Page 150 - Radiochemistry and nuclear chemistry

Absorption of Nuclear Radiation 135

6.4.1. Ionization

Beta-particles lose their energy primarily by the same mechanism as et-particles (Fig. 6.7a
and b); however, there are several important differences. Since the masses of the/3-particles
and of the orbital electrons are the same at non-relativistic velocities, the/3-particles can
lose a large fraction of their energy in a single collision. The/3-particle undergoes a wide
angle deflection in such collisions and consequently/3-particles are scattered out of the
beam path all along the length. The secondary electrons ionized from the atom have such
high energies that they cause extensive secondary ionization which provides 70-80 % of the
total ionization in 13-absorption processes (Fig. 6.5b). Approximately half of the total

FIG. 6.8. Schematic description of the five processes accounting for/3-particle absorption.