Radiation sensors and actuators
The modern world has an almost innate fear of nuclear radiation. It may be the heritage of Hiroshima and Nagasaki or it may be that we just fear the unknown, the invisible, and of course there are some very good reasons to be careful. Nuclear radiation can cause damage to cells and in high doses is known to cause cancer or even death. However, radiation comes in many shades and forms. All electromagnetic waves fall in the same general category of radiation, the difference being only in frequency (and with it in energy). If one were to imagine an instrument with a dial that can change the frequency from zero to infmity, then as the frequency would rise, it would first generate low-frequency fields, first in the audio range, then into ultrasonics, then above about 200 kHz, into what colloquially is called radio waves. Further up, the instrument will pass through very high frequency (VHF), ultra-high frequency (UHF), and then into the microwave region. Beyond that lies millimeter waves and then infrared (IR) radiation, followed by visible light and ultraviolet (UV), then into X-rays, α, β, and γ rays, and further up into cosmic rays. As the frequency increases, the energy associated with the waves increases, and the radiation effects become more pronounced. As is generally known, UV and X-rays are harmful radiation and are part of the cumulative effect of radiation in our lives and health. It is expected that people working with X-rays will naturally be exposed to more radiation than those who may only have a scan in a lifetime. Pilots and frequent fliers will necessarily be affected by cosmic rays as are astronauts in space. But beyond these, there is a background radiation level more or less constant over the globe. It is a low-level radiation caused by radioactive isotopes in rocks and soils of the order of 20-50 becquerel/minute (Bq/min) that can be detected with Geiger counters. This radiation is of no consequence to health, as it is too low to do any damage. The exposure level is, on an average, about 2.4 millisievert/year (mSv/yr). But there are locations and conditions in which the background radiation can be higher and of more concern. Granite rocks and hot springs tend to have higher radiation levels, and certain areas around the globe have naturally occurring high radiation levels as high as 250 mSv/yr or higher. On the other hand, sedimentary rocks and limestone have lower levels. Underground locations, including quarries, mines, or even basements, can have higher levels primarily from radon (a decomposition by-product of naturally occurring uranium and its isotopes), and radon can be found in the atmosphere as well as in water. However, beyond reasonable caution, it should be remembered that these are natural sources that have been there from time immemorial and will be with us for any imaginable future.
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