Absorption of Cosmic Rays in Lead

Abstract

THE absorption curve for cosmic radiation in lead for small thicknesses of absorber (0–30 cm.) has been measured by many observers. The general shape of the curve is not in doubt, but several observers have obtained differences in detail. Clay¹ and co-workers, using ionization chambers, have obtained three maxima at 1.5, 17 and 25 cm. These maxima disappeared when a Geiger–Müller telescope was employed and the absorber was placed within the telescope. With the absorber above the telescope, two rather extended maxima appeared at about 15 and 30 cm. Clay associates these with maxima observed in the absorption curve for showers. George and Appapillai² have used a counter telescope with the absorber placed within it, and find a plateau region at about 10–17 cm., but no maxima. More recently, Fenyves and Haiman³ have obtained pronounced maxima in the absorption curve at 17 and 25 cm. They used counter telescopes and determined two consecutive points simultaneously. (The position of the absorber is not mentioned.) George, Jánossy and McCaig⁴ report that the second maximum in the shower curve is instrumental and not real, unless it be very small.