Isotopes of silicon

has 25 known isotopes, with mass number ranging from 22 to 46. ²⁸Si, ²⁹Si, and ³⁰Si are stable. The longest-lived radioisotope is ³²Si, which occurs naturally in tiny quantities from cosmic [ray spallation] of argon. Its half-life has been determined to be approximately 157 years; it beta decays with energy 0.21 MeV to ³²P, which in turn beta-decays, with half-life 14.269 days to ³²S; neither step has gamma emission. After ³²Si, ³¹Si has the second longest half-life at 157.2 minutes. All others have half-lives under 7 seconds.

List of isotopes

Silicon-28

Silicon-28, the most abundant isotope of silicon, is of particular interest in the construction of quantum computers when highly enriched, as the presence of ²⁹Si in a sample of silicon contributes to quantum decoherence. Extremely pure samples of ²⁸Si can be produced through selective ionization and deposition of ²⁸Si from silane gas. Due to the extremely high purity that can be obtained in this manner, the Avogadro project sought to develop a new definition of the kilogram by making a sphere of the isotope and determining the exact number of atoms in the sample.
Silicon-28 is produced in stars during the alpha process and the oxygen-burning process, and drives the silicon-burning process in massive stars shortly before they go supernova.

Silicon-29

Silicon-29 is of note as the only stable silicon isotope with a nonzero nuclear spin. As such, it can be employed in nuclear magnetic resonance and hyperfine transition studies, for example to study the properties of the so-called A-center defect in pure silicon.

Silicon-34

Silicon-34 is a radioactive isotope with a half-life of 2.8 seconds. In addition to the usual N = 20 closed shell, the nucleus also shows a strong Z = 14 shell closure, making it behave like a doubly magic spherical nucleus, except that it is also located two protons above an island of inversion. Silicon-34 has an unusual "bubble" structure where the proton distribution is less dense at the center than near the surface, as the 2s_1/2 proton orbital is almost unoccupied in the ground state, unlike in ³⁶S where it is almost full. Silicon-34 is one of the known cluster decay emission particles; it is produced in the decay of ²⁴²Cm with a branching ratio of approximately.