Au198

Au198 is the longest-lived radioactive isotope of gold. It has a half-life of 2.695 days and decays primarily by beta minus emission to mercury-198, with a small percentage of electron capture to platinum-198. The beta decay leads to the formation of excited states of mercury-198, which then emit gamma rays. These gamma rays, with energies of 411.8 keV, are a characteristic signature of Au198.

Au198 is produced artificially, typically in nuclear reactors through neutron activation of stable gold-197. This process involves bombarding gold-197 atoms with neutrons, which are absorbed to form Au198. Due to its relatively short half-life and energetic gamma emissions, Au198 has found limited but specific applications.

Historically, Au198 was used in brachytherapy, a form of radiation therapy where radioactive sources are placed directly inside or near a tumor. Its gamma radiation could be used to target and destroy cancer cells. However, its use in medicine has largely been superseded by other radioisotopes with more favorable properties, such as longer half-lives or more targeted delivery mechanisms. It has also been employed in industrial radiography for inspecting welds and castings, though this application is also less common today.