Alpha radiation from outer space can't penetrate the atmosphere, for much the same reason you can't fire bullets 1km underwater from the surface. The only sourc

Alpha radiation from outer space can't penetrate the atmosphere, for much the same reason you can't fire bullets 1km underwater from the surface. The only source of alphas from cosmic radiation would be from some sort of indirect effects such as direct fissioning (at ground level) of a nuclide by cosmic radiation into an alpha + daughter.