The Differential Range Spectrum of Cosmic-Ray Mesons

A counter-controlled cloud chamber has been used to investigate the differential range spectrum of mesons at sea level. The chamber contains eight lead plates each 7½ in. wide and one-half in. thick. A lead absorber of variable thickness, up to 27 in., may be placed above the chamber. The number of mesons observed the stop in the chamber per unit time has been found for various thicknesses of absorber above the chamber. A plot of the counting rate of particles which stop versus the thickness of absorber above the chamber reveals a broad low peak which has its maximum at a 6-in. thickness of absorber. The counting rate at the peak is 2.20×${10}^{-6\mathrm{}}$ count/sec./sterad/g, about 10 percent higher than the counting rate with no absorber. Correction has been made for particles lost through scattering in the absorber. The corrected results show a more marked peak whose maximum occurs with a 9-in. thickness of absorber. The counting rate at the maximum of the corrected curve is 3.73×${10}^{-6\mathrm{}}$ count/sec./sterad/g.