Radiation Exposure

How energy from radiation is transferred to the body depends on the type of radiation. Visible light and infrared radiation, for example, transfer their energy to entire molecules. The absorbed energy causes greater molecular vibration, which can be measured as heat (or thermal energy).

With many forms of ionizing radiation, energy is transferred to electrons that surround atomic nuclei. Atoms affected by x rays usually absorb enough energy to lose some of their electrons, and so become ionized. (An atom is ionized when it gains or loses electrons and acquires a net electric charge.) Ultraviolet radiation causes electrons to absorb energy and jump to a higher energy orbit around the atomic nucleus. The sun and sunlamps emit enough ultraviolet radiation to cause sunburn, premature aging of the skin, and skin cancers. Exposure of humans and animals to ultraviolet radiation also results in the production of vitamin D, a biochemical necessary for good health.

Radiation that consists of charged particles can knock electrons out of their orbit around atoms. This also creates ions. Such radiation can also cause atoms to enter an exited state, if the electrons are bumped into higher-energy orbits. These changes result in atoms and molecules (including biochemicals) that are chemically reactive. Seeking to become stable, they interact with unaffected atoms and molecules, which may be damaged (i.e., changed) in the process, and are then unable to perform their usual metabolic functions. For example, nuclear material such as DNA molecules may be damaged to the degree that they can no longer be accurately copied. This may lead to impaired cell function, cell death, or genetic abnormalities.

Neutral particles of radiation, such as neutrons, transfer their energy to nuclei rather than to electrons. Often, neutrons strike a single proton, like that in a hydrogen nucleus, causing it to "recoil" and in the process be separated from its electrons, leaving a single, positively charged proton (this is also an ionization reaction). The neutron is then less energetic, and is captured by another nucleus, which releases charged particles in turn.

The specific effects of radiation on living beings depends on the type of radiation, the dose, the length of exposure, and the type of tissue exposed to the radiation. Damage caused by exposure to high levels of radiation is divided into two categories: somatic and genetic. Somatic refers to effects on the physiological functioning of the body; genetic refers to damage caused to reproductive cells, including heritable effects that can affect offspring.

Genetic damage can include mutations or broken chromosomes, the structures in cell nuclei that house DNA, and the all the genetic information of an organism. Many mutations, or changes in genes, are harmful. Mutations caused by radiation are fundamentally the same as mutations caused by any other influence.

Somatic damage from high doses of ionizing radiation is indicated by burns and radiation sickness, with symptoms of nausea, vomiting, and diarrhea. Long-term effects can include cancers such as leukemia. Cells are killed outright if a high dose of ionizing radiation is delivered in a short amount of time. Symptoms may appear within hours or days. The same dose delivered over a long time will not produce the same symptoms, because the body has time to repair some of the damage caused during a long-term exposure. However, some cells may experience genetic damage that causes some forms of cancer to develop years later (this is called a latent effect).

Exposure to intense doses of high-energy electro-magnetic radiation, of the kind occurring close to radar towers or large radio transmitters, is less common than exposure to radioactivity. However, when it does occur it can cause cataracts, organ damage, hearing loss, and other disorders to develop. The health consequences of exposure to low doses of electromagnetic radiation are the subject of much controversy. Significant health effects have so far been difficult to detect.