That's what I was afraid of. So it is not going to be a simple matter to detect all the possible dangers, is it?
Rolenrock,
Detecting very tiny amounts of contamination is difficult-to-impossible for most of us under field conditions. One example is alpha particles. These can be stopped by a sheet of paper or a thin film of water. Alpha emitters are extremely dangerous if they are inhaled or ingested and lodge in body tissue. There they will intensely irradiate surounding body tissue. Alpa containation is food is very difficult to detect unless it is on the surface. The food becomes self-shielding if the emitter is even slightly below the surface.
Fortunately, alpha emitters are rarely encountered alone in reactor contamination. They usually occur in combinations with other beta and gamma emitters, making detection easier. Still, very tiny amounts of contamination are hard to detect. As an example, uranium 238 has a half life of 4.5 billion years. If we had a hypothetical single atom of U-238 we could expect one disintegration somewhere in the next 4.5 billion years. I wouldn't sit around holding my breath waiting for it! Even if we knew exactly when that disintegration was to occur and had our geiger counter standing by, there is no guarantee that the geiger-mueller tube would pick up this single event!
In the real world, you don't have to worry about detecting single atoms of anything. Even microscopic contamination particles consist of countless trillions of atoms, usually consisting of different isotopes with varying decay rates. Still, as a general rule it can be stated that smaller amounts of isotopes are more difficult to detect than larger samples.
In some cases, a suspected sample might be placed near a GM tube and the count rate would then be measured over a period of minutes, hours or days compared to a known, non-contaminated sample. Another common method to test suspected contaminated surfaces is the wipe test, where are large area of suspected contamination is wiped with a sample collector (such as a paper towel dampened with water) and then measured. Obviously, one reaches a point of diminishing returns for the effort as sample sizes become progressively smaller and - unfortunately - even the smallest emitter can theoretically cause a cancer!
Fortunately, In the real world, we are constantly surrounded by radiation emitters (both natural and man made) and the vast majority of them do no harm ... or do slight harm that the body repairs.
It becomes a numbers game. Think of it as nuclear roulette, where you try to reduce exposures to reduce your chances of disease. Areas of higher contamination are more likely to result in radiation-related disease than are areas of lower contamination. It really is - ultimately - that simple.
This is the problem with Fukushima and the dynamic that so many people either ignorantly or intentionally avoid dealing with honestly. Contamination rates are still relatively low in North America, but they do exist. This is beyond dispute. Some areas are more seriously contaminated than others. Also beyond dispute. Higher contamination rates result in greater incidents of disease. Period. People can argue the numbers, but not these three basic tenets.
Fukushima effects, in North America at this time, are not about massive amounts of radioactive contamination causing acute radiation sickness or people keeling over dead with their hair falling out. For us, at this time, it is about relatively small amounts of contamination causing relatively small increases in disease and death. In future, it can reasonably be expected to become more severe.
Best regards
Doc
