# Isotopes of krypton

There are 34 known isotopes of krypton ($_{36}$Kr) with atomic mass numbers from 67 to 103. Naturally occurring krypton is made of five stable isotopes and one ($^{78}$ Kr ) which is slightly radioactive with an extremely long half-life, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere.

## 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 |
| $^{67}$Kr | 36 | 31 | 66.98331(46)# | 7.4(29) ms | β$^+$? (63%) | $^{67}$Br | 3/2-# | | |
| $^{67}$Kr | 36 | 31 | 66.98331(46)# | 7.4(29) ms | 2p (37%) | $^{65}$Se | 3/2-# | | |
| $^{68}$Kr | 36 | 32 | 67.97249(54)# | 21.6(33) ms | β$^+$, p (>90%) | $^{67}$Se | 0+ | | |
| $^{68}$Kr | 36 | 32 | 67.97249(54)# | 21.6(33) ms | β$^+$? (<10%) | $^{68}$Br | 0+ | | |
| $^{68}$Kr | 36 | 32 | 67.97249(54)# | 21.6(33) ms | p? | $^{67}$Br | 0+ | | |
| $^{69}$Kr | 36 | 33 | 68.96550(32)# | 27.9(8) ms | β$^+$, p (94%) | $^{68}$Se | (5/2−) | | |
| $^{69}$Kr | 36 | 33 | 68.96550(32)# | 27.9(8) ms | β$^+$ (6%) | $^{69}$Br | (5/2−) | | |
| $^{70}$Kr | 36 | 34 | 69.95588(22)# | 45.00(14) ms | β$^+$ (>98.7%) | $^{70}$Br | 0+ | | |
| $^{70}$Kr | 36 | 34 | 69.95588(22)# | 45.00(14) ms | β$^+$, p (<1.3%) | $^{69}$Se | 0+ | | |
| $^{71}$Kr | 36 | 35 | 70.95027(14) | 98.8(3) ms | β$^+$ (97.9%) | $^{71}$Br | (5/2)− | | |
| $^{71}$Kr | 36 | 35 | 70.95027(14) | 98.8(3) ms | β$^+$, p (2.1%) | $^{70}$Se | (5/2)− | | |
| $^{72}$Kr | 36 | 36 | 71.9420924(86) | 17.16(18) s | β$^+$ | $^{72}$Br | 0+ | | |
| $^{73}$Kr | 36 | 37 | 72.9392892(71) | 27.3(10) s | β$^+$ (99.75%) | $^{73}$Br | (3/2)− | | |
| $^{73}$Kr | 36 | 37 | 72.9392892(71) | 27.3(10) s | β$^+$, p (0.25%) | $^{72}$Se | (3/2)− | | |
| $^{73m}$Kr | 433.55(13) keV | 433.55(13) keV | 433.55(13) keV | 107(10) ns | IT | $^{73}$Kr | (9/2+) | | |
| $^{74}$Kr | 36 | 38 | 73.9330840(22) | 11.50(11) min | β$^+$ | $^{74}$Br | 0+ | | |
| $^{75}$Kr | 36 | 39 | 74.9309457(87) | 4.60(7) min | β$^+$ | $^{75}$Br | 5/2+ | | |
| $^{76}$Kr | 36 | 40 | 75.9259107(43) | 14.8(1) h | β$^+$ | $^{76}$Br | 0+ | | |
| $^{77}$Kr | 36 | 41 | 76.9246700(21) | 72.6(9) min | β$^+$ | $^{77}$Br | 5/2+ | | |
| $^{77m}$Kr | 66.50(5) keV | 66.50(5) keV | 66.50(5) keV | 118(12) ns | IT | $^{77}$Kr | 3/2− | | |
| $^{78}$Kr | 36 | 42 | 77.92036634(33) | 9.2 $^{+5.5}$ $_{−2.6}$ ±1.3×10$^{21}$ y | Double EC | $^{78}$Se | 0+ | 0.00355(3) | |
| $^{79}$Kr | 36 | 43 | 78.9200829(37) | 35.04(10) h | β$^+$ | $^{79}$Br | 1/2− | | |
| $^{79m}$Kr | 129.77(5) keV | 129.77(5) keV | 129.77(5) keV | 50(3) s | IT | $^{79}$Kr | 7/2+ | | |
| $^{80}$Kr | 36 | 44 | 79.91637794(75) | Stable | Stable | Stable | 0+ | 0.02286(10) | |
| $^{81}$Kr | 36 | 45 | 80.9165897(12) | 2.29(11)×10$^5$ y | EC | $^{81}$Br | 7/2+ | 6×10$^{−13}$ | |
| $^{81m}$Kr | 190.64(4) keV | 190.64(4) keV | 190.64(4) keV | 13.10(3) s | IT | $^{81}$Kr | 1/2− | | |
| $^{81m}$Kr | 190.64(4) keV | 190.64(4) keV | 190.64(4) keV | 13.10(3) s | EC (0.0025%) | $^{81}$Br | 1/2− | | |
| $^{82}$Kr | 36 | 46 | 81.9134811537(59) | Stable | Stable | Stable | 0+ | 0.11593(31) | |
| $^{83}$Kr | 36 | 47 | 82.914126516(9) | Stable | Stable | Stable | 9/2+ | 0.11500(19) | |
| $^{83m1}$Kr | 9.4053(8) keV | 9.4053(8) keV | 9.4053(8) keV | 156.8(5) ns | IT | $^{83}$Kr | 7/2+ | | |
| $^{83m2}$Kr | 41.5575(7) keV | 41.5575(7) keV | 41.5575(7) keV | 1.830(13) h | IT | $^{83}$Kr | 1/2− | | |
| $^{84}$Kr | 36 | 48 | 83.9114977271(41) | Stable | Stable | Stable | 0+ | 0.56987(15) | |
| $^{84m}$Kr | 3236.07(18) keV | 3236.07(18) keV | 3236.07(18) keV | 1.83(4) μs | IT | $^{84}$Kr | 8+ | | |
| $^{85}$Kr | 36 | 49 | 84.9125273(21) | 10.728(7) y | β$^−$ | $^{85}$Rb | 9/2+ | 1×10$^{−11}$ | |
| $^{85m1}$Kr | 304.871(20) keV | 304.871(20) keV | 304.871(20) keV | 4.480(8) h | β$^−$ (78.8%) | $^{85}$Rb | 1/2− | | |
| $^{85m1}$Kr | 304.871(20) keV | 304.871(20) keV | 304.871(20) keV | 4.480(8) h | IT (21.2%) | $^{85}$Kr | 1/2− | | |
