Americium from smoke-detectors, of course not the whole piece is Americium.
The easiest way to get some radioactive material to start with, is to take apart smoke-detectors. Smoke-detectors is now more replaced with the optical variant, but in the ionizing type there is a small amount of Americium (Am-241), an α-emitter with a half-life of 432 years.
The Americium-piece lie on about 37 kBq, 37 000 bequerel. The background-radiation is on about 35 Bq. But for my project you need much, much more. About 100 of smoke-detectors. But later I will try another material, instead of getting so many smoke-detectors