Other Early Designs of Micropattern Detectors Developed Between 1998 and 2003

Other Early Designs of Micropattern Detectors Developed Between 1998 and 2003

DOI: 10.4018/978-1-4666-6014-4.ch007
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Abstract

This chapter focuses on the intense developments of micropattern detectors that happened between 1998 and 2003. In this period, many new designs were invented and manufactured by means of a photolithographic technology. These detectors include microwire detectors, microslit detectors, LEAK multiplication structures, microgap parallel-plate chambers, micro-hole strip plate gaseous detectors, etc. Some of them remain simply as interesting exercises demonstrating the great capability of microelectronic technique. Some of them are used in practice, for example in 2 dimensional and 3 dimensional mammographic scanners. These scanners are based on microgap parallel-plate chambers and give high quality X-ray images at a reduced radiation dose delivered to the patients. Early versions of the LEAK detector were intensively used in plasma diagnostics. Micro-hole strip plate gaseous detectors are currently used in some prototypes of photodetectors. This chapter also describes an MSGC type MWPC invented by Charpak et al. in an attempt to overcome the problems associate with the MSGC (i.e. charging up effects and poor rate characteristics).
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1. Introduction

In the previous chapters we described the main designs of micropattern detectors developed in 1988-1998, the first decade after the MSGC invention. The MICROMEGAS and GEMs are nowadays the most popular of those detectors. The exciting development of the MICROMEGAS and the GEM triggered a chain of other inventions. Due to the vast research and development performed during the last 15 years in micropattern detectors, it will be convenient to divide these developments in two periods:

  • 1.

    1998-2003 and

  • 2.

    2004-present time.

In the period 1998-2003 a lot of studies were performed aiming to understand the physics behind the operation of micropattern detectors (see Chapter 9). These new results strongly influenced the developments performed after 2003.

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2. Some Original Designs: The Microwire And Microslit Detectors

Microelectronic technology offers the possibility to build various, sometimes very complicated and exotic, electrode structures. Some authors have tried to exploit this technique to create new designs of micropattern detectors.

2.1 The Microwire Detector

The microwire detector is a 3D version of the MSGC (Adeva, 1999). It is manufactured from a 25-50 µm thick Kapton foil metalized on both sides. On one side, a pattern of square holes, 70x70 μm2, are lithographically etched. On the opposite side, 25 μm wide strips located in the middle of each square hole are etched. The bare Kapton is then chemically removed leaving only insulating mechanical joints between the anode strips the cathode mesh (see Figure 1).

Figure 1.

Design of the microwire detector (Adeva, 1999)

The gas gain achieved with such a detector is typical for all micropattern detectors: 104 for 6 keV photons (Figure 2). With further modification (adding another cathode grid) it becomes a miniature version of MWPC.

Figure 2.

Gas gain curves measured on microwire detectors manufactured from 25 μm and 50 μm thick Kapton sheets using an 55Fe source

2.2 The Microslit Detector

A schematic drawing of a microslit detector is shown in Figures 3 and 4. As in the previous detector, it is manufactured from a 50 μm thick Kapton foil metallized on both sides (Claude Labbe, 1999). A matrix of rectangular round-corner slits, 105 μm wide and 6 mm long (with a period of 200 μm), is lithographically etched on one side of the Kapton (Figures 3 and 4). On the other side of the Kapton, a pattern of 30 μm wide strips with 200 μm pitch positioned in the middle of each slit are etched. When the Kapton in the slit area is removed, the final structure has 30 μm strips suspended by 300 μm Kapton joints. As can be seen, this detector is actually a substrate–less MSCG.

Figure 3.

Artistic view of the microslit detector

Figure 4.

More detailed picture of the microslit detector design

The gain curves, shown in Figure 5, are measured using an X-ray tube. As usual, the maximum achievable gain is around 103. At higher gains sparks developed.

Figure 5.

Gain curves measured with a microslit detector in various gas mixtures

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