Irradiation of the pregnant animals - and the foetuses in utero caused an astonishing decrease of the mortality rate of the infected baby mice. [Mayr and Paulas, Unexpected effects of a whole body irradiation on the mortality rate of baby mice after an experimental infection with the vesicular stomatitis virus (VSV), Zentralbl. Veterinaermed, 36, 577, 1989.]
As a rule, I don't think much of animal experiments. No, I'm not a member of People for the Ethical Treatment of Animals (PETA); in fact, I think many test animals (that would have never existed were it not for testing requirements) have it a whole lot better than their cousins who live in the wild. Can you th ink of anything worse than being a mouse that is in the process of being swallowed whole by a snake? And besides not having to be constantly on the lookout for snakes, cats, and hawks, some of these test critters have a pretty active social life - especially those involved in reproductive studies.
My problem with much of the animal testing is similar to the problem I have with the LNT - it is based on extrapolation with no consideration of a possible (and likely) threshold. For example, cancer researchers will load up some rat - which has been bred for a propensity to have tumors - with the human equivalent of two boxcars per day of an artificial sweetener, and then declare the substance to be a human carcinogen when a few tumors appear. No consideration is given to the possibility that there is a threshold, above which the rat's resistance is overwhelmed, but below which there is no effect.
Fortunately, mouse experiments related to disproving the LNT and demonstrating hormesis are not in this category. A single datum point on the accompanying graphs is often the average of hundreds of mouse lifetimes, and the curves subsequently drawn lie within the range of these experimental data so that no extrapolation is necessary. Besides most of the tested mice should be happy campers, since ionizing radiation in the hormesis range generally promotes health and longevity.
This chapter will look into the effects of low-level (and a few not so low-level) X-rays and gamma radiation on the mice. Most of it is related to cancer, sinc, as we are aware, this disease is commonly associated with radiation and is, in fact, the major detrimental effect of exposure. Other topics include growth rate, life span, radio-resistance (which all parents of teenagers should have), and one inexplicable effect of radiation received by the parents of the test mice.
In the following studies, exposures (rads/Gy) and doses (rems/Sv) are equal, since only gamma and X-ray radiation are involved.
Showing posts with label X-rays. Show all posts
Showing posts with label X-rays. Show all posts
Sunday, February 14, 2016
Monday, February 1, 2016
A Day or So in the Life of a Cell
Hormesis is not the action of radiation on a single isolated cell. But when a society of cells, such as an organ, is subjected to low-doses of radiation, protective action occurs.
Hormesis, as discussed in Chapter 4, is the stimulatory action of a low dose of an agent that would be poisonous in larger amounts. Two of the questions that come to mind in considering the radiation hormesis phenomenon are:
How does radiation affect the body?
What physiological processes could cause the hormetic effect?
Circle the Wagons
Many of us have heard that the problem with radiation stems from radioactive particles smashing into our cells, breaking up the genes, crushing chromosomes, and mutilating the DNA - thus causing a cell to grow wildly out of control, which we call a cancer. (If you didn't think that, there must be something wrong with you, because that's what most people think.") When visualizing such cellular violence, I suspect that most of us have some kind of model in mind. Mine was a golf ball-sized alpha particle crashing into a basketball-sized cell, trashing pencil-sized chromosomes - all relatively speaking, of course. In the worst case, there was the dreaded "double-strand break," whereby a golf ball would slice through both pencil-like DNA strands, leaving the cell with no template by which to repair the damage, as it normally would do. Call the oncologist.
When I learned a little more about what goes on in a cell during its workaday world - which we'll be getting to shortly - my model just wasn't making much sense. So I decided to look at the relative sizes of cells and their atomic enemies in hopes of being able to better imagine the processes that were going on during the collisions. It was surprising.
Let us consider an average animal cell, which is about 20 microns (millionths of a meter) in diameter, and hypothetically expand its cross-sectional area until it is the size of the field in Yankee stadium. And then let's take an alpha particle - the shot put or bowling ball of the radioactive world - and enlarge it in the same proportion. [The nuclei of all atoms are surprisingly close to the same size. Uranium, while more than 200 times heavier, is only about three times as large as a hydrogen atom. The nuclei of both are on the order of one barn in cross-section, with the bar being 10^-24 cm2. (The term was occasioned when an early researcher remarked that a particular element's cross section looked as "wide as a barn.")]
What would you think? The alpha particle would be the size of a dump truck? A Volkswagen? (Too big.) A volley-ball? A baseball? (Too big.) A pea? A B-B? (Too big.) The alpha particle, in relation to a Yankee-Stadium-sized-cell, would be about 0.0003 inches in diameter - nearly the same as a human hair.
