Fragment-Mass Ratios inCf252Fission Versus Prompt Gamma-Ray Energy

$\gamma$ rays associated with the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ have been observed in the energy range 10-16 MeV using two 7.6-cm- by 29.2-cm-diam NaI(T1) crystals in coincidence with two solid-state fission counters. Evidence is presented for a $\gamma$ ray multiplicity of 2 implying the presence of a collective mode of fragment deexcitation. The fission-fragment-mass-ratio distribution shows an increase in the number of symmetric fissions when the detected $\gamma$ energy exceeds 14 MeV. It is suggested that deexcitation of the fragments by the giant dipole resonance may be responsible for the presence of the high-energy $\gamma$ rays.