We have been led to believe - on the basis of the LNT theory and collective dose - that terrorists could mount an effective attack by the use of "dirty bombs," i.e., bombs that spread radioactive materials by use of conventional explosives. At present, such bombs would be an effective weapon, since the fear of radiation, as in Goia and Three Mile Island, would doubtlessly cause panic and result in deaths from heart attacks, auto accidents and the like. But if we understand the actual effects of radiation, we can respect it without allowing it to overcome our rational thought. Let's look at the worst case.
Terrorists park a car bomb filled with strontium 90, which has a long half-life (twenty-nine years) and the propensity for replacing calcium in bones. At noon, with the maximum numbers of people walking down Wall Street on the way to lunch, the bomb is exploded, and strontium 90 is blasted into the air. Radioactive debris is scattered by the wind over an area of many blocks.
Let's look at this scenario as graduates of Hormesis U. First, where are the terrorists going to get a carload of strontium 90? It is a product of nuclear explosions and found in reactor "wastes." Like so many other "waste" radionuclides, it is a valuable commodity being used in medical and agricultural tracers as well as in RTGs (radio thermo-electric generators) for navigational beacons and weather stations. Medically, it is used for treatment of eye diseases and bone cancer. It is a valuable commodity and certainly not widely available in quantities like the ammonium nitrate and fuel oil used in the Oklahoma City bombing.
The EPA's Radiation Information website [www.epa.gov/radiation/radionuclides/strontium.htm] tells us that "swallowing Sr-90 with food or water is the primary pathway of intake."
The same source tells us that strontium 90 is a beta emitter. Graduates of Hormesis U. know that beta radiation can travel only a few feet through air and causes minor burns (beta burns) to exposed skin. Knowing this, what action would be required after a terrorist went to the trouble and expense to disburse this most dreaded of radioactive materials in the canyons of Manhattan? I would suggest a warning to the local inhabitants not to lick the pavement or buildings. After that, I would wait for a rain that would wash the dust down the sewers leading to the Atlantic Ocean, where there are already quadrillions of curies (septillions of becquerels) that will still be there long after the vestiges of strontium 90 have disappeared. A potential problem: the sewer rats might be affected bio-positively and take charge of the large metropolitan cities.
So much for dirty bombs.
Showing posts with label beta burns. Show all posts
Showing posts with label beta burns. Show all posts
Sunday, April 10, 2016
Sunday, January 31, 2016
A Very Short History of Radiation Hormesis
The extremely tall people on Niue Island (averaging height 6'6") receive 10 times more radiation from the soil than the world average. [Eugaster, Subradiation experiments concerning the concept of the natural radiation background, Aerospace Medicine, 35, 524, 1964.]
Why, you might logically ask, was the hormesis phenomenon not discovered until some eighty years after Roentgen, Becquerel, and the Curies made their contributions to radiation science? Why was there not an earlier Professor Luckey? [Professor Luckey is credited with coining the term "Radiation Hormesis" from his 1981 book Hormesis with Ionizing Radiation.]
Actually there was of sorts, and he, oddly enough, was also a professor at the University of Missouri. In 1896, Professor W. Shrader inoculated guinea pigs with the diphtheria bacillus. [Shrader, W. Experiments with X-rays upon germs. Electrical Engineering, 22, 170, 1896.]
The group exposed to X-rays prior to inoculation survived; the unexposed cohort died within twenty-four hours. Shrader, in the same series of experiments, was apparently the first person to discover that "Roentgen Rays" could be used to kill germs.
During the early twentieth century, radiation was used for a variety of experimental therapies, but the doses were generally far above hormetic levels and may well have caused more harm than good. Patent medicines such as "Radithor" (more on this in chapter 24) were popular, with single doses having nearly a million times the daily radium intake allowed by current government regulators. Hundreds of thousands of vials of elixirs were consumed without any widespread harm occurring and with a sizable number of "miracle cures" being reported. Few controls, however, were employed to scientifically assess the actual worth of the treatments leaving one to believe that most of these "cures" may have been either the product of advertising hype or a placebo effect.
