Geiger tube planes as a trigger for the nucleon lifetime experiment in the Frejus tunnel (France)

Abstract

Geiger tubes of 6 m length made of extruded aluminium in 6 m lsx 6 m planes been developed at Orsay to be used as a trigger for the nucleon lifetime experiment in the Frejus tunnel (Aachen-Orsay-Palaiseau-Saclay-Wuppertal Collaboration). There will be 185 trigger planes which correspond to about 65 000 tubes. The use of aluminium tubes is advantageous because of their low cost mass production, but obtaining a stable Geiger mode operation of aluminium tubes of such dimensions is difficult and requires a preliminary mechanical treatment of the surface. Safety regulations in the tunnel limit the choice of gas. The gas used is a non-inflammable mixture of argon, ethyl-alcohol (2%) and Freon (0.05%). The two characteristics parts of the Geiger pulse: steep rise in about 50 ns, followed by a long part lasting about 30–70 μs are both advantageously used, the first to build a fast trigger, the second as a kind of natural memory. Moreover, the relatively high Gieger signal reduces amplification requirements, thereby simplifying the electronics.