Shaun D. Clarke

Correlated neutron emissions from 252Cf

Abstract This paper presents new experimental results of correlated, prompt neutron emission from the spontaneous fission of 252Cf. Specifically, we present correlated-neutron emission probabilities and average energies for two detected neutrons as a function of the angle between the two neutrons. Experimental results are compared to several Monte Carlo models that include the number, energy, and angular distributions of prompt neutrons from fission.

Computational evaluation of neutron multiplicity measurements of polyethylene-reflected plutonium metal

Abstract Simulations of neutron multiplicity measurements of a highly multiplicative plutonium sphere measured with a moderated array of 3He proportional counters have consistently overpredicted the mean and variance of the measured multiplicity distribution. In contrast, identical experiments using a 252Cf source have been accurately simulated. This paper outlines a sensitivity analysis of several key parameters that could account for the overprediction in the simulation of the plutonium sphere. Parameters that were analyzed include source-detector distance, detector dead time, variations in density and volume of the plutonium, and the value of for v̄ 239Pu-induced fission. Of these parameters, the only factor that accounted for the overprediction within reasonable bounds was a change in the value of the 239Pu v̄. The sensitivity analysis showed that a small change (1.14% reduction) in the value of v̄ dramatically improved the simulated results.

Dual-particle imager for standoff detection of special nuclear material

An advanced dual-particle imaging system is being developed for standoff, passive detection of special nuclear material. This system consists of three detector planes and will be capable of imaging both photons and fast neutrons. The ability of the system to detect fast neutrons makes it more difficult to effectively shield a threat source. This feature has an advantage over the commonly used Compton-camera systems, which are only sensitive to photons. Additionally, the detection of fast neutrons will allow for increased performance in regions with high levels of photon background radiation. The first two planes of the system consist of EJ-309 liquid scintillators and the third plane consists of NaI scintillators. This detector/plane combination allows image reconstruction using both neutrons and photons. In the liquid scintillators, neutron interactions are distinguished from photon interactions using an optimized pulse shape discrimination technique. The Monte Carlo transport code MCNPX-PoliMi has been used for the initial studies of this system due to its ability to track detailed information on interactions of interest and time-correlated particle production. This information has been used to optimize system parameters and has also allowed for investigation of image reconstruction techniques including simple backprojection and maximum likelihood expectation maximization (MLEM). A small-scale prototype is being developed for testing and validation of the simulations. This paper will analyze preliminary measurements and will also discuss simulations of several shielded source scenarios.

Correlated Prompt Fission Data in Transport Simulations

Abstract.Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and

Active neutron and gamma-ray imaging of highly enriched uranium for treaty verification

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Detection of Special Nuclear Material by means of promptly emitted radiation following photonuclear stimulation

γ-ray observables. Beyond simple average quantities, the study of distributions and correlations in prompt data, e.g., multiplicity-dependent neutron and

Neutron cross-talk characterization of liquid organic scintillators

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Application of Bayes' theorem for pulse shape discrimination

γ-ray spectra, angular distributions of the emitted particles, n -n, n -

Digital data acquisition and processing for a neutron-gamma-ray imaging system

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Time-of-flight measurement for energy-dependent intrinsic neutron detection efficiency

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