A large-area transition radiation detector

The construction and the operation of a large-area transition radiation detector (TRD) for the NA31 experment at CERN are described. The TRD incorporates several novel features for stabilizing the detector response. The density of the gas mixture (xenon + helium + methane) in the detection chambers is matched to the carbon dioxide gas in the surrounding radiators by tuning the helium concentration to avoid a hydrostatic pressure difference, which would deform the chamber walls. The chamber pressure is continuously regulated by computer control to maintain it to within 1 μbar of the radiator pressure. The gas gain of each of the four chambers is regulated to better than 0.2% by changing the high voltage under computer control, using the pulse-height spectra of 16 109Ca sources mounted on the chambers. The results of performance studies are described. The detector has a pion efficiency of 98.7% with an electron rejection of a factor of 10. (orig.)