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.

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.