| it's an important topic in fission physics to study the relations between theproduct yields from fission of 235U and the energy of induced neutrons. Also, Fissionyield data have significant application in nuclear engineering problems such asmeasuring burn-up of reactor's fuel rods and calculating the power of nuclearweapons. As far as the yield data formerly acquired are concerned, only the therlnaland 14.8MeV data were measured by many labs and were evaluated well. But forother neutron energies, the yield data are sparse and in relatively large difference. Fordecades, our Fission Yield group in China Institute of Atolnic Energy(CIAE) havemeasured several times in different period for the product yields from thermal, 3MeV.5MeV, 8MeV and 14MeV neutrons induced fission of 235U. These important yielddata have helped to clarify the contradiction of data in these energy regions, andprovided substantial support for the determination of Fission Yield-Neutron Energycurve. In this work, we continue the measurement in the energy of 0.57MeV. 1.0MeVand 1.5MeV. The results of this work should be helpful to determine how the fissionyield depends on the energy of induced neutrons in this energy region and evenregions adjacent.The chain yields of fission products were determined for the fission of235U induced by 0.57MeV,1.0MeV and 1.5MeV neutrons. Absolute fission rate wasmonitored with a double-fission chamber. Fission product activities were measured byHPGeγ-ray spectrometry. MCNP IVB was applied to simulate neutron spectrum inthe Uranium samples, and the effects of all kinds of secondary neutrons on fissionyield data were discussed. Among them, the effects of blanket target neutrons on thefission yields are less than 0.03% and then can be neglected. For the secondaryneutrons arising from elastic and inelastic scattering of monoenergetic neutrons by theaccelerator target tube and fission chamber, small corrections were made for theircontribution. Further corrections were made as required by cascade coincidence losses,self-absorption ofγ-ray in the Uranium targets, fission of isotope 238U and so on. Thenthe ultimate results of fission yields were delivered. The yield data were compared with those of other labs. Though the results of CIAE are in accordance with those ofANL within the extension of experimental uncertainties, small discrepancies of about3% do exist between the two systems. And possible reasons for the smalldifferences were presented. |
