tritium

noun

tri·​ti·​um ˈtri-tē-əm  ˈtri-shē- 

: a radioactive isotope of hydrogen that has one proton and two neutrons in its nucleus and that has three times the mass of ordinary hydrogen

—symbol T

Examples of tritium in a Sentence

Recent Examples on the Web

Scientists have figured out how to collect helium-3 produced by the decay of tritium in nuclear weapons and power plants, but that yields less than 20 kg a year. —Jeremy Bogaisky, Forbes.com, 2 Sep. 2025

These neutrons interact with the lithium to eventually produce tritium. —New Atlas, 2 Sep. 2025

For context, his initial estimates suggest that a two-gigawatt deuterium-tritium (D-T) fusion energy plant would require about 247 pounds (112 kilograms) of tritium annually to operate at full capacity. —Georgina Jedikovska, Interesting Engineering, 1 Sep. 2025

Their decay energies go from a few kiloelectron volts (for tritium, or hydrogen-3) to a few megaelectron volts (for yttrium-90). —IEEE Spectrum, 25 Aug. 2025

Word History

Etymology

New Latin, from Greek tritos third — more at third entry 1

First Known Use

1933, in the meaning defined above

Kids Definition

tritium

noun

tri·​ti·​um ˈtrit-ē-əm  ˈtrish-ē- 

: a rare radioactive form of hydrogen having atoms with three times the mass of ordinary light hydrogen atoms

Medical Definition

tritium

noun

tri·​ti·​um ˈtrit-ē-əm  ˈtrish-ē- 

: a radioactive isotope of hydrogen that has three times the mass of ordinary hydrogen

—symbol T