Radiation in Daily Life

  1. Do ONE of the following; then discuss with your counselor the principles of radiation safety:
    1. Using a radiation survey meter and a radioactive source, show how the counts per minute change as the source gets closer to or farther from the radiation detector. Place three different materials between the source and the detector, then explain any differences in the measurements per minute. Explain how time, distance, and shielding can reduce an individual’s radiation dose.
    2. Describe how radon is detected in homes. Discuss the steps taken for the long-term and short-term test methods, tell how to interpret the results, and explain when each type of test should be used. Explain the health concern related to radon gas and tell what steps can be taken to reduce radon in buildings.
    3. Visit a place where X-rays are used. Draw a floor plan of this room. Show where the unit, the unit operator, and the patient would be when the X-ray unit is operated. Explain the precautions taken and the importance of those precautions.

Principles of Radiation Safety

Medical Principles

From a medical perspective, there are three principles of radiation safety1: justification, optimization, and dose limit.

The first, justification, means that any deliberate exposure should have a compelling reason. X-rays, CT scans, etc. are not just because we can, but because the information we obtain is necessary and the benefit of having that information outweighs the risks from the radiation exposure.

Optimization means that the principle of ALARA is used. The exposure should be as low as reasonably achievable (ALARA) while still obtaining the necessary information. For example, if one X-ray is sufficient, don't do two or three.

In a medical setting, dose limits are not usually a consideration. If radiation exposure is being considered at all, it is likely because the health issue being addressed has a significantly higher risk than the radiation. Effectively, dose limits are addressed by the initial justification question.

Radiation Worker Principles

Here, there are also three principles: time, distance, and shielding.

Ionizing radiation sources emit at different rates, specific to the source. So the longer you are exposed by a source, the greater the total amount of radiation you will receive.

Ionizing radiation from a source is (generally) emitted in all directions and so, like light and gravity, decreases with distance a the inverse square of the distance. That is, twice as far away results in four times less radiation exposure.

Shielding refers to material that can absorb and block ionizing radiation. As discussed in earlier sections, alpha particle typically require minimal shielding, as little as a sheet of paper is sufficient. Beta particles require the equivalent of a few millimeters of aluminum, while X-rays and gammas generally require thick lead shielding. Neutrons as best blocked by water shielding.

One reason many nuclear research facilities are built partially underground or have a large earthen berm surrounding them is to act as shielding. This is also why major facilities, like CERN (in Europe) have the accelerator ring completely underground.

Radon in Homes

In the 1980s, a set of circumstances lead to the discovery of radon accumulating in homes, generally in the basements of newer homes.2. Uranium breaks down in to radium which in turn decays to radon, a noble gas which is also radioactive. In some sections of the country, notably in parts of Pennsylvania and northern New Jersey, the natural rock formations have uranium in them. With newer construction homes which tend to be more "air-tight" for efficient heating and cooling, radon levels can build up.3

How Radon Detectors Work

There are two general types of detectors: passive and active.

Passive detectors require no power to operate. They contain a material which detects radon by the trails of radioactive decays radon leaves. These detectors are generally left sitting in the space you want to test for as little as 2-4 days and then returned to a laboratory which will analyze the tracks and send you a report.4 A short-term test is generally considered anything from 2-90 days.5

Active detectors generally need to be operated/installed by a professional technician and calibrated correctly. The setup may cost more than the detector.

Both short and long term detectors are used because radon levels can vary significantly from day-to-day. The general procedure is to do a short term test and, if it shows high levels, follow-up with either another short-term or a long-term test. While there is technically no such thing as a "safe" level of radon, the general recommendation is that levels above 4 pCi/L on a long-term test require remediation.

You'll find other papers on radon exposure which reference SI units. 1 pCi/L is 37 Bq/m3, so 4 pCi/L is 148 Bq/m3. There is approximately a 10% increase in lung cancer risk for every 100 Bq/m3 of radon concentration.6

Radon Mitigation

Radon mitigation falls into a few general methods.7

Seal entry points. Depending on the nature of your basement, this may or may not be feasible. For unfinished basements, sealing cracks, sealing around pipe entrances, etc., can reduce radon entry.

Ventilation. Circulating air from the basement to other parts of the house and outside will reduce concentrations. Radon levels are generally higher in the winter simply because homes are closed up to conserve heat. However, air doe still escape. Since radon is a heavy case, it tends to accumulate in the basement. If levels are not too high, circulating air may be sufficient.

Pressurizing the basement. Putting the basement under positive air pressure reduces the tendency for radon to seep into the home in the first place.

Filtering. Normal air filters do absolutely nothing. Really. There are rather expensive solutions involving carbon/charcoal bed filters onto which radon will be adsorbed (no, that is not a typo, look up the word). My impression from what I've read is that this isn't a particularly good route.