Isotopes of silicon

Isotopes of silicon (14Si)
Main isotopes 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)
  • [28.08428.086]
  • 28.085±0.001 (abridged)

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) 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.

List of isotopes

Nuclide
Z N Isotopic mass (Da)
Half-life
Decay
mode

Daughter
isotope

Spin and
parity
Natural abundance (mole fraction)
Excitation energy Normal proportion 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 β (51%) 42P 0+
β, n (48%) 41P
β, 2n (1%) 40P
43Si 14 29 43.02612(43)# 13(4 (stat), 2 (sys)) ms 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
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. ^ a b # – 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.

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 (>99.9998%) 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 93.75 mm (3.691 in) sphere of the isotope and determing 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 nuclear spin (I = 1/2). 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 wth 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 2s1/2 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 1×10−16.


This page was last updated at 2024-04-17 13:39 UTC. Update now. View original page.

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