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Measurements of Equilibrium and Time-Dependent Energy Spectra of Beta Rays from Californium-252 Fission Fragments

R. A. Knief, B. W. Wehring, M. E. Wyman

Nuclear Science and Engineering

Volume 53 / Number 1 / January 1974 / Pages 47-60


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Absolute measurements were made for the equilibrium and time-dependent beta-ray energy spectra from fission fragments produced by spontaneous fission of 252Cf. The beta rays were detected by a plastic scintillator and the fission rate was monitored by a semiconductor detector. The equilibrium spectrum was measured from a 252 Cf source permanently encapsulated between two Mylar foils thick enough to stop the fragments. The time-dependent measurements used a 252Cf source supported on a thin nickel foil and covered with a thin collodion foil. Virtually all fragments from this second source escaped the foils. By use of a special transport system, the time dependence of the 252Cf beta-ray energy spectrum was measured for two cases: (a) buildup of the spectrum following initiation of fragment collection on clean catcher foils, and (b) decay of the spectrum following a period of fragment collection. The measured spectra were corrected for energy resolution effects by unfolding them with the use of a measured system response function. The measured data were used to generate empirical expressions for the equilibrium and time-dependent beta-ray spectra from 252 Cf fission fragments. The total number of beta rays from one fission was estimated to be 6.7 ± 0.3, while the total beta-ray energy was estimated to be 6.1 ± 0.5 MeV. The results of the measurements were compared with the analogous measurements for thermal-neutron fission of 235U. High-energy transitions (5 to 10 MeV) found for 235U fission were not found for 252Cf fission.

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