Design Considerations for Positron Transmission Tomograph Used for Non-Medical Applications

Design considerations for a positron transmission tomograph to be used for the crosssectional density distribution and dimensions measurements of metal or plastic sheets is described. A low cost piece of equipment constructed for performance studies of the transmission tomography is also described. The camera design consists of a small detector ring with a fixed positron active source in the middle of it. This transmission camera is independent of short half-life isotopes and a nearby cyclotron. It is possible to determine the type of an interaction between a photon and the object material and also the geometric line where the first interaction has taken place using positron annihilation coincidence detection. One of the photons in every annihilation pair escapes from the source into a known direction. A photon will scatter once or more in the object, penetrate it or become totally absorbed by it. The density distribution or the dimensions of the object material can be reconstructed from the count rates of interactions correponding to different projection angles. The detector array with a 10 cm (inner) and 40 cm (outer) diameter consisting of 34 crystals is capable of detecting an annihilation count rate of 1500 events/s¿Ci. Thie calculated maximum cross-sectional area of the photon beam is from 3×3 mm2 to 8.4×9.2 mm2 in the middle and 16×18 mm2 at each end of the view.