Progress in micro-pattern gaseous detectors and their applications
2009 3rd International Workshop on Advances in sensors and Interfaces
In the last decade, several new imaging gaseous detectors, called "micro-pattern gaseous detectors", have been conceived and rapidly developed. In this paper, the most popular designs of these detectors and their applications to high energy physics and astrophysics experiments will be described. The main focus of this review will however be on the ongoing activities on practical applications of micropattern detectors to medicine and industry 1. Micro-Pattern Gaseous Detectors At the end of the
... At the end of the last century, the main imaging gaseous detector, widely used in various scientific researches and applications, was the multi-wired proportional chamber (MWPC) invented in 1968 by G. Charpak . This detector was able to obtain fast electronic images of photons and tracks of elementary charged particles with a 1-D position resolution better than 100 μm. For this great invention, which really revolutionized the detection technique, G. Charpak was awarded in 1992 with the Nobel Prize in physics. However, the triumph of the MWPCs did not last very long. In the beginning of 1990, a new breakthrough happened in the technology of gaseous detectors as a result of the efforts of several teams, the so-called micro-pattern gaseous detectors were developed. These novel detectors are characterized by the following two features: 1) the gap between the anode and the cathode electrodes is usually very small, sometimes smaller than 50 μm, 2) the electrode structures are manufactured via microelectronic technology enabling to achieve a very high granularity and thus a position resolution much better than in the case of the MWPCs. Nowadays, there exist quite a lot of various designs of micro-pattern detectors; which can roughly classified into four categories: strip-type, dot-type, hole-type and a parallelplate type. A detailed description of these detectors can be found in several review articles, see for example [2, 3]; we would like to focus in this paper only on the most popular designs of today: the hole-and the parallel-plate-types. In a few words, the hole-type detector is a dielectric sheet metalized on both sides in which an array of holes are etched (Figure 1 ). If a voltage drop V is applied across the metalized surfaces, the field lines will exhibit a focusing effect inside the holes as shown in Figure 2 , whereas a very high electric field can be created in this region so that at some critical value of V (V>Vc) the avalanche multiplication of primary electrons happens. This effect was first demonstrated in ; later, glass capillary plates were developed  and finally F. Sauli suggested a very elegant version of the hole-type detector in which the dielectric sheet was manufactured from a 50 μm thick Kapton  . He named this detector: Gas Electron Multiplier (GEM).This latter modification allowed the production of large-area detectors of various shapes. GEM detectors offer very good position resolutions: about 50 µm for photons and even better for tracks of charged particles.