  Neutron veto detector based on liquid scintillator containing hydrogen atoms
is an integral part of any underground experiment for dark matter search. So
far, a flammable mixture of liquid hydrocarbons was used as a liquid
scintillator in such detectors. A safe alternative might be a liquid
scintillator based on liquid argon doped with methane. In this work, we have
studied the primary scintillations in pure liquid argon and its mixtures with
methane, the CH4 content varying from 100 ppm to 5%. The primary scintillations
have for the first time been observed in liquid argon doped with methane, in
the visible and near infrared range, and their relative light yields have been
measured as a function of the CH4 content.
