Government was tightening industrial radioactive emission standards to ridiculously low levels, while demanding that homeowners modify their homes to the point where radon doses to the average citizen were hundreds of times greater than the levels dictated to nuclear workers.
Radon is the heaviest of the "noble gases," so named because it - like its cousins neon, argon, krypton, and xenon - does not react with other elements to form compounds. It is radon's "nobility" that minimizes its effects on the body, since it is mostly a transient that is breathed in and then expelled without any chemical reaction taking place. When radon decays in the body, however, it spawns a series of short half-life progeny that are not only chemically reactive with tissue, but are - as we would suspect from their half-lives - also highly radioactive.
[When uranium decays (which isn't very often with a half-life of 4.5 billion years), the products of the decay go through four more stages (taking a couple of million years) until radium is formed. With a half-life of 1,600 years, radium 226 decays into radon gas with a half-life of 3.8 days. The daughters of radon are polonium 218, lead 214, bismuth 214, polonium 214 - and a couple of others. The aforementioned have very short half-lives and are therefore highly radioactive.]
Hazard to Miners?
For years, radon has been thought to be a hazard to miners, and a special confusing unit of activity - the Working Level (WL) - was derived to measure the danger. [One WL is the activity of air containing 100 pCi (3.7 Bq) of radon in equilibrium with its daughters (which, by the way, virtually never happens in the real world) per liter of air. For an approximation, a Working Level Month (WLM) is equivalent to a one-time whole body dose of about 300 mrem (0.3 cGy).]
Recently, however, as evidence of radiation hormesis has emerged, the jury is back out to deliberate a reconsideration of radon's guilt. It is now recognized that other carcinogens - in particular, the particulates suspended in the air of all mines and, more recently, the fumes from diesel engines - were present, but never considered. Radon was assumed to be the carcinogenic culprit, a theory that appears now to be based on flimsy circumstantial and anecdotal evidence.
A related re-evaluation of lung cancer in the Joachimsthal mining community [a famous mine in Czechoslovakia] noted that victims were invariably "pensioners," i.e. miners (not their unexposed, above-ground cohorts) who had made it to a retirement age, which was about ten years longer than their life expectancy. One might easily speculate that the cancer was caused by microscopic dust lodged in the lungs, and the miners' long lives a beneficial product of radon gas. [One of Europe's most famous health spas is Bad Gastein near Salzburg, Austria, which advertises "air with the highest radon content in Europe." The activity of its water is noted in Table 6, in this blog's entry on Monday, January 25, "Specific Activities."]
There has also been a piece of the puzzle right under our noses.
Radon gives its dose of mixed radiation primarily to the bronchial epithelium (fancy scientific words for "windpipe"), hence one would expect cancers caused by radon to be concentrated in this area. Au contraire! The miners' cancers are deep in the lungs [Nobel Laureate Rosalyn Yalow, Radiation and Society, Interdisciplinary Science Reviews, 16, 4, 1991], similar to the cancers caused by the South African amphibole-type asbestos [not to be confused with the common, domestic serpentine type of asbestos, which has not been shown to cause disease], used in ships because of its resistance to brine, acids, and oils.
It is difficult not to see the parallel between non-degradable asbestos fibers in the lungs and non-soluble silica particulates found in most mining environments.
Showing posts with label xenon. Show all posts
Showing posts with label xenon. Show all posts
Saturday, February 6, 2016
Wednesday, February 3, 2016
You Can Run, But You Can't Hide
If an increase in low-level background radiation caused any problems, decades of anecdotal evidence would have made Denver a ghost town.
No one escapes radiation. As mentioned earlier, the average person receives 15,000 "hits" each second, while a medical X-ray may easily score some 100 billion cellular incidents. [Risk of Nuclear Power by Bernard L. Cohen, University of Pittsburg professor. You can read the entire article at http://www.physics.isu.edu/radinf/np-risk.htm.]
Those who say that "it takes only one gamma ray to cause cancer" may be technically correct, but they neglect to mention a small statistical detail: The odds against any particular gamma ray causing cancer in an affected cell are 1 out of 30,000,000,000,000,000. (That's 30 quadrillion, or 30 x 10^15, to one.) Besides, hormesis evidence indicates that the gamma ray of concern is more likely to prevent cancer than to cause it.
