Download or read book Prompt Fission Neutron Spectra and Average Prompt Neutron Multiplicities written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We present a new method for calculating the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity anti nu/sub p/ as functions of the fissioning nucleus and its excitation energy. The method is based on standard nuclear evaporation theory and takes into account (1) the motion of the fission fragments, (2) the distribution of fission-fragment residual nuclear temperature, (3) the energy dependence of the cross section sigma/sub c/ for the inverse process of compound-nucleus formation, and (4) the possibility of multiple-chance fission. We use a triangular distribution in residual nuclear temperature based on the Fermi-gas model. This leads to closed expressions for N(E) and anti nu/sub p/ when sigma/sub c/ is assumed constant and readily computed quadratures when the energy dependence of sigma/sub c/ is determined from an optical model. Neutron spectra and average multiplicities calculated with an energy-dependent cross section agree well with experimental data for the neutron-induced fission of 235U and the spontaneous fission of 252Cf. For the latter case, there are some significant inconsistencies between the experimental spectra that need to be resolved. 29 references.
Download or read book New Calculation of Prompt Fission Neutron Spectra and Average Prompt Neutron Multiplicities written by David G. Madland and published by . This book was released on 1981 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fission Neutrons written by Nikolay Kornilov and published by Springer. This book was released on 2014-07-25 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the fission of heavy nuclei was discovered over 75 years ago, many problems and questions still remain to be addressed and answered. The reader will be presented with an old, but persistent problem of this field: The contradiction between Prompt Fission Neutron (PFN) spectra measured with differential (microscopic) experiments and integral (macroscopic and benchmark) experiments (the Micro-Macro problem). The difference in average energy is rather small ~3% but it is stable and we cannot explain the difference due to experimental uncertainties. Can we measure the PFN spectrum with high accuracy? How may we compare results of different experiments to provide better accuracy? Are our traditional theoretical models correct? What can be done to solve the Micro-Macro problem in future? These questions are discussed in this monograph for the reader. The current work will be of interest to graduate students and researchers, particularly those working in nuclear and neutron physics.
Download or read book Prompt Fission Neutron Spectra and Anti Nu P written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Methods used to obtain the evaluated prompt fisson neutron spectrum N(E) and the average prompt neutron multiplicity anti .nu./sub p/ are reviewed. The relative influence of experimental data; interpolated, extrapolated, and fitted experimental data; systematics; and nuclear theory are considered for the cases where (a) abundant experimental data exist, (b) some experimental data exist, and (c) no experimental data exist. The Maxwellian and Watt distributions, and the determination of the parameters of these distributions by data fitting, are described and compared to recent new theoretical work on the calculation of N(E). Similarly, various expressions for anti .gamma./sub p/ that have been obtained by data fitting and systematics are described and compared to recent new theoretical work. Complications in the evaluation of N(E) and anti .gamma./sub p/ due to the onset of multiple-chance fission and the interrelationships between N(E), anti .gamma delta./sub p/ and the multiple-chance fission cross section are discussed using the example of the fission of 235U. Some statistics and comments are given on the evaluations of N(E) and anti .gamma./sub p/ contained in ENDF/B-V, and a number of concluding recommendations are made for future evaluation work.
Download or read book Prompt Fission Neutron Spectra written by International Atomic Energy Agency and published by . This book was released on 1972 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Study of Fission Neutron Spectra with High energy Activation Detectors written by J. A. Grundl and published by . This book was released on 1963 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prompt Neutron Fission Spectrum Mean Energies for the Fissile Nuclides and 252Cf written by and published by . This book was released on 1985 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The international standard for a neutron spectrum is that produced from the spontaneous fission of 252Cf, while the thermal neutron induced fission neutron spectra for the four fissile nuclides, 233U, 235U, 239Pu, and 241Pu are of interest from the standpoint of nuclear reactors. The average neutron energies of these spectra are tabulated. The individual measurements are recorded with the neutron energy range measured, the method of detection as well as the average neutron energy for each author. Also tabulated are the measurements of the ratio of mean energies for pairs of fission neutron spectra. 75 refs., 9 tabs. (LEW).
Download or read book Measurement of the Average Multiplicity Prompt fission neutrons from 238 u n F and 235 u n F from 0 7 to 200 MeV written by and published by . This book was released on 2004 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prompt-fission-neutron multiplicities were measured at a 'white' neutron source for the fission of 238U and 235U up to 200 MeV. The data are of great importance in the connection of accelerator-coupled nuclear reactor systems incinerating actinides, with uranium considered as a prototype actinide. We report that the fission induced by 200 MeV neutrons produces (almost equal to)10 more prompt neutrons than the fission induced by reactor neutrons. In conclusion, new data on {bar {nu}}{sub p} are reported with errors {
Download or read book Prompt fission neutron Spectra of 233U 235U 239Pu and 24 Pu Relative to that of 252Cf 550 and 850 KeV written by and published by . This book was released on 1979 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The prompt-neutron-induced-fission spectra of 233U, 235U, 239Pu, and 24°Pu are measured relative to the prompt-spontaneous-fission-neutron spectrum of 252Cf. The fission of 233U, 235U, and 239Pu is induced by approx. = 550-keV neutrons, and that of 24°Pu, by approx. = 850-keV neutrons. The emitted fission neutrons are observed over the energy range less than or equal to 0.5 to 10.0 MeV by use of time-of-flight techniques. Analysis of the measured values indicates that the average-fission-neutron energies are -123 +- 30 (233U), -157 +- 24 (235U), -76 +- 29 (239Pu), and -46 +- 29 (24°Pu) keV relative to the energy for 252Cf. The experimental results are compared with those of ENDF/B-V, and a simple behavior of average-prompt-fission-neutron energies is suggested.
