Operation of sealed microstrip gas chambers at the ILL

Microstrip gas chambers (MSGCs) were introduced at the Institut Lane Langev in [(ILL), Grenoble, France] as a response to the problem of fabricating th e large-area neutron detector of the D20 neutron powder diffractometer. Thi s banana-like detector consists of 48 MSGCs, each comprising 32 counting ce lls. It was in operation during 18 months before being stopped due to the p rogressive deterioration of the anode strips. To increase its lifetime, sig nificant modifications were introduced in the recently assembled new versio n. Another instrument was equipped with a modular unidimensional detector m ade of nine MSGCs, each of them in an individual gas vessel. The ILL has al so 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 operat ion of these detectors.