Introduction to Radiation

From the time radiation was first discovered, it has been a term that evokes a certain degree of mystery. Therefore, to really understand various radiation issues, we first need to define the most basic terms.

Radiation = "energy emitted from a source," or "energy that travels."

For example, when you beat a drum, there is a compression of air that occurs upon impact. That air compression travels (radiates) from the drum to your ear, where it may then be perceived as sound. Another example: if you throw a rock into a lake, when the rock hits the water, a circular wave is created that travels (radiates) from the initial impact of the rock. So, radiation is around us all the time. Of course, when you hear of concerns over radiation exposure, it is not because of sound waves or waves in a lake. That brings us to the next definition.

Ionizing radiation = radiation of sufficient energy to ionize atoms and molecules in its path.

An ion is any charged atomic particle (i.e., there is a different # of electrons and protons for the atom). If your body happens to be in the path of ionizing radiation, that ionization may result in health effects (we'll get to the non-ionizing radiation later in this course).

A free radical is any atom with an unpaired electron. Electrons like to occur in pairs, so any unpaired electron is much more likely to be reactive with its surrounding materials. If a free radical is in your body, it will therefore react with all kinds of molecules. Once again, this may exert health effects.

Isotope = any atom with a number of neutrons that is altered from its "normal" state. For example, hydrogen (normally a nucleus of one proton) has two different isotopes by the name of deuterium (a proton plus a neutron) and tritium (a proton plus two neutrons).

A radioactive isotope is an isotope that is relatively unstable and therefore likely to throw off various atomic particles. Once again, if your body is in its path, those particles may exert a health effect.

For all of the above definitions, energy from ionizing radiation is our central concern. That brings us to a set of definitions regarding the four fundamental interactions (or forces) at the atomic level.

1. Gravity = attraction between larger bodies (such as planets and stars).

At the atomic level, gravity is the weakest of all the forces. It cannot adequately explain the interactions at the atomic level. For example, the idea that an atom and its electrons are somehow analogous to the sun and its planets really doesn't hold up, particularly if we are somehow imagining gravitational forces. We need further understanding.

2. Weak forces = forces within certain nuclear particles

The best known example of a weak force is a neutron, which is made up of an electron within a proton. In order to stay intact, it is the weak forces that hold the neutron together. Despite its name, "weak" forces are actually much more more powerful than gravity.

3. Electromagnetic forces = the attraction of opposite charged particles

For example, ionic bonds between negative and positive charged atoms represent electromagnetic forces. This is the second most powerful force at the atomic level, and it helps to explain the bonding of countless chemical bonds.

4. Strong forces = forces that hold a nucleus together

Strongest of all the forces, this is the "awesome force" we refer to when we talk about unleashing the power of the atom, and it is inherent in the energy from nuclear bombs and nuclear power plants. To understand how powerful this force is, consider any atom other than Hydrogen (Hydrogen has only one proton). All the other atoms have more than one proton in the nucleus. But wait a minute! Protons, since they have similar charges, should repel each other. The nucleus should be flying apart if two protons are sitting next to each other, and if that were really the case, the only atom that would ever exist would be hydrogen. Something has to hold these nuclei together, and it happens to be the strong forces.

Now that we have defined the four fundamental forces, we can now define the four fundamental nuclear particles. Of course, there are countless atomic particles that go well beyond the model of neutron - proton - electron. Rather than define and discuss each of these particles, we discuss these four categories.

1. baryons = "heavy particles" that all decay into protons. They include:

  • nucleons = found in nucleus (e.g., protons and neutrons)
  • hyperons = heavier than neutrons (highly unstable, they decay to neutrons or protons) 

2. mesons = "middle particles" found in strong interactions that bind nucleons.

3. leptons = "little particles" that are not subject to strong interactions. The best known example is the electron.

4. photons = particles with zero rest mass (found in light).


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Health Effects of Radiation


1. radioactive half life: time for material to lose half of its radioactivity

2. biological half life: time for living tissue to eliminate, through biological processes, half of a given amount of substance

3. effective half life: (biological half-life * radioactive half-life) / (biological half-life + radioactive half-life)

For example, if the radiaoactive half life of a material is 6 days and the biological half life is 3 days, then:

effective half life = (6*3) / (6+3) = 18/9 = 2 days


Acute effects

4. CNS syndrome:

5. GI syndrome:

6. Bone marrow syndrome:

7. Other:


Chronic effects

8. somatic: skin conditions, alopecia (hair loss), infection, cataracts, cancer

9. genetic (DNA): mutations, birth defects


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Radiation Controls

A. Agencies

1. Nuclear Regulatory Commission: "inside the fence" (of nuclear facilities)

The NRC has principle jurisdiction for regulating nuclear facilities (i.e., "inside the fence").

2. Environmental Protection Agency: "outside the fence" (of nuclear facilities)

The EPA has principle jurisdictin for setting standards in the community (i.e., "outside the fence" of nuclear facilities)

3. Dept. of Energy: research and development

The DOE is also the principle jurisdiction for investigating accidents at nuclear facilities.

4. Others:

  • Public Health Service (standards for medical treatment)
  • Dept. of Transportation (transporting nuclear materials)
  • Dept. of Interior (mining of nuclear materials)
  • NIOSH, OSHA (occupational standards for radiation)
  • FDA (medical devices)
  • NCRP -- National Council on Radiation Protection
  • ICRP -- International Council on Radiation Protection

5. California: California Radiation Control Law (CA Health and Safety Code)


B. Standards

6. 500 mREMs / year: general population

7. 5,000 mREMs / year: occupational population

The reason that occupational populations are allowed more exposure in a year is because they tend to be a healthier population, they tend to have closer monitoring of exposures, and it is generally easier to remove them from a radiation source should the exposures increase.

8. 25 mREMs / year: outside nuclear facilities

Notice that the standards for exposures outside a nuclear facility is very strict in comparison to the general standards listed above. Part of this is due to the fact that it is only one source of radiation exposure, and part of it is undoubtedy due to the public concerns of nuclear facilities.

9. ALARA: as low as reasonably achievable

A principle that can be found thought radiation controls is that exposures should always be as low as is reasonably achievable, even if it is much lower than the above standards. This principle is related to the Best available Technology that we have mentioned in air quality standards.

C. Technological Controls

10. distance: (between source and person) inverse square law

The inverse square law says that the exposure from a radiation source is inversely proportional to the square of the distance. This means that if we double the distance (2), the exposure is cut to one fourth of the original exposure ( 1 / 22 ). If we tripled the distance (3), the exposure is cut to one ninth of the original exposure ( 1 / 32 ). This tells us that there is a tremendous benefit in putting distance between you and the source of radiatio exposure.

11. time: (minimize); spacing allows for recovery

It may seem obvious that the less time we are exposed to radiation, the better off we are. But the benefits are magnified by the fact that spacing of exposures allows the body to recover. For example, if a single exposure of 100 milli-REMs is compared to 10 exposures of 10 milli-REMs, the effect is much less if the dose is spread out over the 10 exposures.

12. monitoring: film badges, finger rings, etc.

13. shielding: barrier between source and person (half value layer: thickness needed to cut radiation in 1/2)

14. contamination prevention: filters, hoods, protective clothing, respirators

15. equipment testing: X-ray equipment, etc.


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