That's not really accurate, but rather than explaining why, I'll just give the abbreviated rundown on plutonium: Plutonium 238 is a powerful alpha emitter with

That's not really accurate, but rather than explaining why, I'll just give the abbreviated rundown on plutonium: Plutonium 238 is a powerful alpha emitter with a half-life of 87.7 years, making it a great element for powering mars rovers. It's produced by exposing Neptunium 237 to neutron flux. You can get Np-237 out of nuclear waste from ordinary reactors. The US has mostly been buying Pu-238 from Russia, but we're running out, and starting up our own production again is kind of expensive. We can do it, though. Plutonium 239 is the kind that gets used in bombs. It's fissile. It's produced by exposing Uranium 238 ("depleted uranium") to neutron flux in a nuclear reactor. It's tricky to make weapons-grade Pu-239, because it tends to be contaminated with Pu-240. Plutonium 240 is annoying and nobody likes it.