In 1946, The Mound site (Dayton, Ohio - U.S.A.) construction began under the Manhattan Engineering District of War Department.
In 1949, it started to produce Polonium and thus was the first Post-War Atomic Energy Commision site in the U.S.A.
The site was run by Monsanto Research Corp. (Yes, the same Multinational company that produces herbicide)
Our interest turns now to Radioisotopic Thermoelectric Generators or RTG.
(They also researched and produced explosives weapons among others.)
The researchers John Birden and Kenneth Jordan invented the first RTG in 1954-5, it was fueled with Polonium-210 which decay produces heat (see patent below).
A generator (called SNAP for Space Nuclear Auxiliary Power) was used as soon as 1959 in Space on a Transit mission (launching a satellite for military navigation system).
The second and most successful SNAP generation used Polonium-238. Its research started in 1961 at the Mound site.
The shielding used for the Polonium-238 is very low - just 2,5mm of lead can stop its radiation. This makes it easier and lighter to wrap up.
The Polonium-238 will be used for generators on various spatial missions like Voyager 1 & 2 (Outer Solar system) or Cassini (Saturn).
If you are interested in the use of RTG in Space, read this: pdf
Such a practical energy source that its use in household was considered.
I am very proud today to present the one-and-only Atomic coffee machine:
I have no idea how many of you are interested in this, but here is the patent for the first Radioactive battery: