The Time Variation of Cosmic-Ray Heavy Nuclei

Two 4×4 Ilford G-5 photographic emulsions in contact were exposed to the cosmic radiation in such a way that one plate was moved slowly and uniformly with respect to the other. By this technique it is possible to determine the time at which heavy nuclei pass through the plates. The plates were exposed above 90 000 feet on June 4, 1952, for 8 hours during the day. A reliable altitude record was available and was used to correct for the altitude changes during the 8 hours. 947 heavy nuclei with more than 10 delta rays per 100 microns, corresponding to $Z$ greater than about 10, were traced through and their time of passage measured. This was done by new techniques which are described in detail. The data have been divided into three time intervals. The intensity during the middle interval between noon and 2 p.m. is greater by 25±8.5 percent than the average of the other two. It is concluded that this is due to a real fluctuation in the intensity of of cosmic-ray heavy nuclei at the top of the atmosphere. The possibility that this may be due to a dipole magnetic field of the sun is discussed.