Iodine-129

Iodine-129, 129I

General
Symbol| 129I
Names| iodine-129, I-129
Protons| 53
Neutrons| 76
Nuclide data
Natural abundance| Trace
Half-life| 1.614(12)×107 years[1]
Decay products| 129Xe
Isotope mass| 128.9049836(34)Template:AME2020 II u
Decay modes
Decay mode| Decay energy (MeV)
β−| 0.189
Isotopes of Chemistry:iodine
Complete table of nuclides

Iodine-129 (129I) is a long-lived radioisotope of iodine that occurs naturally, but is of greater interest as a man-made nuclear fission product, where it is a potential radiological contaminant. The same contamination, though, together with its long half-life, make it serve as a tracer of environmental processes that have nothing to do with its creation.

## Contents

* 1 Formation and decay
* 2 Long-lived fission product
* 3 Release by nuclear fuel reprocessing
* 4 Applications
* 4.1 Groundwater age dating
* 4.2 Meteorite age dating
* 5 See also
* 6 References
* 7 Further reading
* 8 External links

## Formation and decay

* v
* t
* e

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

1. ↑ Decay energy is split among β, neutrino, and γ if any.
2. ↑ Per 65 thermal-neutron fissions of U-235 and 35 of Pu-239.
3. ↑ Has decay energy 380 keV,
but decay product Sb-126 has decay energy 3.67 MeV.
4. ↑ 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 have been released into the atmosphere by nuclear weapons testing in the 1950s and 1960s, by nuclear reactor accidents, and most of all by the (both military and civilian) reprocessing of spent nuclear fuel.[2]

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 16.14 million years, with low-energy beta and gamma emissions, to stable xenon-129 (129Xe).[5]

## Long-lived fission product

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.[6] 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 the radionuclide of most very-long-term concern as it may seep out of an undisturbed repository before it has decayed.

Since 129I has a modest neutron absorption cross-section of 30 barns,[7] 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[8] or gamma irradiation.[9]

Yield, % per fission[6] | 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

This section contains too many or overly lengthy quotations for an encyclopedic entry. Please help improve the article by presenting facts as a neutrally-worded summary with appropriate citations. Consider transferring direct quotations to Wikiquote. (August 2023)

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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.[2] At least for civil reprocessing plants, special scrubbers are supposed to withhold 99.5% (or more) of the Iodine by adsorption,[2] 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.[2] 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."[2]

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".[2] 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".[2] 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"[2] 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."[10] 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.[11]

## 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 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.[12][13][14]

### 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.[15][16]

## See also

* Isotopes of iodine
* Iodine in biology

## References

1. ↑ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties". Chinese Physics C 45 (3). doi:10.1088/1674-1137/abddae. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf.
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 "An INVESTIGATION of AIRBORNE RADIOACTIVE EFFLUENT from an OPERATING NUCLEAR FUEL REPROCESSING PLANT". https://www.osti.gov/servlets/purl/4043274.
3. ↑ Edwards, R. R. (1962). "Iodine-129: Its Occurrence in Nature and Its Utility as a Tracer". Science 137 (3533): 851–853. doi:10.1126/science.137.3533.851. PMID 13889314. Bibcode: 1962Sci...137..851E.
4. ↑ "Radioactives Missing From The Earth". http://www.don-lindsay-archive.org/creation/isotope_list.html.
5. ↑ https://www.nndc.bnl.gov/nudat3/decaysearchdirect.jsp?nuc=129I&unc=nds, NNDC Chart of Nuclides, I-129 Decay Radiation, accessed 7 May 2021.
6. ↑ 6.0 6.1 http://www-nds.iaea.org/sgnucdat/c3.htm Cumulative Fission Yields, IAEA
7. ↑ 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.
8. ↑ Rawlins, J. A. (1992). "Partitioning and transmutation of long-lived fission products". Proceedings International High-Level Radioactive Waste Management Conference (Las Vegas, USA). https://www.osti.gov/biblio/5788189.
9. ↑ 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. doi:10.1007/s00340-003-1306-4. Bibcode: 2003ApPhB..77..387M.
10. ↑ Grossman, Daniel (1 January 1994). "Hanford and Its Early Radioactive Atmospheric Releases". The Pacific Northwest Quarterly 85 (1): 6–14. doi:10.2307/3571805. PMID 4157487.
11. ↑ F. Stampfli: Ionenchromatographische Analysen an Eisproben aus einem hochgelegenen Alpengletscher. Lizentiatsarbeit, Inst. anorg. anal. und phys. Chemie, Universität Bern, 1989.
12. ↑ Watson, J. Throck; Roe, David K.; Selenkow, Herbert A. (1 January 1965). "Iodine-129 as a "Nonradioactive" Tracer". Radiation Research 26 (1): 159–163. doi:10.2307/3571805. PMID 4157487. Bibcode: 1965RadR...26..159W.
13. ↑ Santschi, P. (1998). "129Iodine: A new tracer for surface water/groundwater interaction.". Lawrence Livermore National Laboratory. https://e-reports-ext.llnl.gov/pdf/234761.pdf.
14. ↑ 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. doi:10.1016/j.apgeochem.2006.12.011. Bibcode: 2007ApGC...22..692S.
15. ↑ Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis (2nd ed.). University of Chicago Press. pp. 75. ISBN 978-0226109534. https://archive.org/details/principlesofstel0000clay.
16. ↑ "John H. Reynolds, Physics: Berkeley". The University of California, Berkeley. 2007. http://content.cdlib.org/xtf/view?docId=hb1r29n709&doc.view=content&chunk.id=div00061&toc.depth=1&brand=oac&anchor.id=0.

## Further reading

* Snyder, G. T.; Fabryka-Martin, J. T. (2007). "129I and 36Cl in dilute hydrocarbon waters: Marine-cosmogenic, in situ, and anthropogenic sources". Applied Geochemistry 22 (3): 692. doi:10.1016/j.apgeochem.2006.12.011. Bibcode: 2007ApGC...22..692S.
* Snyder, G.; Fehn, U. (2004). "Global distribution of 129I in rivers and lakes: Implications for iodine cycling in surface reservoirs". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 223–224: 579–586. doi:10.1016/j.nimb.2004.04.107. Bibcode: 2004NIMPB.223..579S.

## External links

* ANL factsheet
* Monitoring iodine-129 in air and milk samples collected near the Hanford Site: an investigation of historical iodine monitoring data
* Studies with natural and anthropogenic iodine isotopes: iodine distribution and cycling in the global environment
* Some Publications using 129I Data from IsoTrace, 1997-2002

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