Isotopes of krypton

There are 33 known isotopes of krypton (Kr) with atomic mass numbers from 69 through 101.^[1] Naturally occurring krypton is made of six stable isotopes, two of which might theoretically be slightly radioactive, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere.

The spectral signature of krypton can be observed to have several very sharp lines. When krypton is placed into an electric discharge tube, it emits visible light with a distinctive orange-red color.

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 605 nm (orange) spectral line of a krypton-86 atom.

Radioactive krypton-81 is the product of reactions with cosmic rays that strike the atmosphere, along with some of the other isotopes of krypton. Krypton-81 has a half-life of about 229,000 years.

Krypton-81 has been used for dating old (50,000- to 800,000-year-old) groundwater.^[2] Krypton-85 is a radioisotope of krypton that 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 inevitable that krypton-85 is released during the reprocessing of fuel rods from nuclear reactors.

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.^[3] 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. See the article on nuclear reprocessing for more information.

All of the other radioisotopes of krypton have half-lives of less than one day, except for krypton-79, which has a half-life of about 35.0 hours. This isotope decays by the emission of positrons and thus becoming bromine.

Relative atomic mass: 83.798.

Table

nuclide symbol	Z(p)7	N(n)	isotopic mass (u)	half-life	decay mode(s)[4][n 1]	daughter isotope(s)[n 2]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^69Kr	36	33	68.96518(43)#	32(10) ms	β^+	^69Br	5/2−#
^70Kr	36	34	69.95526(41)#	52(17) ms	β^+	^70Br	0+
^71Kr	36	35	70.94963(70)	100(3) ms	β^+ (94.8%)	^71Br	(5/2)−
					β^+, p (5.2%)	^70Se
^72Kr	36	36	71.942092(9)	17.16(18) s	β^+	^72Br	0+
^73Kr	36	37	72.939289(7)	28.6(6) s	β^+ (99.32%)	^73Br	3/2−
					β^+, p (.68%)	^72Se
^73mKr	433.66(12) keV			107(10) ns			(9/2+)
^74Kr	36	38	73.9330844(22)	11.50(11) min	β^+	^74Br	0+
^75Kr	36	39	74.930946(9)	4.29(17) min	β^+	^75Br	5/2+
^76Kr	36	40	75.925910(4)	14.8(1) h	β^+	^76Br	0+
^77Kr	36	41	76.9246700(21)	74.4(6) min	β^+	^77Br	5/2+
^78Kr	36	42	77.9203648(12)	Observationally Stable[n 3]			0+	0.00355(3)
^79Kr	36	43	78.920082(4)	35.04(10) h	β^+	^79Br	1/2−
^79mKr	129.77(5) keV			50(3) s			7/2+
^80Kr	36	44	79.9163790(16)	Stable			0+	0.02286(10)
^81Kr[n 4]	36	45	80.9165920(21)	2.29(11)×10^5 y	EC	^81Br	7/2+	trace
^81mKr	190.62(4) keV			13.10(3) s	IT (99.975%)	^81Kr	1/2−
					EC (.025%)	^81Br
^82Kr	36	46	81.9134836(19)	Stable			0+	0.11593(31)
^83Kr[n 5]	36	47	82.914136(3)	Stable			9/2+	0.11500(19)
^83m1Kr	9.4053(8) keV			154.4(11) ns			7/2+
^83m2Kr	41.5569(10) keV			1.83(2) h	IT	^83Kr	1/2−
^84Kr[n 5]	36	48	83.911507(3)	Stable			0+	0.56987(15)
^84mKr	3236.02(18) keV			1.89(4) µs			8+
^85Kr[n 5]	36	49	84.9125273(21)	10.776(3) y	β^−	^85Rb	9/2+	trace
^85m1Kr	304.871(20) keV			4.480(8) h	β^− (78.6%)	^85Rb	1/2−
					IT (21.4%)	^85Kr
^85m2Kr	1991.8(13) keV			1.6(7) µs [1.2(+10-4) µs]			(17/2+)
^86Kr[n 6][n 5]	36	50	85.91061073(11)	Observationally Stable[n 7]			0+	0.17279(41)
^87Kr	36	51	86.91335486(29)	76.3(5) min	β^−	^87Rb	5/2+
^88Kr	36	52	87.914447(14)	2.84(3) h	β^−	^88Rb	0+
^89Kr	36	53	88.91763(6)	3.15(4) min	β^−	^89Rb	3/2(+#)
^90Kr	36	54	89.919517(20)	32.32(9) s	β^−	^90mRb	0+
^91Kr	36	55	90.92345(6)	8.57(4) s	β^−	^91Rb	5/2(+)
^92Kr	36	56	91.926156(13)	1.840(8) s	β^− (99.96%)	^92Rb	0+
					β^−, n (.033%)	^91Rb
^93Kr	36	57	92.93127(11)	1.286(10) s	β^− (98.05%)	^93Rb	1/2+
					β^−, n (1.95%)	^92Rb
^94Kr	36	58	93.93436(32)#	210(4) ms	β^− (94.3%)	^94Rb	0+
					β^−, n (5.7%)	^93Rb
^95Kr	36	59	94.93984(43)#	114(3) ms	β^−	^95Rb	1/2(+)
^96Kr	36	60	95.94307(54)#	80(7) ms	β^−	^96Rb	0+
^97Kr	36	61	96.94856(54)#	63(4) ms	β^−	^97Rb	3/2+#
					β^−, n	^96Rb
^98Kr	36	62	97.95191(64)#	46(8) ms			0+
^99Kr	36	63	98.95760(64)#	40(11) ms			(3/2+)#
^100Kr	36	64	99.96114(54)#	10# ms [>300 ns]			0+
^101Kr [n 8]	36	65	unknown	>635 ns	β^−, 2n	^99Rb	unknown
					β^−, n	^100Rb
					β^−	^101Rb

1. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
3. Believed to decay by β⁺β⁺ to ⁷⁸Se with a half-life of more than >1.1×10²⁰ years
4. Used to date groundwater
5. Fission product
6. Formerly used to define the meter
7. Believed to decay by β⁻β⁻ to ⁸⁶Sr
8. New isotope.

Notes

• The isotopic composition refers to that in air.
• Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
• Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

1. "Chart of Nuclides". Brookhaven National Laboratory.
2. N. Thonnard; L. D. MeKay; T. C. Labotka (2001). "Development of Laser-Based Resonance Ionization Techniques for 81-Kr and 85-Kr Measurements in the Geosciences" (PDF). University of Tennessee, Institute for Rare Isotope Measurements. pp. 4–7.
3. "Resources on Isotopes". U.S. Geological Survey. Retrieved 2007-03-20.
4. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. Check date values in: |access-date= (help)
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.

External links

• Brookhaven National Laboratory: Krypton-101 information