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

The high-energy neutrons produced during fusion, being electrically neutral, escape towards the walls of the tokamak, allowing most of the energy produced to be recovered (and ultimately creating tritium in collisions with lithium). —Prabhat Ranjan Mishra, Interesting Engineering, 12 Sep. 2025

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

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