Alexander Barzilov

3D imaging using combined neutron-photon fan-beam tomography: A Monte Carlo study

The application of combined neutron-photon tomography for 3D imaging is examined using MCNP5 simulations for objects of simple shapes and different materials. Two-dimensional transmission projections were simulated for fan-beam scans using 2.5MeV deuterium-deuterium and 14MeV deuterium-tritium neutron sources, and high-energy X-ray sources, such as 1MeV, 6MeV and 9MeV. Photons enable assessment of electron density and related mass density, neutrons aid in estimating the product of density and material-specific microscopic cross section- the ratio between the two provides the composition, while CT allows shape evaluation. Using a developed imaging technique, objects and their material compositions have been visualized.

Study of Doppler broadening of gamma-ray spectra in 14-MeV neutron activation analysis

Neutron reactions producing characteristic photons of isotopes are important for nondestructive analysis of materials. Technique to determine the intensity of neutron induced gamma rays by fitting a spectrum with a Gaussian function using detector resolution curves derived from isotopic sources may fail if the peak is Doppler-broadened. This leads to the miscalculation of the area of the peak and, therefore, to misidentification of the material. This work shows that Doppler broadening occurs in the 14-MeV neutron analysis with photons emitted in inelastic scattering reactions on light nuclei with excited states whose lifetimes are much smaller than the time of flight of a recoiling nucleus in the material. It provides groundwork for analysis of gamma ray spectra utilizing detector response functions measured with a 14-MeV neutron source using actual geometry of an active interrogation system.

Remote sensing of neutron and gamma radiation using aerial unmanned autonomous system

The system based on unmanned aerial vehicles was designed for remote sensing of neutron and gamma radiation. A swarm of small-scale quadcopters with navigational and sensing capabilities was studied to perform radiation monitoring with dynamically tracked measurements that could be used for analysis and prognostics in temporal and space domains. A Cs2LiYCl6:Ce3+ scintillation detector equipped with a digital data analysis system was developed for simultaneous gamma-ray spectroscopy and neutron sensing. Pulse shape discrimination was used to segregate neutron and photon signatures. The maximum likelihood estimation technique was employed to search for unattended radiation sources using the data obtained cooperatively by multiple UAVs.

Sparse-view neutron-photon computed tomography: Object reconstruction and material discrimination

Taking into account the advantages of both neutron- and photon-based systems, we propose combined neutron-photon computed tomography (CT) under a sparse-view setting and demonstrate its performance for 3D object visualization and material discrimination. We use a high-performance regularization method for CT reconstruction by combining regularization based on total variation (TV) and curvelet transform in cone beam geometry. It is coupled with proposed 2D material signatures which is pairs of photon to neutron transmission ratios and neutron transmission values per object space voxels. Classification of materials is performed by association of a voxel signature with library signatures; and per object - by majority of voxels in the object. Representation of object-material pairs, for the model in our experiment, a complex scene with group of high-Z and low-Z materials, attains the reconstruction accuracy of 92.1% and the overall high-Z discrimination accuracy of object representation is 85%, and by about 7.5% higher discrimination accuracy than that with 1D signatures which are ratios of photon to neutron transmissions. With a relative noise level of 10%, the method yields the reconstruction accuracies of 87.2%. The analyses are performed in cone beam configuration, with Monte Carlo modeling of neutron-photon transport for the model of object geometry and material contents.

Scintillation properties of a Cs2LiLa(Br6)90%(Cl6)10%:Ce (CLLBC) crystal

In investigations of Ce3+-doped Cs2LiLa(Br6)90%(Cl6)10% (CLLBC) elpasolite crystals, the crystals show an excellent neutron and gamma (n/γ) radiation response. The results of our studies on the scintillation properties of CLLBC viz. radioluminescence, energy resolution, light yield, decay times, and nonproportionality are discussed. The CLLBC detector can provide energy resolution as good as 4.1% at 662 keV (FWHM), which is better than that of NaI:Tl. Because the crystal contains 6Li, CLLBC can also detect thermal neutrons. In the energy spectra, the full energy thermal neutron peak appears near or above 3 MeV gamma equivalent energy. This high-energy signature for the thermal neutron peak means that very effective pulse height discrimination is possible. Unfortunately, because the core-to-valence luminescence observed in other elpasolites that can be exploited for effective pulse shape discrimination (PSD) is not observed in the CLLBC, other strategies for obtaining the PSD of CLLBC are needed. The n/γ discrimination capability of CLLBC detectors may be optimized by tuning the cerium doping content for maximum effect on n/γ pulse shape differences. The value of adding a chlorine component to the nominal CLLB crystal is discussed. Because the crystal contains chlorine, its sensitivity to fast neutrons is better than that of Cs2LiLaBr6 (CLLB). Further, an array of three of these CLLBC detectors may be able to perform directional detection in both the neutron and gamma channels simultaneously.

