Ultra-long microstrip gas counter for spallation neutron source facilities

We are developing a new ultra-long multi-grid-type microstrip gas counter (648 mm long) for neutron scattering experiments at spallation neutron source facilities. We implemented a global–local charge division method for fast readout method where we divide a cathode signal into two categories. From one cathode strip a rough position is obtained and the other cathode strip provides a fine position. We also implemented a graded cathode pattern. Each cathode strip is composed of two conductive elements. We alter the ratio of two conductive areas according to the incident position by using a periodic electrode pattern. A test plate was successfully fabricated. X-ray tests showed an energy resolution of ∼13.3% FWHM at 8 keV. The uniform gas gain was obtained throughout entire active length. Position resolution of 1–4 mm FWHM is obtained and the principle of this method is successfully demonstrated. An initial neutron beam test was performed. The gas gain of 300 was achieved for 3He (0.5 bar) and CF4 (2.5 bar) gas mixture. Measured global and local resolutions were 16 mm and 5.5 mm, respectively. This method can be used for a very large tiled 2-D detector at a reasonable cost.