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Usually any alpha emitter, when absorbed and held in proximity to tissue is a carcinogen. An alpha decay typically gives off a gamma around 1/2 MeV, and the alphas from most natural isotopes are 4-5MeV. In WWII, young women painted altimeter dials with radium luminous paint. Radium occupies the same row in the periodic table as calcium. The women's bones were still growing, and the body took up Group IIA metals thinking they were calcium. This included Radium 226. Many died of bone cancers years later. Photomicrographs of bone showed "Alpha Tracks" made by the particles over the years. Addtionally, one carcinogen suspect in tobacco smoke is Polonium 210, which is found in the superphosphate fertilizers used on the crop. Lung cancers from Radons are caused not by the radon, but by the daughter isotopes that float around in the air, and attract dust particles so the clumps are exactly the right size (4-10 microns) to make it into the lung.