Development and deployment of the Collimated Directional Radiation Detection System

The Collimated Directional Radiation Detection System (CDRDS) is capable of imaging radioactive sources in two dimensions (as a directional detector). The detection medium of the CDRDS is a single Cs2LiYCl6:Ce3+ scintillator cell enriched in 7Li (CLYC-7). The CLYC-7 is surrounded by a heterogeneous high-density polyethylene (HDPE) and lead (Pb) collimator. These materials make-up a coded aperture inlaid in the collimator. The collimator is rotated 360° by a stepper motor which enables time-encoded imaging of a radioactive source. The CDRDS is capable of spectroscopy and pulse shape discrimination (PSD) of photons and fast neutrons. The measurements of a radioactive source are carried out in discrete time steps that correlate to the angular rotation of the collimator. The measurement results are processed using a maximum likelihood expectation (MLEM) algorithm to create an image of the measured radiation. This collimator design allows for the directional detection of photons and fast neutrons simultaneously by utilizing only one CLYC-7 scintillator. Directional detection of thermal neutrons can also be performed by utilizing another suitable scintillator. Moreover, the CDRDS is portable, robust, and user friendly. This unit is capable of utilizing wireless data transfer for possible radiation mapping and network-centric applications. The CDRDS was tested by performing laboratory measurements with various gamma-ray and neutron sources.

Control of an Aerial Manipulator With an On-Board Balancing Mechanism

Multirotor Unmanned Aerial Systems (UAS) are highly mobile in flight and possess stable hovering capabilities. Because of their unique flight characteristics, the utilization of the platform for active tasks such as aerial manipulation is highly attractive. Much work has been done in recent years towards the implementation of multirotor for aerial manipulation, however, progress in the field has been slow due to the many challenges involved in the implementation of robust rotor control. In an attempt to reduce the effects of the manipulator, a technique for disturbance rejection using a novel balancing mechanism is proposed. In this paper, the dynamic equations of a coupled multirotor and manipulator are analyzed as a single body for use in the attitude control of the platform. By mounting the mechanism, the platform effectively gains marginal control over the positioning of its center of gravity relative to a body fixed frame. It can be shown that the increased mobility can be utilized to reduce rotor saturation for any given flight condition and improve the effectiveness of previously developed rotor control methods.Copyright

DD and DT neutron generator yield measurements using EJ-299-33A detector

Neutron generators are widely used in security applications, industry, medicine, and research. The neutron-based methods require precise measurement of the neutron yield to normalize the measured data. To address this need, the technology of fast neutron flux monitoring was developed. The output of DD and DT neutron generators was characterized using the EJ-299-33A plastic scintillator. This detector enabled count rate measurements for fast neutrons and energy spectroscopy. Monoenergetic neutron responses were measured for this detector using the accelerator-based neutron source for energies between 0.1 MeV and 20.2 MeV with a gap between 8.2 MeV and 12.2 MeV. The T(p, n)3He, D(d, n)3He, and T(d, n)4He reactions were employed. Digital pulse shape discrimination was used to separate the neutron component of the measured responses. The experimental neutron responses were used in the spectral unfolding based on polynomial fitting. The unfolding technique was experimentally verified using DD and DT sources.

Maximum likelihood source localization using elpasolite crystals as a dual gamma neutron directional detector

The problem of accurately detecting extremely low levels of nuclear radiation is rapidly increasing in importance in nuclear counter-proliferation, verification, and environmental and waste management. Because the 239Pu gamma signature may be weak, for instance, even when compared to the natural terrestrial background, coincidence counting with the 239Pu neutron signature may improve overall 239Pu detection sensitivity. However, systems with sufficient multiple-particle detectors require demonstration that the increased sensitivity be sufficiently high to overcome added cost and weight. We report the results of measurements and calculations to determine sensitivity that can be gained in detecting low levels of nuclear radiation from use of a relatively new detector technology based on elpasolite crystals. We have performed investigations exploring cerium (Ce3+)-doped elpasolites Cs2LiYCl6:Ce3+0.5% (CLYC) and Cs2LiLa(Br6)90%(Cl6)10%:Ce3+0.5% (CLLBC:Ce). These materials can provide energy resolution (r(E) = 2.35σ(E)/E) as good as 2.9% at 662 keV (FWHM). The crystals show an excellent neutron and gamma radiation response. The goals of the investigation were to set up the neutron/gamma pulse shape discrimination electronics for elpasolite detectors; perform limited static source benchmarking, testing, and evaluation to validate system performance; and explore application of a maximum likelihood algorithm for source location. Data were measured and processed through a maximum likelihood estimation algorithm, providing a direction to the radioactive source for each individual position. The estimated directions were good representations for the actual directions to the radioactive source. This paper summarizes the maximum likelihood results for our elpasolite system.