The effects of radiation on plant materials depend on both the type of radiation and the type of material. This chapter discusses atomic displacements resulting from the various types of radiation.

EO 1.16 STATE how the following types of radiation interact with metals.

a. Gamma d. Fast neutron

b. Alpha e. Slow neutron

c. B eta

EO 1.17 DEFINE the following terms:

a. Knock-on b. Vacancy c. Interstitial

Overview

Ionization and excitation of electrons in metals is produced by beta and gamma radiation. The ionization and excitation dissipates much of the energy of heavier charged particles and does very little damage. This is because electrons are relatively free to move and are soon replaced. The net effect of beta and gamma radiation on metal is to generate a small amount of heat.

Heavier particles, such as protons, -particles, fast neutrons, and fission fragments, will usually transfer sufficient energy through elastic or inelastic collisions to remove nuclei from their lattice (crystalline) positions. This addition of vacancies and interstitial atoms causes property changes in metals. This effect of nuclear radiation is sometimes referred to as radiation damage.

In materials other than metals in which chemical bonds are important to the nature of the material, the electronic interactions (ionizations) are important because they can break chemical bonds. This is important in materials such as organics. The breaking of chemical bonds can lead to both larger and smaller molecules depending on the repair mechanism.

In either case there are material property changes, and these changes tend to be greater for a given dose than for metals, because much more of the radiation energy goes into ionization energy than into nuclear collisions.