Gold-197
Gold (Au) has one stable isotope, 197Au, and 18 radioisotopes, with 195Au being the most stable with a half-life of 186 days.
Gold is currently considered the heaviest monoisotopic element (bismuth formerly held that distinction, but bismuth-209 has been found to be slightly radioactive).
Relative atomic mass: 196.966569(5).
Inside coker units at oil refineries, gold-198 is used to study the hydrodynamic behavior of solids in fluidized beds and can also be used to quantify the degree of fouling of bed internals.
Gold-198 is a beta emitter with range in tissue of about 11 mm and half life 2.7 days. It is used in some cancer treatments and for treating other diseases. Gold-198 nanoparticles are being investigated as an injectable treatment for prostate cancer.
Gold has been proposed as a material for creating a salted nuclear weapon (cobalt is another, better-known salting material). A jacket of natural 197Au, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope 198Au with a half-life of 2.697 days and produce approximately .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. Gold has been used in thermonuclear weapons as radiation mirrors within the secondary assembly. Ivy Mike used a thin layer of gold on the secondary casing walls to enhance the blackbody effect, trapping more energy in the foam to enhance the implosion.
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