Acute Radiation Syndrome

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

Table 8 Source: "Terrorism With Ionizing Radiation General Guidance: Pocket Guide," produced by the Employee Education System for the Office of Public Health and Environmental Hazards, Department of Veterans Affairs.

Some may think that certain data are emphasized in this and other chapters in an attempt to minimize the dangers of exposure to radiation. This is not at all true. I am trying to put the dangers in perspective and eliminate the Pavlovian negative response to even the very mention of the subject. Table 8 shows the accepted syndrome from short-term exposures. Please note that this table is in rems (not millirems) and can be mentally converted to centisieverts (cSvs) of the same numerical value. Radiation can obviously be very dangerous. But so can an unreasonable fear of radiation.

The International Standard (SI) Units

In the International Standard measuring system, there is no equivalent for the roentgen - which is just as well as far as we're concerned because it is seldom used in relation to human exposure. The following relationships exist between the USA and SI units:
100 rad = 1 gray or Gy
and
100 rem = 1 sievert or Sv

One gray or sievert represents and enormous amount of radiation - about four times as much as a U.S. resident would normally receive in a 76-year lifetime. Smaller units, the centigray, cGy, and the centisievert, cSv, are more commonly used. These conveniently convert to USA units -
1 cGy = 1 rad = 1000 millirad (mrad)
and
1 cSv = 1 rem = 1000 millirem (mrem).

If learning these measuring systems seems too complicated, try learning a few reference exposures and compare the value in question to these. Here are the ones I use, which then give me a feel for other values. After a while, they start all becoming second nature.

• Sleeping with your spouse for a year - 1 mrem or 0.001 cSv (for the ambitious learner, 0.01 mSv). Since your spouse emits gamma rays; the rads, rems, cSv and cGy are all the same. In almost all of the cases (except internal radium and plutonium) that we're going to be examining, this will be the case.
• Background radiation in the United States - 300 mrem or 0.3 cSv. In the International System, the millisievert - one-tenth of the centisievert - is often used in this range. Our normal background dose in this unit is 3 mSv. Since a good portion of this radiation is from radon sources (an alpha emitter); rads, rems, Gy, and Sv are not interchangeable.
• Radiation sickness - ensues at about 100,000 mrem, or 100 rem, or 100 cSv, or 1 Sv. Because doses of this magnitude are usually low LET radiation, units of 100,000 mrad, 100 rads, 100 cGy, or 1 Gy may be used interchangeably. By the way, sickness results from an acute exposure of 1 Sv over a period of a couple of days or less. The same radiation over a longer exposure time gives no symptoms.

If you'll commit these three points to memory (or place a bookmark here), it will give you some frame of reference with which to compare other doses. Your bookmark will also give you easy access to Table 7, which gives some typical millirem and cSv values for other exposure situations.

Table 7 – Selected Radiation Doses Per Year
Source of Exposure	mrem	cSv
Nuclear plant within 50 miles	0.01	0.00001
Average Three Mile Island dose	0.1	0.0001
Color television	1	0.001
One coast-to-coast jet flight/trip	5	0.005
Border of nuclear power plant	5	0.005
From food	25	0.025
Cosmic radiation	27	0.027
Building materials	34	0.034
Your own blood (Potassium 40)	45	0.045
On-site for duration, TMI accident	80	0.080
One shoe X-ray (SXR)	175	0.175
Grand Central Station	525	0.525
Living on Colorado plateau	600	0.6
Barium enema	800	0.8
Max permissible for nuclear worker	5,000	5
Radiation sickness (50% people) [acute exposure over a day or two]	100,000	100
Death (50% of people) [acute exposure over a day or two]	400,000	400

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:

• the roentgen (pronounced rent'-gen),
• the rad, and 
• the rem.

To understand these you might imagine yourself on a sunny beach. The roentgen is analogous to the intensity of the sunlight striking the beach. The rad (radiation absorbed dose) corresponds to the amount of sunlight absorbed by your skin, while the rem (roentgen equivalent man) is comparable to the biological effect of the sunlight exposure. In the case of the rem, however, the difference in its effect is not due to your sunscreen, skin pigment, or hours spent in the tanning salon - but in the type of radiation being absorbed.

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.]

Getting a Handle on Radiation Doses

How many atomic explosions in our cities would you accept before deciding that nuclear power is not safe - no complexities, just a number? - Ralph Nader, 1974

A significant source of confusion regarding the measurement of radiation parameters is the simultaneous use of two systems of units. As noted in chapter 7, "activity" is measured in curies in the USA system and Becquerels in the International System of units. A similar duality is found in the measurement of "doses" of radiation, as will be discussed in this chapter.

