U + Ra-226
Uranium + Radium-226 (natural uranium)
Main emission lines: 186keV, 242keV, 395keV, 351keV, 609keV, 1120keV, 1760keV, 2200keV
In natural uranium (uranium and radium are in equilibrium), radium dominates the spectrum. At the beginning of the spectrum, the lines are broader because of the merging X-ray lines of uranium and radium. It is found in minerals, building materials (often granite), and some foods (e.g. Brazil nuts).