Na23

Na-23, often written as Na-23, is the only stable isotope of the element sodium. It has a mass number of 23, consisting of 11 protons and 12 neutrons (Z = 11, N = 12). Natural sodium is effectively 100% Na-23.

Because Na-23 is stable, it does not undergo radioactive decay under ordinary conditions. There are other isotopes of sodium, such as Na-22 and Na-24, which are radioactive and occur in nature only in trace amounts or are produced in reactors and by cosmic-ray interactions.

Nuclear properties of Na-23 include a ground-state spin I = 3/2+ and a nuclear magnetic moment of about +2.217 μN. The isotope is bound with a binding energy characteristic of light, odd-A nuclei in this region. In stellar environments, Na-23 is produced in the Ne-22(p, γ)Na-23 reaction as part of the Ne-Na cycle, and it can be consumed by subsequent proton captures to form Mg-24.

Na-23 has important applications in nuclear magnetic resonance and imaging. Its gyromagnetic ratio γ/2π is about 11.262 MHz per tesla, enabling 23Na NMR spectroscopy and, in some cases, 23Na MRI to study tissue sodium concentration and ion homeostasis. In liquids, 23Na signals are relatively sharp, while in solids quadrupolar interactions broaden the lines due to the I = 3/2 nucleus.

Historically, the identification of Na-23 as the sole stable sodium isotope helped establish the elemental isotopic composition observed today, with mass spectrometry playing a key role in confirming its stability and abundance.