| $^{85m2}$Kr | 1991.8(2) keV | 1991.8(2) keV | 1991.8(2) keV | 1.82(5) μs | IT | $^{85}$Kr | (17/2+) | | |
| $^{86}$Kr | 36 | 50 | 85.9106106247(40) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.17279(41) | |
| $^{87}$Kr | 36 | 51 | 86.91335476(26) | 76.3(5) min | β$^−$ | $^{87}$Rb | 5/2+ | | |
| $^{88}$Kr | 36 | 52 | 87.9144479(28) | 2.825(19) h | β$^−$ | $^{88}$Rb | 0+ | | |
| $^{89}$Kr | 36 | 53 | 88.9178354(23) | 3.15(4) min | β$^−$ | $^{89}$Rb | 3/2+ | | |
| $^{90}$Kr | 36 | 54 | 89.9195279(20) | 32.32(9) s | β$^−$ | $^{90m}$Rb | 0+ | | |
| $^{91}$Kr | 36 | 55 | 90.9238063(24) | 8.57(4) s | β$^−$ | $^{91}$Rb | 5/2+ | | |
| $^{91}$Kr | 36 | 55 | 90.9238063(24) | 8.57(4) s | β$^−$, n? | $^{90}$Rb | 5/2+ | | |
| $^{92}$Kr | 36 | 56 | 91.9261731(29) | 1.840(8) s | β$^−$ (99.97%) | $^{92}$Rb | 0+ | | |
| $^{92}$Kr | 36 | 56 | 91.9261731(29) | 1.840(8) s | β$^−$, n (0.0332%) | $^{91}$Rb | 0+ | | |
| $^{93}$Kr | 36 | 57 | 92.9311472(27) | 1.287(10) s | β$^−$ (98.05%) | $^{93}$Rb | 1/2+ | | |
| $^{93}$Kr | 36 | 57 | 92.9311472(27) | 1.287(10) s | β$^−$, n (1.95%) | $^{92}$Rb | 1/2+ | | |
| $^{94}$Kr | 36 | 58 | 93.934140(13) | 212(4) ms | β$^−$ (98.89%) | $^{94}$Rb | 0+ | | |
| $^{94}$Kr | 36 | 58 | 93.934140(13) | 212(4) ms | β$^−$, n (1.11%) | $^{93}$Rb | 0+ | | |
| $^{95}$Kr | 36 | 59 | 94.939711(20) | 114(3) ms | β$^−$ (97.13%) | $^{95}$Rb | 1/2+ | | |
| $^{95}$Kr | 36 | 59 | 94.939711(20) | 114(3) ms | β$^−$, n (2.87%) | $^{94}$Rb | 1/2+ | | |
| $^{95}$Kr | 36 | 59 | 94.939711(20) | 114(3) ms | β$^−$, 2n? | $^{93}$Rb | 1/2+ | | |
| $^{95m}$Kr | 195.5(3) keV | 195.5(3) keV | 195.5(3) keV | 1.582(22) μs | IT | $^{85}$Kr | (7/2+) | | |
| $^{96}$Kr | 36 | 60 | 95.942998(62) | 80(8) ms | β$^−$ (96.3%) | $^{96}$Rb | 0+ | | |
| $^{96}$Kr | 36 | 60 | 95.942998(62) | 80(8) ms | β$^−$, n (3.7%) | $^{95}$Rb | 0+ | | |
| $^{97}$Kr | 36 | 61 | 96.94909(14) | 62.2(32) ms | β$^−$ (93.3%) | $^{97}$Rb | 3/2+# | | |
| $^{97}$Kr | 36 | 61 | 96.94909(14) | 62.2(32) ms | β$^−$, n (6.7%) | $^{96}$Rb | 3/2+# | | |
| $^{97}$Kr | 36 | 61 | 96.94909(14) | 62.2(32) ms | β$^−$, 2n? | $^{95}$Rb | 3/2+# | | |
| $^{98}$Kr | 36 | 62 | 97.95264(32)# | 42.8(36) ms | β$^−$ (93.0%) | $^{98}$Rb | 0+ | | |
| $^{98}$Kr | 36 | 62 | 97.95264(32)# | 42.8(36) ms | β$^−$, n (7.0%) | $^{97}$Rb | 0+ | | |
| $^{98}$Kr | 36 | 62 | 97.95264(32)# | 42.8(36) ms | β$^−$, 2n? | $^{96}$Rb | 0+ | | |
| $^{99}$Kr | 36 | 63 | 98.95878(43)# | 40(11) ms | β$^−$ (89%) | $^{99}$Rb | 5/2−# | | |
| $^{99}$Kr | 36 | 63 | 98.95878(43)# | 40(11) ms | β$^−$, n (11%) | $^{98}$Rb | 5/2−# | | |
| $^{99}$Kr | 36 | 63 | 98.95878(43)# | 40(11) ms | β$^−$, 2n? | $^{97}$Rb | 5/2−# | | |
| $^{100}$Kr | 36 | 64 | 99.96300(43)# | 12(8) ms | β$^−$ | $^{100}$Rb | 0+ | | |
| $^{100}$Kr | 36 | 64 | 99.96300(43)# | 12(8) ms | β$^−$, n? | $^{99}$Rb | 0+ | | |
| $^{100}$Kr | 36 | 64 | 99.96300(43)# | 12(8) ms | β$^−$, 2n? | $^{98}$Rb | 0+ | | |
| $^{101}$Kr | 36 | 65 | 100.96932(54)# | 9# ms [>400 ns] | β$^−$? | $^{101}$Rb | 5/2+# | | |
| $^{101}$Kr | 36 | 65 | 100.96932(54)# | 9# ms [>400 ns] | β$^−$, n? | $^{100}$Rb | 5/2+# | | |
| $^{101}$Kr | 36 | 65 | 100.96932(54)# | 9# ms [>400 ns] | β$^−$, 2n? | $^{99}$Rb | 5/2+# | | |
| $^{102}$Kr | 36 | 66 | | | | | 0+ | | |
| $^{103}$Kr | 36 | 67 | | | | | | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Kr – 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: n:Neutron emission
* ↑ Bold italics symbol as daughter – Daughter product is nearly stable.
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* ↑ Primordial radionuclide
* ↑ Used to date groundwater
* 1 2 3 4 5 6 Fission product
* ↑ Formerly used to define the meter
* ↑ Believed to decay by β$^−$β$^−$ to $^{86}$Sr
* The isotopic composition refers to that in air.

