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.
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| Standard atomic weight Ar°(Si) | ||||||||||||||||||||||||||||||||||||
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List of isotopes
| Nuclide [n 1] | Z | N | Isotopic mass (Da)[4] [n 2][n 3] | Half-life[1] [n 4] | Decay mode[1] [n 5] | Daughter isotope [n 6] | Spin and parity[1] [n 7][n 4] | Natural abundance (mole fraction) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Excitation energy | Normal proportion[1] | Range of variation | |||||||||||||||||
| 22Si | 14 | 8 | 22.03611(54)# | 28.7(11) ms | β+, p (62%) | 21Mg | 0+ | ||||||||||||
| β+ (37%) | 22Al | ||||||||||||||||||
| β+, 2p (0.7%) | 20Na | ||||||||||||||||||
| 23Si | 14 | 9 | 23.02571(54)# | 42.3(4) ms | β+, p (88%) | 22Mg | 3/2+# | ||||||||||||
| β+ (8%) | 23Al | ||||||||||||||||||
| β+, 2p (3.6%) | 21Na | ||||||||||||||||||
| 24Si | 14 | 10 | 24.011535(21) | 143.2 (21) ms | β+ (65.5%) | 24Al | 0+ | ||||||||||||
| β+, p (34.5%) | 23Mg | ||||||||||||||||||
| 25Si | 14 | 11 | 25.004109(11) | 220.6(10) ms | β+ (65%) | 25Al | 5/2+ | ||||||||||||
| β+, p (35%) | 24Mg | ||||||||||||||||||
| 26Si | 14 | 12 | 25.99233382(12) | 2.2453(7) s | β+ | 26Al | 0+ | ||||||||||||
| 27Si | 14 | 13 | 26.98670469(12) | 4.117(14) s | β+ | 27Al | 5/2+ | ||||||||||||
| 28Si | 14 | 14 | 27.97692653442(55) | Stable | 0+ | 0.92223(19) | 0.92205–0.92241 | ||||||||||||
| 29Si | 14 | 15 | 28.97649466434(60) | Stable | 1/2+ | 0.04685(8) | 0.04678–0.04692 | ||||||||||||
| 30Si | 14 | 16 | 29.973770137(23) | Stable | 0+ | 0.03092(11) | 0.03082–0.03102 | ||||||||||||
| 31Si | 14 | 17 | 30.975363196(46) | 157.16(20) min | β− | 31P | 3/2+ | ||||||||||||
| 32Si | 14 | 18 | 31.97415154(32) | 157(7) y | β− | 32P | 0+ | trace | cosmogenic | ||||||||||
| 33Si | 14 | 19 | 32.97797696(75) | 6.18(18) s | β− | 33P | 3/2+ | ||||||||||||
| 34Si | 14 | 20 | 33.97853805(86) | 2.77(20) s | β− | 34P | 0+ | ||||||||||||
| 34mSi | 4256.1(4) keV | <210 ns | IT | 34Si | (3−) | ||||||||||||||
| 35Si | 14 | 21 | 34.984550(38) | 780(120) ms | β− | 35P | 7/2−# | ||||||||||||
| β−, n? | 34P | ||||||||||||||||||
| 36Si | 14 | 22 | 35.986649(77) | 503(2) ms | β− (88%) | 36P | 0+ | ||||||||||||
| β−, n (12%) | 35P | ||||||||||||||||||
| 37Si | 14 | 23 | 36.99295(12) | 141.0(35) ms | β− (83%) | 37P | (5/2−) | ||||||||||||
| β−, n (17%) | 36P | ||||||||||||||||||
| β−, 2n? | 35P | ||||||||||||||||||
| 38Si | 14 | 24 | 37.99552(11) | 63(8) ms | β− (75%) | 38P | 0+ | ||||||||||||
| β−, n (25%) | 37P | ||||||||||||||||||
| 39Si | 14 | 25 | 39.00249(15) | 41.2(41) ms | β− (67%) | 39P | (5/2−) | ||||||||||||
| β−, n (33%) | 38P | ||||||||||||||||||
| β−, 2n? | 37P | ||||||||||||||||||
| 40Si | 14 | 26 | 40.00608(13) | 31.2(26) ms | β− (62%) | 40P | 0+ | ||||||||||||
| β−, n (38%) | 39P | ||||||||||||||||||
| β−, 2n? | 38P | ||||||||||||||||||
| 41Si | 14 | 27 | 41.01417(32)# | 20.0(25) ms | β−, n (>55%) | 40P | 7/2−# | ||||||||||||
| β− (<45%) | 41P | ||||||||||||||||||
| β−, 2n? | 39P | ||||||||||||||||||
| 42Si | 14 | 28 | 42.01808(32)# | 15.5(4 (stat), 16 (sys)) ms[5] | β− (51%) | 42P | 0+ | ||||||||||||
| β−, n (48%) | 41P | ||||||||||||||||||
| β−, 2n (1%) | 40P | ||||||||||||||||||
| 43Si | 14 | 29 | 43.02612(43)# | 13(4 (stat), 2 (sys)) ms[5] | β−, n (52%) | 42P | 3/2−# | ||||||||||||
| β− (27%) | 43P | ||||||||||||||||||
| β−, 2n (21%) | 41P | ||||||||||||||||||
| 44Si | 14 | 30 | 44.03147(54)# | 4# ms [>360 ns] | β−? | 44P | 0+ | ||||||||||||
| β−, n? | 43P | ||||||||||||||||||
| β−, 2n? | 42P | ||||||||||||||||||
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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-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.[10][11]
Silicon-29
Silicon-29 is of note as the only stable silicon isotope with a nuclear spin (I = 1/2).[12] 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.[13]
Silicon-34
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]