Isotopes of molybdenum

Molybdenum (42Mo) has 33 known isotopes, ranging in atomic mass from 83 to 115, 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.[4]

"Mo-99" redirects here. For MO99 Freon mix R438A, see refrigerant.
Isotopes of molybdenum (42Mo)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
92Mo 14.7% stable
93Mo synth 4×103 y ε 93Nb
94Mo 9.19% stable
95Mo 15.9% stable
96Mo 16.7% stable
97Mo 9.58% stable
98Mo 24.3% stable
99Mo synth 65.94 h β− 99mTc
γ –
100Mo 9.74% 7.1×1018 y β−β− 100Ru
Standard atomic weight Ar°(Mo)
  • 95.95±0.01
  • 95.95±0.01 (abridged)[2][3]

Molybdenum-100 is the only naturally occurring isotope that is not stable. Molybdenum-100 has a half-life of approximately 1×1019 y and undergoes double beta decay into ruthenium-100. Molybdenum-98 is the most common isotope, comprising 24.14% of all molybdenum on Earth. Molybdenum isotopes with mass numbers 111 and up all have half-lives of approximately .15 s.[4]

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
[n 6]		 Spin and
parity
[n 7][n 8]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
83Mo 42 41 82.94874(54)# 23(19) ms
[6(+30-3) ms]		 β+ 83Nb 3/2−#
β+, p 82Zr
84Mo 42 42 83.94009(43)# 3.8(9) ms
[3.7(+10-8) s]		 β+ 84Nb 0+
85Mo 42 43 84.93655(30)# 3.2(2) s β+ 85Nb (1/2−)#
86Mo 42 44 85.93070(47) 19.6(11) s β+ 86Nb 0+
87Mo 42 45 86.92733(24) 14.05(23) s β+ (85%) 87Nb 7/2+#
β+, p (15%) 86Zr
88Mo 42 46 87.921953(22) 8.0(2) min β+ 88Nb 0+
89Mo 42 47 88.919480(17) 2.11(10) min β+ 89Nb (9/2+)
89mMo 387.5(2) keV 190(15) ms IT 89Mo (1/2−)
90Mo 42 48 89.913937(7) 5.56(9) h β+ 90Nb 0+
90mMo 2874.73(15) keV 1.12(5) μs 8+#
91Mo 42 49 90.911750(12) 15.49(1) min β+ 91Nb 9/2+
91mMo 653.01(9) keV 64.6(6) s IT (50.1%) 91Mo 1/2−
β+ (49.9%) 91Nb
92Mo 42 50 91.906811(4) Observationally Stable[n 9] 0+ 0.14649(106)
92mMo 2760.46(16) keV 190(3) ns 8+
93Mo 42 51 92.906813(4) 4,000(800) y EC 93Nb 5/2+
93mMo 2424.89(3) keV 6.85(7) h IT (99.88%) 93Mo 21/2+
β+ (.12%) 93Nb
94Mo 42 52 93.9050883(21) Stable[n 10] 0+ 0.09187(33)
95Mo[n 11] 42 53 94.9058421(21) Stable[n 10] 5/2+ 0.15873(30)
96Mo 42 54 95.9046795(21) Stable[n 10] 0+ 0.16673(30)
97Mo[n 11] 42 55 96.9060215(21) Stable[n 10] 5/2+ 0.09582(15)
98Mo[n 11] 42 56 97.90540482(21) Observationally Stable[n 12] 0+ 0.24292(80)
99Mo[n 11][n 13] 42 57 98.9077119(21) 2.7489(6) d β− 99mTc 1/2+
99m1Mo 97.785(3) keV 15.5(2) μs 5/2+
99m2Mo 684.5(4) keV 0.76(6) μs 11/2−
100Mo[n 14][n 11] 42 58 99.907477(6) 8.5(5)×1018 a β−β− 100Ru 0+ 0.09744(65)
101Mo 42 59 100.910347(6) 14.61(3) min β− 101Tc 1/2+
102Mo 42 60 101.910297(22) 11.3(2) min β− 102Tc 0+
103Mo 42 61 102.91321(7) 67.5(15) s β− 103Tc (3/2+)
104Mo 42 62 103.91376(6) 60(2) s β− 104Tc 0+
105Mo 42 63 104.91697(8) 35.6(16) s β− 105Tc (5/2−)
106Mo 42 64 105.918137(19) 8.73(12) s β− 106Tc 0+
107Mo 42 65 106.92169(17) 3.5(5) s β− 107Tc (7/2−)
107mMo 66.3(2) keV 470(30) ns (5/2−)
108Mo 42 66 107.92345(21)# 1.09(2) s β− 108Tc 0+
109Mo 42 67 108.92781(32)# 0.53(6) s β− 109Tc (7/2−)#
110Mo 42 68 109.92973(43)# 0.27(1) s β− (>99.9%) 110Tc 0+
β−, n (<.1%) 109Tc
111Mo 42 69 110.93441(43)# 200# ms
[>300 ns]		 β− 111Tc
112Mo 42 70 111.93684(64)# 150# ms
[>300 ns]		 β− 112Tc 0+
113Mo 42 71 112.94188(64)# 100# ms
[>300 ns]		 β− 113Tc
114Mo 42 72 113.94492(75)# 80# ms
[>300 ns]		 0+
115Mo 42 73 114.95029(86)# 60# ms
[>300 ns]
This table header & footer:
  1. mMb – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. Bold half-life – nearly stable, half-life longer than age of universe.
  5. Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
    n:Neutron emission
    p:Proton emission
  6. Bold symbol as daughter – Daughter product is stable.
  7. ( ) spin value – Indicates spin with weak assignment arguments.
  8. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  9. Believed to decay by β+β+ to 92Zr with a half-life over 1.9×1020 years
  10. Theoretically capable of spontaneous fission
  11. Fission product
  12. Believed to decay by β−β− to 98Ru with a half-life of over 1×1014 years
  13. Used to produce the medically useful radioisotope technetium-99m
  14. Primordial radionuclide