So what about damage inflicted by beta particles and gamma rays?
Beta rays are just speedy electrons, with 1/1836 the mass of any one of the two protons and two neutrons making up an alpha particle. In terms of mass, the beta "particle" is a ping-pong ball compared with a 7.3-pound alpha-particle brick. When piercing our Yankee-Stadium-sized cell, the wound would be invisibly small, even with a magnifying glass. Say, maybe our cells aren't necessarily such wimpy victims after all.
Gamma rays and X-rays consist of photons, which, though devastating when loaded in Star Trek torpedoes, are "packets," or quanta, of energy that have essentially zero mass and therefore, zero size. [If you really want to be picky, the photon can be considered to have a mass because of the Einsteinian equivalency between mass and energy. But the photon exists in the form of energy and not mass as we know it.]
Neither of these forms of ionizing radiation would make anything like a visible hole in our Yankee-Stadium-sized cell, but would pass through the cell walls like light through a dirty window.
With respect to the cell as a whole, radiation seems like mosquitoes attacking a circus tent, but once inside, high-energy particles or rays can wreak havoc upon individual atoms and molecules that make up our cellular structure. Alpha particles, protons, and neutrons scatter whatever is in their path, using their mass energy to separate electrons from their parent nuclei. Beta rays whiz through a thin layer of cells, knocking other electrons out of their orbits until their rather limited energy is expended. Gamma and X-rays act similarly, but with a vengeance proportional to their energies and inversely proportional to their wavelengths. [Light, which is part of the same electromagnetic spectrum as both X-rays and gamma rays, behaves similarly. Long wavelength infrared light - otherwise known as radiant heat - has very little energy compared to short wavelength ultraviolet light... which can "ultraviolate" you on the beach if you don't use sunblock.]
Usually they still have plenty of spunk after zipping through our bodies, stripping some 10,000 electrons out of their formerly contented orbits in the process.
Whenever an electron and its former nucleus partner (the proton) are separated, the atom is ionized - with the electron being a negative ion and the electron-starved nucleus being a positive ion. While we've been taught that the dreaded "double-strand breaks" are the main problem, the cell has a way to take care of these, which we'll get to soon. The primary cause of cellular damage from ionizing radiation is, by gosh - ionization.
When an electron is stripped away from a water molecule - and these make up some 99% of a cell's cytoplasm (the stuff inside the cell's membrane but outside the nucleus) - the normally placid water molecule turns into the Mr. Hyde of the cellular world. Good old H2O is converted into strange entities like hydroxyl radicals (OH-), which will fight anybody or anything to hook up with another electron. These are the feared "free radicals," which are the targets of heroic "anti-oxidants" seen in all health food magazines.
Just as I was completely off base on my concept of relative sizes of atoms and cells, I also had misconceptions about cell activities. I assumed they lived a rather boring life interrupted occasionally by having to split into two cells. From time to time, however, a bullet of radiation might penetrate the cell, causing it to marshal its defenses - for a battle that would often be lost - and an almost inevitable cancer would result. It's not a totally irrational model if you've been led to believe that all radiation is hazardous. But it's not even close to being true.
Just in case your cellular biology is a bit rusty, let's look for a moment at a typical animal cell. It is surrounded by a membrane that somehow knows what substances to let into and out of the cell. Inside the cell - besides cytoplasm - is the nucleus, which contains the nucleoli and the chromosomes. (The nucleoli busy themselves making the RNA and protein.) Chromosomes are long, threadlike bodies consisting of a single DNA molecule coiled tightly inside. In humans, the molecule is thought to be around sixteen inches long, but so thin that it cannot be resolved with an electron microscope. [In the Yankee Stadium example, the DNA molecule would be about 4,000 miles long but possibly too thin to be seen with the naked eye.]
Only about 10% of the DNA is active in providing instructions for the cell's growth, functioning, and reproduction. The remainder (essentially archives of the cell's history) is sometimes referred to as "junk DNA."
As far as being a peaceful environment, the cell makes a beehive appear to be laid-back. There are roughly 200,000 DNA repairs every day in every cell with some 30,000 unrepaired breaks existing at any given time. About 2% of these are the dreaded-double-strand breaks.
So most of this is caused by radiation? Hardly.
Normal oxidative damage - arising from thermal instability, replication, and free-radicals spawned by normal cell activities - is the overwhelming cause of DNA alterations. For the average U.S. citizen receiving a background dose of 0.3 cSv (300 mrem), the radiation-produced DNA breaks number six per cell per year. Even a fatal dose of 1000 cGy (1,000,000 mrad) produces only 20,000 breaks per cell - a mere 0.03% of the normally occurring 70 million altercations per year.
