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Iodine-129

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

Iodine-129, 129I
General
Symbol129I
Namesiodine-129, 129I, I-129
Protons (Z)53
Neutrons (N)76
Nuclide data
Natural abundanceTrace
Half-life (t1/2)1.614(12)×107 years[1]
Isotope mass128.9049836(34)[2] Da
Decay products129Xe
Decay modes
Decay modeDecay energy (MeV)
β−0.189
Isotopes of iodine
Complete table of nuclides

Formation and decay

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Long-lived fission products
Nuclide t1⁄2 Yield Q[a 1] βγ
(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
135Cs 1.33  6.9110[a 4] 269 β
93Zr 1.53  5.4575 91 βγ
107Pd 6.5   1.2499 33 β
129I 16.14   0.8410 194 βγ
  1. ^ Decay energy is split among β, neutrino, and γ if any.
  2. ^ Per 65 thermal neutron fissions of 235U and 35 of 239Pu.
  3. ^ Has decay energy 380 keV, but its decay product 126Sb has decay energy 3.67 MeV.
  4. ^ Lower in thermal reactors because 135Xe, its predecessor, readily 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 by nuclear weapons testing in the 1950s and 1960s, by nuclear reactor accidents and by both military and civil reprocessing of spent nuclear fuel.[3]

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.[4][5]

129I decays with a half-life of 16.14 million years, with low-energy beta and gamma emissions, to stable xenon-129 (129Xe).[6]

Long-lived fission product

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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.[7] 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,[8] 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[9] or gamma irradiation.[10]

Yield, % per fission[7]
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 ?

Release by nuclear fuel reprocessing

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A large fraction of the 129I contained in spent fuel is released into the gas phase, when spent fuel is first chopped and then dissolved in boiling nitric acid during reprocessing.[3] At least for civil reprocessing plants, special scrubbers are supposed to withhold 99.5% (or more) of the Iodine by adsorption,[3] before exhaust air is released into the environment. However, the Northeastern Radiological Health Laboratory (NERHL) found, during their measurements at the first US civil reprocessing plant, which was operated by Nuclear Fuel Services, Inc. (NFS) in Western New York, that "between 5 and 10% of the total 129I available from the dissolved fuel" was released into the exhaust stack.[3] They further wrote that "these values are greater than predicted output (Table 1). This was expected since the iodine scrubbers were not operating during the dissolution cycles monitored."[3]

 
Straight Line: I-129-deposits at Fiescherhorn glacier (Switzerland):
dashed line: estimate of the I-129-deposit rate from the increase of the atmospheric Kr-85 concentration
dot-dash: calculated bomb fallout
triangles: from Cs-137 data calculated I-129 fallout
circles: tree ring data Karlsruhe

The Northeastern Radiological Health Laboratory further states that, due to limitations of their measuring systems, the actual release of 129I may have even been higher, "since [129I] losses [by adsorption] probably occurred in the piping and ductwork between the stack and the sampler".[3] Furthermore, the sample taking system used by the NERHL had a bubbler trap for measuring the tritium content of the gas samples before the iodine trap. The NERHL found out only after taking the samples that "the bubbler trap retained 60 to 90% of the 129I sampled".[3] NERHL concluded: "The bubblers located upstream of the ion exchangers removed a major portion of the gaseous 129I before it reached the ion exchange sampler. The iodine removal ability of the bubbler was anticipated, but not in the magnitude that it occurred." The documented release of "between 5 and 10% of the total 129I available from the dissolved fuel"[3] is not corrected for those two measurement deficiencies.

Military isolation of plutonium from spent fuel has also released 129I to the atmosphere: "More than 685,000 curies of iodine 131 spewed from the stacks of Hanford's separation plants in the first three years of operation."[11] As 129I and 131I have very similar physical and chemical properties, and no isotope separation was performed at Hanford, 129I must have also been released there in large quantities during the Manhattan project. As Hanford reprocessed "hot" fuel, that had been irradiated in a reactor only a few months earlier, the activity of the released short-lived 131I, with a half-life time of just 8 days, was much higher than that of the long-lived 129I. However, while all of the 131I released during the times of the Manhattan project has decayed by now, over 99.999% of the 129I is still in the environment.

Ice borehole data obtained from the university of Bern at the Fiescherhorn glacier in the Alpian mountains at a height of 3950 m show a somewhat steady increase in the 129I deposit rate (shown in the image as a solid line) with time. In particular, the highest values obtained in 1983 and 1984 are about six times as high as the maximum that was measured during the period of the atmospheric bomb testing in 1961. This strong increase following the conclusion of the atmospheric bomb testing indicates that nuclear fuel reprocessing has been the primary source of atmospheric iodine-129 since then. These measurements lasted until 1986.[12]

Applications

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Groundwater age dating

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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 older groundwaters based on the amount of natural 129I (or its 129Xe decay product) present, as well as identifying younger groundwaters by the increased anthropogenic 129I levels since the 1960s.[13][14][15]

Meteorite age dating

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See also: Radiometric dating § The 129I–129Xe chronometer

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.[16][17]

See also

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References

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  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. ^ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
  3. ^ a b c d e f g h "An INVESTIGATION of AIRBORNE RADIOACTIVE EFFLUENT from an OPERATING NUCLEAR FUEL REPROCESSING PLANT".
  4. ^ 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.
  5. ^ "Radioactives Missing From The Earth".[permanent dead link‍]
  6. ^ https://www.nndc.bnl.gov/nudat3/decaysearchdirect.jsp?nuc=129I&unc=nds, NNDC Chart of Nuclides, I-129 Decay Radiation, accessed 7 May 2021.
  7. ^ a b http://www-nds.iaea.org/sgnucdat/c3.htm Cumulative Fission Yields, IAEA
  8. ^ http://www.nndc.bnl.gov/chart/reColor.jsp?newColor=sigg Archived 2017-01-24 at the Wayback Machine, NNDC Chart of Nuclides, I-129 Thermal neutron capture cross-section, accessed 16-Dec-2012.
  9. ^ 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.
  10. ^ 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.
  11. ^ Grossman, Daniel (1 January 1994). "Hanford and Its Early Radioactive Atmospheric Releases". The Pacific Northwest Quarterly. 85 (1): 6–14. doi:10.2307/3571805. JSTOR 40491426. PMID 4157487.
  12. ^ F. Stampfli: Ionenchromatographische Analysen an Eisproben aus einem hochgelegenen Alpengletscher. Lizentiatsarbeit, Inst. anorg. anal. und phys. Chemie, Universität Bern, 1989.
  13. ^ 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.
  14. ^ Santschi, P.; et al. (1998). "129Iodine: A new tracer for surface water/groundwater interaction" (PDF). Lawrence Livermore National Laboratory. OSTI 7280.
  15. ^ 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.
  16. ^ Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis (2nd ed.). University of Chicago Press. pp. 75. ISBN 978-0226109534.
  17. ^ Bolt, B. A.; Packard, R. E.; Price, P. B. (2007). "John H. Reynolds, Physics: Berkeley". The University of California, Berkeley. Retrieved 2007-10-01.

Further reading

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