Au-198

Gold-198 (Au-198) is a radioactive isotope of gold with a half-life of approximately 2.7 days. It decays by beta emission, producing stable mercury-198 (Hg-198), and emits gamma radiation during the process. Au-198 is produced artificially by irradiating stable gold-197 (Au-197) with neutrons in a nuclear reactor.

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Gold has been proposed as a material for creating a salted nuclear weapon (cobalt is another, better-known salting material). A jacket of natural 197.
Au (the only stable gold isotope), irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope Au-198 with a half-life of 2.697 days and produce approximately 0.411 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several days. Such a weapon is not known to have ever been built, tested, or used.

The highest amount of 198Au detected in any United States nuclear test was in shot "Sedan" detonated at Nevada Test Site on July 6, 1962. Au-198 is primarily used in medical applications, particularly in brachytherapy for cancer treatment. Small seeds or wires containing Au-198 are implanted near or within tumors, where its beta and gamma radiation help destroy cancer cells while minimizing damage to surrounding healthy tissue. It has been used to treat prostate cancer, liver cancer, and other localized tumors. Au-198 is also utilized in scientific research, such as studying gold’s behavior in biological systems or tracing gold particles in chemical and environmental processes. Additionally, Au-198 is used in industrial radiography and leak detection systems, where its radiation properties enable precise imaging and tracing.

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Au-198 does not occur naturally and is produced exclusively in controlled environments, such as nuclear reactors, through neutron activation of gold. It is encountered in medical facilities, research laboratories, and industrial settings where it is used for its radioactive properties. Due to its short half-life, Au-198 is handled shortly after production and is typically used in applications that require its radiation before it decays into stable mercury-198. Its use is regulated to ensure safety in medical and industrial practices.