Isotopes of selenium

Selenium (34Se) has six natural isotopes that occur in significant quantities, along with the trace isotope 79Se, which occurs in minute quantities in uranium ores. Five of these isotopes are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last three also occur as fission products, along with 79Se, which has a half-life of 327,000 years,[4][5] and 82Se, which has a very long half-life (~1020 years, decaying via double beta decay to 82Kr) and for practical purposes can be considered to be stable. There are 23 other unstable isotopes that have been characterized, the longest-lived being 79Se with a half-life 327,000 years, 75Se with a half-life of 120 days, and 72Se with a half-life of 8.40 days. Of the other isotopes, 73Se has the longest half-life, 7.15 hours; most others have half-lives not exceeding 38 seconds.

Isotopes of selenium (34Se)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
72Se synth 8.4 d ε 72As
γ –
74Se 0.860% stable
75Se synth 119.8 d ε 75As
γ –
76Se 9.23% stable
77Se 7.60% stable
78Se 23.7% stable
79Se trace 3.27×105 y β− 79Br
80Se 49.8% stable
82Se 8.82% 1.08×1020 y β−β− 82Kr
Standard atomic weight Ar°(Se)
  • 78.971±0.008
  • 78.971±0.008 (abridged)[2][3]

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
[n 4][n 5]		 Decay
mode
[n 6]		 Daughter
isotope
[n 7]		 Spin and
parity
[n 8][n 5]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
65Se 34 31 64.96466(64)# <50 ms β+ (>99.9%) 65As 3/2−#
β+, p (<.1%) 64Ge
66Se 34 32 65.95521(32)# 33(12) ms β+ 66As 0+
67Se 34 33 66.95009(21)# 133(11) ms β+ (99.5%) 67As 5/2−#
β+, p (.5%) 66Ge
68Se 34 34 67.94180(4) 35.5(7) s β+ 68As 0+
69Se 34 35 68.93956(4) 27.4(2) s β+ (99.955%) 69As (1/2−)
β+, p (.045%) 68Ge
69m1Se 39.4(1) keV 2.0(2) μs 5/2−
69m2Se 573.9(10) keV 955(16) ns 9/2+
70Se 34 36 69.93339(7) 41.1(3) min β+ 70As 0+
71Se 34 37 70.93224(3) 4.74(5) min β+ 71As 5/2−
71m1Se 48.79(5) keV 5.6(7) μs 1/2− to 9/2−
71m2Se 260.48(10) keV 19.0(5) μs (9/2)+
72Se 34 38 71.927112(13) 8.40(8) d EC 72As 0+
73Se 34 39 72.926765(11) 7.15(8) h β+ 73As 9/2+
73mSe 25.71(4) keV 39.8(13) min IT 73Se 3/2−
β+ 73As
74Se 34 40 73.9224764(18) Observationally Stable[n 9] 0+ 0.0089(4)
75Se 34 41 74.9225234(18) 119.779(4) d EC 75As 5/2+
76Se 34 42 75.9192136(18) Stable 0+ 0.0937(29)
77Se 34 43 76.9199140(18) Stable 1/2− 0.0763(16)
77mSe 161.9223(7) keV 17.36(5) s IT 77Se 7/2+
78Se 34 44 77.9173091(18) Stable 0+ 0.2377(28)
79Se[n 10] 34 45 78.9184991(18) 3.27(8)×105 y β− 79Br 7/2+
79mSe 95.77(3) keV 3.92(1) min IT (99.944%) 79Se 1/2−
β− (.056%) 79Br
80Se 34 46 79.9165213(21) Observationally Stable[n 11] 0+ 0.4961(41)
81Se 34 47 80.9179925(22) 18.45(12) min β− 81Br 1/2−
81mSe 102.99(6) keV 57.28(2) min IT (99.948%) 81Se 7/2+
β− (.052%) 81Br
82Se[n 12] 34 48 81.9166994(22) 0.97(5)×1020 y β−β− 82Kr 0+ 0.0873(22)
83Se 34 49 82.919118(4) 22.3(3) min β− 83Br 9/2+
83mSe 228.50(20) keV 70.1(4) s β− 83Br 1/2−
84Se 34 50 83.918462(16) 3.1(1) min β− 84Br 0+
85Se 34 51 84.92225(3) 31.7(9) s β− 85Br (5/2+)#
86Se 34 52 85.924272(17) 15.3(9) s β− 86Br 0+
87Se 34 53 86.92852(4) 5.50(12) s β− (99.64%) 87Br (5/2+)#
β−, n (.36%) 86Br
88Se 34 54 87.93142(5) 1.53(6) s β− (99.01%) 88Br 0+
β−, n (.99%) 87Br
89Se 34 55 88.93645(32)# 0.41(4) s β− (92.2%) 89Br (5/2+)#
β−, n (7.8%) 88Br
90Se 34 56 89.93996(43)# 300# ms [>300 ns] β−, n 89Br 0+
β− 90Br
91Se 34 57 90.94596(54)# 270(50) ms β− (79%) 91Br 1/2+#
β−, n 90Br
92Se 34 58 91.94992(64)# 100# ms [>300 ns] β− 92Br 0+
93Se 34 59 92.95629(86)# 50# ms [>300 ns] 1/2+#
94Se 34 60 93.96049(86)# 20# ms [>300 ns] 0+
This table header & footer:
  1. mSe – 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. Bold half-life – nearly stable, half-life longer than age of universe.
  5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  6. Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  7. Bold symbol as daughter – Daughter product is stable.
  8. ( ) spin value – Indicates spin with weak assignment arguments.
  9. Believed to decay by β+β+ to 74Ge
  10. Long-lived fission product
  11. Believed to decay by β−β− to 80Kr
  12. Primordial radionuclide