Medical research wasn't the big draw for world-class physicists. We might remember that in the early days of radiation experimentation important discoveries were being made almost daily, while health considerations - except, possibly, for the annoying, minor and superficial skin "beta burns" - were considered to be of no consequence. The doses of radiation these unprotected experimenters received are estimated to exceed by thousands of times the maximums under which today's nuclear industry workers are allowed to continue on the job.
Madame Curie, discoverer of both polonium and radium, offers a good example of the "non-standards" of the day. [In 1516, a silver lode was discovered in St. Joachim's Dale (Joachimsthal), which was - naturally - confiscated by the government of Count von Schlick. Coins minted from this mine were known as Joachimsthalers, which (for obvious reasons) came to be known as thalers - in English, dollars. It was from this mine that the Curies obtained pitchblende - an ore rich in uranium and its daughters, radium and polonium.]
It is anecdotal that whenever Marie Sklodowska [in case you were curious why she named her first discovery for Poland] Curie walked into a room, electroscopes immediately discharged. [Gold is so malleable that it can be pressed into leaves less than 1/10,000 of an inch thick. If you hang two pieces of leaf in an air-filled jar, with provision to charge both - you have an electroscope. Charging the leaves with the same polarity causes them to "push apart" and, because they are so light, the electrostatic "pushing" force exceeds the gravitational force that would cause them to "droop" into a vertical position. Such devices were used to assay the content of uranium ores - not from the non-penetrating alpha radiation of the uranium, but from the accumulated daughters of which the gamma ray emitting radium was a significant component. Air, when ionized, is a conductor that discharged the electroscope at a rate proportional to the amount of ionizing radiation present.]
It is almost certain that she had an enormous lung burden of radium - the element she was extracting from uranium ore - which took quite a bit of patience, since there are only about 0.003 grams of radium per ton of ore. Madam Curie died almost certainly from the effects of long-term and extremely high doses of radiation. Yet, at age sixty-six, she still exceeded by ten years the life expectancy of her day.
Later in the century, the subject of hormesis would have doubtlessly been trifling compared to other matters. From August 1939 - when a letter from Albert Einstein was delivered to Franklin Roosevelt recommending the development of an atomic bomb - until the end of World War II, the focus of virtually the entire nulcear physics community became the Manhattan project. (This venture, equivalent in size to the total automotive industry at that time, is described in fascinating detail in The Making of the Atomic Bomb [Richard Rhodes, Simon & Schuster, New York, 1986].)
Certainly the scientists were aware of potential dangers from radiation - especially the highly penetrating neutrons from "atomic piles" - but these risks were minimal, compared with the reality of thousands of deaths from the war every day. Concerns about low-level radiation - either harmful or beneficial - weren't even on the radar scope.
Interestingly, the only health physics experiment I've ever come across that occurred during the Manhattan project was indicative of radiation hormesis:
"In 1943, a group of [radiation scientists] on the Manhattan District Project were worried about the unknown toxicity of uranium. They grew a colony of rats in an atmosphere laden with sufficient uranium dust to kill them fast (the Manhattan Project didn't have time for fancy radiobiologists). As a control, a similar colony breathed clean air. After several months, nothing happened, but eventually the rats lived out their natural lifespans, with one surprise: the first health physics experiment demonstrated that rats who breathed uranium dust lived longer and were happier (i.e., had a better reproductive history) than normal rats. Not a tumor in the bunch." [From a letter by Marshall Brucer, M.D. to Time magazine (from the files of Petr Beckmann).]
During this period there are reports of relatively minor medical experimentation to determine the effect of ionizing radiation on the healing of wounds. The exposure levels, however, were high (1 Gy or 100 rem) - suggesting its use as a bactericide. The availability of antibiotics in 1942, and the post-Hiroshima bombing concerns over high-level dangers, caused a loss of interest in research of this nature by the end of World War II.
After the war, the Japanese cities of Hiroshima and Nagasaki became laboratories for research on the effects of radiation on humans. But the focal point was on the high-dose subjects - in particular on their excess cancers and the possible mutational effects on children. When low-dose victims showed beneficial health effects, the data were ignored as being anomalies (a fancy scientific words for "it doesn't fit in with what we're expecting").
