# Isotopes of selenium

Selenium ($_{34}$Se) has six natural isotopes that occur in significant quantities, along with the trace isotope $^{79}$Se, which occurs in minute quantities in uranium ores. Five of these isotopes are stable: $^{74}$Se, $^{76}$Se, $^{77}$Se, $^{78}$Se, and $^{80}$Se. The last three also occur as fission products, along with $^{79}$Se, which has a half-life of 327,000 years, and $^{82}$Se, which has a very long half-life (~10$^{20}$ years, decaying via double beta decay to $^{82}$Kr) and for practical purposes can be considered to be stable. There are 23 other unstable isotopes that have been characterized, the longest-lived being $^{79}$Se with a half-life 327,000 years, $^{75}$Se with a half-life of 120 days, and $^{72}$Se with a half-life of 8.40 days. Of the other isotopes, $^{73}$Se has the longest half-life, 7.15 hours; most others have half-lives not exceeding 38 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 |
| $^{63}$Se | 34 | 29 | 62.98191(54)# | 13.2(39) ms | β$^+$, p (89%) | $^{62}$Ge | 3/2−# | | |
| $^{63}$Se | 34 | 29 | 62.98191(54)# | 13.2(39) ms | β$^+$ (11%) | $^{63}$As | 3/2−# | | |
| $^{63}$Se | 34 | 29 | 62.98191(54)# | 13.2(39) ms | 2p? (<0.5%) | $^{61}$Ge | 3/2−# | | |
| $^{64}$Se | 34 | 30 | 63.97117(54)# | 22.6(2) ms | β$^+$? | $^{64}$As | 0+ | | |
| $^{64}$Se | 34 | 30 | 63.97117(54)# | 22.6(2) ms | β$^+$, p? | $^{63}$Ge | 0+ | | |
| $^{65}$Se | 34 | 31 | 64.96455(32)# | 34.2(7) ms | β$^+$, p (87%) | $^{64}$Ge | 3/2−# | | |
| $^{65}$Se | 34 | 31 | 64.96455(32)# | 34.2(7) ms | β$^+$ (13%) | $^{65}$As | 3/2−# | | |
| $^{66}$Se | 34 | 32 | 65.95528(22)# | 54(4) ms | β$^+$ | $^{66}$As | 0+ | | |
| $^{66}$Se | 34 | 32 | 65.95528(22)# | 54(4) ms | β$^+$, p? | $^{65}$Ge | 0+ | | |
| $^{67}$Se | 34 | 33 | 66.949994(72) | 133(4) ms | β$^+$ (99.5%) | $^{67}$As | 5/2−# | | |
| $^{67}$Se | 34 | 33 | 66.949994(72) | 133(4) ms | β$^+$, p (0.5%) | $^{66}$Ge | 5/2−# | | |
| $^{68}$Se | 34 | 34 | 67.94182524(53) | 35.5(7) s | β$^+$ | $^{68}$As | 0+ | | |
| $^{69}$Se | 34 | 35 | 68.9394148(16) | 27.4(2) s | β$^+$ (99.95%) | $^{69}$As | 1/2− | | |
| $^{69}$Se | 34 | 35 | 68.9394148(16) | 27.4(2) s | β$^+$, p (.052%) | $^{68}$Ge | 1/2− | | |
| $^{69m1}$Se | 38.85(22) keV | 38.85(22) keV | 38.85(22) keV | 2.0(2) μs | IT | $^{69}$Se | 5/2− | | |
| $^{69m2}$Se | 574.0(4) keV | 574.0(4) keV | 574.0(4) keV | 955(16) ns | IT | $^{69}$Se | 9/2+ | | |
| $^{70}$Se | 34 | 36 | 69.9335155(17) | 41.1(3) min | β$^+$ | $^{70}$As | 0+ | | |
| $^{71}$Se | 34 | 37 | 70.9322094(30) | 4.74(5) min | β$^+$ | $^{71}$As | (5/2−) | | |
| $^{71m1}$Se | 48.79(5) keV | 48.79(5) keV | 48.79(5) keV | 5.6(7) μs | IT | $^{71}$Se | (1/2−) | | |
| $^{71m2}$Se | 260.48(10) keV | 260.48(10) keV | 260.48(10) keV | 19.0(5) μs | IT | $^{71}$Se | (9/2+) | | |
