Is Radiation Really Safe?

Radiation is a form of energy that is present all around us. There are different types of radiation - some have more energy than others. Radiation released into the environment is measured in units called curies. However, the dose of radiation that a person receives is measured in units called rem. Any living tissue in the human body can be damaged by ionizing radiation. The body attempts to repair the damage, but sometimes the damage is too severe or widespread. There are several types of ionizing radiation:

• X-rays and gamma rays
• alpha particles
• beta particles
• cosmic radiation
• neutrons

People are exposed to small amounts of radiation every day, both from naturally occurring sources (such as elements in the soil or cosmic rays from the sun), and man-made sources. Man-made sources include some electronic equipment (such as microwave ovens and television sets), medical sources (such as x-rays, CT scan, fluoroscopy and some cancer treatments), and from nuclear weapons testing. The amount of radiation from natural or man-made sources to which people are exposed is usually small; a radiation emergency (such as a nuclear power plant accident or a terrorist event) could expose people to small or large doses of radiation, depending on the situation.

In general, the amount and duration of radiation exposure affects the severity or type of health effect. There are two broad categories of health effects: stochastic and non-stochastic.

Stochastic effects are associated with long-term, low-level (chronic) exposure to radiation. ("Stochastic" refers to the likelihood that something will happen.) Increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect. Cancer is considered by most people as the primary health effect from radiation exposure. Cancer is the uncontrolled growth of cells. Radiation can cause changes in DNA, the "blueprints" that ensure cell repair and replacement produces a perfect copy of the original cell. Sometimes the body fails to repair these mutations or even creates mutations during repair. The mutations can be teratogenic or genetic. Teratogenic mutations affect only the individual who was exposed. Genetic mutations are passed on to offspring.

Non-stochastic effects appear in cases of exposure to high levels of radiation, and become more severe as the exposure increases. Short-term, high-level exposure is referred to as 'acute' exposure. Many non-cancerous health effects of radiation are non-stochastic. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. Radiation sickness is also called 'radiation poisoning.' It can cause premature ageing or even death.

Exposure (rem)	Health effect	Time of onset
5-10	Changes in blood chemistry
50	Nausea	Hours
70	Vomiting
55	Fatigue
75	Hair loss	2-3 weeks
90	Diarrhoea
100	Haemorrhage
1,000	-Destruction intestinal lining, -Internal bleeding, -Death	1-2 weeks
2,000	-Damage to central nervous system, -Loss of consciousness, -Death	Minutes Hours to days

Children are more sensitive to radiation than adults because children are growing more rapidly, there are more cells dividing and a greater opportunity for radiation to disrupt the process. Fetuses are also highly sensitive to radiation. However, the period during which they may be exposed is short. Other than cancer, the most prominent long-term health effects are teratogenic and genetic mutations. Teratogenic mutations result from the exposure of fetuses (unborn children) to radiation. They can include smaller head or brain size, poorly formed eyes, abnormally slow growth, and mental retardation. Studies indicate that fetuses are most sensitive between about eight to fifteen weeks after conception. They remain somewhat less sensitive between six and twenty-five weeks of gestation. Pregnant women should consult their doctors if they have any concern about radiation exposure to their unborn baby.

The three basic ways to reduce radiation exposure are through:

Time

One should decrease the amount of time spent near the source of radiation. The amount of radiation exposure increases and decreases with the time people spend near the source of radiation.

For example, exposures to radiation is expressed in terms of a committed dose. A committed dose is one that accounts for continuing exposures over long periods of time (such as 30, 50, or 70 years). It refers to the exposure received from radioactive material that enters and remains in the body for many years. In order to assess the potential for exposure in a situation, the amount of time a person is likely to spend in the area of contamination is considered. For example, in assessing the potential exposure from radon in a home, how much time people are likely to spend in the basement is estimated.

Distance

One should increase the distance from a radiation source. Distance is a prime concern when dealing with gamma rays, because they can travel long distances. Alpha and beta particles do not have enough energy to travel very far. As a rule, if one doubles the distance, one reduces the exposure by a factor of four. Halving the distance, increases the exposure by a factor of four.

Shielding

One should increase the shielding between one and the radiation source. Shielding is anything that creates a barrier between people and the radiation source. Depending on the type of radiation, the shielding can range from lead sheets, a plate of window glass or several feet of concrete. Being inside a building or a vehicle can provide shielding from some kinds of radiation. The greater the shielding around a radiation source, the smaller the exposure.

Alpha: A thin piece of light material, such as paper, or even the dead cells in the outer layer of human skin provides adequate shielding because alpha particles cannot penetrate it.

Beta: Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin.

Gamma: Thick, dense shielding, such as lead, is necessary to protect against gamma rays. The higher the energy of the gamma ray, the thicker the lead must be.

It is taken into account the type of shielding that might be provided by soil when sites are assessed that have been contaminated or used for disposal of radioactive material. Also shielding provided by buildings for a person working or living at a site that has been cleaned up is taken into consideration.