Plutonium-239 is an alpha emitter. Nuclear missiles on submarines actually have to spend more money to create highly pure Plutonium-239 specifically because it'

Plutonium-239 is an alpha emitter. Nuclear missiles on submarines actually have to spend more money to create highly pure Plutonium-239 specifically because it's long half life means it has a low rate of spontaneous emissions. This makes it safer for crew who have to live and work in close quarters with these missiles.