Use of radioisotopes

The isotope selenium-75 has radiopharmaceutical uses. For example, it is used in high-dose-rate endorectal brachytherapy, as an alternative to iridium-192.[6]

In paleobiogeochemistry, the ratio in amount of selenium-82 to selenium-76 (i.e, the value of δ82/76Se) can be used to track down the redox conditions on Earth during the Neoproterozoic era in order to gain a deeper understanding of the rapid oxygenation that trigger the emergence of complex organisms.[7][8]

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: Selenium". CIAAW. 2013.
  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. The half-life of 79Se Archived September 27, 2011, at the Wayback Machine
  5. Jorg, Gerhard; Buhnemann, Rolf; Hollas, Simon; Kivel, Niko; Kossert, Karsten; Van Winckel, Stefaan; Gostomski, Christoph Lierse v. (2010). "Preparation of radiochemically pure 79Se and highly precise determination of its half-life". Applied Radiation and Isotopes. 68 (12): 2339–51. doi:10.1016/j.apradiso.2010.05.006. PMID 20627600.
  6. Shoemaker T; Vuong T; Glickman H; Kaifi S; Famulari G; Enger SA (2019). "Dosimetric Considerations for Ytterbium-169, Selenium-75, and Iridium-192 Radioisotopes in High-Dose-Rate Endorectal Brachytherapy". Int J Radiat Oncol Biol Phys. 105 (4): 875–883. doi:10.1016/j.ijrobp.2019.07.003. PMID 31330175. S2CID 198170324.
  7. Pogge von Strandmann, Philip A. E.; Stüeken, Eva E.; Elliott, Tim; Poulton, Simon W.; Dehler, Carol M.; Canfield, Don E.; Catling, David C. (2015-12-18). "Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere". Nature Communications. 6 (1): 10157. doi:10.1038/ncomms10157. ISSN 2041-1723.
  8. Stüeken, Eva E. "Selenium isotopes as a biogeochemical proxy in deep time" (PDF). core.ac.uk.
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