Before defining the units used to measure radiation exposure, you may recall we used the SXR (shoe X-ray) as a yardstick to compare the dangers posed by various radiation sources. As you may have guessed, the SXR is not exactly a reference unit recognized by the scientific community. A more convenient benchmark would be the average background exposure that we receive from the various natural and man-made sources. But, as we'll see, this "natural background" value varies by a factor of a hundred or so in different locales on planet Earth - almost all of which is the fault of nature, not man. Still, it would be desirable to reference other levels of radiation to some normal amount; so we'll arbitrarily use, as a definition of "natural background," the exposure to the average U.S. citizen - previously mentioned to be 300 mrem from natural sources and 63 mrem from man-made (mostly medical) origins.
Until the twentieth century, the average background dose of radiation for a human being had continually decreased over our specie's existence because of the slow decay of the primordial radionuclides such as thorium 232, uranium 238, and potassium 40. So what happened during the 1900s that turned the curve upward?
Most people would answer (a) fallout from atom/hydrogen bomb testing, and (b) nuclear power plants. Nice try, but no cigar. Bomb tests did inject huge amounts of highly radioactive materials into the atmosphere, where most decayed to safe levels within ten days of testing. Other longer-half-life isotopes from fallout caused a temporary worldwide increase of background radiation in the neighborhood of 1% to 4% depending mainly on location. [The one of primary concern being strontium 90 with a half-life of twenty-nine years and a propensity to replace calcium in bones.] Today it amounts to less than 1/1000 of the average background level. As mentioned, there has been only a single "fall-out fatality" from atom/hydrogen bomb testing, which occurred on the misnamed Lucky Dragon. While anti-nuclear statistics have killed off many (theoretical) thousands in their quest for an atomic scapegoat, our inaccurate friends have been unable to directly attribute any other death or injury to radiation from fallout, except as a statistical article-of-faith based on the discredited LNT and "collective dose" theories.
Nuclear power plants, on the other hand, have known emissions of radioactive products such as xenon (a non-reactive "noble" gas), but these are so low in practice as to be immeasurable. It is calculated that the average U.S. resident receives a dose considerably less than 1 mrem from all nuclear power plants combined - again, as with fallout, about 1/1000 of the normal background radiation. For those truly troubled by potential radiation exposure, it is not necessary to avoid being in the vicinity of power plants, but you might want to stay away from the U.S. Capitol building and Grand Central Station, both of which emit considerably more radiation than would be legal for any U.S. nuclear power plant to emit.
So where did the increase come from?
If we are to believe a report from the National Academy of Sciences Committee on the Biological Effect of Ionizing Radiation (BEIR IV), most of the increase came from weather-stripping storm doors, and polyethylene wrapping of new homes. Not that any of these products was unusually radioactive, but because they made houses "tight," thus causing radon gas, which bubbles up from decaying radionuclides in the soil, to be trapped in the living areas. This, they calculate, amounts to 200 mrem per year - unless, as well shall see, you are fortunate enough to get more.
The second largest component of the increase is from X-rays and nuclear medicine. The averages used for medically related exposures are somewhat misleading, however, since they range from a 1-mrem dental X-ray to about 100,000 mrem (100 cGy) for a thyroid ablation. [In 1979, the University of Michigan outfitted the husband of a woman undergoing radioactive iodine diagnosis with a dosimeter. They found that he received a dose of 2,500 mrem(!) during their vacation - which would no doubt cause the EPA to forbid them to sleep together.]
In other words, most people fall well below the combined 53 mrem medical dose, while a few have relatively massive doses. As the evidence section will show, even these huge doses of X-rays or medical radioisotopes produce no measurable increase in cancer - and indeed are seen to have a hormetic effect in those cases where low-level effects were investigated.
Finally, about 10 mrem comes from consumer products such as smoke detectors, television receivers, and tritium watch dials. None comes from the process of food irradiation for a very simple reason: The process physically can not make the food radioactive. Does having an X-ray make you radioactive? Same thing.
Table 9 gives a breakdown of sources in the United States, according to the BEIR committee. Obviously, for most of us, our largest dose of radiation comes from natural sources. The exposures from "man-made" sources are almost entirely voluntary. If you don't want to have a dental X-ray, then don't. If your doctor wants to check your thyroid function using iodine 131, tell him, "No thanks, I'll just feel awful for the rest of my life." If you don't want a smoke detector in your home, then don't buy one; burn your family up if that's your preference. Don't watch television or use a computer terminal.
But to avoid the natural background radiation, you need to take some pretty serious steps. Moving to Antarctica or living underwater in a nuclear submarine are your best bets. Or you could also move from high-background-radiation Colorado (with a low age-adjusted cancer death rate) to the low-background-radiation southeastern and eastern coastal states (with high age-adjusted cancer death rates). Then again, you might move out of your high-radon-exposure home in the Reading Prong of Pennsylvania to an area with a lower radon dose rate... but with a higher lung cancer toll.
