Homemade nuclear bomb?

I was looking at what element isotopes were fissile or not and I found a list of critical mes and I remembered that americium 241 was in small amounts in smoke detectors, then I got to thinking...could you just Break into a smoke detector factory and steal 80 pounds of americium 241 and make a sphere of it and surround with high explosives and make a cell phone detonator for it? Is it really that easy for a terrorist to do?