Luckey addresses this subject:
"Statistical analysis of observed data was missing in many reports of experiments involving low doses of ionizing radiation. Most of the reports simply indicated that an unexpected phenomenon had been observed, but the researchers failed to pursue it systematically... Any unexpected result was rejected by the 95% rule: One experiment in each twenty was accepted as a variant. Closer inspection showed this was a consistent result; it usually occurred in the group exposed to the least radiation, the only one in the hormetic range. Hormetic data were ignored because they did not fit the models of the zero thesis." [Radiation Hormesis, p. 45.]
When someone really writes a history of radiation hormesis, the first "official" recognition of the phenomenon will go to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in a 1994 report "Adaptive Responses to Radiation in Cells and Organisms":
"Manifestations of the adaptation described in mammals after exposure to low doses of radiation include accelerated growth rate in the young, increase in reproductive ability, extended life-span, stimulatory effects on the immune system, and a lower than expected incidence of spontaneous tumors."
You might want to read that again.
Why, you might logically ask, was the hormesis phenomenon not discovered until some eighty years after Roentgen, Becquerel, and the Curies made their contributions to radiation science? Why was there not an earlier Professor Luckey? [Professor Luckey is credited with coining the term "Radiation Hormesis" from his 1981 book Hormesis with Ionizing Radiation.]
Actually there was of sorts, and he, oddly enough, was also a professor at the University of Missouri. In 1896, Professor W. Shrader inoculated guinea pigs with the diphtheria bacillus. [Shrader, W. Experiments with X-rays upon germs. Electrical Engineering, 22, 170, 1896.]
The group exposed to X-rays prior to inoculation survived; the unexposed cohort died within twenty-four hours. Shrader, in the same series of experiments, was apparently the first person to discover that "Roentgen Rays" could be used to kill germs.
During the early twentieth century, radiation was used for a variety of experimental therapies, but the doses were generally far above hormetic levels and may well have caused more harm than good. Patent medicines such as "Radithor" (more on this in chapter 24) were popular, with single doses having nearly a million times the daily radium intake allowed by current government regulators. Hundreds of thousands of vials of elixirs were consumed without any widespread harm occurring and with a sizable number of "miracle cures" being reported. Few controls, however, were employed to scientifically assess the actual worth of the treatments leaving one to believe that most of these "cures" may have been either the product of advertising hype or a placebo effect.
Medical research wasn't the big draw for world-class physicists. We might remember that in the early days of radiation experimentation important discoveries were being made almost daily, while health considerations - except, possibly, for the annoying, minor and superficial skin "beta burns" - were considered to be of no consequence. The doses of radiation these unprotected experimenters received are estimated to exceed by thousands of times the maximums under which today's nuclear industry workers are allowed to continue on the job.
Madame Curie, discoverer of both polonium and radium, offers a good example of the "non-standards" of the day. [In 1516, a silver lode was discovered in St. Joachim's Dale (Joachimsthal), which was - naturally - confiscated by the government of Count von Schlick. Coins minted from this mine were known as Joachimsthalers, which (for obvious reasons) came to be known as thalers - in English, dollars. It was from this mine that the Curies obtained pitchblende - an ore rich in uranium and its daughters, radium and polonium.]
It is anecdotal that whenever Marie Sklodowska [in case you were curious why she named her first discovery for Poland] Curie walked into a room, electroscopes immediately discharged. [Gold is so malleable that it can be pressed into leaves less than 1/10,000 of an inch thick. If you hang two pieces of leaf in an air-filled jar, with provision to charge both - you have an electroscope. Charging the leaves with the same polarity causes them to "push apart" and, because they are so light, the electrostatic "pushing" force exceeds the gravitational force that would cause them to "droop" into a vertical position. Such devices were used to assay the content of uranium ores - not from the non-penetrating alpha radiation of the uranium, but from the accumulated daughters of which the gamma ray emitting radium was a significant component. Air, when ionized, is a conductor that discharged the electroscope at a rate proportional to the amount of ionizing radiation present.]
