Modeling the Generation and Isolation of Radioisotopes in Nuclear Medicine

Radioisotopes are naturally decaying atoms that have a wide range of uses in contemporary life. They are routinely used in nuclear medicine to diagnose and treat health conditions such as heart disease, thyroid disorder and cancer. The radioisotope most widely used in medicine is technetium-99m. It is used as a radioactive tracer allowing doctors to obtain images of organs like the heart, liver and lungs by detecting the gamma rays emitted when Tc-99m decays. Radioisotopes are also used for radiotherapy (treatment). Radioisotopes like Actinium-225 are important for targeted alpha therapy in the treatment of malignant tumors. These isotopes can be produced by generators or particle accelerators. However, they almost always need to be separated from other decay products. Ac-225 can be generated from a Thorium-229 generator but can only be isolated every nine weeks and needs to be separated from Ra-225. Ac-225 can also be produced more abundantly by a particle accelerator but requires several separation steps as many radioisotopes (including Ac-226 and Ac-227 are produced). In this project we are modeling a radioisotope generator system and subsequent separation of generator produced radioisotopes. A cesium-137 generator was used to produce barium-137m, which was separated from the parent Cs-137 isotope by "milking" a resin column. A Geiger counter was used to measure radioactivity over time and determine the half-life of the Ba-137m generated. The half-life was determined to be 151 seconds about 1% deviation from the known half-life of 153 seconds (2.55 minutes).