Basic results of investigations of scission neutrons in nuclear fission at low excitation energies

“…The variable ν s denotes the average scission neutron contribution relative to the total prompt neutron multiplicity ν. We assume a ν s ¼ 15% and a standard deviation ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi varðν s Þ p of 50% such that it covers values put forward in [47][48][49]. It is very difficult to measure scission neutrons and hence their existence, spectrum and magnitude of ν s is still controversial and hence, such a covariance term can be questioned.…”

Section: Model Uncertainty Covariancesmentioning

confidence: 98%

“…This covariance term is based on limited information about potential scission neutron contributions to the PFNS of [47][48][49]. According to Ref.…”

Section: Model Uncertainty Covariancesmentioning

confidence: 99%

Evaluation of the 239Pu prompt fission neutron spectrum induced by neutrons of 500 keV and associated covariances

Neudecker

Talou

Kawano

et al. 2015

Nuclear Instruments and Methods in Physics Research Section A:

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a b s t r a c tWe present evaluations of the prompt fission neutron spectrum (PFNS) of 239 Pu induced by 500 keV neutrons, and associated covariances. In a previous evaluation by , surprisingly low evaluated uncertainties were obtained, partly due to simplifying assumptions in the quantification of uncertainties from experiment and model. Therefore, special emphasis is placed here on a thorough uncertainty quantification of experimental data and of the Los Alamos model predicted values entering the evaluation. In addition, the Los Alamos model was extended and an evaluation technique was employed that takes into account the qualitative differences between normalized model predicted values and experimental shape data. These improvements lead to changes in the evaluated PFNS and overall larger evaluated uncertainties than in the previous work. However, these evaluated uncertainties are still smaller than those obtained in a statistical analysis using experimental information only, due to strong model correlations. Hence, suggestions to estimate model defect uncertainties are presented, which lead to more reasonable evaluated uncertainties. The calculated k eff of selected criticality benchmarks obtained with these new evaluations agree with each other within their uncertainties despite the different approaches to estimate model defect uncertainties. The k eff one standard deviations overlap with some of those obtained using ENDF/B-VII.1, albeit their mean values are further away from unity. Spectral indexes for the Jezebel critical assembly calculated with the newly evaluated PFNS agree with the experimental data for selected (n,γ) and (n,f) reactions, and show improvements for highenergy threshold (n,2n) reactions compared to ENDF/B-VII.1.

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“…Most of these neutrons, called post-scission neutrons, are emitted from the fully accelerated Fission Fragments (FF). Some of them are emitted from the excited fissioning nucleus, before fission occurs, called pre-scission neutrons or in the moment of rupture, called scission neutrons (10-15 %) [1]. The experimental results concerning the emission of scission or pre-fission neutrons are rather contradictory due to some arbitrary assumptions made in various analyses.…”

Section: Introductionmentioning

confidence: 99%

“…The experimental results concerning the emission of scission or pre-fission neutrons are rather contradictory due to some arbitrary assumptions made in various analyses. Recently, an approach dealing with fission induced by polarized neutrons has been proposed to solve this situation [1,2] exploiting the dependence between the neutron spatial orientation and the FF flight direction. This approach is extremely difficult mostly because of the reduced events statistics.…”

Section: Introductionmentioning

confidence: 99%

Investigation of neutron emission by n-n correlation function in fission process using an array detector

Companis

Isbasescu

Mirea

et al. 2010

EPJ Web of Conferences

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Abstract. An experimental set-up designed to investigate the origin of the prompt scission neutrons in fission processes by using an array neutron detector is modeled. Quantities of interest as the correlation function strength in the momentum space within a model of independent one-particle pointlike sources, with a Gaussian distribution for the neutron generation points are obtained in a preliminary investigation. Two working hypothesis are used: i) the scission neutrons are emitted from the neck between fragments, in the final stage of the fission process, and ii) the post-scission neutrons are emitted from the accelerated fission fragments. For the scission neutrons emitted from the neck, a n-n correlation strength significantly larger than that obtained for neutrons emitted from the fission fragments is obtained. The results indicate that it is possible to discriminate scission and post-scission neutrons within an time-of-flight experimental set-up consisting from an array neutron detector combined with a VME acquisition system, using (p,xnf) reactions on actinide targets at the Bucharest Tandem.

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Basic results of investigations of scission neutrons in nuclear fission at low excitation energies

Cited by 11 publications

References 6 publications

Event-by-event study of neutron observables in spontaneous and thermal fission

Event-by-event study of neutron observables in spontaneous and thermal fission

Evaluation of the 239Pu prompt fission neutron spectrum induced by neutrons of 500 keV and associated covariances

Investigation of neutron emission by n-n correlation function in fission process using an array detector

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