Improved Gamma-Ray Point Source Quantification in Three Dimensions by Modeling Attenuation in the Scene

Bandstra, Mark S.; Hellfeld, Daniel; Vavrek, Jayson R.; Quiter, Brian J.; Meehan, K.; Barton, Paul; Cates, Joshua; Moran, A.; Negut, Victor; Pavlovsky, Ryan; Joshi, T. H. Y.

doi:10.1109/tns.2021.3113588

Cited by 14 publications

(22 citation statements)

References 36 publications

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“…Generalizations to arrays over hilly surfaces or full 3D environments are possible, but will require a map of the environment to be modeled or measured (e.g., via LiDAR SLAM). In fact when such a map is available, it is possible to account for attenuation in the scene [44] that has made activity reconstruction difficult in similar measurement scenarios [45].…”

Section: Discussionmentioning

confidence: 99%

Design and deployment of radiological point-source arrays for the emulation of continuous distributed sources

Vavrek¹,

Hines²,

Bandstra³

et al. 2022

Preprint

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We demonstrate a method for using arrays of point sources that emulate-when measured from a standoff of at least several meters-distributed gamma-ray sources, and present results using this method from outdoor aerial measurements of several planar arrays each comprising up to 100 ∼7 mCi Cu-64 sealed sources. The method relies on the Poisson deviance to statistically test whether the array source "looks like" its continuous analogue to a particular gamma-ray detector given the counts recorded as the detector moves about 3D space. We use this deviance metric to design eight different mock distributed sources, ranging in complexity from a 36 × 36 m uniform square grid of sources to a configuration where regions of higher and zero activity are superimposed on a uniform baseline. We then detail the design, manufacture, and testing of the ∼7 mCi Cu-64 sealed sources at the Washington State University research reactor, and their deployment during the aerial measurement campaign. We show the results of two such measurements, in which approximate source shapes and qualitative source intensities can be seen. Operationally, we find that the pointsource array technique provides high source placement accuracy and ease of quantifying the true source configuration, scalability to source dimensions of 100 m, ease of reconfiguration and removal, and relatively low dose to personnel. Finally, we consider potential improvements and generalizations of the point-source array technique for future measurement campaigns.

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Section: Discussionmentioning

confidence: 99%

Design and deployment of radiological point-source arrays for the emulation of continuous distributed sources

Vavrek¹,

Hines²,

Bandstra³

et al. 2022

Preprint

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“…Here we will introduce a maximum likelihood-based framework for analyzing the detection of point sources (Point Source Likelihood or PSL), and then we will use it to describe how to calculate the MDA. Some of the notation and concepts used in this section will closely follow the description of PSL given in reference [28].…”

Section: Methodsmentioning

confidence: 99%

“…The PSL algorithm is the reconstruction of a single point source using a freely moving detector in a 3-D environment using maximum likelihood [23], [24], [28], [32], [33]. To perform PSL, we begin with a series of M measurements, indexed by i, that consist of event counts n i in a chosen spectral region of interest (ROI).…”

Section: A Point Source Likelihoodmentioning

confidence: 99%

“…Many have studied the problem of localizing one or more point sources of radiation using a moving detector or an array of static detectors [1], [2], [3], using a variety of methods, such as maximum likelihood [4], [5], [6], [7], [8], [9], Bayesian methods [10], [11], [12], [13], [14], [15], [16], and geometric methods and clustering [17], [18], [19], [20]. The problem has been mostly explored by considering a two-dimensional (2-D) representation of the geometry and assuming bare point sources, but some have focused on 3-D environments [21], [22], [23], [24] and considered attenuation in the scene [25], [26], [27], [28].…”

Section: Introductionmentioning

confidence: 99%

“…Recent advances in freely moving radiation detector systems that can sense their position and orientation in 3-D space as well as map the 3-D environment around them have enabled new search capabilities and prompted the development of new algorithms to fully exploit the contextual data available [29], [30], [31]. One such approach is Point Source Likelihood (PSL), a maximum likelihood method in which photopeak events, detector positioning information, and the environmental map are used as inputs to an algorithm that attempts to locate a single point source in the 3-D scene and obtain accurate estimates and confidence intervals for the source location and activity [23], [24], [32], even in the presence of attenuating material [28]. A notable recent extension of PSL is solving for discrete Gaussian sources, allowing for truly continuous sources to be better fit [33].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mapping the Minimum Detectable Activities of Gamma-Ray Sources in a 3-D Scene

Bandstra¹,

Hellfeld²,

Lee³

et al. 2022

Preprint

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The ability to formulate maps of minimal detectable activities (MDAs) that describe the sensitivity of an ad hoc measurement that used one or more freely moving radiation detector systems would be significantly beneficial for the conduct and understanding of many radiological search activities. In a real-time scenario with a free-moving detector system, an MDA map can provide useful feedback to the operator about which areas have not been searched as thoroughly as others, thereby allowing the operator to prioritize future actions. Similarly, such a calculation could be used to inform subsequent navigation decisions of autonomous platforms. Here we describe a near realtime MDA mapping approach that can be applied when searching for point sources using detected events in a spectral region of interest while assuming a constant, unknown background rate. We show the application of this MDA mapping method to a real scenario, a survey of the interior of a small building using a handheld detector system. Repeated measurements with no sources and with 137 Cs sources of different strengths yield results consistent with the estimated thresholds and MDA values; namely, that for background-only measurements no sources are seen above threshold anywhere in the scene, while when sources are present they are detected above the thresholds calculated for their locations.

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Free-moving Quantitative Gamma-ray Imaging

Hellfeld

Bandstra

Vavrek

et al. 2021

Sci Rep

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The ability to map and estimate the activity of radiological source distributions in unknown three-dimensional environments has applications in the prevention and response to radiological accidents or threats as well as the enforcement and verification of international nuclear non-proliferation agreements. Such a capability requires well-characterized detector response functions, accurate time-dependent detector position and orientation data, a digitized representation of the surrounding 3D environment, and appropriate image reconstruction and uncertainty quantification methods. We have previously demonstrated 3D mapping of gamma-ray emitters with free-moving detector systems on a relative intensity scale using a technique called Scene Data Fusion (SDF). Here we characterize the detector response of a multi-element gamma-ray imaging system using experimentally benchmarked Monte Carlo simulations and perform 3D mapping on an absolute intensity scale. We present experimental reconstruction results from hand-carried and airborne measurements with point-like and distributed sources in known configurations, demonstrating quantitative SDF in complex 3D environments.

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Improved Gamma-Ray Point Source Quantification in Three Dimensions by Modeling Attenuation in the Scene

Cited by 14 publications

References 36 publications

Design and deployment of radiological point-source arrays for the emulation of continuous distributed sources

Design and deployment of radiological point-source arrays for the emulation of continuous distributed sources

Mapping the Minimum Detectable Activities of Gamma-Ray Sources in a 3-D Scene

Free-moving Quantitative Gamma-ray Imaging

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