Fragment mass and kinetic-energy distributions from spontaneous fission of the neutron-deficient isotopes, 1.2-sFm246and 38-sFm248.

We have measured the mass and kinetic-energy distributions for fragments from the spontaneous fission of 1.2-s ${}_{}{}^{246}{}_{}{}^{}\mathrm{Fm}$ and 38-s ${}_{}{}^{248}{}_{}{}^{}\mathrm{Fm}$. The mass distributions are highly asymmetric and the average total kinetic energies of 199±4 MeV and 198±4 MeV, respectively, are consistent with systematics for lower $Z$ actinides. Their properties are in contrast to those of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$ and ${}_{}{}^{259}{}_{}{}^{}\mathrm{Fm}$, whose spontaneous fission results in narrowly symmetric mass distributions accompanied by unusually high total kinetic energies.