Isotopes of boron

Boron (5B) naturally occurs as isotopes 10B and 11B, the latter of which makes up about 80% of natural boron. There are 13 radioisotopes that have been discovered, with mass numbers from 7 to 21, all with short half-lives, the longest being that of 8B, with a half-life of only 770 milliseconds (ms) and 12B with a half-life of 20.2 ms. All other isotopes have half-lives shorter than 17.35 ms. Those isotopes with mass below 10 decay into helium (via short-lived isotopes of beryllium for 7B and 9B) while those with mass above 11 mostly become carbon.

A chart showing the abundances of the naturally occurring isotopes of boron.
Main isotopes of boron (5B)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
10B 20% stable[1]
11B 80% stable[1]
10B content may be as low as 19.1% and as high as 20.3% in natural samples. 11B is the remainder in such cases.[2]
Standard atomic weight Ar, standard(B)
  • [10.806, 10.821][3]
  • Conventional: 10.81

List of isotopes
Nuclide[4]
[n 1]		 Z N Isotopic mass (Da)[5]
[n 2][n 3]		 Half-life

[resonance width]		 Decay
mode
[n 4]		 Daughter
isotope
[n 5]		 Spin and
parity
[n 6][n 7]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
7B 5  2 7.029712(27) 570(14) × 10−24 s
[801(20) keV]		 p 6
Be
[n 8]		 (3/2−)
8B[n 9] 5  3 8.0246073(11) 770(3) ms β+, α 2 4
He
 2+
9B 5  4 9.0133296(10) 800(300) × 10−21 s
[0.54(21) keV]		 p, α 2 4
He
 3/2−
10B 5  5 10.012936862(16) Stable 3+ 0.199(7) 18.929–20.386
11B 5  6 11.009305167(13) Stable 3/2− 0.801(7) 79.614–81.071
12B 5  7 12.0143526(14) 20.20(2) ms β− (98.4%) 12
C
 1+
β−, α (1.6%) 8
Be
[n 10]
13B 5  8 13.0177800(11) 17.33(17) ms β− (99.72%) 13
C
 3/2−
β−, n (0.28%) 12
C
14B 5  9 14.025404(23) 12.5(5) ms β− (93.96%) 14
C
 2−
β−, n (6.04%) 13
C
15B 5 10 15.031088(23) 9.93(7) ms β−, n (93.6%) 14
C
 3/2−
β− (6.0%) 15
C
β−, 2n (0.4%) 13
C
16B 5 11 16.039842(26) > 4.6 × 10−21 s
 n 15
B
 0−
17B[n 11] 5 12 17.04693(22) 5.08(5) ms β−, n (63.0%) 16
C
 (3/2−)
β− (22.1%) 17
C
β−, 2n (11.0%) 15
C
β−, 3n (3.5%) 14
C
β−, 4n (0.4%) 13
C
18B 5 13 18.05560(22) < 26 ns n 17
B
 (2−)
19B[n 11] 5 14 19.06417(56) 2.92(13) ms β−, n (71%) 18
C
 3/2−#
β−, 2n (17%) 17
C
β− (12%) 19
C
20B[6] 5 15 20.07348(86)# [2.50(9) MeV] n 19
B
 (1−, 2−)
21B[6] 5 16 21.08302(97)# < 260 ns
[2.47(19) MeV]		 2n 19
B
 (3/2−)#
  1. mB – 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. Modes of decay:
    n:Neutron emission
    p:Proton emission
  5. Bold symbol as daughter – Daughter product is stable.
  6. ( ) spin value – Indicates spin with weak assignment arguments.
  7. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. Subsequently decays by double proton emission to 4He for a net reaction of 7B → 4He + 3 1H
  9. Has 1 halo proton
  10. Immediately decays into two α particles, for a net reaction of 12B → 3 4He +  e−
  11. Has 2 halo neutrons
  • Neutrinos from boron-8 beta decays within the sun are an important background to dark matter direct detection experiments.[7] They are the first component of the neutrino floor that dark matter direct detection experiments are expected to eventually encounter.

Applications

Boron-10

Boron-10 is used in boron neutron capture therapy (BNCT) as an experimental treatment of some brain cancers.

References
  1. "Atomic Weights and Isotopic Compositions for All Elements". National Institute of Standards and Technology. Retrieved 2008-09-21.
  2. Szegedi, S.; Váradi, M.; Buczkó, Cs. M.; Várnagy, M.; Sztaricskai, T. (1990). "Determination of boron in glass by neutron transmission method". Journal of Radioanalytical and Nuclear Chemistry Letters. 146 (3): 177. doi:10.1007/BF02165219.
  3. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  4. 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.
  5. 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.
  6. Leblond, S.; et al. (2018). "First observation of 20B and 21B". Physical Review Letters. 121 (26): 262502–1–262502–6. arXiv:1901.00455. doi:10.1103/PhysRevLett.121.262502. PMID 30636115.
  7. Cerdeno, David G.; Fairbairn, Malcolm; Jubb, Thomas; Machado, Pedro; Vincent, Aaron C.; Boehm, Celine (2016). "Physics from solar neutrinos in dark matter direct detection experiments". JHEP. 2016 (5): 118. arXiv:1604.01025. Bibcode:2016JHEP...05..118C. doi:10.1007/JHEP05(2016)118.
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