Although radiation hazards are not a new concern, the impact of such hazards on first responders and emergency managers has been brought to the forefront with events such as the terrorist attacks of 11 September 2001 and the earthquake/tsunami nuclear power plant disaster in Fukushima, Japan, earlier this year. These events shed light on the fact that radiation is poorly understood, not only by the public at large, but also (though to a lesser degree) by first responders and emergency managers. That lack of understanding applies both to the terminology involved and to various technical details related to the topic of radiation in general.
The first area in which clarification is needed is in use of the term “radiation.” Many people use the term in a general way, without understanding important distinctions that should be considered. In general, radiation is energy released from a source, and can be listed in two major categories: (a) ionizing radiation, which is caused by the creation of an electrical charge, by stripping away an electron, on a normally neutral atom; and (b) non-ionizing radiation, which comes from energy that is not strong enough to ionize an atom. Non-ionizing energy – such as microwaves, radio frequency radiation, and thermal radiation – imparts energy to an atom, but at levels too low to create a charge on that atom.
In the emergency response field, the type of radiation that raises the greatest concern is ionizing radiation, which releases energy from an atom that is strong enough both to charge atoms and to convert neutral atoms into charged particles. Radioactive materials, the principal sources of ionizing radiation, include both naturally occurring materials in the soil and environment as well as manmade radioactive materials – which are used primarily in industrial and medical applications. Although mechanical devices such as X-ray machines are included in this category, they usually are not a major concern in emergency planning and/or first-response situations because the dangers they might pose can be avoided simply by turning off the device.
Most atoms are stable and do not release radiation; ionizing radiation, though, is released from unstable atoms – i.e., radioactive atoms are ones that release a surplus of energy in order to become stable. An isotope is the version of an element that is unstable and thus releases radiation. The act of releasing energy is known as radioactive decay, which changes an unstable atom into a stable atom. That act can be a one-step process or a multi-step process; in the latter case, an isotope may change sequentially into another unstable atom before becoming stable. The term “half-life” refers to the time that it takes half of a given amount of an isotope to fully decay into its next state, and varies for each isotope.
Alpha, Beta, Gamma – Contamination vs. Exposure
Possibly the most important skill in developing effective radiation protection is understanding the difference between contamination and exposure. Radioactive contamination occurs when particles of material – e.g., dirt, dust, debris – containing radioactive elements become deposited or attached to a person or object. In the field of nuclear weapons this phenomenon is called “fallout” – in the creation, use, and/or disposal of dirty bombs it is called “contamination.” Exposure occurs when the fallout or contamination is close enough to a person for the energy from the radioactive decay to interact with that person's body – whether that exposure causes an obvious reaction or not. Neither contamination with nor exposure to radioactive material changes a person’s stable atoms and/or makes the person radioactive.
The four primary types of ionizing radiation that are of the greatest concern in emergency management and first response are: (α) alpha; (β) beta; (γ) gamma; and (η) neutron. Each can be and isentified by its own unique aspects and by suchentifiable physical characteristics as electrical charge, mass, energy, and prevalence – and, of particular importance, the respective health hazards each poses to human life.
Alpha, beta, and neutron radiation actually possess physical mass. They are tiny portions of the atomic material that are released, whereas gamma radiation is pure energy with no mass. Following are a few additional specifics about each of these types of ionizing radiation:
Alpha – The alpha particle, which is positively charged, is the “large” radiation particle emitted by an atom. Even so, it is only a very small fraction of the total mass of an atom. The combination of its large size and strong charge results in alpha radiation not being able to travel very far and, largely for that reason, being easily prevented from penetrating the human body. Alpha particles travel only a few inches and can be effectively stopped by a piece of paper, normal everyday clothing, or even the layer of dead skin that covers human flesh. An important warning, though: If alpha radiation does manage to get inside the human body, it can be very damaging.
Beta – The beta particle, which is negatively charged, is the smallest radiation particle – significantly smaller than an alpha particle. Its smaller size and smaller charge allow it to travel a greater distance than the alpha can – typically anywhere from a few feet to a few yards. Although it has a greater ability to penetrate, it can still be stopped by a thin piece of plastic. If a large number of beta particles were to come into contact with the skin, they could cause surface skin burns (“beta burns”). As with alpha radiation, any beta radiation can be harmful if it gets inside the body.
Neutron – The electrically neutral neutron, a rather odd creature in the radiation zoo, is rarely encountered. It is much larger than a beta particle, but still only one-fourth the size of the alpha particle. Its lack of electrical charge means that it interacts with very little, making it much more difficult to stop or even detect. Another unusual neutron characteristic is that it seldom exists by itself – outside a nuclear reactor, there are in fact very few sources of neutrons. Typically, neutron radiation is present with some other form of radiation– but some can be generated by the reaction of alpha radiation with certain other materials. Neutron radiation is harmful both inside and outside of the body.
Gamma – This is the most common and by far the deepest penetrating form of radiation; it is also known as X-ray radiation. There is a technical scientific difference between gamma radiation and X-rays, but for planning and response purposes the terms can be used interchangeably. Protection from gamma radiation involves the use of greater amounts of shielding – lead or steel sheets for mobile sources, for example, and concrete walls for stationary sources. Gamma radiation can cause significant physical harm both inside and outside of the body.
Obviously, the immediate availability of radiation detectors is critically important for both emergency responders and emergency managers. Because radiation cannot be detected by a human's physical senses, reliable detection devices are needed to determine its presence. However, most if not quite all such devices are specific to only one type of radiation, and no single device works for all types of radiation. The most useful detector for general use is one for gamma radiation, since many industrial sources have gamma emissions.
In short, a comprehensive understanding of the radiation basics can be a major challenge for first responders and emergency managers. However, knowing the difference between exposure and contamination, as well as the different exposure routes – and the different threats posed by different types of radiation – first responders and emergency managers can and should be able to plan more effectively, and with fewer uncertainties, for most radiological emergencies.