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Jaffke, Patrick John

Publications and source records attributed to Jaffke, Patrick John.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Prompt fission product yields in the U 238 ( n , f ) reaction

Background: Significant yield discrepancies (500-600%) were reported recently between experi- mental results and predictions (from the GEF model) and evaluations (from the JEFF-3.1.1 and ENDF/B-VII.1 libraries) for Mo and Sn fission-fragment yields in fast-neutron induced reactions on 238 U using γ-γ-γ coincidence spectroscopy. The model/evaluations also predict Mo and Sn fragments that are on average ~1 to 2 neutrons richer than the experimental results. Purpose: γ-γ-γ coincidence spectroscopy favors detection of higher-multiplicity γ-ray cascades. An alternative approach is determining the fragment yields using single-γ-ray spectroscopy, as it was attempted here for selected cases where it was feasible. Advantages/drawbacks in both approaches need to be understood and potential systematic errors in the experimental results should be addressed using theoretical models. Methods: Fast neutrons from the LANSCE WNR facility were used to induce fission on 238 U. The emitted γ rays were measured with the GEANIE spectrometer. Results: The yield of selected even-even fission fragments was determined. The selection was based on the ability to reliably determine excitation functions for the detected γ rays. Conclusions: Our single-γ-ray results provide better agreement between experiment and predictions/evaluations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Hauser-Feshbach fission fragment de-excitation with calculated macroscopic-microscopic mass yields

The Hauser-Feshbach statistical model is applied to the de-excitation of primary fission fragments using input mass yields calculated with macroscopic-microscopic models of the potential energy surface. We test the sensitivity of the prompt fission observables to the input mass yields for two important reactions, 235 U (n th , f) and 239 Pu (n th , f) , for which good experimental data exist. General traits of the mass yields, such as the location of the peaks and their widths, can impact both the prompt neutron and γ-ray multiplicities, as well as their spectra. Specifically, we use several mass yields to determine a linear correlation between the calculated prompt neutron multiplicity $\bar{v}$ and the average heavy-fragment mass $\langle$A h $\rangle$ of the input mass yields ∂$\bar{v}$/∂ $\langle$A h $\rangle$ = ± 0.1 (n / f )/u . The mass peak width influences the correlation between the total kinetic energy of the fission fragments and the total number of prompt neutrons emitted, $\bar{v}_T$ ( TKE ) . Finally, typical biases on prompt particle observables from using calculated mass yields instead of experimental ones are δ$\bar{v}$ = 4 % for the average prompt neutron multiplicity, δ$\overline{M}_γ$ = 1% for the average prompt γ-ray multiplicity, δ$\bar{ε}$ $LAB\atop{n}$ = 1 % for the average outgoing neutron energy, δ$\bar{ε}_γ$ = 1 % for the average γ-ray energy, and δ $\langle$TKE$\rangle$ = 0.4 % for the average total kinetic energy of the fission fragments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Sensitivity Analysis of Cf-252 (sf) Neutron and Gamma Observables in CGMF

CGMF is a Monte Carlo code that simulates the decay of primary fission fragments by emission of neutrons and gamma rays, according to the Hauser-Feshbach equations. As the CGMF code was recently integrated into the MCNP6.2 transport code, great emphasis has been placed on providing optimal parameters to CGMF such that many different observables are accurately represented. Of these observables, the prompt neutron spectrum, prompt neutron multiplicity, prompt gamma spectrum, and prompt gamma multiplicity are crucial for accurate transport simulations of criticality and nonproliferation applications. This contribution to the ongoing efforts to improve CGMF presents a study of the sensitivity of various neutron and gamma observables to several input parameters for Californium-252 spontaneous fission. Among the most influential parameters are those that affect the input yield distributions in fragment mass and total kinetic energy (TKE). A new scheme for representing Y(A,TKE) was implemented in CGMF using three fission modes, S1, S2 and SL. The sensitivity profiles were calculated for 17 total parameters, which show that the neutron multiplicity distribution is strongly affected by the TKE distribution of the fragments. The total excitation energy (TXE) of the fragments is shared according to a parameter RT, which is defined as the ratio of the light to heavy initial temperatures. The sensitivity profile of the neutron multiplicity shows a second order effect of RT on the mean neutron multiplicity. A final sensitivity profile was produced for the parameter alpha, which affects the spin of the fragments. Higher values of alpha lead to higher fragment spins, which inhibit the emission of neutrons. Understanding the sensitivity of the prompt neutron and gamma observables to the many CGMF input parameters provides a platform for the optimization of these parameters.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Developing Diagnostic Tools for Low-Burnup Reactor Samples

We test common neutron fluence diagnostics in the very-low-burnup regime for natural uranium reactor samples. The fluence diagnostics considered are the uranium isotopics ratios 235 U / 238 U and 236 U/ 235 U, for which we find that simple analytic formulas agree well with full reactor simulation predictions. Both ratios agree reasonably well with one another for fluences in the (mid -10 19 ) - n/cm 2 range. However, below about 10 19 n/cm 2 , the concentrations of 236 U are found to be sufficiently low that the measured 236 U/ 235 U ratios become unreliable. We also derive and test diagnostics to determine the cooling times in situations where very low burnup and very long cooling times render many standard diagnostics impractical, such as the 241 Am / 241 Pu ratio. Here, we find that using several fragment ratios is necessary to detect the presence of systematic errors such as fractionation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Determining Reactor Fuel Type from Continuous Antineutrino Monitoring

In this work, we investigate the ability of an antineutrino detector to determine the fuel type of a reactor. A hypothetical 5-ton antineutrino detector is placed 25 m from the core and measures the spectral shape and rate of antineutrinos emitted by fission fragments in the core for a number of 90-d periods. Our results indicate that four major fuel types can be differentiated from the variation of fission fractions over the irradiation time with a true positive probability of detection at approximately 95%. In addition, we demonstrate that antineutrinos can identify the burnup at which weapons-grade mixed-oxide (MOX) fuel would be reduced to reactor-grade MOX, on average, providing assurance that plutonium-disposition goals are met. We also investigate removal scenarios where plutonium is purposefully diverted from a mixture of MOX and low-enriched uranium fuel. Lastly, we discuss how our analysis is impacted by a spectral distortion around 6 MeV observed in the antineutrino spectrum measured from commercial power reactors.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