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From: (Rebecca M. Chamberlin)
Newsgroups: sci.chem
Subject: Re: what's the deal with technetium?
Date: Sun, 10 Jan 1999 15:06:52 -0700

In article <77b43n$>, af524@FreeNet.Carleton.CA
(Stewart Rowe) wrote:

> Kurt Foster ( writes:
> > In <>, Edwin said:
> >
> > . I'm just curious why Technetium isn't found in nature?  or is it?  I
> > . just find it odd because is just seems to be this oddball element in the
> > . periodic table.  Thanks.
> >
> >   There are no stable isotopes.  The "Sourcebook on Atomic Energy" has the
> > following in a footnote to Chapter 16, section 77: All isotopes are
> > radioactive; and the longest lived, 43Tc99, has a half-life of only
> > 200,000 years.  There are probably traces on Earth, due to fission of
> > U-235 and capture of cosmic-ray neutrons by Molybdenum.  Spectoscopy
> > indicates an unecpectedly large amount of Technetium in some stars,
> > indicating ongoing synthesis of the element.
> >
> OK, now someone please explain how they can inject some into me and
> measure it's distribution for a heart test.
>         Stewart Rowe

Technetium-99m is the isotope they use for diagnostic imaging.  "99m" means
it's a metastable (high-energy) nuclear isomer with a mass of 99;  within a
few days it decays completely to the ground state isomer Tc-99.  Although
Tc-99 is still radioactive, its half-life is so long that your body
efficiently excretes it before it can have any real negative health

The other nice feature of Tc-99m is that its decay to Tc-99 produces only
gamma (electromagnetic) radiation, but no particle radiation.  This is
important because the gamma rays pass easily through your body tissue and
are detected by the imaging instruments.  If it was a particle emitter your
cells would suffer unnecessary radiation damage from the procedure.

Tc-99m is sufficiently short-lived that the hospitals have to "milk" it
from a longer-lived parent nuclide, Molybdenum-99.  Even so, the Mo-99 has
a half-life of only ~3 days, so they rely on a fairly steady supply.  Mo-99
can be produced by reactor or accelerator methods.


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