Linear Detector Arrays

Linear Detector Arrays (LDAs) or more simply Line Arrays are 1 dimensional x-ray detectors that consist of a single row of x-ray sensitive detectors. In order to obtain a 2 dimensional image from such a detector it is necessary to move the detector, or the object in a direction perpendicular to the length of the array. In order to maintain regular image geometry (square pixels) the speed of movement has to be carefully synchronised with the line exposure time of the array. The width of 2 dimensional images acquired by an LDA are limited by the number of pixels comprising the width of the array, however, the length is unlimited, and LDA are ideally suited to applications where the objects are moving on a conveyor belt, or similar movement system. LDAs are also ideally suited to 2D CT systems which obtain single CT slices through an object. Although slower, 2D CT is preferable to 3D CT (using an area detector) for applications where scatteres x-rays are a problem, for example for high energy applications, or when examining dense materials.

LDA's may be constructed from various types of detector elements, from individual photo-multiplier tubes, to banks of CMOS detectors. These detector elements may be intrinsically sensitive to X-Rays, but more commonly rely on an input scintillator to convert the received X-Ray photons to visible light photons which can then be detected. A wide range of scintillator materials are suitable. For arrays with larger pitches (400 microns and above) individual scintillator crystals can be used, typically of Cadmium Tungstate. For arrays with smaller pitches (200 microns and below) a common scintillator has to be used across all the detector elements, typically Gadolinium Oxysulphide.

Shaw Inspection Systems manufacture a range of integrated LDA solutions, from stand alone detectors, to fully integrated cabinet based X-Rays systems.