There are several isotopes of plutonium that differ in their nuclear-physical but not in their chemical characteristics. The most important one is plutonium-239. Reactor plutonium is more impure. Am-241, in addition to emitting alpha radiation, also emits relatively energetic gamma radiation.
Alpha radiation is relatively easy to screen.
Gamma radiation and neutrons are very penetrating. For this reason it is very difficult to prove that weapons-grade plutonium is in a container by measuring radiation from the outside. Nuclear bombs can also be constructed from reactor plutonium. The most important thing is the right explosive. The compression makes the sphere supercritical and initiates the nuclear explosion.