It is almost certain that she had an enormous lung burden of radium - the element she was extracting from uranium ore - which took quite a bit of patience, since there are only about 0.003 grams of radium per ton of ore. Madam Curie died almost certainly from the effects of long-term and extremely high doses of radiation. Yet, at age sixty-six, she still exceeded by ten years the life expectancy of her day.
Later in the century, the subject of hormesis would have doubtlessly been trifling compared to other matters. From August 1939 - when a letter from Albert Einstein was delivered to Franklin Roosevelt recommending the development of an atomic bomb - until the end of World War II, the focus of virtually the entire nulcear physics community became the Manhattan project. (This venture, equivalent in size to the total automotive industry at that time, is described in fascinating detail in The Making of the Atomic Bomb [Richard Rhodes, Simon & Schuster, New York, 1986].)
Certainly the scientists were aware of potential dangers from radiation - especially the highly penetrating neutrons from "atomic piles" - but these risks were minimal, compared with the reality of thousands of deaths from the war every day. Concerns about low-level radiation - either harmful or beneficial - weren't even on the radar scope.
Interestingly, the only health physics experiment I've ever come across that occurred during the Manhattan project was indicative of radiation hormesis:
"In 1943, a group of [radiation scientists] on the Manhattan District Project were worried about the unknown toxicity of uranium. They grew a colony of rats in an atmosphere laden with sufficient uranium dust to kill them fast (the Manhattan Project didn't have time for fancy radiobiologists). As a control, a similar colony breathed clean air. After several months, nothing happened, but eventually the rats lived out their natural lifespans, with one surprise: the first health physics experiment demonstrated that rats who breathed uranium dust lived longer and were happier (i.e., had a better reproductive history) than normal rats. Not a tumor in the bunch." [From a letter by Marshall Brucer, M.D. to Time magazine (from the files of Petr Beckmann).]
During this period there are reports of relatively minor medical experimentation to determine the effect of ionizing radiation on the healing of wounds. The exposure levels, however, were high (1 Gy or 100 rem) - suggesting its use as a bactericide. The availability of antibiotics in 1942, and the post-Hiroshima bombing concerns over high-level dangers, caused a loss of interest in research of this nature by the end of World War II.
After the war, the Japanese cities of Hiroshima and Nagasaki became laboratories for research on the effects of radiation on humans. But the focal point was on the high-dose subjects - in particular on their excess cancers and the possible mutational effects on children. When low-dose victims showed beneficial health effects, the data were ignored as being anomalies (a fancy scientific words for "it doesn't fit in with what we're expecting").
Luckey addresses this subject:
"Statistical analysis of observed data was missing in many reports of experiments involving low doses of ionizing radiation. Most of the reports simply indicated that an unexpected phenomenon had been observed, but the researchers failed to pursue it systematically... Any unexpected result was rejected by the 95% rule: One experiment in each twenty was accepted as a variant. Closer inspection showed this was a consistent result; it usually occurred in the group exposed to the least radiation, the only one in the hormetic range. Hormetic data were ignored because they did not fit the models of the zero thesis." [Radiation Hormesis, p. 45.]
When someone really writes a history of radiation hormesis, the first "official" recognition of the phenomenon will go to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in a 1994 report "Adaptive Responses to Radiation in Cells and Organisms":
"Manifestations of the adaptation described in mammals after exposure to low doses of radiation include accelerated growth rate in the young, increase in reproductive ability, extended life-span, stimulatory effects on the immune system, and a lower than expected incidence of spontaneous tumors."
You might want to read that again.
Wednesday, January 20, 2016
Types of Ionizing Radiation
There is no amount of radiation that is safe. - Anti-nuclear activist Dr. John Gofman
When a radioactive isotope decays, it emits one or more of three forms of ionizing radiation: alpha particles, beta particles or gamma rays. One problem in discussing the effects of radiation is the lack of understanding of these different types and how they affect the body.
Alpha-particles are actually helium nuclei, which can be seen from the periodic table to have an atomic number of two and an atomic weight of four. [In alpha-decay, the radioactive isotope is changed to the isotope of an element with an atomic number two less and an atomic weight four less than the original element.]
