Operation of sealed microstrip gas chambers at the ILL

Microstrip gas chambers (MSGCs) were introduced at the Institut Lane Langevin [(ILL), Grenoble, France] as a response to the problem of fabricating the large-area neutron detector of the D20 neutron powder diffractometer. This banana-like detector consists of 48 MSGCs, each comprising 32 counting cells. It was in operation during 18 months before being stopped due to the progressive deterioration of the anode strips. To increase its lifetime, significant modifications were introduced in the recently assembled new version. Another instrument was equipped with a modular unidimensional detector made of nine MSGCs, each of them in an individual gas vessel. The ILL has also developed bidimensional MSGCs with a charge division readout. All these detectors employ sealed vessels containing a gas mixture at a pressure that can be as high as 15 bars, necessitating very clean conditions. This paper describes the experience acquired at the ILL in the fabrication and operation of these detectors.