Jun 22 2010
Scientists from the Bulgarian Academy of Sciences’ (BAS) the Institute for Nuclear Energy and Nuclear Research and the Institute of Electronics have created the notional basis of a novel type of lidar, named ‘Gamma RAY Detection And Ranging’ (GRAYDAR) that can be utilized for gamma-ray single-sided tomography and sensing of optically-opaque dense media.
The primary component of the GRAYDAR involves the utilization of impulsive electron-positron annihilation for creation of two well known energy gamma photons that are simultaneously radiated in opposite directions.
BAS tomographic return-signal image of an aluminium object containing Fe enclosure and air cavities
One of the two photons is focused on to the object under investigation, while the other related backscattered Compton photon generates a start light pulse. There will be a difference between the start pulse and the received backscattered photon, which can be used to find out the range between the object’s scattering volume and the Gamma radiator.
Time-coincidence, energy discrimination, and adequately narrow acceptance angle techniques are used to select the signal photons that undergo backscatter only once.
The GRAYDAR sensing concept can be used for applications in the domain of industrial tomography and defectoscopy for non-destructive analysis of objects that can be accessed from only one side like large-scale industrial apparatus, flying apparatus, and nuclear reactors.
Active remote-sensing instruments like sonars, radars, sodars and lidars, and techniques are a potent tool for control and large-scale investigation of earth, atmosphere, and ocean. Lidar-based investigations aim to ascertain the medium’s physical characteristics’ distribution within the line of sight (LOS) based on the sensed return signal profiles. The LOS is scanned to generate the object’s tomographic or 3D images.
The suggested technique has considerable benefits as compared to other techniques, permitting unambiguous and simultaneous determination, with resolution and accuracy, which can be controlled, of the Compton backscattering coefficients and extinction inside an object under study. It can also ascertain the final result related to the distribution and mass densities of various ingredients in the object.
It was demonstrated by computer simulations and analytically that the technique helps users to precisely ascertain the presence, the shape, the disposition, and the type of various homogeneous cavities, ingredients, and flaws inside single-material surroundings with non-uniform or uniform distribution of density, and find out distribution of density inside single-material objects.
Source: http://www.bas.bg