Special information is implicated in energy spectra of high-energy (Eγ>3 MeV) γ-rays from the products decaying after neutron-induced fission. At Lawrence Livermore National Laboratory

a method to use the spectral information of high-energy γ-rays has been established to detect special nuclear materials. Having been exploring such a new method to measure number of nuclear fission

we experimented with enriched 235U samples irradiated by reactor thermo neutrons to measure total counts of high-energy γ-rays from the fission products at different times after fission. A variety of 3-5MeV γ-rays after 235U single nuclear fission vs time was investigated

and intensity changes of 3-5MeV γ-rays at various times after 235U fission are given in the paper.