Search for massive neutrinos in muon-capture: development of a gas scintillation detector

A measurement of the triton recoil-spectrum from the reaction mu /sup -/+/sup 3/He+/sup 3/H+ nu /sub mu / should allow the observation of possible heavy neutrinos in the mass range 30-90 MeV. The ideal tool for the determination of the kinetic energy of the triton in a gas scintillation proportional chamber (GSPC). Two problems have to be solved in building a Helium-GSPC. The first one is that there is a mismatch of the emission spectrum (600-1000 A ) with the sensitive region of the photomultiplier. The goal of these tests is to show that small quantities of nitrogen (100-5000 p.p.m.) added to the gas can replace the normally used wavelength shifters. Secondly, with its quenching property, nitrogen should prevent the UV-light to reach the walls of the counter where these hard photons from He/sub 2//sup +/ can cause photoeffect and liberate new electrons.