Technetium-99

Last updated
Technetium-99, 99Tc
General
Symbol 99Tc
Names technetium-99, 99Tc, Tc-99
Protons (Z)43
Neutrons (N)56
Nuclide data
Natural abundance trace
Half-life (t1/2)211100±1200 years
Spin 9/2+
Excess energy −87327.9±0.9 keV
Binding energy 8613.610±0.009 keV
Decay products 99Ru
Decay modes
Decay mode Decay energy (MeV)
Beta decay 0.2975
Isotopes of technetium
Complete table of nuclides

Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting beta particles, but no gamma rays. It is the most significant long-lived fission product of uranium fission, producing the largest fraction of the total long-lived radiation emissions of nuclear waste. Technetium-99 has a fission product yield of 6.0507% for thermal neutron fission of uranium-235.

Contents

The metastable technetium-99m (99mTc) is a short-lived (half-life about 6 hours) nuclear isomer used in nuclear medicine, produced from molybdenum-99. It decays by isomeric transition to technetium-99, a desirable characteristic, since the very long half-life and type of decay of technetium-99 imposes little further radiation burden on the body.

Radiation

The weak beta emission is stopped by the walls of laboratory glassware. Soft X-rays are emitted when the beta particles are stopped, but as long as the body is kept more than 30 cm away these should pose no problem. The primary hazard when working with technetium is inhalation of dust; such radioactive contamination in the lungs can pose a significant cancer risk.[ citation needed ]

Role in nuclear waste

Yield, % per fission [1]
Thermal Fast 14 MeV
232Th not fissile 2.919 ± .0761.953 ± 0.098
233U 5.03 ± 0.144.85 ± 0.173.87 ± 0.22
235U 6.132 ± 0.0925.80 ± 0.135.02 ± 0.13
238U not fissile 6.181 ± 0.0995.737 ± 0.040
239Pu 6.185 ± 0.0565.82 ± 0.13 ?
241Pu 5.61 ± 0.254.1 ± 2.3 ?

Due to its high fission yield, relatively long half-life, and mobility in the environment, technetium-99 is one of the more significant components of nuclear waste. Measured in becquerels per amount of spent fuel, it is the dominant producer of radiation in the period from about 104 to 106 years after the creation of the nuclear waste. [2] The next shortest-lived fission product is samarium-151 with a half-life of 90 years, though a number of actinides produced by neutron capture have half-lives in the intermediate range.

Releases

Long-lived fission products
Nuclide t1⁄2 Yield Q [a 1] βγ
(Ma)(%) [a 2] (keV)
99Tc 0.2116.1385294β
126Sn 0.2300.10844050 [a 3] βγ
79Se 0.3270.0447151β
135Cs 1.33 6.9110 [a 4] 269β
93Zr 1.53 5.457591βγ
107Pd 6.5  1.249933β
129I 15.7  0.8410194βγ
  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.

An estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment up to 1994 by atmospheric nuclear tests. [2] The amount of technetium-99 from civilian nuclear power released into the environment up to 1986 is estimated to be on the order of 1000 TBq (about 1600 kg), primarily by outdated methods of nuclear fuel reprocessing; most of this was discharged into the sea. In recent years, reprocessing methods have improved to reduce emissions, but as of 2005 the primary release of technetium-99 into the environment is by the Sellafield plant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea. From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year. [3]

In the environment

The long half-life of technetium-99 and its ability to form an anionic species make it (along with 129I) a major concern when considering long-term disposal of high-level radioactive waste.[ citation needed ] Many of the processes designed to remove fission products from medium-active process streams in reprocessing plants are designed to remove cationic species like caesium (e.g., 137Cs, 134Cs) and strontium (e.g., 90Sr). Hence the pertechnetate escapes through these treatment processes. Current disposal options favor burial in geologically stable rock. The primary danger with such a course is that the waste is likely to come into contact with water, which could leach radioactive contamination into the environment. The natural cation-exchange capacity of soils tends to immobilize plutonium, uranium, and caesium cations. However, the anion-exchange capacity is usually much smaller, so minerals are less likely to adsorb the pertechnetate and iodide anions, leaving them mobile in the soil. For this reason, the environmental chemistry of technetium is an active area of research.

Separation of technetium-99

Several methods have been proposed for technetium-99 separation including: crystallization, [4] [5] liquid-liquid extraction, [6] [7] [8] molecular recognition methods, [9] volatilization, and others.

In 2012 the crystalline compound Notre Dame Thorium Borate-1 (NDTB-1) was presented by researchers at the University of Notre Dame. It can be tailored to safely absorb radioactive ions from nuclear waste streams. Once captured, the radioactive ions can then be exchanged for higher-charged species of a similar size, recycling the material for re-use. Lab results using the NDTB-1 crystals removed approximately 96 percent of technetium-99. [10] [11]

Transmutation of technetium to stable ruthenium-100

An alternative disposal method, transmutation, has been demonstrated at CERN for technetium-99. This transmutation process bombards the technetium (99
Tc as a metal target) with neutrons, forming the short-lived 100
Tc (half-life 16 seconds) which decays by beta decay to stable ruthenium (100
Ru). Given the relatively high market value of Ruthenium [12] and the particularly undesirable properties of Technetium, this type of nuclear transmutation appears particularly promising.

