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Nonionizing radiation—Radiation is a general term that simply refers to the emission of energy in the form of waves or particles. Because radio waves, microwaves and ultraviolet radiation are all types of radiation, “radiation-emitting devices” include common sources of daily exposure such as cell phone towers and microwave ovens (Figure 2). These types of radiation, as well as others, are called nonionizing because they lack the energy necessary to remove an electron from a target atom. While most significant clinical injuries are caused by ionizing radiation, in certain circumstances nonionizing radiation can also have biological effects.
Ionizing radiation—An atom consists of a nucleus of positively charged protons and uncharged neutrons orbited by a cloud of negatively charged electrons. In an electrically stable atom, the positive and negative charges cancel each other out, resulting in a neutrally charged atom. On impact, ionizing radiation has enough enrgy to strip an orbiting electron from an atom. The remaining atom then becomes positively charged since the lost electron carried a negative charge. As a result, ionizing radiation poses a significant biologic threat because of its potential to physically alter the structure and charge structure of atoms or molecules.
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hGray, Sievert, Rem and Rad: Radiation Terminology for EMS
Several key concepts are necessary to assess the biological effects of radiation exposure. Clinically relevant radioactive materials emit ionizing radiation that can transfer energy into tissue. Absorbed dose (or simply dose) is the term used to describe the amount of this energy deposited into tissue. In the United States, the traditional unit of dose measurement is the rad (radiation absorbed dose), which is equal to 100 ergs of energy deposited into 1 gram of material. In contrast, the commonly referenced international unit of dose measurement is the gray (Gy), which is equal to 1 joule of energy deposited into 1 kilogram of tissue. One Gy equals 100 rad; conversely, 1 rad equals 0.01 Gy, or 10 mGy. The Absorbed Dose Conversion Chart reproduced in Figure 5 is from The Medical Aspects of Radiation Incidents.10
A common way to quantify biological radiation damage and estimate a resultant risk profile is via the terms rem in the U.S. (Roentgen equivalent man) and sievert (Sv) internationally. These units of measurement are referred to as dose equivalents. They are equal to the delivered radiation dose (rad or Gy) multiplied by a dimensionless weighting factor that benchmarks resultant biological damage to a hypothetical exposure from a standard radiation source (usually gamma or x-rays). In other words, the rem is defined as the dosage of a particular radiation type (measured in rad) that will cause the same degree of biologic injury as 1 rad of either gamma or x-rays. The Dose Equivalent/Equivalent Dose Conversion Chart comparing U.S. and international units of measure reproduced in Figure 6 is from The Medical Aspects of Radiation Incidents.10
Dose Equivalent/Equivalent Dose Conversions
Radioactive materials are quantified differently than many other materials. Instead of using traditional units (e.g., ounces or grams), activity is used. Activity is defined as the number of disintegrations that occur per unit of time (disintegrations per minute, dpm, or disintegrations per second, dps). A disintegration is accompanied by the release of one or more radiation types (e.g., a beta particle or gamma ray). The curie (Ci) is the primary unit of activity in the U.S. and is equal to 3.7 x 1010 dps or 2.22 x 1012 dpm. Internationally the becquerel (Bq) is used, where 1 Bq equals 1 dps.
Read more at Radiation Injury, Burns and Illness: A Review of Best Practices
