Hormesis U.: A Review

Before leaving dear old Hormesis U., here is a short review to see if you've got a handle on the curriculum. You should know...

• Elements are identified by the number of protons in the nucleus (atomic number).
• Isotopes of elements have different numbers of neutrons (n + p = atomic weight).
• Atoms of some isotopes are stable, while others are radioactive and, over time, will disintegrate (decay) into other elements of a lower atomic number.
• Alpha and beta particles have a short range (a few inches and a few feet respectively).
• Gamma rays and X-rays can penetrate several inches of steel or feet of concrete.
• The half-life of a radioactive isotope is the time it takes half of the original amount to decay; after thirty half-lives the original amount is considered to be gone.
• The longer the half-life, the lower the activity of an isotope.
• A curie is 37 billion becquerels.
• A pCi is a picocurie and is equal to one-trillionth (10^-12) of a curie.
• Absorbed doses of radiation are measured in rads or grays; 100 rads equal 1 gray.
• Biological doses are measured in rems or sieverts; 100 rems equal 1 sievert.
• The absorbed dose and the biological dose are the same for gamma and X-rays. 
• A fatal acute dose is about 4 sieverts or 400 rems (50% fatalities in thirty days) when received in a relatively short time (a few days or less).
• Radiation sickness occurs at about 1 sievert or 100 rems (50% of those exposed over a short time). 
• Doses below 1 sievert or 100 rems (100,000 millirems) have no immediate biologic effects but are generally thought to increase the risk of cancer in the future.

Thanks for your attendance at Hormesis U. No doubt you'll find the rest of the information on radiation hormesis much more understandable now than when you were a mere freshman. Oh, and be sure to send in your contribution to the Alumni Fund.

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.