Americium: How a small element could power the next century of space exploration
Americium: How a small element could power the next century of space exploration
interestingengineering.com
Americium: How a long-life nuclear fuel will transform space travel
Americium, a much more common element, may replace plutonium in long-life nuclear batteries, powering spacecraft for centuries.

"The isotope of interest for space is americium-241....Its half-life is a staggering 432 years, five times longer than plutonium-238."