Nuclear Terminology: Getting It Right, Part II

This morning on National Public Radio, I heard reports of the third reactor fire in Japan, and a fire now in a storage area. They are reporting an hourly release of radiation into the environment. To follow up on Gary Scronce’s previous blog post (Nuclear Terminology: Getting it Right), I wanted to discuss radiation measurement. The CDC Radiation Emergencies website explains it all very clearly. As Gary wrote, there is a difference between emitted radiation and absorbed radiation dose. To measure both, a sensor needs to be in place to provide that measurement. As a nurse, part of what I have always done is to teach patients and their families about treatments and their effects.

Just to make things more confusing there are different naming conventions for describing radiation that is emitted into the environment—radiation dose and radiation risk. There are “conventional units” (or terminology) that some of us old-timers remember such as the Curie (Ci), rad and rem. Then there is the newer System Internationale (SI) that uses the terms becquerel (Bq), gray (Gy) and sievert (Sv). Reporters have been using both versions of the terminology to describe the events surrounding the fires around the reactor site in Japan.

For emitted radiation that is given off or that is being discussed, the unit of measurement is a becquerel or Curie. However, the news this morning reported that the amount of radiation being released into the environment from the fires was 400 mSv per hour. That term was actually describing the biological risk, not the amount of emitted radiation.

Biological risk from radiation is described using the terms sievert (Sv)  or rem. The older term is rem, however the units of measurement are different. One Sv equals 100 rem. When I recently went through an x-ray unit at security screening at our airport, the TSA agent described my radiation risk in terms of milli-rem or m-rem.

Radiation dose,that is what is deposited in the tissues within the body (the digestive system, through breathing, or absorbed such as with the thyroid) is described using the terms rad or gray. (Gy). For example, individuals who receive external beam radiation therapy for various types of cancer will hear their treatment dose described in rads or Gy per fraction (fraction means the amount of radiation absorbed by the tissue being treated for each time they have their treatment). Remember that therapeutic radiation therapy is designed to kill rapidly dividing cancer cells, which is why it is used as part of a treatment regime. We also know that when our skin and tissues receive too large a dose at one time, a negative consequence can occur, such as with a sunburn.  Too many sunburns or prolonged exposure to the sun over a lifetime can lead to skin changes and/or the development of certain types of skin cancer.

See IEM’s website for more information on our capabilities and experience in Radiological Emergency Preparedness, Nuclear Safety and Security, medical consequence modeling, health and emergency preparedness.


Author: Debbie Kim APRN, MSN, Sr. Health Care System Analyst