Download or read book Theory of Neutron Emission in Fission written by and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Following a summary of the observables in neutron emission in fission, a brief history is given of theoretical representations of the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity /bar /nu///sub p/. This is followed by descriptions, together with examples, of modern approaches to the calculation of these quantities including recent advancements. Emphasis will be placed upon the predictability and accuracy of the modern approaches. In particular, the dependence of N(E) and /bar /nu///sub p/ on the fissioning nucleus and its excitation energy will be discussed, as will the effects of and competition between first-, second- and third-chance fission in circumstances of high excitation energy. Finally, properties of neutron-rich (fission-fragment) nuclei are discussed that must be better known to calculate N(E) and /bar /nu///sub p/ with higher accuracy than is currently possible. 17 refs., 11 figs.
Download or read book Refinements in the Los Alamos Model of the Prompt Fission Neutron Spectrum written by and published by . This book was released on 2016 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper presents a number of refinements to the original Los Alamos model of the prompt fission neutron spectrum and average prompt neutron multiplicity as derived in 1982. The four refinements are due to new measurements of the spectrum and related fission observables many of which were not available in 1982. Here, they are also due to a number of detailed studies and comparisons of the model with previous and present experimental results including not only the differential spectrum, but also integal cross sections measured in the field of the differential spectrum. The four refinements are (a) separate neutron contributions in binary fission, (b) departure from statistical equilibrium at scission, (c) fission-fragment nuclear level-density models, and (d) center-of-mass anisotropy. With these refinements, for the first time, good agreement has been obtained for both differential and integral measurements using the same Los Alamos model spectrum.
Download or read book Theoretical Descriptions of Neutron Emission in Fission written by and published by . This book was released on 1990 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt: Brief descriptions are given of the observables in neutron emission in fission together with early theoretical representations of two of these observables, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. This is followed by summaries, together with examples, of modern approaches to the calculation of these two quantities. Here, emphasis is placed upon the predictability and accuracy of the new approaches. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are discussed. Then, recent work in multiple-chance fission and other recent work involving new measurements are presented and discussed. Following this, some properties of fission fragments are mentioned that must be better known and better understood in order to calculate N(E) and {bar {nu}}{sub p} with higher accuracy than is currently possible. In conclusion, some measurements are recommended for the purpose of benchmarking simultaneous calculations of neutron emission and gamma emission in fission. 32 refs., 26 figs.
Download or read book Calculation of Prompt Fission Neutron Spectra 0 53 MeV written by and published by . This book was released on 1979 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new calculation of the prompt fission neutron spectrum N(E) is presented as a function of both the fissioning nucleus and its excitation energy. The calculation, based upon standard nuclear-evaporation theory, accounts for the physical effects of the distribution of fission-fragment residual nuclear temperature and the energy dependence of the cross section for the inverse process of compound-nucleus formation. With the use of a residual nuclear temperature distribution based upon the Fermi-gas model, calculations were performed for two different assumptions concerning the cross section for compound-nucleus formation. Use of a constant cross section leads to a closed expression for the neutron energy spectrum, while use of an energy-dependent cross section, calculated with the optical model, yields a numerical integration. Results obtained for the two assumptions agree well with experimental data, although there is a preference for the energy-dependent cross section calculation. 7 figures.
Download or read book Event by Event Study of Prompt Neutrons from 239Pu written by and published by . This book was released on 2010 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: Employing a recently developed Monte Carlo model, we study the fission of 24°Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies of less than 2 MeV.
Download or read book Post scission Fission Theory written by and published by . This book was released on 1997 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.
Download or read book The Need for Precise and Well documented Experimental Data on Prompt Fission Neutron Spectra from Neutron induced Fission of 239Pu written by and published by . This book was released on 2016 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The spectrum of neutrons emitted promptly after 239Pu(n, f)--a so-called prompt fission neutron spectrum (PFNS)--is a quantity of high interest, for instance, for reactor physics and global security. However, there are only few experimental data sets available that are suitable for evaluations. In addition, some of those data sets differ by more than their 1-[sigma] uncertainty boundaries. We present the results of MCNP studies indicating that these differences are partly caused by underestimated multiple scattering contributions, over-corrected background, and inconsistent deconvolution methods. A detailed uncertainty quantification for suitable experimental data was undertaken including these effects, and test-evaluations were performed with the improved uncertainty information. The test-evaluations illustrate that the inadequately estimated effects and detailed uncertainty quantification have an impact on the evaluated PFNS and associated uncertainties as well as the neutron multiplicity of selected critical assemblies. A summary of data and documentation needs to improve the quality of the experimental database is provided based on the results of simulations and test-evaluations. Furthermore, given the possibly substantial distortion of the PFNS by multiple scattering and background effects, special care should be taken to reduce these effects in future measurements, e.g., by measuring the 239Pu PFNS as a ratio to either the 235U or 252Cf PFNS.
Download or read book Prompt Fission Neutron Spectra written by Międzynarodowa Agencja Energii Atomowej and published by . This book was released on 1972 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
