Part 1: Interpolating the Curves

In studying health, we frequently test using very high doses then interpolate linearly to make assumptions about lower exposures. There is no easy and ethical means of measuring all exposure levels. So we interpolate from available data.

But the real effect might not follow the cause linearly. This will lead to very poor estimates.

With radiation, some things are considered logarithmic rather than linear. Both the linear model and the logarithmic model may be inaccurate for predicting the effects of low exposures to radiation.

Over a range of about a decade and a half the square root curve follows closely to the log curve which is normally used to plot radiation's intensity.

Might this imply that the square root curve would be a better choice for plotting radiation, or even a better model for understanding the effects of radiation?

Many Types of Radiation
We use the words radiation and radioactivity to cover a broad range of emissions. Usually, we use the term radiation to mean ionizing radiation, but sometimes we use the term to refer to electromagnetic radiation. Each type of radiation has its own distinct energy and way of interacting. We frequently use the same sensors to detect the presence of many of them. But, each can have a different impact on living tissue.

Many Dimensions of Effects
Just as there a many types of radiation, radiation can have many different effects on materials such as living tissues. Each of these effects will have different health impacts with quite different nonlinear curves.

• Heating: Radiation will heat the tissues that absorb it. A large dose will cause burning. A mild dose some heating. A background dose will cause no observable variations from normal temperatures. For example, turning on the lights in a room cause no observable temperature change for your body. Standing in the bright sun will make you sweat and tan. Staying in tropical sun can cause serious burning even with relatively short exposures. From this example, we recognize that the health impact depends on time. The same dose that is harmful over a short time may actually be good for you over a longer time.
• Current generation: Radiation can create electrical currents in the materials it hits. This is how solar cells work. It is the basis of the discussion in part one. As shown, the effect is known to be nonlinear. How such currents might affect living tissues is not well studied.
• Ionization: Nuclear radiation is also called ionizing radiation. It can ionize, break apart, molecules that it hits. Those molecules become altered. Altered molecules in living tissues will no longer function in the cells as they should. Each cell contains billions of molecules. Ionizing certain molecules will just interfere with the cell temporarily, altering others may cause cell death, and altering DNA may cause mutations that reproduce and spread in future cells. Some of these changes may lead to cancer or birth defects.
• Chemical bonding: Radionuclides are chemical elements so they can deposit in the body the same as any other chemical or poison. This depositing can have unusual delayed effects. For example, the thyroid absorbs iodine. When the iodine decays it emits beta and gamma radiation. The radiation will ionize surrounding molecules. After the decay the thyroid no longer has iodine where it needs iodine, it now has xenon which it doesn't need. The transmutation iodine to xenon will alter the molecules in which it was bonded. Thus, radionuclides have both radiation and chemical impacts on living tissues.
• Resonance: Tissues may absorb non-ionizing radiation through resonance. The best known example is the microwave which heats by vibrating molecules of water and some organic molecules. Although resonance effects have not been highly studied there is evidence that some electromagnetic frequencies change the speeds at which specific biological reactions occur and may alter brain waves.

Each of these effects is most likely nonlinear For heating a specific dose spread out over a long time has much less impact than the same dose over a short time. Doses do not add up. For some of the other effects a specific dose over a long might have a greater effect than the same dose over a short time. There is no easy means to determine the impact of long term exposures.

Many Dimensions of Absorption

Ionizing radiation, neutrons, and radioactive elements are each absorbed differently by different materials. Thus, the definition of a radioactive field is not constant or easy to define. The measure of the radioactive field is totally dependent on which material it is passing through and what type of radiation it is. Thus, the same radiation passing through the air in the room will be different passing through your body (possibly higher, possibly lower), and different as it passes through the walls, and different as it passes through detectors.

Many Sources of Radiation

Radiation has many natural sources - some natural, some anthropogenic. There is a common misconception that humans create radiation and without humans there would be no radiation. This is not true. All living things spend their entire lives bathed in radiation, and always have. It is good to consider where our exposures to radiation come from.

Natural sources

• Mineral deposits
• Cosmic rays
• The sun
• Lightning

Anthropogenic sources

• Wells: water wells bring various buried minerals to the surface including radioactives such as radon.
• Coal burning power plants: coal contains uranium, thorium and other radioactives. When coal is burned the radioactive particles go up the chimney with the ash.
• X-rays& medical isotopes
• Nuclear weapons testing
• Nuclear power accidents (Chernobyl, Three Mile Island, Fukushima)
• Non-ionizing sources: transformers, electronic equipment, cell phones, radio towers
  

From these lists we can see that much of our exposure to radiation comes from hidden non-nuclear sources. A person living down wind of a coal burning power plant, drinking well water, may be absorbing more radiation than a person living near a nuclear plant. However, the types of radiation he absorbs will be different. Thus, its not always clear where to do epidemiological studies on radiation exposure.

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