Search of new low-noise patterns of coded apertures with arbitrary rank and transparency

For gamma-ray imaging in nuclear environment methods of either an obscure camera or coded aperture (masks) have been used. In the latter case, hexagonal masks of the sixth and ninth ranks of the URA family were used. These masks are most often used in practice, which is stipulated by the advantages intrinsic to the indicated family of coded apertures. At the same time, the application of these masks is associated with a number of restrictions hampering the attainment of ultimate characteristics of imagers. We note, e.g., that the transparency of URA masks, (i.e., the ratio of the number of transparent elements to the total number of mask elements) cannot be arbitrary and attains approximately 50%. In a number of experimental situations, this fact hampers the improvement of parameters of a gamma-ray visualizing system. The goal of studies is the development of a method for finding patterns of coded apertures free from the restrictions mentioned above. In this case, the advantages of the URA-mask family are conserved, which are important for applications in practice. We consider hexagonal masks based on quasi-random linear sets with arbitrary ratio of open and closed elements (as less 1 both more 1). The selection of mask is based of studies of properties of elements of the inverse matrix corresponding to linear set which may be formally used for reconstruction of shadow grams coded by mask. Optimal patterns were found for different mask transparency and their imaging characteristics were studied by simulation of imaging of different point and extended sources.