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Delayed Gammas from Fast-Neutron Fission of Th 232 , U 233 </mml:…

1964; American Institute of Physics; Volume: 134; Issue: 4B Linguagem: Inglês

10.1103/physrev.134.b796

1536-6065

P. C. Fisher, L.B. Engle,

Nuclear reactor physics and engineering

Results of an experiment are presented in which the energy and time dependence of gammas emitted after instantaneous fast-neutron-induced fission of ${\mathrm{Th}}^{232}$, ${\mathrm{U}}^{233}$, ${\mathrm{U}}^{235}$, ${\mathrm{U}}^{238}$, and ${\mathrm{Pu}}^{239}$ were measured. Gammas having energies between 0.12 and 6.5 MeV were detected during five short time intervals between 0.2 sec and 45.0 sec after fission occurred. The measured spectra and seventeen bin distributions of the absolute number of photons/fission-sec-MeV and intercomparisons and integrations over energy and time of these distributions are given. The rate of energy emission from the products of ${\mathrm{Th}}^{232}$+$n$ was found to be 4.5 times higher than that from ${\mathrm{Pu}}^{239}$+$n$ during the first time interval after fission. Delayed gamma spectra from the products of ${\mathrm{Th}}^{232}$+$n$ are noticeably harder than those from ${\mathrm{Pu}}^{239}$+$n$ during all five time intervals measured. The several uranium isotopes' behavior is intermediate to that of the products of ${\mathrm{Th}}^{232}$+$n$ and ${\mathrm{Pu}}^{239}$+$n$ in both rate of energy emission and hardness of energy spectra. The significant differences in the measured characteristics of the delayed gammas from the five fissionable isotopes permit the isotopes to be arranged in a sequence. Approximate position in the sequence depends on $\overline{z}$, the average displacement of the initial fragment distribution from fission. It appears possible to predict approximate values of delayed neutron yield, which Keepin has shown to also depend on $\overline{z}$, of other fissionable isotopes on the basis of delayed gamma measurements.