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Physical Review Letters 08/2008; 101(3):039202. · 7.37 Impact Factor
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ABSTRACT: Taking advantage of the neutron source of the LANCSE, it has been possible to obtain a measure of the velocity distribution and the number of prompt-neutrons emitted in the neutron-induced fission of 238U and 237Np over a broad incident neutron energy range. The mean kinetic energy was extracted and is shown as a function of the incident-neutron energy. We confirm here the observation, for both reactions, of a dip around the second-chance fission which is explained by the lower kinetic energy of the pre-fission neutrons. Such a observation is reproduced by Los Alamos model as implemented at Bruyères-le-Châtel and by the Maslov model. As far as the neutron multiplicity is concerned, a similar dip is observed.
http://dx.doi.org/10.1051/ndata:07676. 01/2008;
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ABSTRACT: Prompt-fission-neutron multiplicities were measured for 238U(n,f) and 235U(n,f) from 0.4 to 200 MeV. The data are of great importance in connection with accelerator-coupled nuclear reactor systems incinerating actinides. We report that fission induced by 200 MeV neutrons produces approximately 10 more prompt neutrons than fission induced by reactor neutrons. Most neutrons are evaporated from the fission fragments and the prefission compound nucleus, as the preequilibrium emission of energetic neutrons accounts for a maximum of 15% of the prompt neutrons at 200 MeV.
Physical Review Letters 03/2005; 94(5):052701. · 7.37 Impact Factor
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ABSTRACT: A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR ''white'' neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg=cm 2 of pure 238 U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20–50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented. r 2002 Elsevier Science B.V. All rights reserved.
Nuclear Instruments and Methods in Physics Research A. 01/2002; 490:559-565.
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ABSTRACT: Energy distributions of prompt neutrons in coincidence with fission induced on 238U were measured for incident neutron energies up to 200 MeV. The double time-of-flight technique was used to deduce incident and emitted neutron energies. The experimental average and standard deviations of the fission neutron spectra (FNS), for emitted neutron energies from 0.65 to 7.5 MeV, are reported. The results compare well to predictive calculations with the improved Los Alamos model below 20 MeV incident neutron energy. The observed dip at the opening of the second chance fission channel at 6 MeV is confirmed and analyzed. Above 20 MeV, the experimental results of the FNS are smaller than the calculated ones. At 50 MeV and higher, the data suggest a slight increase of the temperature and the kinetic energy of the fission fragments.
Physics Letters B.
