Message #204426

[Jennifer Murdoch]

Drake proposed the used of Technetium (Tc) for this  purpose.   This
       element is not  found  on  Earth  and  its presence is observed very
       weakly in the Sun, in part because  it  is  short-lived.   Tc's most
       stable form decays  radioactively  within  an  average   of   twenty
       thousand years.  Thus,  for  the  case  of Tc, we need to distribute
       some 1.3x10exp11 grams, or 1.3x10exp5 tons, of this element into the
       stellar spectrum.  However, technetium  lines have not been found in
       stars of solar spectral type, but rather only in peculiar ones known
       as S stars.   We  must know more than we do about  both  normal  and
       peculiar stellar spectra  before we can reasonably conclude that the
       presence of an unusual atom in an  stellar  spectrum  is  a  sign of
       extraterrestrial intelligence.

       Whitmire and Wright  (1980)  considered  the possible  observational
       consequences of galactic  civilizations  which  utilize  their local
       star as a repository for radioactive  fissile  waste material.  If a
       relatively small fraction  of  the nuclear sources  present  in  the
       crust of a   terrestrial-type  planet  were  processed  via  breeder
       reactors, the resulting  stellar   spectrum   would  be  selectively
       modified over geological time periods, provided that  the star has a
       sufficiently shallow outer  convective  zone.   They  have estimated
       that the abundance anomalies resulting from the slow neutron fission
       of plutonium-239 and uranium-233 could  be duplicated (compared with
       the natural nucleosynthesis processes), if this process takes place.