On the absorption of the hard component of the cosmic radiation

A phenomenological theory of absorption of mesotrons in the atmosphere and in dense materials at and below sea-level is given. The calculations are based on the following assumptions: (1) absorption due entirely to energy loss caused by electric interactions of charged particles and to spontaneous decay, (2) the localization of mesotron production in an equivalent layer 10 per cent. below the top of the homogeneous atmosphere, and (3) neglect of scattering. From the absorption of vertically incident mesotrons in thick layers of rock the energy distribution in the formation layer is deduced. The energy distribution at sea-level is then determined, without approximations in the analysis, and compared with observations. It is shown that fair agreement is obtained for any reasonable value of the proper lifetime but that a value of about 2 × 10^?6 sec. allows the most favorable comparison of the calculated results and the data. The integral energy distribution and the angular distribution at sea-level are obtained. For the latter it is assumed, as is plausible, that the initial angular distribution is isotropic and that the primary energy distribution is independent of the original direction of motion. The agreement between calculated and observed angular distributions is very satisfactory. The absorption in lead and in light materials for vertically incident mesotrons at sea-level is considered. The need for a more precise definition of equivalent thicknesses is pointed out and the stopping powers of lead and light substances are compared. The absorption in lead is calculated and comparison with the data indicates a slightly larger absorption than is found theoretically. However, the absorption at large lead thicknesses (over 100 cm.) and the qualitative behavior of the absorption coefficient with increasing depth below sea-level are in accord with experiment. The consideration of absorption above sea-level indicates that there should be appreciable mesotron production at elevations comparable to that of Mt. Evans (4,300 meters). This is borne out by recent observations.