The Secondary and Tertiary Particles Produced by Cosmic Rays

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Abstract
A search, by means of Geiger counters, was made for scattered cosmic rays in the region around a large iron block but no scattering could be detected. Experiments were tried with one counter just above a metal plate and two counters, placed side by side below it. It was found that the metal plate increased the number of triple coincidences between the three counters. The increase in the number of triple coincidences rose to a maximum and then diminished to zero as the thickness of the metal plate was increased. This effect was observed with plates of lead, tin and aluminum. It was greatest with lead and very small with aluminum. The results can be explained by supposing that secondary particles from the air above the apparatus produce tertiary particles in the metal plate which pass through the lower counters. The absorption coefficient of the air secondaries in lead was found to be 0.5 and that of the lead tertiaries to be 2.58.

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