AZIMUTHALLY CONTROLLED OBSERVATION OF HEAVY COSMIC-RAY PRIMARIES BY MEANS OF THE BALLOON-BORNE EMULSION CHAMBER

We have exposed an emulsion chamber with an area of 1.22 m(2) on board of the balloon at an atmospheric depth of 8.9 g/cm(2) for 15.8 h, whi ch has been azimuthally controlled within the accuracy of Delta phi = 0.5 degrees. With the use of the east-west asymmetry effect of arrivin g cosmic-ray primaries, we can obtain the energy spectra for individua l elements in the kinetic energy range from a few GeV/nucleon up to si milar to 15 GeV/nucleon. We present also the energy spectra obtained b y the opening-angle method for the higher energy region, 5-1000 GeV/nu cleon, for the elements not lighter than silicon. We find that the ene rgy spectra obtained by the former method continue smoothly to those o btained by the latter, indicating that the energy determination using the opening-angle method is performed correctly, We compare also the p resent results with those obtained by the previous work. We find that the iron flux is in nice agreement with that obtained by the previous observation, the differential spectral index being constant, similar t o 2.5, up to a few TeV/nucleon, while in the case of the silicon compo nent, it is similar to 2.7 for 10-1000 GeV/nucleon in this work, signi ficantly harder than the previous one, similar to 2.9. We also report the flux of the sub-iron component and its abundance ratio to the iron component. We find the abundance ratio of [Z = 21-25]/iron is slightl y less than those obtained previously in the higher energy region, gre ater than or similar to 100 GeV/n.