Re: Alternative isotopes in RTGs?

["J. Andrew Tompkins" <JATALBQ@ix.netcom.com>]

Mike McNaughton wrote:
> 
> When considering alternative nuclides for Cassini, there are several
> additional questions to consider. For example:
> 1. is the daughter short-lived or long-lived? U-232 and Ac-227 daughters are
> short lived, so each decay is soon followed by a string of decays emitting
> betas and high-energy gammas. In contrast, the first Pu-238 daughter is long
> lived, so the grand-daughters do not grow in.
> 2. What is the spontaneous fission cross section? (this could be a problem
> for Cf-250)
> 3. What is the availability. Po-209 looks like it would work, but is it
> available?
> 
> >Given all the attention to the Pu-238 in the Cassini RTGs
> >I was wondering what other isotopes might have been suitable
> >for this application.  Below are those alpha emitters with
> >half-lifes of 10 to 150 years.
> >
> >   Po- 209   103   a
> >   Ac- 227    21.8 a
> >   U - 232    72.0 a
> >   Pu- 238    87.7 a
> >   Cm- 243    28.5 a
> >   Cm- 244    18.1 a
> >   Cf- 250    13.1 a
> 
> "Shlala gashle" (Zulu greeting meaning "stay safe") mike

Cm-244 RTG heat sources have been fabricated as an R&D project at ORNL. 
There is plenty of Cm-244 in the HLW tanks at Hanford but no one seems
to have a large bankroll to implement that project.

Cf-252 is generally available in mg quantities not the gram or kg
quantities necessary for these heat sources.  There are strict
specifications on neutron generation by these heat sources since that
would be difficult to shield and will have a negative effect on some
sensors.

There was a nice balanced piece on CNN in the midday about why we have
Pu-238 heat sources.  Some of the capsule testing and alternatives
considered were discussed.  However I only saw that piece one time
during the entire day.  It's a shame they did not run that piece two
weeks ago when the furor over the Pu-238 was at its peak.