22Na

Sodium-22 (22Na) is a radioactive isotope of sodium with a mass number of 22. It decays primarily by positron emission and electron capture to the stable nucleus neon-22, with a half-life of about 2.6 years. The decay path produces characteristic radiation, including a positron that annihilates with electrons to yield two 511 keV gamma photons, and, in most decays, a prompt 1.275 MeV gamma ray from the de-excitation of the daughter nucleus to its ground state.

Nuclear properties of 22Na include its long half-life compared with many practical PET isotopes, and its decay scheme that generates both positrons and prompt gamma radiation. This combination provides convenient coincidence signals for detector testing and energy calibration.

Production of 22Na is typically achieved in cyclotrons by irradiating neon-22 targets with protons through reactions such as 22Ne(p,n)22Na. It can also arise from other spallation processes in high-energy environments. Due to its long half-life, 22Na is manufactured as a sealed source for laboratory calibration and instrument testing rather than for medical use in vivo.

Applications of 22Na center on detector calibration and validation. The simultaneous emission of 511 keV annihilation photons and a 1.275 MeV gamma ray allows for testing energy resolution, timing performance, and coincidence measurement in gamma-ray spectrometers and PET scanner components. Safety considerations include radiological protection and shielding, given its gamma and positron emissions and long half-life. Proper handling and regulatory compliance are required for any practical use.