The question arises as to which units should be used in this book. Personally, I think in terms of the USA units and find that most people actively involved in radiation related disciplines in the United States do likewise. On the other hand, most scientific papers are written using the S.I. values - certainly all the recent ones on hormesis.

Since neither way will satisfy all readers, it will be the policy herein to use both in the next few chapters - generally the S.I. units followed by the USA units in parenthesis unless a quotation or other source is expressed in the USA units... in which case the S.I. units are given parenthetically. Hopefully this repetition will get you accustomed to both systems of units and the relationship between them. Later chapters will use the same units as found in the source material. The plan is for you to become familiar with both by then and to make any necessary conversions in your head. (Or refer to Table 6 on page 51 or to Table 7, coming up on page 56, another good place for a bookmark.)

We will start with the more familiar (at least to me) USA units.

Specific Activities

When interested in relatively low-level radioactive material, the picocurie, or pCi (one-trillionth of a curie, remember?), is used. In Table 6, the activity is in pCi per liter and in Bq per liter. [You will also run across Bq per cubic meter (Bq/m3) in some radon studies. Multiply Bq/l by 1,000.]

Table 6 – Specific Activities of Common Substances
Material	Picocuries/liter	Becquerels/liter
Normal air	2	0.074
Typical radon level in homes	3	0.111
EPA limit: Ra-226 in drinking water	5	0.185
Nuclear power plant leak	15	0.555
“Contaminated” milk at TMI*	22	0.814
Rainwater **	360	13.3
Whiskey	1,200	44.4
Salad oil	4,900	181.5
Spa waters of Bad Gastein	16,200	599
Drinking water in Maine***	53,700	1,987
*The increase in radioactive iodine in Harrisburg after the Three Mile Island “disaster” was 1/20 that caused by Chinese A-bomb tests in 1976. You remember how Jane Fonda and Ralph Nader protested those, don’t you?
**Measured at Santa Fe, 5/11/1986. (Probably atmospheric carbon 14 and wind-blown potassium 40 salts.)
***Based on an average of 226 samples. Radiation Controversy, Ralph Lapp, Reddy Communications, 1979.

Since most Americans have no idea what danger might lurk in a glass of water having 200 picocuries per liter, we are at the mercy of those who might use this lack of knowledge to their political advantage. Professor Petr Beckmann pointed out that activity in a well-publicized reactor leak at Indian Point power plant outside New York City was equivalent to that in a pint bottle of salad oil. Without this knowledge, an interested citizen would be led to believe (a) nuclear power was unreliable, and (b) such technology was a danger to life and limb - exactly what anti-techologists Nader, Commoner, Ehrlich and their fellow primitivists would have us believe. Exactly the opposite of the truth.

You might want to bookmark this page, for easy reference to Table 6 as you read on.

In answer to the question posed in the chapter title, 100 picocuries is the approximate activity in a handful of average soil produced by the disintegration of potassium 40. (I always knew there was something dangerous about working out in the yard.)

Next we'll take a look at how the effect of ionizing radiation on the human body is measured.

100 Picocuries - That's a Lot! (Or is it?)

Since most Americans have no idea what danger might lurk in a glass of water with 200 picocuries per liter, we are at the mercy of those who might use this lack of knowledge to their political advantage.

Imagine sitting in a chair three feet away from a gram of an unknown radioactive metal, about the size of a penny, on the floor in front of you. Should you be concerned? I know I would be - at least until I knew more about what it was. Obviously we would be interested in what type of radiation was being emitted. It if were alpha or beta particles, there would be no problem as the 3 feet of air would stop any significant amount. But what if it were gamma rays? Then we would want to know just how "active" the source was - with the activity of a radioactive source being measured in the number of atoms that disintegrate every second.

Let's suppose our one gram of material is radium, specifically 226Ra. Would you care to guess the number of disintegrations per second? A mere 37,000,000,000 (37 billion)! This, by the way, is the number of disintegrations defined as 1 curie, or 1 Ci, since the curie is defined as the activity of one gram of radium. You needn't run away, but you might not want to hang around. If it were one gram of cesium 134, a quick exit would be advisable. [Cesium 134 is a gamma and beta emitter that has about fifteen times the activity of the Goian cesium 137, which is only a beta emitter.]

The curie, a United States (USA) unit, is still in common use but is gradually being replaced by the International Standard (SI) becquerel or Bq, which is defined as one disintegration per second. Obviously, then, 1 curie is equal to 37 billion Bq - not exactly the easiest conversion constant to work with, especially when you have to go the other way: 1 Bq = 2.7 x 10^-11 Ci = 27 pCi.

A few elements of interest and their specific activities - that is, their activity per gram - are given in Table 5.

