This paper gives the results of a study of single-pion production by the weak charged current utilizing the wide-band muon-type-neutrino beam at the Argonne Zero Gradient Synchrotron. The data were obtained from hydrogen and deuterium fillings of the 12-ft bubble chamber. The methods of event selection and separation from background are given as are the details of the corrections and systematic effects in the data sample. The energy-dependent cross sections and differential distributions are presented for the three single-pion production reactions vp -p p y + , vn +p and vn -p -n r f . An isospin decomposition shows that the ratio of I = , to I = amplitudes is 0.68k0.04 with a relative phase of (90.7k4.6)" for M ( N a ) < 1.4 GeV. This agrees with theoretical models, particularly the detailed calculation of Adler. Using the data of the reaction vp -p-pa+, the characteristic mass of the nucleon axial-vector elastic form factor is measured to be 0.98' ::;GeV when analyzed within the context of the Adler model. The data are also compared to other parametrizations of the nucleon axial-vector form factor. 1161

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