(The average number of prompt neutron v /SUB p/ and the distributions of prompt neutron number probability P(v) for spontaneous fission of /sup 240/Pu, /sup 242/Cm, and /sup 244/Cm relative to v /SUB p/ (/sup 252/Cf) have been measured using a large gadolinium-loaded liquid scintillation counter with a coincidence method.)The results were v /SUB p/ (/sup 240/Pu)=2.141+ or 0.016, v /SUB p/ (/sup 242/Cm)=2.562 + or - 0.020, and v /SUB p/ (/sup 244/Cm)= 2.721 + or - 0.021. Lastly, experimental data suggest that the lighter fragment is disproportionately excited. The shape of the correlation function depends on how the excitation energy is partitioned between the two fission fragments. Conclusions: The asymmetry in the measured neutron-neutron angular distributions can be predicted by FREYA. The agreement between data and simulation is overall very good for 252Cf ( sf ) and 240Pu ( sf ). The 240Pu data in this analysis was the first available to quantify the energy partition for this isotope. The measured asymmetry enabled us to adjust the FREYA parameter x in 240Pu, which controls the energy partition between the fragments and is so far inaccessible in other measurements. Results: The neutron-neutron correlation modeled by FREYA depends strongly on the sharing of the excitation energy between the two fragments.
The second method has the advantage of being truly detector independent. The first is based on setting a more » light output threshold while the second imposes a time-of-flight cutoff. Method: Two different analysis methods were used to study the neutron-neutron correlations with varying energy thresholds.
SPONTANEOUS FISSION OF CF 252 GENERATOR
To compare these correlations to simulations combining the Monte Carlo radiation transport code MCNPX with the fission event generator FREYA. Purpose: To measure the neutron-neutron angular correlations from the spontaneous fission of 252Cf and 240Pu oxide samples using a liquid scintillator array capable of pulse-shape discrimination. Such an anisotropy arises because the emitted neutrons are boosted along the direction of the parent fragment. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment Additional Journal Information: Journal Volume: 830 Journal Issue: C Journal ID: ISSN 0168-9002 Publisher: Elsevier Country of Publication: United States Language: English Subject: 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY 98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION Fission neutron anisotropy Plutonium Nuclear safeguards = ,īackground: Angular anisotropy has been observed between prompt neutrons emitted during the fission process. of Michigan, Ann Arbor, MI (United States) Sponsoring Org.: USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation OSTI Identifier: 1487063 Alternate Identifier(s): OSTI ID: 1341190 OSTI ID: 1365835 Grant/Contract Number: NA0002534 NE0000393 LA14-FY14-027-PD2J Resource Type: Accepted Manuscript Journal Name: Nuclear Instruments and Methods in Physics Research. European Commission at the Joint Research Centre, Ispra (Italy).of Nuclear Engineering and Radiological Sciences of Michigan, Ann Arbor, MI (United States). Stronger anisotropy was observed in Cf-252 spontaneous fission prompt neutrons than in Pu-240 neutrons. As light output threshold increases, the observed anisotropy increases due to spectral effects arising from fission fragment momentum transfer to emitted neutrons. Fewer coincidences were observed at detector angles near 90°, relative to higher and lower detector angles. The effect of cross-talk, estimated with MCNPX-PoliMi simulations, is removed from neutron-neutron coincidences as a function of the angle between detector pairs. Furthermore, a liquid organic scintillation detector array was used with pulse shape discrimination techniques to produce neutron-neutron cross-correlation time distributions and angular distributions from spontaneous fission in a 252Cf, a 0.84 g 240Pu eff metal, and a 1.63 g 240Pu eff metal sample. We observed an anisotropic neutron angular distribution, in the laboratory reference frame, because prompt fission neutrons carry momentum from fully accelerated fission fragments. Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy.
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