Iodine-129

Iodine-129, ¹²⁹I
General
Symbol	129I
Names	iodine-129, I-129
Protons	53
Neutrons	76
Nuclide data
Natural abundance	Trace
Half-life	1.57×107 years[1]
Decay products	129Xe
Isotope mass	128.904984[2] u
Spin	7/2+
Decay modes
Decay mode	Decay energy (MeV)
β−	1.89
	Isotopes of iodine ; Complete table of nuclides

Iodine-129 (¹²⁹I) is a long-lived radioisotope of iodine which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant.

Formation and decay

Long-lived fission products
Nuclide	t_¹⁄₂	Yield	Decay energy[a 1]	Decay mode
	(Ma)	(%)[a 2]	(keV)
⁹⁹Tc	0.211	6.1385	294	β
¹²⁶Sn	0.230	0.1084	4050[a 3]	βγ
⁷⁹Se	0.327	0.0447	151	β
⁹³Zr	1.53	5.4575	91	βγ
¹³⁵Cs	2.3	6.9110[a 4]	269	β
¹⁰⁷Pd	6.5	1.2499	33	β
¹²⁹I	15.7	0.8410	194	βγ
Decay energy is split among β, neutrino, and γ if any. Per 65 thermal-neutron fissions of U-235 and 35 of Pu-239. Has decay energy 380 keV, but decay product Sb-126 has decay energy 3.67 MeV. Lower in thermal reactor because predecessor absorbs neutrons.

¹²⁹I is one of seven long-lived fission products. It is primarily formed from the fission of uranium and plutonium in nuclear reactors. Significant amounts were released into the atmosphere as a result of nuclear weapons testing in the 1950s and 1960s.

It is also naturally produced in small quantities, due to the spontaneous fission of natural uranium, by cosmic ray spallation of trace levels of xenon in the atmosphere, and by cosmic ray muons striking tellurium-130.[3][4]

¹²⁹I decays with a half-life of 15.7 million years, with low-energy beta and gamma emissions, to xenon-129 (¹²⁹Xe).[5]

Fission product

Actinides and fission products by half-life
Actinides[6] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield[7]
4n	4n+1	4n+2	4n+3		Fission products of ²³⁵U by yield[7]
4n	4n+1	4n+2	4n+3			4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a	†		¹⁵⁵Eu^þ
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a		⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a		¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
²⁴⁸Bk[8]	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ[9]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	‡	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka			⁷⁹Se^₡
				1.53 Ma		⁹³Zr
	²³⁷Np^ƒ			2.1–6.5 Ma		¹³⁵Cs^₡	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma			¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma[10]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma[10]
Legend for superscript symbols ₡ has thermal neutron capture cross section in the range of 8–50 barns ƒ fissile m metastable isomer № primarily a naturally occurring radioactive material (NORM) þ neutron poison (thermal neutron capture cross section greater than 3k barns) † range 4–97 a: Medium-lived fission product ‡ over 200 ka: Long-lived fission product

Yield, % per fission[11]
	Thermal	Fast	14 MeV
²³²Th	not fissile	0.431 ± 0.089	1.68 ± 0.33
²³³U	1.63 ± 0.26	1.73 ± 0.24	3.01 ± 0.43
²³⁵U	0.706 ± 0.032	1.03 ± 0.26	1.59 ± 0.18
²³⁸U	not fissile	0.622 ± 0.034	1.66 ± 0.19
²³⁹Pu	1.407 ± 0.086	1.31 ± 0.13	?
²⁴¹Pu	1.28 ± 0.36	1.67 ± 0.36	?

¹²⁹I is one of the seven long-lived fission products that are produced in significant amounts. Its yield is 0.706% per fission of ²³⁵U.[11] Larger proportions of other iodine isotopes such as ¹³¹I are produced, but because these all have short half-lives, iodine in cooled spent nuclear fuel consists of about ⁵⁄₆ ¹²⁹I and ¹⁄₆ the only stable iodine isotope, ¹²⁷I.

Because ¹²⁹I is long-lived and relatively mobile in the environment, it is of particular importance in long-term management of spent nuclear fuel. In a deep geological repository for unreprocessed used fuel, ¹²⁹I is likely to be the radionuclide of most potential impact at long times.

Since ¹²⁹I has a modest neutron absorption cross-section of 30 barns,[12] and is relatively undiluted by other isotopes of the same element, it is being studied for disposal by nuclear transmutation by re-irradiation with neutrons[13] or by high-powered lasers.[14]

Applications

Groundwater age dating

¹²⁹I is not deliberately produced for any practical purposes. However, its long half-life and its relative mobility in the environment have made it useful for a variety of dating applications. These include identifying very old waters based on the amount of natural ¹²⁹I or its ¹²⁹Xe decay product, as well as identifying younger groundwaters by the increased anthropogenic ¹²⁹I levels since the 1960s.[15][16][17]

Meteorite age dating

In 1960 physicist John H. Reynolds discovered that certain meteorites contained an isotopic anomaly in the form of an overabundance of ¹²⁹Xe. He inferred that this must be a decay product of long-decayed radioactive ¹²⁹I. This isotope is produced in quantity in nature only in supernova explosions. As the half-life of ¹²⁹I is comparatively short in astronomical terms, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the ¹²⁹I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System, as the ¹²⁹I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.[18][19]

