Ionization Chamber Measurements of the Absorption of theN-Component of Cosmic Rays in Lead

Abstract

A detecting system that responds only to ionization bursts produced by nuclear interactions of the so-called $N$-component of cosmic radiation is described. The burst rate observed with this detector has been measured as a function of the thickness of lead absorber above the system at sea level and at 10,600 feet.The absorption of the $N$-component in lead cannot be represented by an exponential variation of the intensity with absorber thickness; instead the "absorption curve" shows an initial increase in intensity. This behavior may be explained by the assumption that $\ensuremath{\pi}$-mesons with energies of several Bev, which are produced in the nuclear interactions, can give rise to further nuclear interactions.From the altitude variation of the smallest recorded bursts produced by the $N$-component, one finds a value of 119\ifmmode\pm\else\textpm\fi{}5 g ${\mathrm{cm}}^{\ensuremath{-}2}$ for the absorption thickness of the producing radiation in air. The absorption thickness decreases with increasing energy of the nuclear event detected.In the same experiment, other kinds of events were also recorded, which could be produced either by $N$-rays or by $\ensuremath{\mu}$-mesons. The bursts produced by these two components were separated on the basis of the experimental altitude variation of $N$-rays and of the computed altitude variation of the $\ensuremath{\mu}$-meson induced bursts. For our particular ionization chamber about 50 percent of the bursts at sea level produced by charged particles incident on the 219 g ${\mathrm{cm}}^{\ensuremath{-}2}$ lead ionization chamber shield were caused by $\ensuremath{\mu}$-mesons and 50 percent by the $N$-component.