Gamma-Ray Backscattering Tomography Approach Based on the Lidar Principle

Abstract

An approach is proposed, and its potentialities are studied, for single-sided gamma-ray in-depth sensing and tomography of dense opaque media. The approach is based on lidar (LIgth Detection And Ranging) principle or, in the present case, graydar (Gamma RAY Detection And Ranging) principle, that is, time-to-range resolved detection of the backscattering-due radiative returns from the probed object irradiated by pulsed gamma-photon pencil beams. The basic analysis and data processing delta-pulse single-scattering graydar equation is formulated by analogy with the lidar equation and is shown to be applicable, under some determinate conditions, to the problems of gamma-ray in-depth profiling of dense media. It is shown analytically and by computer simulations that the approach developed in the work would enable one, at large-enough but reasonable sensing photon fluxes and measurement time intervals, to determine with good controllable accuracy and resolution the location, the material content, and the mass density of different homogeneous ingredients inside the probed object as well as the mass (or electron) density distribution within one-material objects. This approach can be widely applied, e.g., for nondestructive material examination in industry and aviation, detection of landmines and explosives, investigating the constitution of archeological artifacts, etc.

On the Possibility of Determining the Distribution of a Substance Penetrating into a Dense Medium Using Gamma-Ray Detection and Ranging Approach

“…It is shown, for instance, that, at a number of 10 9 sensing photons deposited along one LOS, one may establish with 2-3 mm longitudinal and transversal resolution the presence, the disposition, the shape, and the kind of different homogeneous ingredients, cavities and flaws within a homogeneous surrounding material (aluminum); the presence of more than one flaw along one LOS is shown to not lead to noticeable masking effect [15]. It is shown as well that the graydar approach is capable of finding, identifying, and imaging homogeneous ingredients (plastic TNT landmines) in homogeneous or inhomogeneous soil, at depths to 20 cm, density-contrast from 5%-8% to 20%, and longitudinal (along the LOS) and transversal resolution of 1-2 mm and 8-10 mm, respectively [14,16].…”

“…Thus, in practice, a time-to-range resolved return signal or graydar profile F = F (t, ∆t) = F (z, ∆z) can be obtained. The main instrument for quantitative analysis concerning graydar is the so-called single-backscattering graydar equation [13] that describes the relation between the graydar profile F (t, ∆t), the parameters of the radiation-transceiving system (incident-photon rate, receiving detector area, receiving efficiency, sampling interval in the time or range domain, etc. ), the energy E f of the sensing gamma photons, and the LOS distribution of the physical characteristics (extinction and backscattering coefficients) of the medium under investigation.…”

“…In the case of "heavy" materials the broadening effect will be larger and the question about the disturbance of the energy selection requires a separate profound investigation. A regime of δ-pulse sensing could be achieved [13] by using a monostatic sensing system (see Fig. 1) emitting spontaneously a narrow beam of incident on the probed object gamma photons of energy E f and detecting the Compton backward-scattered photons of energy E bc .…”

“…The graydar (Gamma RAY Detection And Ranging) approach [13][14][15][16] is free of the above-mentioned difficulties. Instead, it allows to determine simultaneously, in a relatively simple unambiguous one-sided way and with controllable accuracy and resolution, the profiles of the extinction and Compton-backscattering coefficients within an object of interest.…”

“…This in turn would allow one to determine the internal distribution of differ- * corresponding author; e-mail: lugurdev@ie.bas.bg ent constituent substances and their mass density. The capabilities of the graydar sensing have been studied and demonstrated in [13,14], where three typical cases have been considered. In the first case, the graydar line of sight (LOS, sensing beam axis) penetrates homogeneous regions of different substances.…”