Subject: hydrogen isotopes (was Re: Spacecraft design)
From: Henry Spencer <henry@zoo.toronto.edu> 
Date: Apr 24 1996
Newsgroups: sci.space.shuttle,sci.space.tech

In article <4lglaj$pn9@hammer.msfc.nasa.gov> Rick Ballard <rick.ballard@hsv.sverd
rup.com> writes:
>...Deuterium occurs in nature (0.015% of hydrogen 
>in nature is deuterium).  Tritium is not found in nature.

Actually, not so, not quite.  There is a minute amount of tritium in
natural hydrogen, from cosmic-ray interactions.

There is a story -- whose truth I can't attest to -- that Rutherford's
last project was an attempt to prepare "superheavy water", by distilling
most of the world's supply of heavy water until only a small amount of
liquid remained.  (This process works, although inefficiently, as a way of
getting heavy water out of normal water.)  At the time, tritium was unknown
and there was some thought that it might be stable.  Alas, the atomic
weight of the hydrogen in his final sample remained 2.  He retired, and
died shortly thereafter.  It had never occurred to him to check whether
his "superheavy water" sample was radioactive.  Years later, when tritium
had been discovered and its properties understood, it occurred to someone
to check.  The sample was still in storage; it did indeed show a small but
noticeable amount of radioactivity, from beta decay of a small percentage
of tritium. 

Actually, when you know what to look for and look carefully, a lot of
things which "don't occur in nature" can be found in small amounts.  For
example, neptunium, plutonium, and americium are all found in uranium ore,
although in decidedly small quantities.
-- 
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |   henry@zoo.toronto.edu