29Si

29Si is a stable isotope of silicon with mass number 29. It makes up about 4.7% of natural silicon. The nucleus has spin I = 1/2 and a magnetic moment of approximately -0.555 μN, which makes 29Si the only stable silicon isotope that is NMR-active under normal conditions (28Si and 30Si have spin 0).

Because of its nuclear spin, 29Si is widely used in nuclear magnetic resonance (NMR) spectroscopy and solid-state NMR studies. 29Si NMR provides information about the local chemical environment of silicon atoms; chemical shifts reflect oxidation state, coordination, and bonding in materials such as silicates, silicon oxides, organosilicon compounds, and semiconductor crystals. Experiments often use techniques like magic-angle spinning and cross-polarization to enhance sensitivity.

Beyond spectroscopy, 29Si plays a role in silicon-based quantum information science. Interactions between 29Si nuclear spins and electron or donor spins influence coherence times for silicon qubits. In isotopically engineered silicon, reducing 29Si concentration (by enriching 28Si) improves qubit performance, while controlled use of 29Si enables quantum memory and sensing experiments.

29Si is non-radioactive and occurs naturally within silicon minerals and bulk silicon. It can be enriched for research by isotope separation methods when higher 29Si content is desired for spectroscopy or quantum experiments.