You're not going to do any of these things. Why? Because if an increase in low-level background radiation caused any problems, we would see evidence - in the form of dead bodies. Decades of anecdotal evidence would have made Denver a ghost town, and Leadville, Colorado - the city with the highest altitude, therefore the most cosmic radiation - would have only monuments to its former short-lived citizens. But the only people who think that there is any such danger are the regulators, anti-nuclear activists, "environmentalists," and government scientists - who cling to the Linear No-Threshold (LNT) Hypothesis. We will be discussing this concept as applied to ionizing radiation, but since our government is so concerned about the doses we receive in this country, let's see what the situation would be if we lived with the background radiation experienced by fellow human beings who live in places outside the United States.
Remember, the average background radiation in the United States is 300 mrem (.3 cGy) plus an average of 63 mrem, primarily from medical sources. And remember that the radiation rules-makers are out to regulate public exposures down to a single mrem (.001 cGy); they intend to put a limit on public exposures at 100 mrem (0.1 cGy).
No one escapes radiation. As mentioned earlier, the average person receives 15,000 "hits" each second, while a medical X-ray may easily score some 100 billion cellular incidents. [Risk of Nuclear Power by Bernard L. Cohen, University of Pittsburg professor. You can read the entire article at http://www.physics.isu.edu/radinf/np-risk.htm.]
Those who say that "it takes only one gamma ray to cause cancer" may be technically correct, but they neglect to mention a small statistical detail: The odds against any particular gamma ray causing cancer in an affected cell are 1 out of 30,000,000,000,000,000. (That's 30 quadrillion, or 30 x 10^15, to one.) Besides, hormesis evidence indicates that the gamma ray of concern is more likely to prevent cancer than to cause it.
Before defining the units used to measure radiation exposure, you may recall we used the SXR (shoe X-ray) as a yardstick to compare the dangers posed by various radiation sources. As you may have guessed, the SXR is not exactly a reference unit recognized by the scientific community. A more convenient benchmark would be the average background exposure that we receive from the various natural and man-made sources. But, as we'll see, this "natural background" value varies by a factor of a hundred or so in different locales on planet Earth - almost all of which is the fault of nature, not man. Still, it would be desirable to reference other levels of radiation to some normal amount; so we'll arbitrarily use, as a definition of "natural background," the exposure to the average U.S. citizen - previously mentioned to be 300 mrem from natural sources and 63 mrem from man-made (mostly medical) origins.
Until the twentieth century, the average background dose of radiation for a human being had continually decreased over our specie's existence because of the slow decay of the primordial radionuclides such as thorium 232, uranium 238, and potassium 40. So what happened during the 1900s that turned the curve upward?
Most people would answer (a) fallout from atom/hydrogen bomb testing, and (b) nuclear power plants. Nice try, but no cigar. Bomb tests did inject huge amounts of highly radioactive materials into the atmosphere, where most decayed to safe levels within ten days of testing. Other longer-half-life isotopes from fallout caused a temporary worldwide increase of background radiation in the neighborhood of 1% to 4% depending mainly on location. [The one of primary concern being strontium 90 with a half-life of twenty-nine years and a propensity to replace calcium in bones.] Today it amounts to less than 1/1000 of the average background level. As mentioned, there has been only a single "fall-out fatality" from atom/hydrogen bomb testing, which occurred on the misnamed Lucky Dragon. While anti-nuclear statistics have killed off many (theoretical) thousands in their quest for an atomic scapegoat, our inaccurate friends have been unable to directly attribute any other death or injury to radiation from fallout, except as a statistical article-of-faith based on the discredited LNT and "collective dose" theories.
Nuclear power plants, on the other hand, have known emissions of radioactive products such as xenon (a non-reactive "noble" gas), but these are so low in practice as to be immeasurable. It is calculated that the average U.S. resident receives a dose considerably less than 1 mrem from all nuclear power plants combined - again, as with fallout, about 1/1000 of the normal background radiation. For those truly troubled by potential radiation exposure, it is not necessary to avoid being in the vicinity of power plants, but you might want to stay away from the U.S. Capitol building and Grand Central Station, both of which emit considerably more radiation than would be legal for any U.S. nuclear power plant to emit.
So where did the increase come from?
