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196 results on '"Pozzi, S.A."'

7. Investigation of organic scintillators for neutron-gamma noise measurements in a zero power reactor

Author

Darby F.B., Pakari O., Hua M.Y., Lamirand V., Clarke S.D., Pautz A., and Pozzi S.A.

Subjects
power spectral density, organic scintillators, pulse-shape discrimination, Physics, QC1-999
Abstract

Noise measurements in light water reactor systems aid in generating validation data for integral point kinetic parameter predictions and monitoring parameters for reactor safety and safeguards. The CROCUS zero-power reactor has been used to produce both data types to date, using thermal neutron detectors to observe neutron noise and inorganic scintillators to observe gamma noise. Also, the cross-correlation of gamma and neutron noise has been investigated at CROCUS with separate gamma and neutron detectors. Organic scintillators can be used to cross-correlate gamma and neutron noise with only one detector type, within a single detector volume, and provide nanosecond timing resolution for time-correlated measurements. Dual-particle measurements require particle-type discrimination and are hence possible with organic scintillators since such detectors have the property of presenting statistically different pulse shapes for gamma rays and fast neutrons. The fine timing precision increases the signal-to-noise ratio relative to moderated thermal neutron detectors for correlated measurements and the dual-particle sensitivity allows for multiple modalities of estimating the prompt neutron decay constant. In this work, we present data obtained with 5.08 cm-length by 5.08 cm-diameter trans-stilbene cylindrical detectors set in the water reflector of CROCUS. Preliminary results estimate the prompt neutron decay constant to be (155 ±5) s−1 at delayed critical.

Published
2023
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30. FAST ROSSI-ALPHA MEASUREMENTS OF PLUTONIUM USING ORGANIC SCINTILLATORS

Author

Hua M.Y., Bravo C.A., MacDonald A.T., Hutchinson J.D., McKenzie G.E., Grove T.J., Goda J.M., McSpaden A.T., Clarke S.D., and Pozzi S.A.

Subjects
neutron noise, rossi-alpha, 3he, organic scintillator, Physics, QC1-999
Abstract

In this work, Rossi-alpha measurements were simultaneously performed with a 3He-based detection system and an organic scintillator-based detection system. The assembly is 15 kg of plutonium (93 wt% 239Pu) reflected by copper and moderated by lead. The goal of Rossi-alpha measurements is to estimate the prompt neutron decay constant, alpha. Simulations estimate keff = 0:624 and α = 52:3 ± 2:5 ns for the measured assembly. The organic scintillator system estimated α = 47:4 ± 2:0 ns, having a 9.37% error (though the 1.09 standard deviation confidence intervals overlapped). The 3He system estimated α = 37 μs. The known slowing down time of the 3He system is 35-40 μs, which means the slowing down time dominates and obscures the prompt neutron decay constant. Subsequently, the organic scintillator system should be used for assemblies with alpha much less than 35 μs.

Published
2021
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49. Measurement of neutron yields from UF (sub 4)

Author

Bell, Z.W., Ohmes, Martin F., Yunlin Xu, Downar, T., and Pozzi, S.A.

Subjects
Neutrons -- Research, Business, Electronics, Electronics and electrical industries
Published
2010

50. Correlations in prompt neutrons and gamma-rays from Cf-252 spontaneous fission

Author

Marcath M.J., Shin T.H., Fulvio A. Di, Clarke S.D., and Pozzi S.A.

Subjects
Physics, QC1-999
Abstract

New event-by-event fission models have prompt neutrons and gamma-rays that are correlated in time, energy, and multiplicity, however there is limited measurement data available to validate these models. Measurement of high-order fission neutron and gamma-ray coincidences is difficult and there has previously been little motivation to measure properties of both particle types simultaneously. High-order Cf-252 spontaneous fission neutron and gamma-ray coincidences were measured with a cylindrical array of 22 liquid organic and 8 NaI(Tl) scintillation detectors, 50 cm from a central axis. Waveforms were acquired and saved for post-processing using four time-synchronized CAEN V1720 digitizers. Liquid organic scintillator waveforms were analyzed with off-line pulse shape discrimination techniques to categorize neutron and gamma-ray detections. Detected multiplicity was compared with MCNPX-PoliMi simulation results, where built-in fission models and event-by-event fission models, CGMF and FREYA, have been implemented. Additionally, measured neutron energy by time-of-flight and gamma-ray energy correlated by detected multiplicity were compared to simulated results.

Published
2017
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