| $^{72}$Se | 34 | 38 | 71.9271405(21) | 8.40(8) d | EC | $^{72}$As | 0+ | | |
| $^{73}$Se | 34 | 39 | 72.9267549(80) | 7.15(9) h | β$^+$ | $^{73}$As | 9/2+ | | |
| $^{73m}$Se | 25.71(4) keV | 25.71(4) keV | 25.71(4) keV | 39.8(17) min | IT (72.6%) | $^{73}$Se | 3/2− | | |
| $^{73m}$Se | 25.71(4) keV | 25.71(4) keV | 25.71(4) keV | 39.8(17) min | β$^+$ (27.4%) | $^{73}$As | 3/2− | | |
| $^{74}$Se | 34 | 40 | 73.922475933(15) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.0086(3) | |
| $^{75}$Se | 34 | 41 | 74.922522870(78) | 119.78(3) d | EC | $^{75}$As | 5/2+ | | |
| $^{76}$Se | 34 | 42 | 75.919213702(17) | Stable | Stable | Stable | 0+ | 0.0923(7) | |
| $^{77}$Se | 34 | 43 | 76.919914150(67) | Stable | Stable | Stable | 1/2− | 0.0760(7) | |
| $^{77m}$Se | 161.9223(10) keV | 161.9223(10) keV | 161.9223(10) keV | 17.36(5) s | IT | $^{77}$Se | 7/2+ | | |
| $^{78}$Se | 34 | 44 | 77.91730924(19) | Stable | Stable | Stable | 0+ | 0.2369 (22) | |
| $^{79}$Se | 34 | 45 | 78.91849925(24) | 3.27(28)×10$^5$ y | β$^−$ | $^{79}$Br | 7/2+ | | |
| $^{79m}$Se | 95.77(3) keV | 95.77(3) keV | 95.77(3) keV | 3.900(18) min | IT (99.94%) | $^{79}$Se | 1/2− | | |
| $^{79m}$Se | 95.77(3) keV | 95.77(3) keV | 95.77(3) keV | 3.900(18) min | β$^−$ (0.056%) | $^{79}$Br | 1/2− | | |
| $^{80}$Se | 34 | 46 | 79.9165218(10) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.4980(36) | |
| $^{81}$Se | 34 | 47 | 80.9179930(10) | 18.45(12) min | β$^−$ | $^{81}$Br | 1/2− | | |
| $^{81m}$Se | 103.00(6) keV | 103.00(6) keV | 103.00(6) keV | 57.28(2) min | IT (99.95%) | $^{81}$Se | 7/2+ | | |
| $^{81m}$Se | 103.00(6) keV | 103.00(6) keV | 103.00(6) keV | 57.28(2) min | β$^−$ (.051%) | $^{81}$Br | 7/2+ | | |
| $^{82}$Se | 34 | 48 | 81.91669953(50) | 8.76(15)×10$^{19}$ y | β$^−$β$^−$ | $^{82}$Kr | 0+ | 0.0882(15) | |
| $^{83}$Se | 34 | 49 | 82.9191186(33) | 22.25(4) min | β$^−$ | $^{83}$Br | 9/2+ | | |
| $^{83m}$Se | 228.92(7) keV | 228.92(7) keV | 228.92(7) keV | 70.1(4) s | β$^−$ | $^{83}$Br | 1/2− | | |
| $^{84}$Se | 34 | 50 | 83.9184668(21) | 3.26(10) min | β$^−$ | $^{84}$Br | 0+ | | |
| $^{85}$Se | 34 | 51 | 84.9222608(28) | 32.9(3) s | β$^−$ | $^{85}$Br | (5/2)+ | | |
| $^{86}$Se | 34 | 52 | 85.9243117(27) | 14.3(3) s | β$^−$ | $^{86}$Br | 0+ | | |
| $^{86}$Se | 34 | 52 | 85.9243117(27) | 14.3(3) s | β$^−$, n? | $^{85}$Br | 0+ | | |
| $^{87}$Se | 34 | 53 | 86.9286886(24) | 5.50(6) s | β$^−$ (99.50%) | $^{87}$Br | (3/2+) | | |
| $^{87}$Se | 34 | 53 | 86.9286886(24) | 5.50(6) s | β$^−$, n (0.60%) | $^{86}$Br | (3/2+) | | |
| $^{88}$Se | 34 | 54 | 87.9314175(36) | 1.53(6) s | β$^−$ (99.01%) | $^{88}$Br | 0+ | | |
| $^{88}$Se | 34 | 54 | 87.9314175(36) | 1.53(6) s | β$^−$, n (0.99%) | $^{87}$Br | 0+ | | |