Table 5 – Specific Activities of Selected Elements
Element	Curies	Becquerels	Half-Life
Thorium 232	0.000000166	4,316	14.05 billion years
Uranium 238	0.000000333	12,300	4.47 billion years
Potassium 40	0.00000722	267,200	1.27 billion years
Radium 226	1	37 billion	1,620 years
Strontium 90	139	5,143 billion	28.8 years
Cesium 134	1,290	47,900 billion	2.06 years
Iodine 131	124,000	4,588 trillion	8.04 days
Tellurium 133	113,000,000	4,200,000 trillion	12.4 minutes

Note that the half-life of the low activity 238U is very long - 4.5 billion years, while one-half the very active 131I isotope is gone in 8.04 days. We would expect this, since there are a finite number of atoms in a gram of any substance, and if the rate of decay (i.e., the activity) is high, it will take less time for the substance to lose its radioactivity. This is verified by the very low relative activity of the primordial radionuclides such as thorium, uranium and potassium, which have extremely long half-lives since these were presumably created at the same time as the Earth - estimated by most cosmologists as some 4.6 billion years ago. The shorter half-life isotopes - say a mere few million years or so - are long gone, although some are being replaced by decay products of the low activity elements.

Units of Measurement

There's just no way to avoid the next subject, because, unless you get at least semi-comfortable with certain units of measurement, most of the book is not going to make much sense. We'll start by looking at a little shorthand "trick" used by lazy scientists and engineers.

One curie of radioactivity is a sizable amount. Many times a much smaller unit is needed especially when referring to amounts contained in milk, water supplies and other common products. We could write this unit as 0.000000000001 curie, or 1 x 10^-12 curie or spell it out as one-trillionth of a cure. But that's time consuming and a heck of a lot of trouble when you're writing it fifty times a day. The shorthand version for a trillionth of a curie is generally written as 1 pCi - or even 1 pC - with the "p" standing for pico and pCi referred to as a picocurie.

Similarly, 1 becquerel is a very tiny amount of activity amounting to one radioactive disintegration per second, while we often are interested in millions or billions of decays for a single gram of a radioactive isotope. So instead of a million Bq or 10^6Bq, it is written as MBq, with the M standing for mega.

Table 4 shows prefixes and their corresponding powers of ten. Since I find that use of so many prefixes makes comparisons difficult, I'll be limiting them to as few as possible. However, others will occur in quotations and in literature you might run across.

Table 4 - International Standard (SI) Prefixes
Quintillion = 10^18 = exa = E
Quadrillion = 10^15 = peta = P
Trillion = 10^12 = tera = T
Billion = 10^9 = giga = G
Million = 10^6 = mega = M
Thousand = 10^3 = kilo = k
Hundred = 10^2 = hecto = h
Ten = 10^1 = deka = da
Tenth = 10^-1 = deci = d
Hundredth = 10^-2 = centi = c
Thousandth = 10^-3 = milli = m
Millionth = 10^-6 = micro = Greek letter mu
Billionth = 10^-9 = nano = n
Trillionth = 10^-12 = pico = p
Quadrillionth = 10^-15 = femto = f
Quintillionth = 10^-18 = atto = a

Well, we now know that radiation is caused by an atom suddenly going to pieces, but so far there is no clue as to why these particles are dangerous - if indeed they really are. So let's move on to some quantitative information about the effect of these atomic disintegrations.

Waste 'n' Time

Uh, oh. I'm afraid I've kind of painted myself into a corner here by minimizing the "problem" of nuclear wastes. If I give it short shrift, it will appear that I'm avoiding the subject. On the other hand, while the matter of nuclear wastes is somewhat afield from our general topic, there is a connection that might be of interest.

The only danger even attributed to nuclear wastes is that of causing cancer in future generations that are too stupid not to bit into a glassified chunk of power-plant waste. As we shall see, there is a threshold below which - even for those future glass munchers - there is no fear of increased cancer risk. But even if there weren't such a threshold, there are a number of issues regarding nuclear wastes that have been ignored in the media's misreporting of the subject that you should know about.

• More than 95% of the long half-life "waste" in nuclear fuel is not waste at all, but uranium and plutonium that may be reprocessed into fresh fuel assemblies. Most other industrialized nations do just this, as our government promised the utilities, but the Carter administration reneged on the agreement. (More about this later.)
• Among the "wastes" that anti-nuclear activists are eager to bury are valuable medical radionuclides that are produced at high cost in specialty reactors. As in the case of the reprocessable fuel, the baby is being thrown out with the bath water.
• The most sensible way to eliminate the unusable wastes from reprocessed fuel (which about to about 1% of their volume) is to dilute it a few millionfold and pour it down the drain, or to dump it into ocean abysses where there is no biological activity. Man's puny efforts at creating radionuclide wastes are dwarfed by the enormous amounts existing in nature. There are, for example, 36 billion curies of rubidium 87 and 380 billion curies of potassium 40 in the oceans, almost all of which will still be there when the few million curies of man's wastes have long since decayed to undetectable amounts. 

