[en] In the Standard Model, the weak interaction is purely V-A in character. However in semileptonic reactions the strong force induces additional couplings. One of these, the induced pseudoscalar coupling g_p, is still very poorly determined experimentally. Using PCAC and the Goldberger-Treiman relation, one can obtain the estimate g_p/g_a = 6.8 for the nucleon. At present, the world average of 5 measurements of the rate of ordinary muon capture (each with an error in excess of 40%) yields g_p/g_a = 6.9 ± 1.5. Radiative Muon Capture (RMC) is considerably more sensitive to the pseudoscalar coupling. Due to the extremely small branching ratio (∼ 6 x 10^-8), the elementary reaction μ^-p→ μnγ has never been measured. Effort to date has concentrated on nuclear RMC where the branching ratio is much larger, but the interpretation of these results is hindered by nuclear structure uncertainties. A measurement is being carried out at TRIUMF to determine the rate of RMC on hydrogen to a precision of 8% leading to a determination of g_p with an error of 10%. The detection system is based on a large-volume drift chamber acting as a pair spectrometer. The drift chamber covers a solid angle of about 2π. At a magnetic field of 2.4 kG the acceptance for 70 MeV photons is about 0.9% using a 1.2 mm thick Pb photon converter. The expected photon energy resolution is about 10% FWHM. A detailed discussion of the systematic errors expected in the experiment and the preliminary results on the performance of the detector will be presented