It would appear from this that radiation should have little effect on us one way or the other. Insofar as directly causing cancer, that is indeed what the evidence in future chapters will show. As Theodore Rockwell puts it:
"It is the repair and removal process (or lack of it) that kills us. Like other toxins, high-level radiation degrades those processes, but low-level actually stimulates them." [Ted Rockwell, Sc.D. is the former technical director of U.S. Naval Reactors. The American Nuclear Society's Lifetime Contribution Award has been named the Rockwell Award in his honor.]
As anyone with the least familiarity with radiation knows, high levels of radiation are dangerous and can kill you (Table 8). The low-level effects may be new to you, but they are real and are arguably far more important for society than the almost infinitesimally rare occurrences of high-level exposures.
Hormesis, as discussed in Chapter 4, is the stimulatory action of a low dose of an agent that would be poisonous in larger amounts. Two of the questions that come to mind in considering the radiation hormesis phenomenon are:
How does radiation affect the body?
What physiological processes could cause the hormetic effect?
Circle the Wagons
Many of us have heard that the problem with radiation stems from radioactive particles smashing into our cells, breaking up the genes, crushing chromosomes, and mutilating the DNA - thus causing a cell to grow wildly out of control, which we call a cancer. (If you didn't think that, there must be something wrong with you, because that's what most people think.") When visualizing such cellular violence, I suspect that most of us have some kind of model in mind. Mine was a golf ball-sized alpha particle crashing into a basketball-sized cell, trashing pencil-sized chromosomes - all relatively speaking, of course. In the worst case, there was the dreaded "double-strand break," whereby a golf ball would slice through both pencil-like DNA strands, leaving the cell with no template by which to repair the damage, as it normally would do. Call the oncologist.
When I learned a little more about what goes on in a cell during its workaday world - which we'll be getting to shortly - my model just wasn't making much sense. So I decided to look at the relative sizes of cells and their atomic enemies in hopes of being able to better imagine the processes that were going on during the collisions. It was surprising.
Let us consider an average animal cell, which is about 20 microns (millionths of a meter) in diameter, and hypothetically expand its cross-sectional area until it is the size of the field in Yankee stadium. And then let's take an alpha particle - the shot put or bowling ball of the radioactive world - and enlarge it in the same proportion. [The nuclei of all atoms are surprisingly close to the same size. Uranium, while more than 200 times heavier, is only about three times as large as a hydrogen atom. The nuclei of both are on the order of one barn in cross-section, with the bar being 10^-24 cm2. (The term was occasioned when an early researcher remarked that a particular element's cross section looked as "wide as a barn.")]
What would you think? The alpha particle would be the size of a dump truck? A Volkswagen? (Too big.) A volley-ball? A baseball? (Too big.) A pea? A B-B? (Too big.) The alpha particle, in relation to a Yankee-Stadium-sized-cell, would be about 0.0003 inches in diameter - nearly the same as a human hair.
So what about damage inflicted by beta particles and gamma rays?
Beta rays are just speedy electrons, with 1/1836 the mass of any one of the two protons and two neutrons making up an alpha particle. In terms of mass, the beta "particle" is a ping-pong ball compared with a 7.3-pound alpha-particle brick. When piercing our Yankee-Stadium-sized cell, the wound would be invisibly small, even with a magnifying glass. Say, maybe our cells aren't necessarily such wimpy victims after all.
Gamma rays and X-rays consist of photons, which, though devastating when loaded in Star Trek torpedoes, are "packets," or quanta, of energy that have essentially zero mass and therefore, zero size. [If you really want to be picky, the photon can be considered to have a mass because of the Einsteinian equivalency between mass and energy. But the photon exists in the form of energy and not mass as we know it.]
Neither of these forms of ionizing radiation would make anything like a visible hole in our Yankee-Stadium-sized cell, but would pass through the cell walls like light through a dirty window.
With respect to the cell as a whole, radiation seems like mosquitoes attacking a circus tent, but once inside, high-energy particles or rays can wreak havoc upon individual atoms and molecules that make up our cellular structure. Alpha particles, protons, and neutrons scatter whatever is in their path, using their mass energy to separate electrons from their parent nuclei. Beta rays whiz through a thin layer of cells, knocking other electrons out of their orbits until their rather limited energy is expended. Gamma and X-rays act similarly, but with a vengeance proportional to their energies and inversely proportional to their wavelengths. [Light, which is part of the same electromagnetic spectrum as both X-rays and gamma rays, behaves similarly. Long wavelength infrared light - otherwise known as radiant heat - has very little energy compared to short wavelength ultraviolet light... which can "ultraviolate" you on the beach if you don't use sunblock.]
