On 3/20/2013 8:31 AM, dpb wrote:
On 3/20/2013 12:02 AM, Martin Eastburn wrote:
Look at the atomic numbers - there is 72 for light bulbs and
9x, 1xx for the various depletion - meaning the half life is
reducing the radiation...
...

???

The half-life of 92U238 is ~4.5x10E9 _yrs_...(that's 4 billion w/ a B
years). One doesn't observe much change in specific radioactivity w/
time in a normal lifetime.

And, BTW, the depletion in depleted U is the deficiency of concentration
of U235 relative to that naturally occurring which is roughly 0.72% (or
iow, 99.28% U238). But, the half-life of U235 (also an alpha-emitter)
while shorter than that of U238 is still 700x10E8 yrs so the amount of
additional depletion owing to natural decay is infinitesimally small in
any observable time.

For example, in 100 yr, N(t)/N0 ~ 2^(-100/700E6) = 0.99999990 for U235.
Add another roughly another couple of nines or a little less for U238
since the half-life is ~10X longer (X (1/2)^ratio half-lives).

(Sorry, but the old NucE in me just has to escape every once't in a
while...I'll fade away now.. )

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