Radiation and radiation injury are complex; however, two important concepts facilitate understanding: radioisotopes and ionization The first, radioisotopes (also called isotopes or radionuclides are the physical substances which release ionizing radiation as they decay. These radioisotopes can be toxic on their own without consideration to their radioactivity (or ability to release ionizing radiation). Radioisotopes can be found in any physical state (solid, powder, liquid, vapor, gas, even salts or other compounds). The second concept to understand is ionizing radiation. This is the “irradiation” portion of radioisotopes. Ionizing radiation is the invisible dose of energy that causes biological damage. This damage only occurs when exposed to a radioisotope.2

Four potential sources of radiation injury are:

1. Irradiation (no contamination, similar to an x-ray exposure).
2. External contamination (a radioisotope physically present on the patient that may also be irradiating the patient).
3. Internal contamination (a radioisotope has been inhaled, ingested, or injected into the patient: the radioisotope may also be irradiating the patient internally).
4. Incorporation (uptake of the radioisotope into the cells or tissue: in addition to the potentially heavy metal poisoning, the radioisotope is irradiating the patient internally).

Ionizing radiation is radiation that has enough energy to detach electrons from atoms, creating ions. Ions are atoms that have a positive or negative charge. There are five types of ionizing radiation: alpha, beta, gamma, neutron, and x-ray.3,4 Details of the sources and properties can be found in Table 1. All of these types of radiation can cause clinically significant impacts to a casualty. Clinical effects are determined by isotope, route of exposure, length of time exposed, and strength of and distance from the radiation source.5

Exposure to ionizing radiation can occur from natural and artificial sources. Of greatest concern to healthcare providers is release of ionizing radiation from artificial sources. These include industrial radiography, diagnostic and therapeutic clinical sources, nefarious use as part of a radiological exposure device (RED), radiological dispersal device (RDD), or through nuclear weapon detonation. Table 2 discusses potential radiological and nuclear weapons which can be used to expose a population to ionizing radiation.6,7

Isotopes are two or more forms of the same element that contain a varying number of neutrons. Commonly used isotopes are divided into four categories of concern:

1. The University Five (C14, P32, I125, I131, and Cf252) are used in laboratories and for medical care.
2. The Industrial Three (Ir192, Cs137, and Co60) are found in industrial radiography sources and are prime for terrorist use due to ease of access and the high energy emitted.
3. The Military Five (H3, U235, U238, Pu239, and Am241) are used in making nuclear weapons.
4. Fission products are radioactive decay products released after a nuclear detonation or power plant accident.