Radiation Exposure

Radiation is as natural as water, and like water, it can be either damaging or essential. While we can see water and understand its effects, most radiation is invisible to us, and its effects are only dimly understood.

Radiation can be of three types. One is pure energy such as sunlight or X-rays. Another class consists of the energetic particles from the nuclei of matter such as neutrons or alpha particles. The third type is something between pure energy and pure matter and is usually an energetic free electron. In any case, we are concerned with the radiation ability to energize and disrupt living cells by either breaking apart too much of the cells' material for them to recover, or worse, mutating the genetic code within the cell.

Everyone is being bombarded with natural radiation of one kind or another all the time, and this type of radiation has absolutely nothing to do with any human activity. The amount of natural radiation an average human receives varies with altitude and the character of the local soil and rocks. The unit of measure is a mrem (an acronym for milliroentgen equivalent in a gram of mammal tissue), and measures about 130 per person per year, but ranges about 80 to 180. Man has, of course, added to the total radiation burden. Standard X-rays expose the patient to 50-500 mrem per film; new dental X-ray machines and films allow for much lower doses--about 20 mrem per exposure. The average person receives about 95 mrem per year from diagnostic X-rays. Effects of world-wide nuclear weapon experimentation are small (about 5 mrem per year).

Large controlled doses of radiation can be effective in the treatment of cancer. On the other hand, radiation can also cause cancer. There are numerous ways this may occur. Examples are: exposure to too much sun too often; living at a high altitude (where radiation from the sun is less impeded by the atmosphere) or near natural radioactive deposits) being exposed to a large radiation dose over a relatively short period of time; or having a minute radioactive particle lodged in the body for a long time.

Just because something is radioactive does not necessarily mean that it is harmful. An example of a harmless radioactive substance is the "salt substitute" found in many homes and at most grocery stores-potassium chloride. Potassium is and will always be slightly radioactive. But it is absolutely essential in substantial, but balanced quantities for life, and will trigger a sensitive Geiger counter. The potassium in a human contributes about 3-6 mrem per year to the total radiation burden.

Consider that a single four-hour flight in a modern jet plane adds about 1-3 mrem. A commuter who flies four hours per week receives an additional 50-150 mrem per year and an air crew member receives 400-1100 mrem per year. Are these harmless doses?

Genetic damage in humans will start with about 7000 mrems received over a short period of time (days or less). A technician working with radiation should not receive more than 300 mrem in one week, and is not expected to routinely work near that limit. Once again, we are reduced to relying on accurate statistical studies and experience as to how much radiation is acceptable.