Usually they still have plenty of spunk after zipping through our bodies, stripping some 10,000 electrons out of their formerly contented orbits in the process.
Whenever an electron and its former nucleus partner (the proton) are separated, the atom is ionized - with the electron being a negative ion and the electron-starved nucleus being a positive ion. While we've been taught that the dreaded "double-strand breaks" are the main problem, the cell has a way to take care of these, which we'll get to soon. The primary cause of cellular damage from ionizing radiation is, by gosh - ionization.
When an electron is stripped away from a water molecule - and these make up some 99% of a cell's cytoplasm (the stuff inside the cell's membrane but outside the nucleus) - the normally placid water molecule turns into the Mr. Hyde of the cellular world. Good old H2O is converted into strange entities like hydroxyl radicals (OH-), which will fight anybody or anything to hook up with another electron. These are the feared "free radicals," which are the targets of heroic "anti-oxidants" seen in all health food magazines.
Just as I was completely off base on my concept of relative sizes of atoms and cells, I also had misconceptions about cell activities. I assumed they lived a rather boring life interrupted occasionally by having to split into two cells. From time to time, however, a bullet of radiation might penetrate the cell, causing it to marshal its defenses - for a battle that would often be lost - and an almost inevitable cancer would result. It's not a totally irrational model if you've been led to believe that all radiation is hazardous. But it's not even close to being true.
Just in case your cellular biology is a bit rusty, let's look for a moment at a typical animal cell. It is surrounded by a membrane that somehow knows what substances to let into and out of the cell. Inside the cell - besides cytoplasm - is the nucleus, which contains the nucleoli and the chromosomes. (The nucleoli busy themselves making the RNA and protein.) Chromosomes are long, threadlike bodies consisting of a single DNA molecule coiled tightly inside. In humans, the molecule is thought to be around sixteen inches long, but so thin that it cannot be resolved with an electron microscope. [In the Yankee Stadium example, the DNA molecule would be about 4,000 miles long but possibly too thin to be seen with the naked eye.]
Only about 10% of the DNA is active in providing instructions for the cell's growth, functioning, and reproduction. The remainder (essentially archives of the cell's history) is sometimes referred to as "junk DNA."
As far as being a peaceful environment, the cell makes a beehive appear to be laid-back. There are roughly 200,000 DNA repairs every day in every cell with some 30,000 unrepaired breaks existing at any given time. About 2% of these are the dreaded-double-strand breaks.
So most of this is caused by radiation? Hardly.
Normal oxidative damage - arising from thermal instability, replication, and free-radicals spawned by normal cell activities - is the overwhelming cause of DNA alterations. For the average U.S. citizen receiving a background dose of 0.3 cSv (300 mrem), the radiation-produced DNA breaks number six per cell per year. Even a fatal dose of 1000 cGy (1,000,000 mrad) produces only 20,000 breaks per cell - a mere 0.03% of the normally occurring 70 million altercations per year.
It would appear from this that radiation should have little effect on us one way or the other. Insofar as directly causing cancer, that is indeed what the evidence in future chapters will show. As Theodore Rockwell puts it:
"It is the repair and removal process (or lack of it) that kills us. Like other toxins, high-level radiation degrades those processes, but low-level actually stimulates them." [Ted Rockwell, Sc.D. is the former technical director of U.S. Naval Reactors. The American Nuclear Society's Lifetime Contribution Award has been named the Rockwell Award in his honor.]
As anyone with the least familiarity with radiation knows, high levels of radiation are dangerous and can kill you (Table 8). The low-level effects may be new to you, but they are real and are arguably far more important for society than the almost infinitesimally rare occurrences of high-level exposures.
