Radioisotope thermoelectric generators or RTGs are great machines to obtain a modest amount of electric power (and a lot more heat) in remote areas with no maintenance, but the output cannot be modulated and the fuel pellets are radioactive from the start.

I imagined a controllable variant based on pyroelectric fusion [1] where a pyroelectric crystal is heated to generate high voltages, accelerating deuterium ions into a target also containing deuterium with sufficient kinetic energy to cause nuclear fusion.
The neutrons produced by fusion will activate radioisotope precursors which will then generate beta radiation that can be exploited as a source of non-thermal energy. I used a 1960 report on radioisotope selection for RTGs [2] to narrow down the usable precursors to gaseous krypton or solid tin, but other elements are possible like bismuth-209 which produces Polonium-210.

[1] https://en.wikipedia.org/wiki/Pyroelectric_fusion
[2] http://large.stanford.edu/courses/2.....cs/4807049.pdf