Radiation Exposure

April 2011

Thomas P. Moyer, PhD
Michael K. O’Connor, PhD

Release of nuclear fission byproducts from the nuclear power plant in Fukushima, Japan has caused concern about radiation exposure in areas outside of Japan. This short paper outlines the nature of the radiation from these byproducts, and reviews the radiation levels and dangers associated with this incident relative to the normal background levels of radiation present in the United States.

Types of Radioactivity

There are 3 primary types of radiation—alpha, beta, and gamma. All 3 types of radiation cause harm to the body by depositing some of their energy into the cells. This can damage cells resulting in either impaired cellular function or cell death.

Two types of radiation are particulate–alpha particles and beta particles. Exposure to either alpha or beta particles from outside the body causes damage to skin akin to a sunburn, but the particles cannot penetrate deeply enough to affect internal organs. The major concern for these types of radiation is ingestion or inhalation of alpha- or beta-emitting radioisotopes. Once absorbed, they can cause damage to nearby tissue.

• Alpha particles are released during decay of heavy elements (for example: tellurium); alpha particles are molecules of helium that have very high energy. They do not penetrate surfaces deeply because of their mass.
• Beta particles are electrons released during decay of elements such as iodine-131. They are lower in mass than alpha particles and can penetrate a little further into tissue.

The third type is high energy electromagnetic radiation, called gamma radiation (or x-rays depending on its origin). Gamma and x-rays are energetic enough that they can penetrate and cause damage to the entire body. Gamma rays and x-rays are pure energy, similar to light but at a different wavelength.

Units of Measure

Radioactivity is measured in units of Becquerels or Curies (different scales–like Fahrenheit and Celsius). The most common unit is a megaBecquerel (MBq) and one that we will use below to describe levels of radioactivity. The second unit relevant to this review is exposed radiation dose, ie, how much energy from the radiation was deposited into your body by alpha, beta, or gamma rays. The usual unit of exposed dose is the Sievert. Most common doses are measured in units of milliSieverts (mSv) or microSieverts (uSv), where 1 mSv =1000 uSv.