Gold-198 (¹⁹⁸Au) is a

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...

. It undergoes

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

to stable ¹⁹⁸ Hg with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...

of 2.697 days. The decay properties of ¹⁹⁸Au have led to widespread interest in its potential use in

radiotherapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Rad ...

for cancer treatments. This isotope has also found use in

nuclear weapons A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...

research and as a

radioactive tracer A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by ...

in hydrological research.

Discovery

¹⁹⁸Au was possibly observed for the first time in 1935 by

Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" an ...

et al., though it was not correctly identified at the time. This isotope was conclusively identified in 1937 following neutron irradiation of stable ¹⁹⁷Au and was ascribed a half-life of approximately 2.7 days.

Applications

Nuclear medicine

¹⁹⁸Au is used for radiotherapy in some cancer treatments. Its half-life and beta decay energy are favorable for use in medicine because its 4 mm penetration range in tissue allows it to destroy tumors without nearby non-cancerous tissue being affected by radiation. For this reason, ¹⁹⁸Au nanoparticles are being investigated as an injectable treatment for

prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that su ...

Radioactive tracing

Sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

and water flow can be investigated using radioactive tracers such as ¹⁹⁸Au. This has been used extensively since artificial radioisotopes became available in the 1950s, as a supplement to millennia of investigations using other tracing techniques. Inside

coker unit A coker or coker unit is an oil refinery processing unit that converts the residual oil from the vacuum distillation column into low molecular weight hydrocarbon gases, naphtha, light and heavy gas oils, and petroleum coke. The process thermally ...

s at

oil refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, li ...

, ¹⁹⁸Au 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.

Nuclear weapons

Gold has been proposed as a material for creating a salted nuclear weapon (

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

is another, better-known salting material). A jacket of natural (the only stable gold isotope), irradiated by the intense high-energy neutron flux from an exploding

thermonuclear weapon A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lo ...

, would transmute into the radioactive isotope ¹⁹⁸Au with a half-life of 2.697 days and produce approximately 0.411 MeV of

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

, significantly increasing the radioactivity of the weapon's

fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...

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 The Nevada National Security Site (N2S2 or NNSS), known as the Nevada Test Site (NTS) until 2010, is a United States Department of Energy (DOE) reservation located in southeastern Nye County, Nevada, about 65 miles (105 km) northwest of the ...

on July 6, 1962.

References

{{Therapeutic radiopharmaceuticals

Gold-198 Gold-198 (198Au) is a radioactive isotope of gold. It undergoes beta decay to stable 198 Hg with a half-life of 2.697 days. The decay properties of 198Au have led to widespread interest in its potential use in radiotherapy for cancer treatments. ...