See also

Related Research Articles

<span class="mw-page-title-main">Ruthenium</span> Chemical element, symbol Ru and atomic number 44

Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemicals. Karl Ernst Claus, a Russian-born scientist of Baltic-German ancestry, discovered the element in 1844 at Kazan State University and named ruthenium in honor of Russia. Ruthenium is usually found as a minor component of platinum ores; the annual production has risen from about 19 tonnes in 2009 to some 35.5 tonnes in 2017. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. A minor application for ruthenium is in platinum alloys and as a chemistry catalyst. A new application of ruthenium is as the capping layer for extreme ultraviolet photomasks. Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, and in pyroxenite deposits in South Africa.

<span class="mw-page-title-main">Technetium</span> Chemical element, symbol Tc and atomic number 43

Technetium is a chemical element; it has symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. Technetium and promethium are the only radioactive elements whose neighbours in the sense of atomic number are both stable. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous fission product in uranium ore and thorium ore, or the product of neutron capture in molybdenum ores. This silvery gray, crystalline transition metal lies between manganese and rhenium in group 7 of the periodic table, and its chemical properties are intermediate between those of both adjacent elements. The most common naturally occurring isotope is 99Tc, in traces only.

A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators.

<span class="mw-page-title-main">Nuclear chemistry</span> Branch of chemistry dealing with radioactivity, transmutation and other nuclear processes

Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties.

A radioactive tracer, radiotracer, or radioactive label is a synthetic derivative of a natural compound in which one or more atoms have been replaced by a radionuclide. By virtue of its radioactive decay, it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. Radiolabeling or radiotracing is thus the radioactive form of isotopic labeling. In biological contexts, experiments that use radioisotope tracers are sometimes called radioisotope feeding experiments.

<span class="mw-page-title-main">Nuclear fission product</span> Atoms or particles produced by nuclear fission

Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy, and gamma rays. The two smaller nuclei are the fission products..

The synthesis of precious metals involves the use of either nuclear reactors or particle accelerators to produce these elements.

<span class="mw-page-title-main">Integral fast reactor</span> Nuclear reactor design

The integral fast reactor is a design for a nuclear reactor using fast neutrons and no neutron moderator. IFR would breed more fuel and is distinguished by a nuclear fuel cycle that uses reprocessing via electrorefining at the reactor site.

<span class="mw-page-title-main">Technetium-99m generator</span> A device used to extract the short-lived radioactive isotope Tc-99m from a longer-lived Mo-99 source

A technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a decaying sample of molybdenum-99. 99Mo has a half-life of 66 hours and can be easily transported over long distances to hospitals where its decay product technetium-99m is extracted and used for a variety of nuclear medicine diagnostic procedures, where its short half-life is very useful.

<span class="mw-page-title-main">Pertechnetate</span> Chemical compound or ion

The pertechnetate ion is an oxyanion with the chemical formula TcO−
4. It is often used as a convenient water-soluble source of isotopes of the radioactive element technetium (Tc). In particular it is used to carry the 99mTc isotope which is commonly used in nuclear medicine in several nuclear scanning procedures.

Caesium (55Cs) has 41 known isotopes, the atomic masses of these isotopes range from 112 to 152. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 1.33 million years, 137
Cs
 with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.

Technetium (43Tc) is one of the two elements with Z < 83 that have no stable isotopes; the other such element is promethium. It is primarily artificial, with only trace quantities existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are 97Tc, 98Tc, and 99Tc.

Molybdenum (42Mo) has 39 known isotopes, ranging in atomic mass from 81 to 119, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. All unstable isotopes of molybdenum decay into isotopes of zirconium, niobium, technetium, and ruthenium.

<span class="mw-page-title-main">Sodium pertechnetate</span> Chemical compound

Sodium pertechnetate is the inorganic compound with the formula NaTcO4. This colourless salt contains the pertechnetate anion, TcO−
4 that has slightly distorted tetrahedron symmetry both at 296 K and at 100 K while the coordination polyhedron of the sodium cation is different from typical for scheelite structure. The radioactive 99m
Tc
O−
4 anion is an important radiopharmaceutical for diagnostic use. The advantages to 99m
Tc
 include its short half-life of 6 hours and the low radiation exposure to the patient, which allow a patient to be injected with activities of more than 30 millicuries. Na[99m
Tc
O
4] is a precursor to a variety of derivatives that are used to image different parts of the body.

<span class="mw-page-title-main">Spent nuclear fuel</span> Nuclear fuel thats been irradiated in a nuclear reactor

Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor. It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and, depending on its point along the nuclear fuel cycle, it will have different isotopic constituents than when it started.

