# Isotopes of silicon

Silicon ($_{14}$Si) has 25 known isotopes, with mass numbers ranging from 22 to 46. $^{28}$Si (the most abundant isotope, at 92.23%), $^{29}$Si (4.67%), and $^{30}$Si (3.1%) are stable. The longest-lived radioisotope is $^{32}$Si, 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 $^{32}$P (which has a 14.27-day half-life) and then to $^{32}$S. After $^{32}$Si, $^{31}$Si has the second longest half-life at 157.3 minutes. All others have half-lives under 7 seconds.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{22}$Si | 14 | 8 | 22.03611(54)# | 28.7(11) ms | β$^+$, p (62%) | $^{21}$Mg | 0+ | | |
| $^{22}$Si | 14 | 8 | 22.03611(54)# | 28.7(11) ms | β$^+$ (37%) | $^{22}$Al | 0+ | | |
| $^{22}$Si | 14 | 8 | 22.03611(54)# | 28.7(11) ms | β$^+$, 2p (0.7%) | $^{20}$Na | 0+ | | |
| $^{23}$Si | 14 | 9 | 23.02571(54)# | 42.3(4) ms | β$^+$, p (88%) | $^{22}$Mg | 3/2+# | | |
| $^{23}$Si | 14 | 9 | 23.02571(54)# | 42.3(4) ms | β$^+$ (8%) | $^{23}$Al | 3/2+# | | |
| $^{23}$Si | 14 | 9 | 23.02571(54)# | 42.3(4) ms | β$^+$, 2p (3.6%) | $^{21}$Na | 3/2+# | | |
| $^{24}$Si | 14 | 10 | 24.011535(21) | 143.2 (21) ms | β$^+$ (65.5%) | $^{24}$Al | 0+ | | |
| $^{24}$Si | 14 | 10 | 24.011535(21) | 143.2 (21) ms | β$^+$, p (34.5%) | $^{23}$Mg | 0+ | | |
| $^{25}$Si | 14 | 11 | 25.004109(11) | 220.6(10) ms | β$^+$ (65%) | $^{25}$Al | 5/2+ | | |
| $^{25}$Si | 14 | 11 | 25.004109(11) | 220.6(10) ms | β$^+$, p (35%) | $^{24}$Mg | 5/2+ | | |
| $^{26}$Si | 14 | 12 | 25.99233382(12) | 2.2453(7) s | β$^+$ | $^{26}$Al | 0+ | | |
| $^{27}$Si | 14 | 13 | 26.98670469(12) | 4.117(14) s | β$^+$ | $^{27}$Al | 5/2+ | | |
| $^{28}$Si | 14 | 14 | 27.97692653442(55) | Stable | Stable | Stable | 0+ | 0.92223(19) | 0.92205–0.92241 |
| $^{29}$Si | 14 | 15 | 28.97649466434(60) | Stable | Stable | Stable | 1/2+ | 0.04685(8) | 0.04678–0.04692 |
| $^{30}$Si | 14 | 16 | 29.973770137(23) | Stable | Stable | Stable | 0+ | 0.03092(11) | 0.03082–0.03102 |
| $^{31}$Si | 14 | 17 | 30.975363196(46) | 157.16(20) min | β$^−$ | $^{31}$P | 3/2+ | | |
| $^{32}$Si | 14 | 18 | 31.97415154(32) | 157(7) y | β$^−$ | $^{32}$P | 0+ | trace | cosmogenic |
| $^{33}$Si | 14 | 19 | 32.97797696(75) | 6.18(18) s | β$^−$ | $^{33}$P | 3/2+ | | |
| $^{34}$Si | 14 | 20 | 33.97853805(86) | 2.77(20) s | β$^−$ | $^{34}$P | 0+ | | |
| $^{34m}$Si | 4256.1(4) keV | 4256.1(4) keV | 4256.1(4) keV | <210 ns | IT | $^{34}$Si | (3−) | | |
| $^{35}$Si | 14 | 21 | 34.984550(38) | 780(120) ms | β$^−$ | $^{35}$P | 7/2−# | | |
| $^{35}$Si | 14 | 21 | 34.984550(38) | 780(120) ms | β$^−$, n? | $^{34}$P | 7/2−# | | |
| $^{36}$Si | 14 | 22 | 35.986649(77) | 503(2) ms | β$^−$ (88%) | $^{36}$P | 0+ | | |
| $^{36}$Si | 14 | 22 | 35.986649(77) | 503(2) ms | β$^−$, n (12%) | $^{35}$P | 0+ | | |
| $^{37}$Si | 14 | 23 | 36.99295(12) | 141.0(35) ms | β$^−$ (83%) | $^{37}$P | (5/2−) | | |
| $^{37}$Si | 14 | 23 | 36.99295(12) | 141.0(35) ms | β$^−$, n (17%) | $^{36}$P | (5/2−) | | |
| $^{37}$Si | 14 | 23 | 36.99295(12) | 141.0(35) ms | β$^−$, 2n? | $^{35}$P | (5/2−) | | |
