Re: The Tooth Fairy project

[DWhitfil@kdhe.state.ks.us]

The text, Environmental Radioactivity (4th edition, Eisenbud/Gesell)), has
a very interesting section devoted to the behavior of radionuclides *from*
fallout beginning on page 297 (Chapter 9, Nuclear Weapons). The first
radionuclide discussed is Sr-90 (page 297 to 306). Cs/Sr ratios are
discussed under Cs-137 (pages 306 and 307). Some interesting points (to
entice those interested into reading this book or portions thereof):

Pages 297 and 298

"Essentially all of the 90Sr injected into the atmosphere during the period
of weapons testing prior to the 1963 atmospheric test-ban agreement was
deposited on the earth's surface by 1970."

"Worldwide deposition reached a peak of about 12.5 MCi (460 PBq) by late
1967, at which time Southern Hemisphere deposition was less than one-third
that in the Northern Hemisphere. The amount of 90Sr on the earth's surface
has been diminishing at a rate of 2.5% per year because of radioactive
decay, slightly offset by occasional tests by France and China."

-Note that the references cited for the tests by France and China are dated
1970 and 1982." Chernobyl is also mentioned, especially the "significant
fallout of 137Cs." The radiological consequences of Chernobyl are discussed
on pages 415 to 425 (Chapter 12, Radioactive Contamination Accidents).

"Strontium-90 deposition was far *from* uniform during the period of
maximum fallout,..."

"The band of relatively heavy fallout...in the northern midlatitudes is
conspicuous and is believed to be due to meteorological factors that result
in increased stratospheric-trophoshric transfer during the spring months."

"The dependence of fallout on the amount of precipitation is illustrated
elegantly in Fig..."

Page 304

"...the 90Sr content of U.S. diets diminished for several years with a
half-time of 3.5 to 4 years following the peak values of 1963-1964, when
direct deposition on foliage was far the major contributor. Dietary 90Sr in
recent years has originated almost entirely *from* soil. In subsequent
years, the mean residence time of this nuclide in soil increases to about 9
years."

I would think that non-uniform deposition would be a large confounder in
the Tooth Fairy project (with a half-life of approximately 30 y, I would
expect Sr-90 in the environment to be detected rather easily for at least 3
to 5 half-lives, especially in areas that had higher levels of deposition).

The text also gives a very nice brief on low-level discharges *from*
light-water reactors on pages 232 to 244 (Chapter 8, Power Reactors),
including a section radiation exposure of the public *from* reactor
emissions. Of special note is Table 8-2, Escape rate Coefficients:

Cs, I, Xe, Kr, Rb, Br 1.3E-08 s^-1
 Sr, Ba 1.0E-11 s^-1

It is tough to get a measurable quantity of Sr in the environment from
routine releases without a few other radionuclides tagging along,
especially Cs-134/137 (this has been noted already by several other
people). Also, unlike many chemicals, radiation in the environment is
relatively easy to detect and hard to cover up if a mess has been made. It
is not uncommon to hear a cry that goes something like "I am being punished
for my ability to detect insignificantly low-levels of radiation."

Also interesting is Table 8.5 where discharges *from* a power plant were to
compared fallout *from* weapons tests.

DJWhitfill

Opinions expressed are mine and do not reflect official policies or
positions of the Kansas Department of Health and Environment.

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