Re: Mystery over 1992 El-Al crash

Date:         07 Dec 98 23:19:19 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
References:   1 2 3
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>Depleted uranium is just as radioactive as regular uranium, it's just
>had the fissionable U235 removed.

Not quite.  If you remove more highly radioactive ("fissionable")
material, you can't possibly end up with something that's just as
radioactive as what you started with.

>After all, if the U235 were significantly more radioactive that U238,
>it wouldn't exist in nature.

No, it would just exist in smaller quantities (assuming you started off
with equal quantities), which is exactly what is observed in nature.

The folks at Los Alamos National Laboratory, who know a fair bit about
radioactive materials, have a very nice periodic table of the elements
on one of their web sites.  The Uranium entry is at

   http://cst.lanl.gov/CST/imagemap/periodic/92.html

Here's what they say about the nominal mix, by weight, of naturally
occuring uranium, along with the half-life of each isotope:

   isotope   natural %   half-life
   -------   ---------   ---------
     238     99.28305    4.46e9 yr
     235      0.7110     7.04e8 yr
     234      0.0054     2.45e5 yr
    other     0.00055

LANL only lists the half-life for 238U (at 4.51e9 yr) so I got them
from http://www.shef.ac.uk/chemistry/web-elements/nofr-radio/U.html.

Depleted uranium, according to LANL, has only about 0.2% 235U.  If you
calculated the weighted-average half-life of the uranium in what occurs
naturally, then do the same for depleted uranium, the half-life goes up
by about 0.43% or 20,000 years.  Not a whole lot, but it's not quite as
radioactive as the natural ore.

>And its radiation is measurable.

Yep, LANL says "natural uranium is sufficiently radioactive to expose a
photographic plate in an hour or so."

--
Karl Swartz	|Home	kls@chicago.com		http://www.chicago.com/~kls/
		|Work	kls@netapp.com		http://www.netapp.com/
"The average dog is a nicer person than the average person."
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