<span class="mw-page-title-main">Fission products (by element)</span> Breakdown of nuclear fission results

This page discusses each of the main elements in the mixture of fission products produced by nuclear fission of the common nuclear fuels uranium and plutonium. The isotopes are listed by element, in order by atomic number.

<span class="mw-page-title-main">Technetium-99m</span> Metastable nuclear isomer of technetium-99

Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99, symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical radioisotope in the world.

Uranium-236 (236U) is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in the reprocessed uranium made from spent nuclear fuel.

Long-lived fission products (LLFPs) are radioactive materials with a long half-life produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity, it is necessary to isolate them from humans and the biosphere and to confine them in nuclear waste repositories for geological periods of time. The focus of this article is radioisotopes (radionuclides) generated by fission reactors.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.

References

  1. ↑ "Cumulative Fission Yields". IAEA . Retrieved 18 December 2020.
  2. 1 2 K. Yoshihara, "Technetium in the Environment" in "Topics in Current Chemistry: Technetium and Rhenium", vol. 176, K. Yoshihara and T. Omori (eds.), Springer-Verlag, Berlin Heidelberg, 1996.
  3. ↑ Tagami, Keiko (2003). "Technetium-99 Behavior in the Terrestrial Environment". Journal of Nuclear and Radiochemical Sciences. 4 (1): A1–A8. doi: 10.14494/jnrs2000.4.A1 . ISSN   1345-4749.
  4. ↑ Xie, Rongzhen; Shen, Nannan; Chen, Xijian; Li, Jie; Wang, Yaxing; Zhang, Chao; Xiao, Chengliang; Chai, Zhifang; Wang, Shuao (2021-05-03). "99 TcO 4 – Separation through Selective Crystallization Assisted by Polydentate Benzene-Aminoguanidinium Ligands". Inorganic Chemistry. 60 (9): 6463–6471. doi:10.1021/acs.inorgchem.1c00187. ISSN   0020-1669.
  5. ↑ Volkov, Mikhail A.; Novikov, Anton P.; Grigoriev, Mikhail S.; Kuznetsov, Vitaly V.; Sitanskaia, Anastasiia V.; Belova, Elena V.; Afanasiev, Andrey V.; Nevolin, Iurii M.; German, Konstantin E. (January 2023). "New Preparative Approach to Purer Technetium-99 Samples—Tetramethylammonium Pertechnetate: Deep Understanding and Application of Crystal Structure, Solubility, and Its Conversion to Technetium Zero Valent Matrix". International Journal of Molecular Sciences. 24 (3): 2015. doi: 10.3390/ijms24032015 . ISSN   1422-0067. PMC   9916763 .
  6. ↑ Bulbulian, S. (1984-11-01). "Methyl ethyl ketone extraction of Tc species". Journal of Radioanalytical and Nuclear Chemistry. 87 (6): 389–395. doi:10.1007/BF02166797. ISSN   1588-2780.
  7. ↑ Moir, D. L.; Joseph, D. L. (June 1997). "Determination of99Tc in fuel leachates using extraction chromatography". Journal of Radioanalytical and Nuclear Chemistry. 220 (2): 195–199. doi:10.1007/bf02034855. ISSN   0236-5731.
  8. ↑ Kołacińska, Kamila; Samczyński, Zbigniew; Dudek, Jakub; Bojanowska-Czajka, Anna; Trojanowicz, Marek (July 2018). "A comparison study on the use of Dowex 1 and TEVA-resin in determination of 99Tc in environmental and nuclear coolant samples in a SIA system with ICP-MS detection". Talanta. 184: 527–536. doi: 10.1016/j.talanta.2018.03.034 .
  9. ↑ Paučová, Veronika; Remenec, Boris; Dulanská, Silvia; Mátel, Ľubomír; Prekstová, Martina (2012-08-01). "Determination of 99Tc in soil samples using molecular recognition technology product AnaLig® Tc-02 gel". Journal of Radioanalytical and Nuclear Chemistry. 293 (2): 675–677. doi:10.1007/s10967-012-1710-5. ISSN   1588-2780.
  10. ↑ William G. Gilroy (Mar 20, 2012). "New Method for Cleaning Up Nuclear Waste". Science Daily.
  11. ↑ Wang, Shuao; Yu, Ping; Purse, Bryant A.; Orta, Matthew J.; Diwu, Juan; Casey, William H.; Phillips, Brian L.; Alekseev, Evgeny V.; Depmeier, Wulf; Hobbs, David T.; Albrecht-Schmitt, Thomas E. (2012). "Selectivity, Kinetics, and Efficiency of Reversible Anion Exchange with TcO4− in a Supertetrahedral Cationic Framework". Advanced Functional Materials. 22 (11): 2241–2250. doi:10.1002/adfm.201103081. S2CID   96158262.
  12. ↑ "Daily Metal Price: Ruthenium Price Chart (USD / Kilogram) for the Last 2 years".
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