In the subatomic world, the emission of an alpha-particle is like shooting shot put with a sling shot: there is a lot of mass involved, but it doesn't travel very far. This particle gives up its considerable energy in one-half to two inches of air. It can't penetrate the skin and, consequently, isn't dangerous when outside the body. Because of its mass, however, it is considered to be quite dangerous when inside the body - particularly when inhaled, where it may remain in the lungs in close proximity to lung tissue cells for extended periods. [It is common knowledge that plutonium, an alpha emitter, is deadly when inhaled. You will see in chapter 16 that common knowledge may be terribly mistaken.] Fortunately, there are some very good data on this subject that we'll look into.
Beta-particles are high energy electrons that can penetrate up to three feet of air, or the first layer of skin cells, and can cause a burn not unlike that from falling asleep in the tanning bed. Beta-burns were a particular problem for workers after the Chernobyl chemical explosion and for technicians involved in some phases of the weapons-testing program in Nevada. With a mass some 1/7344 that of an alpha-particle, its energy is derived from its speed, which can approach 99.8% of the speed of light. Relatively speaking, beta "rays" are not considered much of a threat to human health although there can be complications arising from beta-burns.
A third possible product from the decay of a radionuclide (a fancy word for a radioactive isotope) is gamma radiation, which is considered to be the greatest danger from nuclear decay. It is very similar - in fact in some cases identical - to X-rays and can penetrate several feet of concrete or inches of steel. Like any other electromagnetic radiation, its intensity falls off as the square of the distance from the source. For instance, the exposure at 100 yards is 1/900 that at 10 feet; at a quarter mile, the radiation is reduced by a factor of 17,424 compared with the 10-foot value. [Luckey mentions another form of radiation, delta rays, with low energies and penetrating power, but - because of their abundance and proximity to cell structures - are important in radiobiology. See Radiation Hormesis, page 2.]
There are other forms of radiation that should be mentioned even though they are not the normal products of natural decay. The first is cosmic radiation. It consists of various types of particles, sub-particles, and high-energy photons arriving on Earth from every direction in the cosmos. Cosmic radiation, with both solar and galactic components, can have unbelievably high energies, but, fortunately, it poses no danger, since there is so little of it. For instance, protons that originated in far-off galaxies four billion years ago have energies 100 million times greater than can be created in our most advanced particle accelerators. But only about one of these per year is detected by the Akeno Giant Air Shower Array located just west of Tokyo. [Energies are in the range of 3x1020 electron-volts. For more information see Scientific American, January 1999, page 32.]
These cosmic sources make up less than 10% of the background radiation that the average U.S. citizen receives, yet we still receive about 1,500 cosmic "hits" per second, each of which - because of the penetrating nature of all high-energy particles - collides with about 10,000 of the hundred-trillion cells in the adult human body. That's 15 million "cellular events" per second. If the quotation from Dr. Gofman at the beginning of this chapter is accurate, then we are indeed in a heap of trouble.
It is, by the way, the action of cosmogenic (a fancy scientific word for "from outer space) neutrons on atoms of atmospheric nitrogen that produces the carbon 14 used for radiometric dating. [Carbon 14 dating, developed in 1947 by W.F. Libby, is based on the fact that 14C is continually produced by cosmic rays. When the high-energy ray collides with atoms in the atmosphere, free neutrons are produced which, when absorbed by a nitrogen (14N) atom, cause it to eject a proton, thus converting it to 14C. This radioisotope is taken in by plants and animals while they are alive but remains constant after death. By measuring the 14C in comparison with its decay products, the approximate age of the fossil can be determined.]
Other neutron sources - accelerators, nuclear reactors, and bombs - have great potential for danger, as the lack of charge on the neutron allows it to penetrate some eight to ten feet of packed earth - about 50% farther than gamma radiation. Strictly speaking, neutrons are not ionizing radiation, since they have no electrical charge with which to influence the electrical affinity between protons and electrons. But they can smack into light-weight atoms such as hydrogen and cause them to become ionizing projectiles.
