The Effect of Primary Cosmic-Ray Energy Upon Burst Production

The fact that the intensity of burst and shower production increases with altitude much more rapidly than does the cosmic-radiation intensity itself lead one of us to the view that the intensity of burst production was a rapidly increasing function of the energy of the primary cosmic rays. If such is the case, burst production per unit intensity of primary, by primary rays which are limited to a vertical direction, should be much larger than the corresponding quantity for primary rays limited to directions in the neighborhood of 45 degrees, since the latter rays have traveled a much greater thickness of atmosphere. To test this conclusion we set up an apparatus comprising a one-inch thick iron sphere suitably arranged as a burst-measuring ionization chamber. One set of counters was placed vertically above and another was placed vertically below the center. The two were used as a double coincidence set. Coincidences between the counter discharges and the bursts produced serve to indicate which bursts were produced by the vertical rays determined by the counter system. An exactly similar pair of counters arranged at 45 degrees to the vertical gave the information for this direction also. The experiments show that while over a period of 300 hours the numbers of counts obtained by the vertical and 45 degree counters were in the ratio of 1.5 to 1, the corresponding numbers of bursts (involving more than 2×${10}^6$ ions) were in the ratio of 10 to 1, which result confirms the conclusion cited above. It is possible to calculate from the experiments of C. G. and D. D. Montgomery at sea level and at Pike's Peak the magnitude of the effect to be expected in the present experiment on the basis of the general ideas formulated as controlling the phenomenon. The agreement obtained is within the limits of accuracy of the experiments.