Physics:Isotopes of hydrogen

The three commonly discussed isotopes of hydrogen: protium, deuterium, and tritium.

Isotopes of hydrogen are atoms with one proton in the nucleus and different numbers of neutrons. The three named isotopes are protium ($1^{}\mathrm{H}$), deuterium ($2^{}\mathrm{H}$ or D), and tritium ($3^{}\mathrm{H}$ or T).

Hydrogen isotopes are important in atomic physics because the nucleus affects the reduced mass, hyperfine structure, isotope shifts, and precision spectroscopy of hydrogen-like systems.

Main isotopes

Isotope	Symbol	Nucleus	Stability	Notes
Protium	$1^{}\mathrm{H}$	one proton	stable	Most common hydrogen isotope; no neutron.
Deuterium	$2^{}\mathrm{H}$ or D	one proton and one neutron	stable	Used in heavy water, isotope labeling, and precision spectroscopy.
Tritium	$3^{}\mathrm{H}$ or T	one proton and two neutrons	radioactive	Beta emitter with a half-life of about 12.3 years; used in tracing and fusion research.

Quantum effects

Different hydrogen isotopes have slightly different atomic energy levels because the nuclear mass changes the reduced mass of the electron-nucleus system. These isotope shifts are measured in high-precision spectroscopy.

The nuclear spin also affects hyperfine splitting. Ordinary hydrogen and deuterium have different nuclear spin values, so their hyperfine spectra differ. Tritium is radioactive, but it is still useful in nuclear and atomic physics contexts.

Related pages

• Physics:Quantum atoms/hydrogen
• Physics:Quantum atoms/energy level
• Physics:Quantum Spectral lines and series
• Physics:Quantum atomic nucleus
• isotope shifts in atomic spectra

References

• "Hydrogen". https://www.britannica.com/science/hydrogen. 
• "Isotopes of hydrogen". https://www.britannica.com/science/hydrogen/Isotopes-of-hydrogen. 
• "Tritium". United States Environmental Protection Agency. https://www.epa.gov/radiation/radionuclide-basics-tritium. 

Author: Harold Foppele