There are two types of radiation, ionizing and non-ionizing. Ionizing radiation can break chemical bonds in matter and damage or kill living cells. This produces potentially damaging electrically charged particles, called ions, inside the matter struck. This happens because the tightly held electrons orbiting an atom's nucleus are removed. How dangerous ionizing radiation is depends on its energy is and the interaction it has with the matter being penetrated.

There are several types of particles and rays that can create ionizing radiation. Common types are alpha particles, beta particles, Gamma rays, neutrons, x-rays, and various other subatomic particles such as fission fragments. Not all types of radiation have the same biological effect.

Alpha Particles

A positively charged particle given off during radioactive decay. It contains two protons, which are positively charged, and two neutrons, which have no charge. Alpha particles are emitted from the nucleus of some long lived radioactive elements such as uranium-238, plutonium-239, and radium-226. An alpha particle resembles the nucleus of a helium atom. Alpha particles don't penetrate matter very far. Due to this, they release their energy within the small amount of tissue penetrated. Alpha particles are very ionizing. When they penetrate a tissue they deposit a large amount of energy over a short distance.

Beta Particles

A negatively charged electron (negatron) or positively charged (positron) particle emitted from a nucleus of a radioactive atom. Beta particles are smaller and more penetrating than alpha particles. Some radionuclides that emit beta particles are cesium-137 and strontium-90.

Gamma Ray

A bundle of high energy released from the nucleolus of a radioactive atom. Gamma rays are very penetrating. Gamma rays, along with X-rays, are electrically neutral. This means they are not themselves ionizing, but they transfer their energy to electrons that do ionize.

Non-ionizing radiation does not create ions. It releases its energy in the form of heat and is common in everyday life. Examples include microwaves used for cooking, radio waves, and both ultraviolet and visible light.

Health Impacts of Radiation

The potential health impact of radiation is measured in rem, which stands for roentgen equivalent man. The unit millirem (a millionth of a rem) is used to describe what low radiation does such as a routine x-ray. How dangerous radiation is to one's health depends on the type of radiation, how much of it was absorbed, the radionuclide delivering the dose, the tissue exposed, and how the dose was received. If a low radiation dose is received over a period of time, the human cells can normally repair damage done to them. The low level range includes exposure of about 10 rem. An instantaneous whole body exposure of 10 rem would increase an average person's chance of suffering from fatal cancer by 0.8%, or to a 1 in 125 chance. An acute dose, around 100 rem, causes a person to begin to feel clinical symptoms. This happens because cells may not repair themselves, are permanently altered, or die. While dead cells can be replaced by the body, damaged cells may reproduce abnormal cells. These abnormal cells can lead to cancer and/or other abnormalities. A higher acute radiation dose, around 300 rem, will cause cells to not be able to replace themselves fast enough. This will cause tissues to fail. A person's intestinal lining will no longer take water and nutrients, causing the person to experience radiation sickness symptoms such as nausea, diarrhea, and weakness. The immune system can become damaged and it won't fight off infections. A person only has a 50 percent chance of surviving an acute exposure of 300 rem. A higher dose of 1000 rem can cause vascular damage, preventing prevent blood flow and damaging the nervous system and brain functions. People who have received doses this high are the firefighters at the Chernobyl power plant explosion, victims of atomic bomb blasts, and patients with leukemia undergoing chemotherapy.

References

Gephart, R. E. Hanford: a Conversation about Nuclear Waste and Cleanup. Columbus, OH: Battelle, 2003