The absorption coefficient for slow electrons in mercury vapour

Abstract

The effective cross-sectional area of an atom is defined in this paper as that area within which a passing electron is deflected so that it can no longer go through a system of slits defining a beam of electrons. The sum of all these areas in a cubic centimetre of the gas defines the absorption coefficient, the reciprocal of which is the mean free path. The absorption coefficient is a function of the atom studied and the velocity of the electron. It way also depend on the geometry of the apparatus which defines the maximum angle of deflection. From the agreement of the results obtained by several observers with different limiting angles, the variation of the observed absorption coefficient with size of the limiting angle appears to be small. The absorption coefficient is compound from the equation I = I 0 e -α xp , where I is the electron current at the end of the path, I 0 the current at the beginning of the path, x the path length, p the pressure of the gas α the absorption coefficient. Apparatus .—For the measurement of the absorption coefficient a modification of Ramsauer's original apparatus was used. The same modification was previously used for the measurement of the absorption coefficient in other gases giving results in good agreement with those by Ramsauer's more complicated apparatus.