Patent Number: 
Section: description

In the following description, parts that are identical to or similar to parts in the figures described above will have the same references plus 100. As stated above, FIG. 5 is a partial top view of a detection head 140 according to the invention. The detection head comprises a number of elementary detectors 142 placed adjacent to each other in the form of a matrix network to form a detection plane 144. The elementary detectors 142 are CdTe or CdZnTe type detectors with semi-conductors and have a square area in the detection plane 144 with a side dimension of 3 to 5 mm. In the example described, the surface of each detector in the detection plane 144 has a central part 150 that is sensitive to gamma radiation and an insensitive peripheral edge 152. The sensitive central part also has a square surface with a side dimension of 3 to 5 mm. This dimension is shown in the figure with reference L. The thickness E of the peripheral edge 152 is of the order of 3 mm. The detection head also comprises preamplifier circuits to collect signals output from detectors 142 and to send them to a processing unit. These elements are not shown in FIG. 5 for reasons of clarity. The detection head 140 also comprises a collimator 120 placed in front of the detection plane 144. The collimator 120 may be placed directly in contact with the detection plane 144. The collimator has a number of ducts 121 laid out perpendicular to the detection plane, in order to carry gamma radiation. Note that the ducts are not necessarily perpendicular to the detection plane, but may form a divergent or convergent bundle for a particular application. Ducts 121 are placed adjacent to each other and are laid out according to a repetition pattern of the individual ducts, each of which has a square cross-section in the detection plane. The side of each square cross-section is a sub-multiple of the side of the square area of the individual detectors. In the case shown in FIG. 5, the length and width of the repetition pattern are equal to one third of the length and width of the elementary detectors in the detection plane. Thus, 9 ducts including their walls, fit into the area of each detector. In the particular example given, each square duct 121 has an opening with a side e1 of the order of 1.33 mm, and is delimited by a wall 123 with a thickness e1 of the order of 0.1 mm. It can be checked that the proportion of the area of the sensitive central part 150 intercepted by the ducts is the same for each elementary detector 142. Thus good detection uniformity is achieved. FIG. 6 shows a variant embodiment of the detector according to the invention. In the case in FIG. 6, the side (i.e., the width and length of the repetition pattern) is equal to half the side of each elementary detector in the detection plane. The elements shown in FIG. 6, except for their dimensions, are similar to those in FIG. 5. They are denoted by the same references, and the above description contains information about them. In the example in FIG. 6, each duct has an opening with a side l2 equal to 1.7 mm and is surrounded by a wall 123 with a thickness e2 of 0.3 mm. Advantageously, collimators 120 like those shown in FIGS. 5 and 6 may be made by electro-erosion from a solid block of absorbing materials such as a solid block of lead. Electro-erosion pins with a shape corresponding to the shape of the ducts are pushed forwards into the block to form the ducts. This method facilitates manufacture of ducts with a square cross-section, and can produce sharp angles. According to a variant, collimators conform with the invention can also be made by molding. In this case, the ducts are defined by pins with a square cross-section. These pins are preferably slightly pyramid-shaped to facilitate removing collimators from the mold.