Effects of radioactivity

We are continuously bombarded by radiation from both natural and artificial sources. We are exposed to infrared, ultraviolet, and visible radiation from the sun; radio waves from radio and television stations; microwaves from microwave ovens; X-rays from medical procedures; and radioactivity from natural materials. Understanding the different energies of these various kinds of radiation is necessary in order to understand their different effects on matter.

When matter absorbs radiation, the radiation energy can cause atoms in the matter to be either excited or ionized. In general, radiation that causes ionization, called ionizing radiation, is far more harmful to biological systems than radiation that does not cause ionization. The latter, called non-ionizing radiation, is generally of lower energy, such as radiofrequency electromagnetic radiation or slow-moving neutrons.

When ionizing radiation passes through living tissue, electrons are removed from water molecules, forming highly reactive H₂O⁺ ions. An H₂O⁺ ion can react with another water molecule to form an H₃O⁺ ion and a neutral OH molecule:

H₂O⁺ + H₂O → H₃O⁺ + OH

The damage produced by a radiation depends on the activity and energy of the radiation, the length of exposure, and whether the source is inside or outside the body. Gamma rays are particularly harmful outside the body because they penetrate human tissue very effectively, just as X-rays do. Within the body, alpha rays are particularly dangerous because they transfer their energy efficiently to the surrounding tissue, causing a considerable damage.

Figure 6. Relative penetrating abilities of alpha, beta, and gamma radiation.

In general, the tissues damaged most by radiation are those that reproduce rapidly, such as bone marrow, blood-forming tissues, and lymph nodes.

Application of radioactivity

Radioactivity is used to determine the mechanisms of chemical reactions, to trace the movement of atoms in biological systems and the environment, and to date historical artifacts. Nuclear reactions are also used to generate electricity. Other areas of application of radioactivity include medical therapy and diagnosis, food preservation, and pest control.