What is the half-life of radium-226?

The half-life of radium-226 is 1,600 years. In that time, half of a sample’s radium-226 nuclei will undergo radioactive decay; after another 1,600 years, half of what remains will decay again.

Radium-226 is the longest-lived naturally occurring isotope of radium. It is produced within the uranium-238 decay series, a chain of transformations that eventually leads to stable lead-206. During its own decay, radium-226 emits an alpha particle and becomes radon-222, itself a radioactive gas.

The 1,600-year figure is an approximate value commonly used in science references; precise measurements may state it with additional decimal detail. It describes the isotope, not all radium, because different isotopes have different nuclear properties and lifetimes.

A related source of confusion is radon-222, the decay product of radium-226. Radon’s half-life is only about 3.8 days, vastly shorter than radium-226’s, even though both belong to the same decay chain.