References

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.
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.
Edwards, R. R. (1962). "Iodine-129: Its Occurrenice in Nature and Its Utility as a Tracer". Science. 137 (3533): 851–853. Bibcode:1962Sci...137..851E. doi:10.1126/science.137.3533.851. PMID 13889314. S2CID 38276819.
"Radioactives Missing From The Earth".
http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=129I&unc=nds, NNDC Chart of Nuclides, I-129 Decay Radiation, accessed 16-Dec-2012.
Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".
Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is nearly eight quadrillion years.
http://www-nds.iaea.org/sgnucdat/c3.htm Cumulative Fission Yields, IAEA
http://www.nndc.bnl.gov/chart/reColor.jsp?newColor=sigg, NNDC Chart of Nuclides, I-129 Thermal neutron capture cross-section, accessed 16-Dec-2012.
Rawlins, J. A.; et al. (1992). "Partitioning and transmutation of long-lived fission products". Proceedings International High-Level Radioactive Waste Management Conference. Las Vegas, USA. OSTI 5788189.
Magill, J.; Schwoerer, H.; Ewald, F.; Galy, J.; Schenkel, R.; Sauerbrey, R. (2003). "Laser transmutation of iodine-129". Applied Physics B. 77 (4): 387–390. Bibcode:2003ApPhB..77..387M. doi:10.1007/s00340-003-1306-4. S2CID 121743855.
Watson, J. Throck; Roe, David K.; Selenkow, Herbert A. (1 January 1965). "Iodine-129 as a "Nonradioactive" Tracer". Radiation Research. 26 (1): 159–163. Bibcode:1965RadR...26..159W. doi:10.2307/3571805. JSTOR 3571805. PMID 4157487.
Santschi, P.; et al. (1998). "¹²⁹Iodine: A new tracer for surface water/groundwater interaction" (PDF). Lawrence Livermore National Laboratory. OSTI 7280.
Snyder, G.; Fabryka-Martin, J. (2007). "I-129 and Cl-36 in dilute hydrocarbon waters: Marine-cosmogenic,in situ, and anthropogenic sources". Applied Geochemistry. 22 (3): 692–714. Bibcode:2007ApGC...22..692S. doi:10.1016/j.apgeochem.2006.12.011.
Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis (2nd ed.). University of Chicago Press. pp. 75. ISBN 978-0226109534.
Bolt, B. A.; Packard, R. E.; Price, P. B. (2007). "John H. Reynolds, Physics: Berkeley". The University of California, Berkeley. Retrieved 2007-10-01.

External links

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[3] Decay energy is split among β, neutrino, and γ if any.

[4] Per 65 thermal-neutron fissions of U-235 and 35 of Pu-239.

[5] Has decay energy 380 keV,
but decay product Sb-126 has decay energy 3.67 MeV.

[6] Lower in thermal reactor because predecessor absorbs neutrons.

[NUBASE2016-1] 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.

[AME2016_II-2] 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.

[7] Edwards, R. R. (1962). "Iodine-129: Its Occurrenice in Nature and Its Utility as a Tracer". Science. 137 (3533): 851–853. Bibcode:1962Sci...137..851E. doi:10.1126/science.137.3533.851. PMID 13889314. S2CID 38276819.

[8] "Radioactives Missing From The Earth".

[9] ttp://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=129I&unc=nds, NNDC Chart of Nuclides, I-129 Decay Radiation, accessed 16-Dec-2012.

[10] Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.

[11] Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.

[12] Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."

[13] This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".

[14] Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is nearly eight quadrillion years.

[auto-15] ttp://www-nds.iaea.org/sgnucdat/c3.htm Cumulative Fission Yields, IAEA

[16] ttp://www.nndc.bnl.gov/chart/reColor.jsp?newColor=sigg, NNDC Chart of Nuclides, I-129 Thermal neutron capture cross-section, accessed 16-Dec-2012.

[17] Rawlins, J. A.; et al. (1992). "Partitioning and transmutation of long-lived fission products". Proceedings International High-Level Radioactive Waste Management Conference. Las Vegas, USA. OSTI 5788189.

[18] Magill, J.; Schwoerer, H.; Ewald, F.; Galy, J.; Schenkel, R.; Sauerbrey, R. (2003). "Laser transmutation of iodine-129". Applied Physics B. 77 (4): 387–390. Bibcode:2003ApPhB..77..387M. doi:10.1007/s00340-003-1306-4. S2CID 121743855.

[19] Watson, J. Throck; Roe, David K.; Selenkow, Herbert A. (1 January 1965). "Iodine-129 as a "Nonradioactive" Tracer". Radiation Research. 26 (1): 159–163. Bibcode:1965RadR...26..159W. doi:10.2307/3571805. JSTOR 3571805. PMID 4157487.

[20] Santschi, P.; et al. (1998). "¹²⁹Iodine: A new tracer for surface water/groundwater interaction" (PDF). Lawrence Livermore National Laboratory. OSTI 7280.

[21] Snyder, G.; Fabryka-Martin, J. (2007). "I-129 and Cl-36 in dilute hydrocarbon waters: Marine-cosmogenic,in situ, and anthropogenic sources". Applied Geochemistry. 22 (3): 692–714. Bibcode:2007ApGC...22..692S. doi:10.1016/j.apgeochem.2006.12.011.

[22] Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis (2nd ed.). University of Chicago Press. pp. 75. ISBN 978-0226109534.

[23] Bolt, B. A.; Packard, R. E.; Price, P. B. (2007). "John H. Reynolds, Physics: Berkeley". The University of California, Berkeley. Retrieved 2007-10-01.