12.3-minCf256and 43-minMd

Abstract

The new isotope 12.3-min ' Cf was produced via the ' Cf(t,p) reaction, and a new 43-min isomer of ' Md was produced via the ' Es(a,n) reaction. The fragment mass and kinetic energy distributions from the spontaneous fission of" Cf were found to be very similar to those from the spontaneous fission of lighter Cf isotopes. The mass division is primarily asymmetric, and the average total kinetic energy is 189.8+0.9MeV. The 43-min "Md presumably decays by electron capture and provides an opportunity to study the mass and kinetic energy distributions from the spontaneous fission of. the 380-p,s Fm daughter. The observed narrow, symmetric mass distribution and the most probable total kinetic energy of 238+3 MeV are similar to those reported for the spontaneous fission of" Fm but show a sharp increase in symmetric mass division and total kinetic energy compared to Fm and the lighter Fm isotopes. No such abrupt change in properties was observed for "Cf, which, like "Fm, has 158 neutrons. The marked difference between the spontaneous fission properties of the heavier Fm isotopes and those of other spontaneously fissioning nuclides is compared to some theoretical predictions. RADIOACTIVITY, FISSIONCf (SF); measured T&~&, fragment-fragment coin; deduced TKE, mass distribution. Md; measured''~g2, . EC decay to 5 Fm (SF); measured fragment-fragment coin; deduced TKK, mass distribution.

Fission modes ofFm256andFm258in a microscopic app

“…Whichever valley is eventually followed by the spontaneously fissioning nucleus towards scission, the outcome is the same in terms of mass fragmentation since in either valley the configurations are left-right symmetric. This leads thus to a symmetric mass distribution, as was obtained in all the other theoretical sudies and in agreement with experiment [6,7].…”

“…Based on the results from the Argonne group published the following year [4] and showing the asymmetric character of the spontaneous fission of 256 Fm, they concluded that "symmetric mass division in low-energy fission of heavy actinides appears abruptly at 257 Fm". This was confirmed later in the measurements by Hulet and collaborators [5,6,7] who found very narrow symmetric mass distributions in the spontaneous fission of 258 Fm and 259 Fm.…”

“…Another remarkable spontaneous-fission property that rapidly changes along the Fm isotopic chain is the fragment kinetic-energy distribution: it is very well reproduced by a single Gaussian for A 256 with an average total kinetic energy TKE that follows the Viola systematics [6,8], whereas heavier isotopes have a much higher TKE-value. This is particularly the case for 258 Fm where Hulet et al [9] found that the total-kinetic-energy distribution has a non-Gaussian shape which can be unfolded into two Gaussians.…”

Four-dimensional Langevin approach to low-energy nuclear fission of U236

“…In Fig. 5 (b), we compare our E x = 7.5 MeV result with 258 Fm spontaneous fission data [26] and n th + 257 Fm fission data [27]. A strong single peak component can be seen in both experimental data.…”

Actinide production in reactions of heavy ions with 248Cm

“…We have performed several experiments in which the actin1de products from the interactions of 18 o, 86 Kr and 136 xe with 248 cm were ch~mically isolated and their cross sections determined. We use these data, along with literature results from the 48 ca + 248 cm systeml,lO and from the 238 u .…”