If we are to believe a report from the National Academy of Sciences Committee on the Biological Effect of Ionizing Radiation (BEIR IV), most of the increase came from weather-stripping storm doors, and polyethylene wrapping of new homes. Not that any of these products was unusually radioactive, but because they made houses "tight," thus causing radon gas, which bubbles up from decaying radionuclides in the soil, to be trapped in the living areas. This, they calculate, amounts to 200 mrem per year - unless, as well shall see, you are fortunate enough to get more.
The second largest component of the increase is from X-rays and nuclear medicine. The averages used for medically related exposures are somewhat misleading, however, since they range from a 1-mrem dental X-ray to about 100,000 mrem (100 cGy) for a thyroid ablation. [In 1979, the University of Michigan outfitted the husband of a woman undergoing radioactive iodine diagnosis with a dosimeter. They found that he received a dose of 2,500 mrem(!) during their vacation - which would no doubt cause the EPA to forbid them to sleep together.]
In other words, most people fall well below the combined 53 mrem medical dose, while a few have relatively massive doses. As the evidence section will show, even these huge doses of X-rays or medical radioisotopes produce no measurable increase in cancer - and indeed are seen to have a hormetic effect in those cases where low-level effects were investigated.
Finally, about 10 mrem comes from consumer products such as smoke detectors, television receivers, and tritium watch dials. None comes from the process of food irradiation for a very simple reason: The process physically can not make the food radioactive. Does having an X-ray make you radioactive? Same thing.
Table 9 gives a breakdown of sources in the United States, according to the BEIR committee. Obviously, for most of us, our largest dose of radiation comes from natural sources. The exposures from "man-made" sources are almost entirely voluntary. If you don't want to have a dental X-ray, then don't. If your doctor wants to check your thyroid function using iodine 131, tell him, "No thanks, I'll just feel awful for the rest of my life." If you don't want a smoke detector in your home, then don't buy one; burn your family up if that's your preference. Don't watch television or use a computer terminal.
Table 9
|
|||
Sources of Average Annual Radiation for a U.S.
Citizen
|
|||
Natural
Sources
|
mrem/yr
|
cSv/yr
|
%
Total
|
Radon
|
200
|
0.2
|
55
|
Cosmic*
|
27
|
0.027
|
8
|
Terrestrial
|
28
|
0.028
|
11
|
Internal
|
39
|
0.039
|
11
|
Total Natural
|
300
|
0.3
|
82
|
Man-made
sources
|
|||
Medical X-rays
|
39
|
0.039
|
11
|
Nuclear medicine
|
14
|
0.014
|
4
|
Consumer goods
|
10
|
0.010
|
3
|
Nuclear power
|
< 1 **
|
< 0.001
|
-
|
Fallout
|
< 1
|
< 0.001
|
-
|
Total Man-made
|
63
|
0.063
|
18
|
TOTAL
|
363
|
0.363
|
100
|
* Doubles for every 6000 feet in
altitude.
|
|||
** The symbol “<” means “less than.”
|
|||
Source: Department of Energy Report
YMP-0337 from BEIR IV. Available in its entirety at http://www.ocrwm.doe.gov/factsheets/pdf/ymp0337rev1.pdf
|
|||
But to avoid the natural background radiation, you need to take some pretty serious steps. Moving to Antarctica or living underwater in a nuclear submarine are your best bets. Or you could also move from high-background-radiation Colorado (with a low age-adjusted cancer death rate) to the low-background-radiation southeastern and eastern coastal states (with high age-adjusted cancer death rates). Then again, you might move out of your high-radon-exposure home in the Reading Prong of Pennsylvania to an area with a lower radon dose rate... but with a higher lung cancer toll.
You're not going to do any of these things. Why? Because if an increase in low-level background radiation caused any problems, we would see evidence - in the form of dead bodies. Decades of anecdotal evidence would have made Denver a ghost town, and Leadville, Colorado - the city with the highest altitude, therefore the most cosmic radiation - would have only monuments to its former short-lived citizens. But the only people who think that there is any such danger are the regulators, anti-nuclear activists, "environmentalists," and government scientists - who cling to the Linear No-Threshold (LNT) Hypothesis. We will be discussing this concept as applied to ionizing radiation, but since our government is so concerned about the doses we receive in this country, let's see what the situation would be if we lived with the background radiation experienced by fellow human beings who live in places outside the United States.
Remember, the average background radiation in the United States is 300 mrem (.3 cGy) plus an average of 63 mrem, primarily from medical sources. And remember that the radiation rules-makers are out to regulate public exposures down to a single mrem (.001 cGy); they intend to put a limit on public exposures at 100 mrem (0.1 cGy).
Subscribe to:
Posts (Atom)