| $^{89}$Se | 34 | 55 | 88.9366691(40) | 430(50) ms | β$^−$ (92.2%) | $^{89}$Br | 5/2+# | | |
| $^{89}$Se | 34 | 55 | 88.9366691(40) | 430(50) ms | β$^−$, n (7.8%) | $^{88}$Br | 5/2+# | | |
| $^{90}$Se | 34 | 56 | 89.94010(35) | 210(80) ms | β$^−$ | $^{90}$Br | 0+ | | |
| $^{90}$Se | 34 | 56 | 89.94010(35) | 210(80) ms | β$^−$, n? | $^{89}$Br | 0+ | | |
| $^{91}$Se | 34 | 57 | 90.94570(47) | 270(50) ms | β$^−$ (79%) | $^{91}$Br | 1/2+# | | |
| $^{91}$Se | 34 | 57 | 90.94570(47) | 270(50) ms | β$^−$, n (21%) | $^{90}$Br | 1/2+# | | |
| $^{91}$Se | 34 | 57 | 90.94570(47) | 270(50) ms | β$^−$, 2n? | $^{89}$Br | 1/2+# | | |
| $^{92}$Se | 34 | 58 | 91.94984(43)# | 90# ms [>300 ns] | β$^−$? | $^{92}$Br | 0+ | | |
| $^{92}$Se | 34 | 58 | 91.94984(43)# | 90# ms [>300 ns] | β$^−$, n? | $^{91}$Br | 0+ | | |
| $^{92}$Se | 34 | 58 | 91.94984(43)# | 90# ms [>300 ns] | β$^−$, 2n? | $^{90}$Br | 0+ | | |
| $^{92m}$Se | 3072(2) keV | 3072(2) keV | 3072(2) keV | 15.7(7) μs | IT | $^{92}$Se | (9−) | | |
| $^{93}$Se | 34 | 59 | 92.95614(43)# | 130# ms [>300 ns] | β$^−$? | $^{93}$Br | 1/2+# | | |
| $^{93}$Se | 34 | 59 | 92.95614(43)# | 130# ms [>300 ns] | β$^−$, n? | $^{92}$Br | 1/2+# | | |
| $^{93}$Se | 34 | 59 | 92.95614(43)# | 130# ms [>300 ns] | β$^−$, 2n? | $^{91}$Br | 1/2+# | | |
| $^{93m}$Se | 678.2(7) keV | 678.2(7) keV | 678.2(7) keV | 420(100) ns | IT | $^{93}$Se | | | |
| $^{94}$Se | 34 | 60 | 93.96049(54)# | 50# ms [>300 ns] | β$^−$? | $^{94}$Br | 0+ | | |
| $^{94}$Se | 34 | 60 | 93.96049(54)# | 50# ms [>300 ns] | β$^−$, n? | $^{93}$Br | 0+ | | |
| $^{94}$Se | 34 | 60 | 93.96049(54)# | 50# ms [>300 ns] | β$^−$, 2n? | $^{92}$Br | 0+ | | |
| $^{94m}$Se | 2430.0(6) keV | 2430.0(6) keV | 2430.0(6) keV | 680(50) ns | IT | $^{94}$Se | (7−) | | |
| $^{95}$Se | 34 | 61 | 94.96730(54)# | 70# ms [>400 ns] | β$^−$? | $^{95}$Br | 3/2+# | | |
| $^{95}$Se | 34 | 61 | 94.96730(54)# | 70# ms [>400 ns] | β$^−$, n? | $^{94}$Br | 3/2+# | | |
| $^{95}$Se | 34 | 61 | 94.96730(54)# | 70# ms [>400 ns] | β$^−$, 2n? | $^{93}$Br | 3/2+# | | |
| $^{96}$Se | 34 | 62 | | | | | | | |
| $^{97}$Se | 34 | 63 | | | | | | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Se – 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).
* ↑ Bold half-life – nearly stable, half-life longer than age of universe.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: EC:Electron capture 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.
* ↑ Believed to decay by β$^+$β$^+$ to $^{74}$Ge with a half-life over 2.3×10$^{18}$ y.
* ↑ Long-lived fission product
* ↑ Believed to decay by β$^−$β$^−$ to $^{80}$Kr
* ↑ 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.
In paleobiogeochemistry, the ratio in amount of selenium-82 to selenium-76 (i.e, the value of δ$^{82/76}$Se) 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.