MOLYBDATE ION MO-99 is used as a precursos of Tc-99, the last is the most commonly used medical radioisotope. Mo 99 is primarily extracted from U-235 fission products, and then undergoes β decay with a half-life of 66 hours, and the Tc-99 is then chemically extracted. A few micrograms of Mo-99 can produce enough Tc-99 to perform as many as 10,000 tests.