enter image description hereI know that RTG's use Radioactive Isotope that emit Alpha particles generally (ie. NASA uses Pu 238), I also know that these Alpha particles are consiting of 2 Protons and 2 Neutrons, since the RTG has two thermocouple plates that force the protons and the electrons to the cooler side. I was wondering where the electrons come from? Also I was wondering how exactly does the Seeback effect utilize these positive and negative charges with the junction formed to create the electrical charge.

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    $\begingroup$ Did you look at the Wikipedia article on plutonium-238? That isotope has atomic number 94, so it has 94 electrons. When one of those atoms emits an alpha particle, the atom becomes U-234. Since uranium has atomic number 92, it has 92 electrons. And that is where the two electrons come from: 2 = 94 - 92. $\endgroup$
    – Ed V
    May 18, 2021 at 1:22
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    $\begingroup$ The Pu is contained so the alphas don’t make it to the thermoelectric material. It just gets hot to drive the thermal gradient. No net charge is produced. $\endgroup$
    – Jon Custer
    May 18, 2021 at 1:34
  • $\begingroup$ @EdV I was also wondering, in an RTG the electrons come from the decay and not just the free-flowing electrons from the metal of each Semiconductor right (as NASA uses Skutterudite to build the semiconductors)? I was also wondering for the two semiconductors, would one let in protons and the other electrons to create the volage diferential or just electrons for both semiconductors. Please refer to the photo of the diagram above and see if it is accurate. Thank you very much. $\endgroup$ May 19, 2021 at 23:52
  • $\begingroup$ @JonCuster Same question as to EdV above but I was also wondering what material does NASA use in their MMRTG to create the semiconductors, I know they have to be out of two dissimilar metals and read a post on Wikipedia which wrote "The MMRTG design incorporates PbTe/TAGS thermoelectric couples (from Teledyne Energy Systems), where TAGS is an acronym designating a material incorporating tellurium (Te), silver (Ag), germanium (Ge) and antimony (Sb). But that they are trying to use skutterudite, since it needs to be made out of dissimilar metals how would that work? $\endgroup$ May 20, 2021 at 0:04
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    $\begingroup$ The semiconductors in typical examples are doped N type (so you have donor impurities resulting in electrons are majority charge carriers) and P type (so you have acceptor impurities resulting in positively charged holes as majority charge carriers). No protons are involved. You should do some deeper digging on the Seebeck effect : lots of semiconductor physics books discuss its fundamental principles, and that is more than I can do so long after my last courses on that. $\endgroup$
    – Ed V
    May 20, 2021 at 0:31


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