Thanks for the on and off line responses to my SPECMAP question.  I
am dealing with a technical editor of a journal that wants the term
fully defined.  I'll just note that the responses differed
considerably.

My 2 cents on pumping.  For a vacuum line, a good oil diffusion pump
can be purchased off the shelf from Edwards, Varian, etc. for about
$1K, but it will have to be backed by a rotary vane pump which will
cost another $1.5K or so.  However, our college has an instrument
shop and I've been able to purchase rebuilt pumps for as little as
$50. Look around, you might find a similar deal. If you want to use
the pump as a fluorine getter, use a KBr trap like Zach suggested.
But if you want to pump, this is a much cheaper option than a turbo
pump.  It has no moving parts so it will last forever.  If you are
pumping reactive gases, you may have to change the oil frequently,
but it should protect your rotary vane backing pump and you won't
have to deal with Hg. Put a cold trap on the low-vac. side.


>An added concern with Turbo pumps, particularly in the context of earlier
>messages contributed to this discussion, is that they wear out fast when
>used on a fluorination line, even when efforts are made to protect them
>from corrosive vapors.  We have had good experiences with very large ion
>pumps taken off old thermal ionization machines.  These are rare items but
>if you can get them you will find they reach incredibly low baseline
>pressures compared to the norm for stable isotope lines.
>
>John Eiler
--

********************************
Steve Nelson
Dept. of Geology
S389 ESC
Brigham Young University
Provo. Utah  84602

voice:  1-801-378-8688
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FAX:    1-801-378-8143

Q.  How do you spell "scapegoat"?
A.  Wen Ho Lee.
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