Isotopes of silicon

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Silicon (14Si) has 25 known isotopes, with mass number ranging from 22 to 46. 28Si (the most abundant isotope, at 92.24%), 29Si (4.67%), and 30Si (3.07%) 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.

A chart showing the relative abundances of the naturally occurring isotopes of silicon.
Quick facts Main isotopes, Decay ...
Isotopes of silicon (14Si)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
28Si 92.2% stable
29Si 4.67% stable
30Si 3.07% stable
31Si trace 2.62 h β− 31P
32Si trace 157 y β− 32P
Standard atomic weight Ar°(Si)
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List of isotopes

More information Nuclide, Z ...
Nuclide
[n 1]		 Z N Isotopic mass (Da)[4]
[n 2][n 3]		 Discovery
year[5]		 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 22.034168(58)[6] 2007 28.7(11) ms β+, p (62%) 21Mg 0+
β+ (37%) 22Al
β+, 2p (0.7%) 20Na
23Si 14 9 23.025083(17)[6] 1986 42.3(4) ms β+, p (88%) 22Mg 3/2+#
β+ (8%) 23Al
β+, 2p (3.6%) 21Na
24Si 14 10 24.011535(21) 1979 143.2 (21) ms β+ (65.5%) 24Al 0+
β+, p (34.5%) 23Mg
25Si 14 11 25.004109(11) 1963 220.6(10) ms β+ (65%) 25Al 5/2+
β+, p (35%) 24Mg
26Si 14 12 25.99233382(12) 1960 2.2453(7) s β+ 26Al 0+
27Si 14 13 26.98670469(12) 1939 4.117(14) s β+ 27Al 5/2+
28Si 14 14 27.97692653442(55) 1920 Stable 0+ 0.92223(19) 0.92205–0.92241
29Si 14 15 28.97649466434(60) 1920 Stable 1/2+ 0.04685(8) 0.04678–0.04692
30Si 14 16 29.973770137(23) 1924 Stable 0+ 0.03092(11) 0.03082–0.03102
31Si 14 17 30.975363196(46) 1934 157.16(20) min β− 31P 3/2+
32Si 14 18 31.97415154(32) 1953 157(7) y β− 32P 0+ trace cosmogenic
33Si 14 19 32.97797696(75) 1971 6.18(18) s β− 33P 3/2+
34Si 14 20 33.97853805(86) 1971 2.77(20) s β− 34P 0+
34mSi 4256.1(4) keV (1989)[n 8] <210 ns IT 34Si (3−)
35Si 14 21 34.984550(38) 1971 780(120) ms β− 35P 7/2−#
β−, n? 34P
36Si 14 22 35.986649(77) 1971 503(2) ms β− (88%) 36P 0+
β−, n (12%) 35P
37Si 14 23 36.99295(12) 1979 141.0(35) ms β− (83%) 37P (5/2−)
β−, n (17%) 36P
β−, 2n? 35P
38Si 14 24 37.99552(11) 1979 63(8) ms β− (75%) 38P 0+
β−, n (25%) 37P
39Si 14 25 39.00249(15) 1979 41.2(41) ms β− (67%) 39P (5/2−)
β−, n (33%) 38P
β−, 2n? 37P
40Si 14 26 40.00608(13) 1989 31.2(26) ms β− (62%) 40P 0+
β−, n (38%) 39P
β−, 2n? 38P
41Si 14 27 41.01417(32)# 1989 20.0(25) ms β−, n (>55%) 40P 7/2−#
β− (<45%) 41P
β−, 2n? 39P
42Si 14 28 42.01808(32)# 1990 15.5(4 (stat), 16 (sys)) ms[7] β− (51%) 42P 0+
β−, n (48%) 41P
β−, 2n (1%) 40P
43Si 14 29 43.02612(43)# 2002 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)# 2007 4# ms [>360 ns] β−? 44P 0+
β−, n? 43P
β−, 2n? 42P
45Si[8] 14 31 45.03982(64)# 2024 4# ms 3/2−#
46Si[8] 14 32 2024
This table header & footer:
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  1. [1]
    mSi – Excited nuclear isomer.
  2. [2]
    ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. [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. [4]
    # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. [5]
    Modes of decay:
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  6. [6]
    Bold symbol as daughter – Daughter product is stable.
  7. [7]
    ( ) spin value – Indicates spin with weak assignment arguments.
  8. [8]
    Half-life only inferred and not measured.

³¹Si still also has a trace natural occurring abundance.

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.[9] Extremely pure (>99.9998%) samples of 28Si can be produced through selective ionization and deposition of 28Si from silane gas.[10] 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 determining the exact number of atoms in the sample.[11][12]

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.[13][14]

Silicon-29

Silicon-29 is of note as the only stable silicon isotope with a nonzero nuclear spin (I = 1/2).[15] 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.[16]

Silicon-34

Silicon-34 is a radioactive isotope with 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.[17] 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.[18][19] 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.[20]

See also

Daughter products other than silicon

References

External links

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