A nuclear experiment has been designed for use in the undergraduate laboratory. Following a theoretical treatment of alpha barrier penetration and the kinematics andQvalue of alpha decay, a semiclassical calculation is made for the half‐life for alpha decay, followed by a more exact quantum mechanical result. The decay schemes of three commercially available sources are studied. The branching ratios to various excited states in the residual nuclei are measured along with the precise energies of the decay. The absolute activity of one source (241Am) is determined from its measured alpha activity, and from its gamma activity as measured by a low‐energy photon detector.