23Na

23Na is the only stable isotope of sodium, with mass number 23. It consists of 11 protons and 12 neutrons. In nature, sodium is essentially present as 23Na, giving an isotopic abundance effectively of 100% for this isotope. It is non-radioactive and does not undergo radioactive decay.

Nuclear properties of 23Na include a nuclear spin of I = 3/2 and a magnetic dipole moment of about +2.217 nuclear magnetons. Because I > 1/2, it also has a nonzero electric quadrupole moment, which influences its interactions in magnetic fields and in solid-state environments. The isotope is widely studied in nuclear magnetic resonance and related spectroscopies.

Occurrence and production: 23Na is abundant in the Earth's crust and in seawater, where sodium is most commonly found as chloride salts such as NaCl. Trace cosmogenic radionuclides such as Na-22 can be produced by cosmic rays, but these are short-lived and present only in very small amounts.

Applications: 23Na is used in nuclear magnetic resonance (NMR) spectroscopy and in magnetic resonance imaging (MRI) to study sodium ions in chemistry, biology, and medicine. The 23Na nucleus has a gyromagnetic ratio of about 11.262 MHz per tesla, enabling detection at clinical MRI field strengths. Because natural abundance is nearly 100%, isotopic enrichment is not required for most experiments, though sensitivity is lower than that of proton-based imaging, often necessitating higher field strength or longer acquisition times.