Determination of the flux of primary cosmic ray hydrogen and helium nuclei near the geomagnetic equator using nuclear emulsions

Nuclear emulsions exposed to the cosmic radiation over Hyderabad, India, at an altitude of 31·3 km. for six hours, have been used to derermine primary cosmic ray deuteron flux. The flux of deuterons of rigidity ?16·9 GV at the top of the atmosphere is found to be <10 m.^?2 sec.^?1 sterad^?1; this may be compared with the proton fiux of 83±12 m.^?2 sec.^?1 sterad.^?1 in the same rigidity region over Hyderabad.