Table 8 – Acute Radiation Syndrome
|
||||||
Subclinical Range
0 – 100 rads |
Therapeutic Range
100 – 500 rads |
Lethal Range
500+ rads |
||||
100 –
200
|
200 –
300
|
300 –
500
|
500 –
2000
|
2000+
|
||
Appropriate
Action
|
None
|
Clinical surveillance
|
Therapy effective
|
Therapy promising
|
Therapy palliative (comfort patient
only)
|
|
Incidence
of Vomiting
|
None
|
100 rads: 5%
200 rads: 50% |
75%
|
75%
|
100%
|
100%
|
Delay
Time
|
n/a
|
3 hours
|
2 hours
|
1 hour
|
3 min.
|
3 min.
|
Main
Organs Affected
|
None
|
Blood Forming Tissue
|
Gastro-intestinal Tract
|
Central Nervous System
|
||
Characteristic
Signs
|
None
|
White Blood Cell Decrease
|
Fatigue, infection, erythema,
sterilization, loss of hair above 300 rads, hemorrhage
|
Diarrhea, fever, electrolyte
imbalance, bleeding
|
Convulsion, coma, loss of muscle
control, lethargy, tremors
|
|
Critical
Period
|
n/a
|
n/a
|
4 – 6 weeks
|
5 – 14 days
|
1 – 48 hours
|
|
Post-exposure
Therapy
|
Assure of Safety
|
Blood analysis; assure of safety
|
Blood transfusion; anti-biotics
|
Possible bone marrow transplant
|
Maintain electrolyte balance
|
Sedatives
|
Outlook
|
Excellent
|
Excellent
|
Good
|
Guarded
|
Hopeless
|
Hopeless
|
Convalescent
Period
|
None
|
Several weeks
|
1 – 2 months
|
Long
|
n/a
|
n/a
|
Death
Rate
|
None
|
None
|
0% - 40%
|
40% - 100%
|
90% - 100%
|
100%
|
Death
Within
|
n/a
|
n/a
|
2 – 4 weeks
|
2 weeks
|
2 days
|
|
Cause
of Death
|
n/a
|
n/a
|
Hemorrhage, infection
|
Dehydration
|
Respiratory failure; heart attack
|
|
Wednesday, January 27, 2016
Measuring Radiation Doses
In the USA system of radiological measurements, there are three somewhat confusing units for measuring the exposure to and doses of radiation:
You may recall that the different types of radiation were either particles (alpha and beta rays, protons, neutrons) or high-energy photons similar to light (X- and gamma rays). Except for beta rays - which are electrons having some 1/1836 the mass of protons or neutrons - the particles, because of their large masses, have a more catastrophic effect when colliding with a cell in the body. For this reason the quality factor - usually designated as Q - is used to adjust the absorbed dose to its biological counterpart, the rem.
Mathematically, rads x Q = rems.
Fortunately, most of the exposures we will be referring to in the study of hormesis are gamma and X-rays where Q is equal to one, allowing rads and rems to be used interchangeably. (Your radiologist, dental hygienist, and others working with X-rays will usually talk in terms of rads or millirads - but these are the same as rems and millirems, because it is the X-ray source that produces the radiation.) There is one other term with which you should have at least a vague familiarity - Linear Energy Transfer or LET. Beta, famma and X-rays are considered low LET radiation, which means they have a Q of one. High LET particles can have Qs up to 400. A typical alpha particle has a Q of four.
[Wilhelm Roentgen (1845-1923) discovered an unknown emission (X-rays) from cathode ray tubes. It still happens today - that's how X-rays are made today. Incidentally, your TV screen is a cathode ray tube, and it emits many times the radiation we get from nuclear power plants. Somehow this fact escapes notice of the TV doomsayers.]
- the roentgen (pronounced rent'-gen),
- the rad, and
- the rem.
You may recall that the different types of radiation were either particles (alpha and beta rays, protons, neutrons) or high-energy photons similar to light (X- and gamma rays). Except for beta rays - which are electrons having some 1/1836 the mass of protons or neutrons - the particles, because of their large masses, have a more catastrophic effect when colliding with a cell in the body. For this reason the quality factor - usually designated as Q - is used to adjust the absorbed dose to its biological counterpart, the rem.
Mathematically, rads x Q = rems.
Fortunately, most of the exposures we will be referring to in the study of hormesis are gamma and X-rays where Q is equal to one, allowing rads and rems to be used interchangeably. (Your radiologist, dental hygienist, and others working with X-rays will usually talk in terms of rads or millirads - but these are the same as rems and millirems, because it is the X-ray source that produces the radiation.) There is one other term with which you should have at least a vague familiarity - Linear Energy Transfer or LET. Beta, famma and X-rays are considered low LET radiation, which means they have a Q of one. High LET particles can have Qs up to 400. A typical alpha particle has a Q of four.
[Wilhelm Roentgen (1845-1923) discovered an unknown emission (X-rays) from cathode ray tubes. It still happens today - that's how X-rays are made today. Incidentally, your TV screen is a cathode ray tube, and it emits many times the radiation we get from nuclear power plants. Somehow this fact escapes notice of the TV doomsayers.]
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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