A semiconductor $\Delta E-E$ counter telescope was used to identify light charged particles spontaneously emitted from ${\mathrm{Cf}}^{252}$. From the measured partial-energy spectra of the particles, it was possible to estimate by extrapolation the following total yields of the various particle types observed. These are (in number per fission): ${\mathrm{H}}^1$(>1.6×${10}^{-4\mathrm{}}$), (${\mathrm{H}}^1$)(5.1±0.5×${10}^{-5\mathrm{}}$), ${\mathrm{H}}^2$(2.0±0.1×${10}^{-5\mathrm{}}$), ${\mathrm{H}}^3$(1.90±0.06×${10}^{-4\mathrm{}}$), ${\mathrm{He}}^3$(≲2.9×${10}^{-5\mathrm{}}$), ${\mathrm{He}}^4$(3.27±0.10×${10}^{-3\mathrm{}}$), ${\mathrm{He}}^6$(7.8±1.6×${10}^{-5\mathrm{}}$), ${\mathrm{He}}^8$(5.9±1.6×${10}^{-6\mathrm{}}$), ${\mathrm{He}}^{10}$(3±3×${10}^{-7\mathrm{}}$), Li(3.9±2.0×${10}^{-6\mathrm{}}$), Be(>3×${10}^{-7\mathrm{}}$). The ${\mathrm{H}}^1$ energy spectrum is qualitatively different from the spectra of the other particles in that it contains a large component that appears to increase greatly with decrease in energy at the lowest energies. The smaller component that remains after subtraction of this apparent background is denoted (${\mathrm{H}}^1$), and it is speculated that these are the "scission" protons. The yields were all obtained relative to the ${\mathrm{He}}^4$ yield, the value for which was taken from Thomas and Whetstone. The energy spectra of (${\mathrm{H}}^1$), ${\mathrm{H}}^2$, ${\mathrm{H}}^3$, ${\mathrm{He}}^3$, ${\mathrm{He}}^4$, ${\mathrm{He}}^6$, and ${\mathrm{He}}^8$ were found to have maxima at 9±2, 7±2, 8±1, 17±1, 16±0.5, 13±1, and ≲13 MeV and full widths at half-maximum of 6±2, 7±1, 6±1, 9.5±0.5, 11.5±0.5, 8±1, and 8±4, respectively. The yields correlate more or less as expected with Halpern's estimates of the energy required for release of the particles into the region between the fission fragments, and the dependence of the energy spectra on mass can be understood in terms of the Halpern model.

• Received 19 September 1966

DOI:https://doi.org/10.1103/PhysRev.154.1174