228Ra

Radium-228 (Ra-228) is a radioactive isotope of the element radium, with mass number 228 and atomic number 88. It is a member of the thorium-232 decay chain and is produced by the alpha decay of 232Th to 228Ra. The half-life of Ra-228 is about 5.75 years. Ra-228 decays by beta emission to actinium-228 (Ac-228), initiating a short decay chain that eventually forms stable lead-208.

In nature, Ra-228 occurs in trace amounts in thorium-rich rocks and soils, as thorium-232 decays through intermediate nuclides to Ra-228. Because radium behaves like other alkaline earth metals, Ra2+ ions are relatively soluble and can be incorporated into minerals and groundwater. Ra-228 is commonly studied as part of environmental radioactivity and is used in hydrological and oceanographic tracing to illuminate processes such as groundwater discharge and water mass transport. It is often measured alongside other radium isotopes to assess rock-water interactions and radionuclide transport.

Applications of Ra-228 include as a radiotracer in groundwater and coastal studies, where its ingrowth and decay help estimate mixing rates and input with reasonable timescales. It can also serve as a calibration source for gamma detectors in laboratory settings, and its decay products provide information about the behavior of radium in environmental samples.

Safety and regulation: Ra-228 emits beta and gamma radiation and, like other radium isotopes, poses radiological hazards if ingested or inhaled. Proper shielding, handling procedures, and regulatory controls are required for its use and storage.