This nuclear pacemaker was manufactured ca. 1972 by Dr. Orestes Fiandra’s CCC del Uruguay. It was powered by a McDonell-Douglas Betacel 400 which had promethium-147 sandwiched between semiconductor wafers. As the radioactive promethium isotope decays, it emits β-particles (electrons). The impact of the β-particles on a p-n junction causes a forward bias in the semiconductor similar to what happens in a photovoltaic cell (a solar cell).
The Betacel 400 had an open-circuit voltage of 4.7V and a short circuit current of 115μA. The maximum power output was 370μW. CCC’s pacemaker was expected to last for 10 years when powered by this nuclear battery.
Click here for my paper on nuclear-powered pacemakers.
Click here for Dr. Fiandra’s paper (in spanish) about CCC’s atomic pacemaker.
Click here for the authoritative paper on nuclear batteries for pacemakers: Fred N. Huffman, et al., RADIOISOTOPE POWERED CARDIAC PACEMAKERS, Cardiovasc Dis., 1(1): 52–60, 1974. (Copyright notice: This article is free from www.pubmedcentral.nih.gov).
Click here to find out what to do if you find a nuclear pacemaker.
UPDATE, 30 March 2019:
I’m in Uruguay at the moment, and my friend Daniel Villamil showed me the original mold used to cast CCC’s atomic pacemaker in silicone. The mold is made of epoxy resin with rice as the filler. The radiation symbol is a machined steel die. Here are some pictures of this historical piece: