For 10 points, name this particle with a +2 charge and a mass of 4 amu, equivalent to a helium nucleus.
The natural log of a decay constant is related to the energy of these particles in the Geiger-Nuttall law. In one process, these particles are combined to form carbon after undergoing a beryllium intermediate. In an experiment which disproved the plum-pudding model, Geiger and Marsden fired these particles at a gold foil which allowed them to determine the composition of the nucleus. Uranium-238 is converted to Thorium-234 with the release of one of these particles in their namesake decay. For 10 points, name this particle with a +2 charge and a mass of 4 amu, equivalent to a helium nucleus.
The natural log of a decay constant is related to the energy of these particles in the Geiger-Nuttall law.
alpha particles [prompt on nucleus of helium or equivalents]