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Stetcu, Ionel

Publications and source records attributed to Stetcu, Ionel.

72 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Correlated fission data measurements with DANCE and NEUANCE

To enhance the capabilities of the DANCE array, a new detector array NEUANCE was developed to enable simultaneous measurements of prompt fission neutrons and γ rays. NEUANCE was designed and constructed using 21 stilbene organic scintillator crystals. It was installed in the central cavity of the DANCE array. Signals from the 160 BaF 2 detectors of DANCE and the 21 detectors of NEUANCE were merged into a newly designed high-density high-throughput data acquisition system. The excellent pulse shape discrimination properties of stilbene enabled detection of neutrons with energy thresholds as low as 30–40 keVee. A fission reaction tagging method was developed using a NEUANCE γ-ray or neutron signal. The probability of detecting a neutron from the spontaneous fission of 252 Cf using NEUANCE is 47%. New correlated data for prompt fission neutrons and prompt fission rays were obtained for 252 Cf using this high detection efficiency experimental setup. In conclusion, average properties of prompt fission neutron emission as a function of prompt fission γ-ray quantities were also obtained, suggesting that neutron and γ-ray emission in fission are correlated.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Prompt fission neutron and gamma ray properties as a function of incident neutron energy

The CGMF code provides a complete description of the properties of the prompt neutrons and γ rays, emitted before beta decays. It is based on a Monte Carlo implementation of the Hauser-Feshbach statistical model, which provides an accurate phenomenological description of the de-excitation of the fission fragments toward stable configurations via neutron and γ-ray emissions. This approach allows a detailed description of a large number of observables, such as multiplicity probabilities and correlations between the emitted particles. In this contribution, we briefly review the approach and present selected examples of neutron and γ-ray observables for neutron incident energies from thermal to 20 MeV, and compare against available data for 235 U(n,f) reaction.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Late-time emission of prompt fission γ rays

The emission of prompt fission γ rays within a few nanoseconds to a few microseconds following the scission point is studied in the Hauser-Feshbach formalism applied to the deexcitation of primary excited fission fragments. Neutron and γ-ray evaporations from fully accelerated fission fragments are calculated in competition at each stage of the decay, and the role of isomers in the fission products, before β decay, is analyzed. The time evolution of the average total γ-ray energy, the average total γ-ray multiplicity, and the fragment-specific γ-ray spectra is presented in the case of neutron-induced fission reactions of 235 U and 239 Pu, as well as spontaneous fission of 252 Cf. The production of specific isomeric states is calculated and compared to available experimental data. About 7% of all prompt fission γ rays are predicted to be emitted between 10 ns and 5 μs following fission, in the case of 235 U and 239 Pu( n th ,f) reactions, and up to 3% in the case of 252 Cf spontaneous fission. The cumulative average total γ-ray energy increases by 2% to 5% in the same time interval. Lastly, those results are shown to be robust against significant changes in the model input parameters.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Neutron-induced fission: properties of prompt neutron and γ rays as a function of incident energy

We have applied the Hauser-Feshbach statistical theory, in a Monte-Carlo implementation, to the de-excitation of fission fragments, obtaining a reasonable description of the characteristics of neutrons and gamma rays emitted before beta decays toward stability. Originally implemented for the spontaneous fission of 252 Cf and the neutroninduced fission of 235 U and 239 Pu at thermal neutron energy, in this contribution we discuss the extension of the formalism to incident neutron energies up to 20 MeV. For the emission of pre-fission neutrons, at incident energies beyond second-chance fission, we take into account both the pre-equilibrium and statistical pre-fission components. Phenomenological parameterizations of mass, charge and TKE yields are used to obtain the initial conditions for the fission fragments that subsequently decay via neutron and emissions. Finally, we illustrate this approach for 239 Pu(n,f).

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Induced fission of Pu 240 within a real-time microscopic framework

Here, we describe the fissioning dynamics of 240 Pu from a configuration in the proximity of the outer fission barrier to full scission and the formation of the fragments within an implementation of density functional theory extended to superfluid systems and real-time dynamics. The fission fragments emerge with properties similar to those determined experimentally, while the fission dynamics appears to be quite complex, with many excited shape and pairing modes. The evolution is found to be much slower than previously expected, and the ultimate role of the collective inertia is found to be negligible in this fully nonadiabatic treatment of nuclear dynamics, where all collective degrees of freedom (CDOF) are included (unlike adiabatic treatments with a small number of CDOF).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Monte Carlo Hauser-Feshbach Calculations of Prompt Fission Neutrons and Gamma Rays: Application to Thermal Neutron-Induced Fission Reactions on U-235 and Pu-239

We have developed a new code CGMF , implementing a Monte Carlo version of the Hauser-Feshbach statistical theory of nuclear reactions and applied to the de-excitation of fission fragments. A parallel version of the code has been developed as well, and was used to produced the results presented in this report. Prompt fission neutron and gamma-ray characteristics have been computed for the thermal neutron-induced fission reactions on 235 U and 239 Pu. We discuss the status of these calculations and how the results compare to available experimental data.

Atomic and Nuclear Physics↗
DOE OSTI2012

Uncertainty Quantification with Monte Carlo Hauser-Feshbach Calculations of Prompt Fission Neutrons and Gamma Rays

We have performed sensitivity calculations using the CGMF code that implements the statistical Hauser-Feshbach equations in a Monte Carlo fashion to describe the de-excitation of fission fragments by emis sion of prompt neutrons and gamma rays. The specific importance of several input quantities is emphasized. An uncertainty quantification method, considering sources of uncertainty from both model calculations and experiments, is outlined.

Atomic and Nuclear Physics↗