Cloud-Chamber Photographs of Heavy Particles at High Altitudes

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Abstract
A series of 5000 cloud-chamber photographs was obtained at an altitude of 15,500 ft., by use of a chamber in a field of 1165 gauss supplied by a permanent magnet. The determination of mass from cloud-chamber photographs of heavily ionizing particles and knock-on electrons is discussed in general and the methods are applied to specific tracks of the present series. It is shown that the errors of mass determination from cloud-chamber data are large but that there is good evidence for a distribution of mesotron masses. The number of slow mesotrons at 15,500 ft. is about equal to the number of slow protons and amounts to 1 percent of the number of fast mesotrons at that altitude. The extremely rapid increase of slow mesotrons with altitude probably means that they are created as such at high altitudes. One photograph, which shows the pair production of low energy mesotrons, is an example of such a process.