Na22

Sodium-22 (Na-22) is a radioactive isotope of sodium with mass number 22. It is a synthetic, cosmogenic radioisotope produced in particle accelerators or nuclear reactors and commonly supplied as sealed calibration sources for laboratory use. Its half-life is about 2.602 years, making it relatively long-lived among positron emitters.

Na-22 decays by positron emission to neon-22, typically leaving the daughter nucleus in an excited state that promptly emits a gamma ray of 1.275 MeV. The emitted positron quickly annihilates with an electron, producing two 511 keV gamma photons. As a result, Na-22 sources emit both the 1.275 MeV line and annihilation radiation, which is advantageous for detector calibration and performance testing.

Applications for Na-22 are largely centered on instrumentation calibration and quality assurance. It is used to calibrate and characterize gamma cameras, PET and SPECT detectors, and energy-response curves, as well as to cross-calibrate different imaging modalities. The relatively long half-life allows stable, long-term calibration, but the radiation hazard requires proper handling, shielding, and licensing.

Safety and disposal follow standard radiological practices. As a sealed source, Na-22 minimizes direct contamination risks, yet prolonged radioactivity necessitates careful storage, transport, and eventual disposal in licensed facilities in accordance with regulatory requirements.