Re: [asa] Changing rate of radioactive decay (New Scientist)

OK, this is going to be very crude: I've done some things with plasma
physics but am not a solid state guy, & am just doing some back of the
envelope calculations here. So enough pre-emptive excuses -

The Debye shielding length in a plasma, using classical statistics, is
[kT/4*pi*n*e^2]^1/2 k,T, n & e being, respectively, Boltzmann constant,
Kelvin temperature, electron density, & electron charge. This length
will
give an estimate of the region in which electrons are clustered around a
free positive charge. For a solid metal one really ought to use Fermi
statistics but what I'm doing will, I think, give a gross
_over_estimate of
shielding. Assuming that all electrons in a chunk of radium are free
- i.e,
conduction electrons (!), & putting in numbers for Ra-226 at T = 300
K, room
tremperature, we get a shielding length of around 10^-9 cm. That's
smaller
than the Bohr radius but still lots larger than the nuclear radius, ~
7 x
10^-13 cm. If you take the temperature down to 3K as suggested, the
Debye
length is decreased by a factor of 1/10 to around 10^-10 cm, still
over a
hundred times the nuclear radius.

Thus it doesn't seem that the increased electron concentration near the
nucleus would be significant, & that's where they'd have to be to
have an
effect on the Coulomb barrier to decrease alpha lifetimes.

It's true that nuclei are not isolated systems & their environment
can have
some effect on nuclear properties, including lifetimes. But these
effects
will generally be quite small unless conditions are really extreme.

Even if cooling to a few K could decrease lifetimes significantly, the
practical difficulties of achieving & maintaining those temperatures for
years in a material which is generating heat via radioactive decay (&
would
be generating it even faster if you increased the decay rate) would be
formidable. & of course this result would be even less relevant for
calculations of the age of the earth, though I'm sure that if the
YECs get
hold of this they'll imagine some scenario in which Eve biting into
an apple
cooled the earth to millikelvin temperatures.

Caveat: This is a theoretical calculation (& a crude one at that)
indicating that one proposed mechanism for decreased lifetimes at low
temperatures wouldn't work. If it turns out that the effect is real
then
it's real, but some other explanation will have to be sought.

Shalom
George
http://web.raex.com/~gmurphy/

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Received on Fri Oct 27 11:17:49 2006