| $^{38}$Si | 14 | 24 | 37.99552(11) | 63(8) ms | β$^−$ (75%) | $^{38}$P | 0+ | | |
| $^{38}$Si | 14 | 24 | 37.99552(11) | 63(8) ms | β$^−$, n (25%) | $^{37}$P | 0+ | | |
| $^{39}$Si | 14 | 25 | 39.00249(15) | 41.2(41) ms | β$^−$ (67%) | $^{39}$P | (5/2−) | | |
| $^{39}$Si | 14 | 25 | 39.00249(15) | 41.2(41) ms | β$^−$, n (33%) | $^{38}$P | (5/2−) | | |
| $^{39}$Si | 14 | 25 | 39.00249(15) | 41.2(41) ms | β$^−$, 2n? | $^{37}$P | (5/2−) | | |
| $^{40}$Si | 14 | 26 | 40.00608(13) | 31.2(26) ms | β$^−$ (62%) | $^{40}$P | 0+ | | |
| $^{40}$Si | 14 | 26 | 40.00608(13) | 31.2(26) ms | β$^−$, n (38%) | $^{39}$P | 0+ | | |
| $^{40}$Si | 14 | 26 | 40.00608(13) | 31.2(26) ms | β$^−$, 2n? | $^{38}$P | 0+ | | |
| $^{41}$Si | 14 | 27 | 41.01417(32)# | 20.0(25) ms | β$^−$, n (>55%) | $^{40}$P | 7/2−# | | |
| $^{41}$Si | 14 | 27 | 41.01417(32)# | 20.0(25) ms | β$^−$ (<45%) | $^{41}$P | 7/2−# | | |
| $^{41}$Si | 14 | 27 | 41.01417(32)# | 20.0(25) ms | β$^−$, 2n? | $^{39}$P | 7/2−# | | |
| $^{42}$Si | 14 | 28 | 42.01808(32)# | 15.5(4 (stat), 16 (sys)) ms | β$^−$ (51%) | $^{42}$P | 0+ | | |
| $^{42}$Si | 14 | 28 | 42.01808(32)# | 15.5(4 (stat), 16 (sys)) ms | β$^−$, n (48%) | $^{41}$P | 0+ | | |
| $^{42}$Si | 14 | 28 | 42.01808(32)# | 15.5(4 (stat), 16 (sys)) ms | β$^−$, 2n (1%) | $^{40}$P | 0+ | | |
| $^{43}$Si | 14 | 29 | 43.02612(43)# | 13(4 (stat), 2 (sys)) ms | β$^−$, n (52%) | $^{42}$P | 3/2−# | | |
| $^{43}$Si | 14 | 29 | 43.02612(43)# | 13(4 (stat), 2 (sys)) ms | β$^−$ (27%) | $^{43}$P | 3/2−# | | |
| $^{43}$Si | 14 | 29 | 43.02612(43)# | 13(4 (stat), 2 (sys)) ms | β$^−$, 2n (21%) | $^{41}$P | 3/2−# | | |
| $^{44}$Si | 14 | 30 | 44.03147(54)# | 4# ms [>360 ns] | β$^−$? | $^{44}$P | 0+ | | |
| $^{44}$Si | 14 | 30 | 44.03147(54)# | 4# ms [>360 ns] | β$^−$, n? | $^{43}$P | 0+ | | |
| $^{44}$Si | 14 | 30 | 44.03147(54)# | 4# ms [>360 ns] | β$^−$, 2n? | $^{42}$P | 0+ | | |
| $^{45}$Si | 14 | 31 | 45.03982(64)# | 4# ms | | | 3/2−# | | |
| $^{46}$Si | 14 | 32 | | | | | | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Si – Excited nuclear isomer.
* ↑ ( ) – 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).
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: IT:Isomeric transition n:Neutron emission p:Proton emission
* ↑ 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 $^{29}$Si in a sample of silicon contributes to quantum decoherence. Extremely pure (>99.9998%) samples of $^{28}$Si can be produced through selective ionization and deposition of $^{28}$Si 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 determining 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 nonzero 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 with 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 2s$_{1/2}$ proton orbital is almost unoccupied in the ground state, unlike in $^{36}$S where it is almost full. Silicon-34 is one of the known cluster decay emission particles; it is produced in the decay of $^{242}$Cm with a branching ratio of approximately 1×10$^{−16}$.