Event-by-Event Study of Prompt Neutrons from 239Pu

Event-by-Event Study of Prompt Neutrons from 239Pu PDF Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 9

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Book Description
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.

Event-by-Event Study of Prompt Neutrons from 239Pu

Event-by-Event Study of Prompt Neutrons from 239Pu PDF Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 9

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Book Description
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.

Event-by-event Study of Prompt Neutrons from 239Pu(n, F).

Event-by-event Study of Prompt Neutrons from 239Pu(n, F). PDF Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 19

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Book Description
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 1MeV 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.

Event-by-event Evaluation of the Prompt Fission Neutron Spectrum from 239Pu(n, F).

Event-by-event Evaluation of the Prompt Fission Neutron Spectrum from 239Pu(n, F). PDF Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10

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Book Description
We have developed an improved evaluation method for the spectrum of neutrons emitted in fission of 239Pu induced by incident neutrons with energies up to 20 MeV. The v covariance data, including incident energy correlations introduced by the v evaluation method, were used to fix the input parameters in our event-by-event model of fission, FREYA, by applying formal statistical methods. Formal estimates of uncertainties in the evaluation were developed by randomly sampling model inputs and calculating likelihood functions based on agreement with the evaluated v. Our approach is able to employ a greater variety of fission measurements than the relatively coarse spectral data alone. It also allows the study of numerous fission observables for more accurate model validation. The combination of an event-by-event Monte Carlo fission model with a statistical-likelihood analysis is thus a powerful tool for evaluation of fission-neutron data. Our empirical model FREYA follows the complete fission event from birth of the excited fragments through their decay via neutron emission until the fragment excitation energy is below the neutron separation energy when neutron emission can no longer occur. The most recent version of FREYA incorporates pre-equilibrium neutron emission, the emission of the first neutron before equilibrium is reached in the compound nucleus, and multi-chance fission, neutron evaporation prior to fission when the incident neutron energy is above the neutron separation energy. Energy, momentum, charge and mass number are conserved throughout the fission process. The best available values of fragment masses and total kinetic energies are used as inputs to FREYA. We fit three parameters that are not well under control from previous measurements: the shift in the total fragment kinetic energy; the energy scale of the asymptotic level density parameter, controlling the fragment 'temperature' for neutron evaporation; and the relative excitation of the light and heavy fragments, governing the number and energy of neutrons emitted from each fragment. The latter two parameters are assumed to be independent of the incident neutron energy while the first varies with incident energy. We describe our method and the subsequent spectral evaluation and present the results of several standard validation calculations that test our new evaluation. These benchmarks include critical assemblies, sensitive to criticality in fast systems; pulsed sphere measurements testing the spectra at incident neutron energies of 14 MeV; and other tests.

A Microscopic Theory of Fission Dynamics Based on the Generator Coordinate Method

A Microscopic Theory of Fission Dynamics Based on the Generator Coordinate Method PDF Author: Walid Younes
Publisher: Springer
ISBN: 3030044246
Category : Science
Languages : en
Pages : 326

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Book Description
This book introduces a quantum-mechanical description of the nuclear fission process from an initial compound state to scission. Issues like the relevant degrees of freedom throughout the process, the way of coupling collective and intrinsic degrees during the fission process, and how a nucleus divides into two separate daughters in a quantum-mechanical description where its wave function can be non-local, are currently being investigated through a variety of theoretical, computational, and experimental techniques. The term “microscopic” in this context refers to an approach that starts from protons, neutrons, and an effective (i.e., in-medium) interaction between them. The form of this interaction is inspired by more fundamental theories of nuclear matter, but still contains parameters that have to be adjusted to data. Thus, this microscopic approach is far from complete, but sufficient progress has been made to warrant taking stock of what has been accomplished so far. The aim is to provide, in a pedagogical and comprehensive manner, one specific approach to the fission problem, originally developed at the CEA Bruyères-le-Châtel Laboratory in France. Intended as a reference for advanced graduate students and researchers in fission theory as well as for practitioners in the field, it includes illustrative examples throughout the text to make it easier for the reader to understand, implement, and verify the formalism presented.

Nuclear Science Abstracts

Nuclear Science Abstracts PDF Author:
Publisher:
ISBN:
Category : Nuclear energy
Languages : en
Pages : 934

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Measurement of the Average Number of Prompt Neutrons Emitted Per Fission of 239 Pu and 235U

Measurement of the Average Number of Prompt Neutrons Emitted Per Fission of 239 Pu and 235U PDF Author: Oak Ridge National Laboratory. Neutron Physics Division
Publisher:
ISBN:
Category : Prompt neutrons
Languages : en
Pages : 25

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Energy Research Abstracts

Energy Research Abstracts PDF Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 518

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ERDA Energy Research Abstracts

ERDA Energy Research Abstracts PDF Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 652

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Prompt Fission Neutron Spectra

Prompt Fission Neutron Spectra PDF Author: International Atomic Energy Agency
Publisher:
ISBN:
Category : Fast neutrons
Languages : en
Pages : 196

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ERDA Energy Research Abstracts

ERDA Energy Research Abstracts PDF Author: United States. Energy Research and Development Administration
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 646

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