MadSci Network: Physics

Re: An update on the nuclear laser proposal.

Date: Wed Jun 11 13:32:10 2003
Posted By: Steve Nelson, research physicist
Area of science: Physics
ID: 1054605492.Ph

Actually, my last lab is still studying exactly what these people are
talking about.  All the same isotopes, and the same stimulated emission
process.  However, it's not a gamma-laser.  The somewhat fluid definition
of a laser no longer means just what the acronym says (L.ight
A.mplification by S.timulated E.mission of R.adiation), but implies a
coherent source of light.  Generally, the laser light itself stimulates the
emission of further light of the same wavelength, making it coherent.  What
they're talking about is just pumping a nucleus with a low-energy X-ray to
allow it to release energy stored in a higher-energy metastable state as a
gamma ray.  You can't make that coherent radiation, but you can use it to
release stored energy (with very expensive isotopes, .5 g of the best test
isotope we could find we *rented* from Oak Ridge National Lab for
$100,000/year...purchasing would have cost millions for just that half a
gram of Hf).

What these people at UT are talking about is an old concept in nuclear
physics, namely the nuclear battery.  The military is interested, because
it removes the restriction of storing and transporting fuel.  With the
right semi-short-lived isotopes, you could make sure it became
non-radioactive in a few weeks in case it fell into the hands of
terrorists.  But the wavelengths for MeV gamma rays are far too short to
create coherent light out of with any conceivable present technology.  In
theory it might be able to be done (as a superradiant laser, because the
previous answerer was correct about there being no mirrors for gamma rays),
if you could achieve energy densities in the lasing material of well above
the energies being released at the exploding core of a nuclear weapon.  You
would need such high densities to overcome all the parasitic processes that
would prevent you from achieving population inversion in the lasing medium
(for examples, you can google search on "pair production," "Compton
scattering," and the photoelectric effect).

In short, if anyone does it within 50 years I'll be really surprised.  Even
beyond that it will require currently unimaginable technologies to achieve,
but you never know.  Go to grad school in nuclear physics, maybe you'll
find a way someday.

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