Intensity and Rate of Production of Mesotrons in the Stratosphere

Abstract

Two free balloon flights have been made with a coincidence-counter apparatus designed to record the vertical mesotron intensity and also the number of mesotrons produced in a 2-cm lead block by a non-ionizing radiation. The results show that the mesotron intensity at first increases with elevation and reaches a maximum at a pressure at about 6.6 cm Hg where the intensity is about 11 times that at sea level. Above this altitude the intensity falls off until at the lowest pressure reached (3.6 cm Hg) the intensity has decreased to about 8 times the sea-level value. Between $p=8\mathrm{}$ cm and 50 cm Hg the mesotron intensity decreases almost exponentially with the mass of air traversed from which we obtain a constant "absorption coefficient" $\mu =1.2\mathrm{}\times {10}^{-3\mathrm{}}$ ${\mathrm{g}}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ for the mesotrons in this range. The production of mesotrons in the lead block becomes noticeable at about 35 cm pressure and increases with altitude at about the same rate as does the soft component. This is evidence that the photons are the agents responsible for a large part of the observed creation in the lead and on this assumption we calculate a cross section for the creation process ${\sigma }_{\mathrm{ph}}=0.7\mathrm{}\times {10}^{-27\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ per nuclear particle in lead.