Preparation of Single Crystals. With a half-life of 1600 years, Ra is the longest-lived radioisotope of Ra. It is available in milligram quantities but is highly radioactive because of its relatively short half-life. To place this radioactivity in context, one mole of Ra is approximately 2.7 million times more radioactive than an equivalent amount of natural 238 U. Radiological concerns regarding the use of Ra stem from the fact that its direct daughter radionuclide is Rn-222 ( 222 Rn, t1/2 = 3.82 d), a gas that poses a contamination and health risk if not contained properly. Furthermore, the decay of 226 Ra yields several daughter radionuclides that emit high-energy gamma rays, in addition to a total of 5 alpha particles and 4 beta particles. This ionizing radiation will cleave chemical bonds, destroying molecular species both in solution and in the solid state. Thus, any successful crystallization will need to be executed rapidly, reproducibly, and on a small scale.