  Neutrino interactions recorded in a 5.1 fiducial kiloton-year exposure of the
Soudan-2 iron tracking calorimeter are analyzed for effects of neutrino
oscillations. Using contained single track and single shower events, we update
our measurement of the atmospheric nu_mu/nu_e ratio-of-ratios and find R = 0.68
\pm 0.11 \pm 0.06. Assuming this anomalously low R-value is the result of nu_mu
flavor disappearance via nu_mu to nu_tau oscillation, we select samples of
charged current events which offer good resolution, event-by-event, for L/Enu
reconstruction. Oscillation-weighted Monte Carlo events are fitted to these
data events using a chisq function summed over bins of log(L/E_nu). The region
allowed in the (sin^2 2\theta, \Delta m^2) plane at 90% CL is obtained using
the Feldman-Cousins procedure: 0.46 < sin^2 2\theta < 1.0 and 2.2x10^-4 <
\Delta m^2 < 2.2x10^-2 ev^2. A small but relatively energetic sample of
partially contained nu_mu events has also been isolated. Their distribution in
log(L/E_vis) relative to null oscillation Monte Carlo is compatible with nu_mu
to nu_tau oscillation scenarios within the parameter region allowed by our
contained events.
