Search for high energy γ rays from the spontaneous fission of ²⁵²Cf

We have searched for high energy γ rays emitted from the spontaneous fission of ²⁵²Cf. This search was carried out by two methods: the measurement of high energy γ rays in coincidence with fission fragments, and the measurement of high energy γ rays in coincidence with any other γ ray. The first of these two methods allowed us to establish a direct correlation between high energy γ rays and fission fragments. For the fission-fragment/γ-ray measurement, we were able to set an upper limit at the 95% confidence level of 1.8×10^-6 photon per fission for the integrated yield of γ rays with an energy greater than 30 MeV. Additionally, we have established an upper limit at the 95% confidence level of 1.0×10^-5 photon per fission for the integrated yield of photons with energy greater than 30 MeV from the γ-γ measurement. These results are shown to be consistent with a classical model estimate of the upper limit of γ rays produced by a nucleus-nucleus bremsstrahlung process arising from the Coulomb acceleration of the fission fragments.