21Na

Sodium-21, symbolized as 21Na, is a radioactive isotope of sodium with atomic number 11 and mass number 21. It is proton-rich and does not occur naturally in detectable quantities on Earth. 21Na is produced in laboratory settings through nuclear reactions such as proton irradiation of lighter neon isotopes (for example, 20Ne(p,γ)21Na) or by fragmentation of heavier nuclei in accelerators and spallation sources.

Decay and nuclear properties: 21Na decays primarily by beta-plus (positron) emission to the stable neon-21 (21Ne). The decay has a relatively short half-life, on the order of seconds, which necessitates rapid production and handling in experimental setups. The decay process may populate excited states of 21Ne that subsequently de-excite via gamma emission.

Applications and context: Due to its short half-life, 21Na is mainly of interest for research in nuclear physics and astrophysics, including studies of reaction rates near the proton drip line and nucleosynthesis pathways. It is not employed as a medical isotope because of its rapid decay and the logistical challenges of deploying such a short-lived tracer in clinical settings. In experimental nuclear physics, 21Na beams or targets can be used to investigate nuclear structure and reaction mechanisms.

Chemical behavior and safety: Chemically, 21Na behaves like stable sodium, forming +1 ions in solution. However, as a radioactive isotope, it requires appropriate radiological safety measures, shielding, and rapid handling to minimize exposure and ensure safe disposal after decay to 21Ne.

See also: isotopes of sodium, beta decay, proton-rich nuclei.