ATMOSPHERIC MUON NEUTRINO FRACTION ABOVE 1 GEV

A 2.1 ktonyr exposure of data from the Irvine-Michigan-Brookhaven dete ctor has yielded 72 atmospheric neutrino events with a vertex containe d inside the fiducial volume and at least 0.95 GeV of visible Cerenkov energy. The ratio of these two ratios (muonlike/total)(Data)/(muonlik e/total)(MC) was found to be 1.1(-0.12)(+0.07)(stat) +/- 0.11(syst). T he zenith angle dependence of this ratio of ratios is consistent with being flat. The region of sin(2)(2 theta) > 0.5 and delta m(2) > 9.8 x 10(-3) eV(2) has been excluded to the 90% confidence level for nu(mu) --> nu(e) oscillations while the region of sin(2)(2 theta) > 0.7 and delta m(2) > 1.5 X 10(-2) eV(2) has been excluded to the 90% confidenc e level for nu(mu) --> nu tau oscillations.