Science: Ray Riches

For the past four months physicists of the National Bureau of Standards at Washington have been sending clusters of small sounding balloons to great heights in the upper air. Purpose: cosmic ray research. The balloons carry Geiger-Müller cosmic ray counters, barographs, automatic radios which send signals to a ground station every 15 seconds, recording the altitude (in terms of air pressure) and the intensity of the cosmic bombardment. Last week Drs. L. F. Curtiss and A. V. Astin reported that one cluster of six balloons had reached the remarkable height of 23 miles (about 120,000 ft.). This was believed to be a world record for sounding balloons.†

Drs. Curtiss and Astin found that cosmic rays were thickest twelve miles up, where the intensity is 200 times that at sea level. This agrees closely with the findings of Caltech’s famed Robert Andrews Millikan. who sent balloons to 92,000 ft., recorded a cosmic-ray peak at 66,000 ft.

It appears that about twelve miles up there is a rich mixture of primary rays and of secondary rays created by collisions between the primaries and air molecules. Above that height the air is so thin (i.e., molecular targets are so few) that the secondary radiation falls off. Below twelve miles the total intensity also declines because more & more of the primaries are absorbed by atmospheric resistance.

† Leaving out of account a dubious Soviet claim of 24 miles.