Silicon (14Si) has 23 known
isotopes, with
mass numbers ranging from 22 to 44. 28Si (the most abundant isotope, at 92.23%), 29Si (4.67%), and 30Si (3.1%) are stable. The longest-lived radioisotope is 32Si, which is produced by
cosmic ray spallation of
argon. Its
half-life has been determined to be approximately 150 years (with
decay energy 0.21 MeV), and it decays by
beta emission to 32P (which has a 14.27-day half-life)[1] and then to 32S. After 32Si, 31Si has the second longest half-life at 157.3 minutes. All others have half-lives under 7 seconds.
A chart showing the relative abundances of the naturally occurring isotopes of silicon.
^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^
ab# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^Bold symbol as daughter – Daughter product is stable.
^( ) spin value – Indicates spin with weak assignment arguments.
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.[6] Extremely pure (>99.9998%) samples of 28Si can be produced through selective
ionization and
deposition of 28Si from
silane gas.[7] 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 93.75 mm (3.691 in) sphere of the isotope and determing the exact number of atoms in the sample.[8][9]
Silicon-34 is a radioactive isotope wth a half-life of 2.8 seconds.[1] 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.[14] Silicon-34 has an unusual "bubble" structure where the proton distribution is less dense at the center than near the surface, as the 2s1/2 proton orbital is almost unoccupied in the ground state, unlike in
36S where it is almost full.[15][16] 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 1×10−16.[17]
^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003.
doi:
10.1088/1674-1137/abddaf.