Finally, we have X-rays, which are typically produced when an energetic electron is stopped in its tracks. Just as with gamma rays, these can travel long distances and have the potential for doing harm to the body. During the past several decades, the energy - and therefore potential harm - of diagnostic X-rays has greatly decreased because of the increased sensitivity of the film and the detectors being used. Similarly, therapeutic X-ray equipment is designed to focus energy on smaller areas with less effect on healthy tissue. Sadly, an unwarranted fear of radiation causes many people who could be benefited by the use of X-ray diagnosis and therapy to shun such treatment - and thereby become subjected to unnecessary real dangers.
A similar situation is found in the commercial/industrial environment where X-rays are subjected to such overprotective rules that their primary benefit - being able to detect flaws in welds and other material in order to protect human life - is rendered uneconomical. (No doubt there is also reluctance on the part of workers - who are victims of LNT theory fears - to use the equipment.)
All of the above forms of radiation are termed ionizing radiation because they have the ability to strip electrons from their orbits around nuclei, making the lone electron a negative ion and the "left-behind" proton a positive ion. Table 3 shows the electromagnetic spectrum illustrating the various kinds of ionizing and non-ionizing radiation. For all practical purposes, ultra-violet radiation is not ionizing, and it is the action of ionization that defines the beginning of the X-ray portion of the electro-magnetic spectrum. [While UV radiation cannot ionize an atom, it can dissociate a molecule. For example, cosmic UV can smack into an O2 molecule splitting it into two atomic oxygen atoms - which are very chemically active.]
Table 3 - The Electromagnetic Spectrum
Non-ionizing
Ionizing
* The ~ symbol indicates an approximate measure.
When a radioactive isotope decays, it emits one or more of three forms of ionizing radiation: alpha particles, beta particles or gamma rays. One problem in discussing the effects of radiation is the lack of understanding of these different types and how they affect the body.
Alpha-particles are actually helium nuclei, which can be seen from the periodic table to have an atomic number of two and an atomic weight of four. [In alpha-decay, the radioactive isotope is changed to the isotope of an element with an atomic number two less and an atomic weight four less than the original element.]
In the subatomic world, the emission of an alpha-particle is like shooting shot put with a sling shot: there is a lot of mass involved, but it doesn't travel very far. This particle gives up its considerable energy in one-half to two inches of air. It can't penetrate the skin and, consequently, isn't dangerous when outside the body. Because of its mass, however, it is considered to be quite dangerous when inside the body - particularly when inhaled, where it may remain in the lungs in close proximity to lung tissue cells for extended periods. [It is common knowledge that plutonium, an alpha emitter, is deadly when inhaled. You will see in chapter 16 that common knowledge may be terribly mistaken.] Fortunately, there are some very good data on this subject that we'll look into.
Beta-particles are high energy electrons that can penetrate up to three feet of air, or the first layer of skin cells, and can cause a burn not unlike that from falling asleep in the tanning bed. Beta-burns were a particular problem for workers after the Chernobyl chemical explosion and for technicians involved in some phases of the weapons-testing program in Nevada. With a mass some 1/7344 that of an alpha-particle, its energy is derived from its speed, which can approach 99.8% of the speed of light. Relatively speaking, beta "rays" are not considered much of a threat to human health although there can be complications arising from beta-burns.
A third possible product from the decay of a radionuclide (a fancy word for a radioactive isotope) is gamma radiation, which is considered to be the greatest danger from nuclear decay. It is very similar - in fact in some cases identical - to X-rays and can penetrate several feet of concrete or inches of steel. Like any other electromagnetic radiation, its intensity falls off as the square of the distance from the source. For instance, the exposure at 100 yards is 1/900 that at 10 feet; at a quarter mile, the radiation is reduced by a factor of 17,424 compared with the 10-foot value. [Luckey mentions another form of radiation, delta rays, with low energies and penetrating power, but - because of their abundance and proximity to cell structures - are important in radiobiology. See Radiation Hormesis, page 2.]
There are other forms of radiation that should be mentioned even though they are not the normal products of natural decay. The first is cosmic radiation. It consists of various types of particles, sub-particles, and high-energy photons arriving on Earth from every direction in the cosmos. Cosmic radiation, with both solar and galactic components, can have unbelievably high energies, but, fortunately, it poses no danger, since there is so little of it. For instance, protons that originated in far-off galaxies four billion years ago have energies 100 million times greater than can be created in our most advanced particle accelerators. But only about one of these per year is detected by the Akeno Giant Air Shower Array located just west of Tokyo. [Energies are in the range of 3x1020 electron-volts. For more information see Scientific American, January 1999, page 32.]
