Radioisotopes used in medicine typically have short half-lives—for example, the ubiquitous Tc-99m has a half-life of 6.01 hours. It makes Tc-99m essentially impossible to store and prohibitively expensive to transport. Hospitals and other medical facilities use Mo-99 to generate Tc-99. Mo-99 undergoes β decay with a half-life of 66 hours, and the Tc-99 is then chemically extracted. The parent nuclide Mo-99 is part of a molybdate ion, MoO42−; MoO42−; when it decays, it forms the pertechnetate ion, TcO4−.TcO4−. These two water-soluble ions are separated by column chromatography, with the higher charge molybdate ion adsorbing onto the alumina in the column, and the lower charge pertechnetate ion passing through the column in the solution. A few micrograms of Mo-99 can produce enough Tc-99 to perform as many as 10,000 tests.