTANEOUS FISSION