Physical principles and early history

Abstract

The meaning of the term tunnel effect is illustrated by the two parts of Fig. 1. Fig. 1.1a shows a particle of mass m and energy W approaching the left-hand side of a potential energy barrier of height E, and serves as a simple model of a chemical or physical process involving activation energy. Fig. 1.1b shows how G, the probability that the particles will appear on the right-hand side of the barrier (i.e. that reaction will take place) varies with W for a given barrier. G is frequently described as the permeability of the barrier to the particle. The broken line represents the predictions of classical mechanics, and also our everyday experience with macroscopic objects. The probability is zero as long as W < E, rises abruptly to unity when W = E, and remains unity for all higher values of W. This result is independent of the width or shape of the barrier, and also of the mass of the particle.