Why then, you may ask, are there hundreds or thousands of government- (read "taxpayer-") supported scientists busy writing reports on Yucca Mountain? I suggest there may be three reasons: (1) they don't know - or, more than likely, don't care - that low-level radiation is not harmful; (2) it beats having to get a real job; or (3) grants to study the mating habits of the Zambian sweat bee have already been taken.

The Concept of Half-Life

When an atom of a radioactive isotope decays, two things happen. First, energy is given off from the conversion of mass to energy according to Einstein's famous formula, E = mc2. (The newly formed atom and any emitted particles are always lighter than the original atom - and it is this difference in mass that is converted to energy.) Simultaneously the original element is transmuted to an element with a lower atomic number. The secondary element is called the daughter (or progeny) of the first; it can be either a stable isotope or can itself be radioactive and go through a radioactive decay. Eventually, however, the original element decays to a stable form, and no more energy is given off.

One can deduce from this that a radioactive element has a finite amount of energy to emit. Either it emits this energy very rapidly - in which case the radiation is intense and short-lived - or slowly, which would logically result in a relatively low radiation output. You can't have it both ways - a serious problem in nuclear medicine, as some of the intensely emitting therapeutic isotopes cannot be stored for more than a day.

Half-life is the time in which half the initial number of radioactive atoms decay.

If you stop to think about this phenomena, it's difficult not to have some kind of religious experience. Just think: In a tiny piece of (for example) uranium, one atom may have an internal "clock" that commands it to disintegrate in a second, while an adjacent atom in the same small sample will not decay for 13,500,000,000 years. How do they know then to "do their thing?" It's a problem that science may never solve.

Iodine 131 (used in thyroid diagnosis and ablation) has a half-life of about eight days. Thus if we started with a gram of 131I, after eight days and fifty-seven minutes we would have only a half-gram with the other half having been transmuted to stable tellurium. In another eight days we would have only one-fourth. After eighty days - ten half-lives - there is less than 1/1000 of the original specimen; beyond thirty half-lives, the isotope is considered to have disappeared. With its relatively short half-life, 131I is an intensely radioactive isotope.

Let's look for a moment at one of the most ubiquitous radioactive isotopes around: 238U, the primary uranium isotope making up 99.3% of the element's existence on Earth. [There are approximately 5,000 pounds of uranium in a volume of average soil one square mile by one foot deep.] It has a half-life of 4.5 billion years - approximately the same time estimated for Earth's age. Uranium takes 207,000,000,000 times as long to decay as 131I - with an inverse (longer time, less radiation) emission rate in approximately that proportion. Obviously it is a weak sister when it comes to being radioactive - which is fortunate for us or it would all be gone.

So, just in case I haven't made this clear, let me emphasize the following:

Short half-life = intense emitter, but gone after a short time

Long half-life = low activity and inherently not dangerous

Those who oppose nuclear technology want us to believe "Long half-life = dangerous," but it's just not true.

Understanding the concept of half-life and its relationship to intensity makes one realize that Barry Commoner - when he invokes references to a "nuclear priesthood watching over wastes for thousands of years" - is either terribly ignorant himself or is hoping that we are.

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

• 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.

Radioactive Isotopes

About three-fourths of the elements have two or more stable isotopes and many have radioactive (unstable) ones, some of which can be useful, and others of which can be dangerous if we come into contact with them. A few of the more common radioactive isotopes and beneficial uses are noted in Table 2.

****
Table 2 - Some Common Radioactive Isotopes
3H = Tritium = Luminous watch dials
14C = Carbon 14 = Radioactive dating
60Co = Cobalt 60 = Food irradiation
40K = Potassium 40 = Biological tracer
99Tc = Technetium 99 = Medical diagnosis
131I = Iodine 131 = Thyroid-function diagnosis and treatment
238Pu = Plutonium 238 = Spacecraft power supplies, pacemakers
241Am = Americium 241 = Smoke alarms
****

All of the elements heavier than lead in the periodic table have multiple isotopes, and all are naturally radioactive; most of them decay into one of the stable lead isotopes. Uranium and thorium have the greatest number of isotopes - uranium with 22 isotopes and thorium with 28 - though most of these are not naturally occurring. As a rule of thumb, elements are happiest when they have about the same number of protons and neutrons. When there is a sizable difference, they tend to decay until there isn't.

So, what about this radioactive business? How does it work? How dangerous is it? And for how long?

A very interesting subject: Don't miss the next chapter.