They didn't use plutonium at all: they used polonium [1]. The article refers to polonium in some places (correctly), but plutonium in others (incorrectly). [1]

They didn't use plutonium at all: they used polonium [1]. The article refers to polonium in some places (correctly), but plutonium in others (incorrectly). [1]: https://en.wikipedia.org/wiki/Polonium https://en.wikipedia.org/wiki/Polonium