5 ms·

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Criteria_for_selection_of_isotopes https://en.wikipedia.org/wiki/Radioisotope_thermoelectric

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Criteria_for_selection_of_isotopes https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge... There is a nice table that shows, that Americium-241 has low power density, but it's half-life is 432 years. It also mentions that the real reason, why this is interesting, is because Am-241 is a byproduct and a pure isotope that can be used without refining.

Robotbeat 7y ago
Of course, power density is inversely proportional to half-life. Low power density BECAUSE the half-life is 432 years.
- gnode 7y ago
  > power density is inversely proportional to half-life It's not that simple. The energy per event varies by orders of magnitude depending on the specific transition (even within given particle decays, the energy of the emitted particle varies), also the number of atoms per volume or mass varies depending on material.
  - Robotbeat 7y ago
    Clearly. However it IS a good approximation. For RTGs, we desire primarily alpha emitters as alpha particles are generally the easiest type of decay product to shield (the thin metal casing will stop all alpha particles). And common Alpha emitters such as Po-210, Am-241, Pu-238, and U-232 all have a decay energy of about 5-6MeV even though they differ in half life (and thus power density) by 3 orders of magnitude.
    - gnode 7y ago
      The approximation holds true for the heavy elements, with similar atomic mass. I wonder if the power density of any similar half-life lighter nuclei would be significantly greater, or whether the energy of decay reduces roughly proportionately with their mass.
      - Robotbeat 7y ago
        And, of course, almost all alpha emitters are heavier elements: https://www.researchgate.net/profile/Adam_Woolsey2/publication/328224660/figure/fig1/AS:680541158383618@1539265064126/Chart-of-Nuclides-showing-different-types-of-radioactive-decay-2.ppm https://www.researchgate.net/profile/Adam_Woolsey2/publicati...
gnode 7y ago
> that can be used without refining It has to first be separated from the rest of the actinide waste, which is very challenging, as they're chemically similar elements. Previously this had to be done with a centrifuge (separating by mass), but a lot of research effort has gone into developing more practical chemical refining methods.

Robotbeat 7y ago

Of course, power density is inversely proportional to half-life. Low power density BECAUSE the half-life is 432 years.

gnode 7y ago
> power density is inversely proportional to half-life It's not that simple. The energy per event varies by orders of magnitude depending on the specific transition (even within given particle decays, the energy of the emitted particle varies), also the number of atoms per volume or mass varies depending on material.
- Robotbeat 7y ago
  Clearly. However it IS a good approximation. For RTGs, we desire primarily alpha emitters as alpha particles are generally the easiest type of decay product to shield (the thin metal casing will stop all alpha particles). And common Alpha emitters such as Po-210, Am-241, Pu-238, and U-232 all have a decay energy of about 5-6MeV even though they differ in half life (and thus power density) by 3 orders of magnitude.
  - gnode 7y ago
    The approximation holds true for the heavy elements, with similar atomic mass. I wonder if the power density of any similar half-life lighter nuclei would be significantly greater, or whether the energy of decay reduces roughly proportionately with their mass.
    - Robotbeat 7y ago
      And, of course, almost all alpha emitters are heavier elements: https://www.researchgate.net/profile/Adam_Woolsey2/publication/328224660/figure/fig1/AS:680541158383618@1539265064126/Chart-of-Nuclides-showing-different-types-of-radioactive-decay-2.ppm https://www.researchgate.net/profile/Adam_Woolsey2/publicati...

gnode 7y ago

> that can be used without refining It has to first be separated from the rest of the actinide waste, which is very challenging, as they're chemically similar elements. Previously this had to be done with a centrifuge (separating by mass), but a lot of research effort has gone into developing more practical chemical refining methods.