Biological Effects of Radiation

Energy emitted from a source is generally referred to as radiation. Examples include heat or light from the sun, microwaves from an oven, X rays from an x-ray tube, and gamma rays from radioactive elements.

Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized.

Ionizing radiation has enough energy to electrically charge or ionize matter. The cells in living organisms are also made of matter, so they too can be ionized. Cosmic rays, x-rays, gamma rays, alpha particles and beta particles are forms of ionizing radiation. Ionizing radiation may come from a natural source such as the Sun or it may come from a man-made source such as an x-ray machine. The possibility of overexposure to ionizing radiation among members of the general public is minimal. However, there are environments such as hospitals, research laboratories and areas of high level natural background radiation where some potential health risks do exist. The effect of ionizing radiation on the human body or any other living organism depends on three things:

  1. The amount and the rate of ionizing radiation which was absorbed.
  2. The type of ionizing radiation which was absorbed.
  3. The type and number of cells affected.

The amount of radiation an organism receives is a very important factor in determining its biological effect. The greater the amount of ionizing radiation and the greater the number of times an organism is exposed, the greater the health risk if the doses are high. The average Canadian receives about 2.7 mSv (millisieverts) of ionizing radiation per year from both natural and man-made sources but a single CT scan can give you 10 times that amount (27 mSv) all at once. A lethal dose is about 5000 mSv. This means that at 2.7 mSv per year, you would have to live over 1800 years to receive the equivalent dose from your environment, but in order to be lethal that total dose would need to be given all at once.

The type of radiation absorbed is a factor in determining the biological effect of ionizing radiation on an organism. Each type of ionizing radiation has its own characteristics. Alpha particles are fairly large in size and carry a double positive charge, so they tend to travel only a short distance and do not penetrate very far into tissue if at all. However alpha particles will deposit their energy over a smaller volume (possibly only a few cells if they enter a body) and cause more damage to those few cells. Beta particles are much smaller and carry a single negative charge. They will penetrate farther into the body, which means they tend to damage more cells, but with lesser damage to each. Gamma rays and x-rays are pure energy and have no mass. They are deeply penetrating and can easily pass completely through your body, but may still interact with many atoms as they pass through. Both x-rays and gamma rays spread their energy over a larger volume, which causes less damage per collision. Of course, at very high levels of exposure they can still cause a great deal of damage to tissues. Because of their penetrating ability, they can easily reach internal organs and bones which is why large doses can be used to damage cancer tissue.

The type and number of cells affected is also an important factor. Some cells and organs in the body are more sensitive to ionizing radiation than others. Cells that divide rapidly like those found in bone marrow, stomach, intestines, male and female reproductive organs, and developing fetuses are more sensitive to ionizing radiation than cells that make up skin, kidney or liver tissue. Children and young adolescents also are more sensitive to ionizing radiation because their bodies are still growing. The biological effects of ionizing radiation are well known. The nuclear industry is closely monitored and inspected to ensure that safety procedures and regulations are precisely followed to protect workers in the industry, as well as the public and the environment.

Sources:

World Health Organization.(2014).What is Ionizing Radiation? www.who.int/ionizing_radiation/about/what_is_ir/en/index.html.