Mesotron Production in the Atmosphere

Abstract

With Geiger-M\uller tubes arranged for fourfold vertical coincidence, a Rossi-Hsiung type of experiment was performed in an aeroplane up to an altitude of 25,000 feet. A sheet of lead 8.1 cm thick placed between the counter tubes and another lead plate of 2.2 cm thickness was alternately changed from the position above all the tubes to a position between the second and third tubes. From the difference between the counting rates in the two cases, it was found that at an altitude of 25,000 feet an average of 2 ionizing penetrating particles (mesotrons) per minute were ejected in the forward direction from a lead plate (38 cm\ifmmode\times\else\texttimes\fi{}5.2 cm\ifmmode\times\else\texttimes\fi{}2.2 cm) by the action of non-ionizing rays (photons). This value aleads to a cross section for the production of mesotrons by photons which is in at least rough agreement with the theory.