Emission of Long-Range Alpha Particles in the Spontaneous Fission ofCf252

Abstract

An experimental investigation of $\ensuremath{\alpha}$-particle emission in the spontaneous fission of ${\mathrm{Cf}}^{252}$ is described. The measured angular distribution and energy distribution of the $\ensuremath{\alpha}$ particles are presented, as well as the mass-ratio distribution of the fission fragments and the single-fragment energy distribution in fission accompanied by long-range $\ensuremath{\alpha}$ particles (LRA fission). Also shown is the angular distribution of the $\ensuremath{\alpha}$ particles as a function of the $\ensuremath{\alpha}$-particle energy, the total fission-fragment energy, and the mass ratio. The experimental results show the LRA-fission process to be very similar to binary fission until the moment of scission. The angular distribution of the $\ensuremath{\alpha}$ particles as a function of the mass ratio (corrected for $\ensuremath{\alpha}$-particle recoil) confirms the earlier conclusion that the scission point moves towards the light fragment as the mass ratio increases. The experimental results provide evidence that the $\ensuremath{\alpha}$ particle is emitted very close to the scission point and within ${10}^{\ensuremath{-}21}$ sec of the moment of scission. The angular distribution data support the model which explains the variation of the number of neutrons emitted in binary fission as a function of fragment mass on the basis of a variation in the nuclear deformation of the fission fragments at scission.