## Notable isotopes
### Krypton-81

Krypton-81 is useful in determining how old the water beneath the ground is. Radioactive krypton-81 is the product of spallation reactions with cosmic rays striking gases present in the Earth atmosphere, along with the six stable or nearly stable krypton isotopes. Krypton-81 has a half-life of about 229,000 years.
Krypton-81 is used for dating ancient (50,000- to 800,000-year-old) groundwater and to determine their residence time in deep aquifers. One of the main technical limitations of the method is that it requires the sampling of very large volumes of water: several hundred liters or a few cubic meters of water. This is particularly challenging for dating pore water in deep clay aquitards with very low hydraulic conductivity.

### Krypton-85

Krypton-85 has a half-life of about 10.75 years. This isotope is produced by the nuclear fission of uranium and plutonium in nuclear weapons testing and in nuclear reactors, as well as by cosmic rays. An important goal of the Limited Nuclear Test Ban Treaty of 1963 was to eliminate the release of such radioisotopes into the atmosphere, and since 1963 much of that krypton-85 has had time to decay. However, it is almost inevitable that krypton-85 is released during the reprocessing of fuel rods from nuclear reactors.

#### Atmospheric concentration

The atmospheric concentration of krypton-85 around the North Pole is about 30 percent higher than that at the Amundsen–Scott South Pole Station because nearly all of the world's nuclear reactors and all of its major nuclear reprocessing plants are located in the northern hemisphere, and also well-north of the equator. To be more specific, those nuclear reprocessing plants with significant capacities are located in the United States, the United Kingdom, the French Republic, the Russian Federation, Mainland China (PRC), Japan, India, and Pakistan.

### Krypton-86

Krypton-86 was formerly used to define the meter from 1960 until 1983, when the definition of the meter was based on the wavelength of the 606 nm (orange) spectral line of a krypton-86 atom.

### Others

All other radioisotopes of krypton have half-lives of less than one day, except for krypton-79, a positron emitter with a half-life of about 35.0 hours.