These cosmic sources make up less than 10% of the background radiation that the average U.S. citizen receives, yet we still receive about 1,500 cosmic "hits" per second, each of which - because of the penetrating nature of all high-energy particles - collides with about 10,000 of the hundred-trillion cells in the adult human body. That's 15 million "cellular events" per second. If the quotation from Dr. Gofman at the beginning of this chapter is accurate, then we are indeed in a heap of trouble.
It is, by the way, the action of cosmogenic (a fancy scientific word for "from outer space) neutrons on atoms of atmospheric nitrogen that produces the carbon 14 used for radiometric dating. [Carbon 14 dating, developed in 1947 by W.F. Libby, is based on the fact that 14C is continually produced by cosmic rays. When the high-energy ray collides with atoms in the atmosphere, free neutrons are produced which, when absorbed by a nitrogen (14N) atom, cause it to eject a proton, thus converting it to 14C. This radioisotope is taken in by plants and animals while they are alive but remains constant after death. By measuring the 14C in comparison with its decay products, the approximate age of the fossil can be determined.]
Other neutron sources - accelerators, nuclear reactors, and bombs - have great potential for danger, as the lack of charge on the neutron allows it to penetrate some eight to ten feet of packed earth - about 50% farther than gamma radiation. Strictly speaking, neutrons are not ionizing radiation, since they have no electrical charge with which to influence the electrical affinity between protons and electrons. But they can smack into light-weight atoms such as hydrogen and cause them to become ionizing projectiles.
Finally, we have X-rays, which are typically produced when an energetic electron is stopped in its tracks. Just as with gamma rays, these can travel long distances and have the potential for doing harm to the body. During the past several decades, the energy - and therefore potential harm - of diagnostic X-rays has greatly decreased because of the increased sensitivity of the film and the detectors being used. Similarly, therapeutic X-ray equipment is designed to focus energy on smaller areas with less effect on healthy tissue. Sadly, an unwarranted fear of radiation causes many people who could be benefited by the use of X-ray diagnosis and therapy to shun such treatment - and thereby become subjected to unnecessary real dangers.
A similar situation is found in the commercial/industrial environment where X-rays are subjected to such overprotective rules that their primary benefit - being able to detect flaws in welds and other material in order to protect human life - is rendered uneconomical. (No doubt there is also reluctance on the part of workers - who are victims of LNT theory fears - to use the equipment.)
All of the above forms of radiation are termed ionizing radiation because they have the ability to strip electrons from their orbits around nuclei, making the lone electron a negative ion and the "left-behind" proton a positive ion. Table 3 shows the electromagnetic spectrum illustrating the various kinds of ionizing and non-ionizing radiation. For all practical purposes, ultra-violet radiation is not ionizing, and it is the action of ionization that defines the beginning of the X-ray portion of the electro-magnetic spectrum. [While UV radiation cannot ionize an atom, it can dissociate a molecule. For example, cosmic UV can smack into an O2 molecule splitting it into two atomic oxygen atoms - which are very chemically active.]
Table 3 - The Electromagnetic Spectrum
Non-ionizing
- Radio waves (AM) - long wavelength ~100 meters*
- Shortwave radio - low frequence ~1 million Hz
- Television VHF - low energy ~10^-9 electron volts
- Television UHF
- Radar
- Microwaves (including ovens)
- Infrared (heat) radiation
- Red-orange light
- Green-blue light
- Ultraviolet A
- Ultraviolet B
- Ultraviolet C
Ionizing
- Vacuum ultraviolet (absorbed by short path through air)
- Low energy X-rays
- Deep therapy X-rays - short wavelenght ~10^-14 meters
- Gamma rays (overlaps with X-rays) - high frequency ~10^22 Hz
- Cosmic photons - high energy ~100 million electron volts
* The ~ symbol indicates an approximate measure.
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