Isotopes of silicon

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 14.28-day half-life)[4] 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.
Isotopes of silicon (14Si)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
28Si 92.2% stable
29Si 4.7% stable
30Si 3.1% stable
31Si trace 2.62 h β− 31P
32Si trace 153 y β− 32P
Standard atomic weight Ar°(Si)
  • [28.084, 28.086]
  • 28.085±0.001 (abridged)[2][3]

List of isotopes
Nuclide[5]
[n 1]		 Z N Isotopic mass (Da)[6]
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
[n 6]		 Spin and
parity
[n 7][n 4]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
22Si 14 8 22.03579(54)# 29(2) ms β+ (67.6%) 22Al 0+
β+, p (32.4%) 21Mg
23Si 14 9 23.02544(54)# 42.3(4) ms β+, p (88%) 22Mg 3/2+#
β+ (12%) 23Al
24Si 14 10 24.011535(21) 140(8) ms β+ (62.4%) 24Al 0+
β+, p (37.6%) 23Mg
25Si 14 11 25.004109(11) 220(3) ms β+ (64.8%) 25Al 5/2+
β+, p (35.2%) 24Mg
26Si 14 12 25.9923338(12) 2.2453(7) s β+ 26Al 0+
27Si 14 13 26.98670469(12) 4.15(4) s β+ 27Al 5/2+
28Si 14 14 27.9769265350(5) Stable 0+ 0.92223(19) 0.92205–0.92241
29Si 14 15 28.9764946653(6) 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 30.97536319(5) 157.36(26) min β− 31P 3/2+
32Si 14 18 31.9741515(3) 153(19) y β− 32P 0+ trace cosmogenic
33Si 14 19 32.9779770(8) 6.18(18) s β− 33P (3/2+)
34Si 14 20 33.978575(15) 2.77(20) s β− 34P 0+
34mSi 4256.1(4) keV <210 ns IT 34Si (3−)
35Si 14 21 34.98455(4) 780(120) ms β− (94.74%) 35P 7/2−#
36Si 14 22 35.98665(8) 450(60) ms β− (87.5%) 36P 0+
β−, n (12.5%) 35P
37Si 14 23 36.99295(12) 90(60) ms β− (83%) 37P (7/2−)#
β−, n (17%) 36P
38Si 14 24 37.99552(11) 63(8) ms β−, n 37P 0+
β− 38P
39Si 14 25 39.00249(15) 47.5(20) ms β− 39P 7/2−#
40Si 14 26 40.00583(37) 33.0(10) ms β− 40P 0+
41Si 14 27 41.01301(60) 20.0(25) ms β− 41P 7/2−#
42Si 14 28 42.01768(54)# 12.5(35) ms β− 42P 0+
43Si 14 29 43.02480(64)# 13(4 (stat), 2 (sys)) ms[7] β−, n (52%) 42P 3/2−#
β− (27%) 43P
β−, 2n (21%) 41P
44Si 14 30 44.03147(54)# 4# ms [>360 ns] 0+
This table header & footer:
  1. mSi – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. Modes of decay:
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  6. Bold symbol as daughter – Daughter product is stable.
  7. ( ) spin value – Indicates spin with weak assignment arguments.

References
  1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. "Standard Atomic Weights: Silicon". CIAAW. 2009.
  3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  5. Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:
    Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  6. Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003-1–030003-442. doi:10.1088/1674-1137/41/3/030003.
  7. Crawford, H. L.; Tripathi, V.; Allmond, J. M.; et al. (2022). "Crossing N = 28 toward the neutron drip line: first measurement of half-lives at FRIB". Physical Review Letters. 129 (212501): 212501. Bibcode:2022PhRvL.129u2501C. doi:10.1103/PhysRevLett.129.212501. PMID 36461950. S2CID 253600995.
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