Molybdenum-99

Molybdenum-99 is produced commercially by intense neutron-bombardment of a highly purified uranium-235 target, followed rapidly by extraction.[5] It is used as a parent radioisotope in technetium-99m generators to produce the even shorter-lived daughter isotope technetium-99m, which is used in approximately 40 million medical procedures annually. A common misunderstanding or misnomer is that 99Mo is used in these diagnostic medical scans, when actually it has no role in the imaging agent or the scan itself. In fact, 99Mo co-eluted with the 99mTc (also known as breakthrough) is considered a contaminant and is minimised to adhere to the appropriate USP (or equivalent) regulations and standards. The IAEA recommends that 99Mo concentrations exceeding more than 0.15 µCi/mCi 99mTc or 0.015% should not be administered for usage in humans.[6] Typically, quantification of 99Mo breakthrough is performed for every elution when using a 99Mo/99mTc generator during QA-QC testing of the final product.

There are alternative routes for generating 99Mo that do not require a fissionable target, such as high or low enriched uranium (i.e., HEU or LEU). Some of these include accelerator-based methods, such as proton bombardment or photoneutron reactions on enriched 100Mo targets. Historically, 99Mo generated by neutron capture on natural isotopic molybdenum or enriched 98Mo targets was used for the development of commercial 99Mo/99mTc generators.[7][8] The neutron-capture process was eventually superseded by fission-based 99Mo that could be generated with much higher specific activities. Implementing feed-stocks of high specific activity 99Mo solutions thus allowed for higher quality production and better separations of 99mTc from 99Mo on small alumina column using chromatography. Employing low-specific activity 99Mo under similar conditions is particularly problematic in that either higher Mo loading capacities or larger columns are required for accommodating equivalent amounts of 99Mo. Chemically speaking, this phenomenon occurs due to other Mo isotopes present aside from 99Mo that compete for surface site interactions on the column substrate. In turn, low-specific activity 99Mo usually requires much larger column sizes and longer separation times, and usually yields 99mTc accompanied by unsatisfactory amounts of the parent radioisotope when using γ-alumina as the column substrate. Ultimately, the inferior end-product 99mTc generated under these conditions makes it essentially incompatible with the commercial supply-chain.

In the last decade, cooperative agreements between the US government and private capital entities have resurrected neutron capture production for commercially distributed 99Mo/99mTc in the United States of America.[9] The return to neutron-capture-based 99Mo has also been accompanied by the implementation of novel separation methods that allow for low-specific activity 99Mo to be utilized.

References
  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. "Standard Atomic Weights: Molybdenum". CIAAW. 2013.
  3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press. Section 11. ISBN 978-0-8493-0487-3.
  5. Frank N. Von Hippel; Laura H. Kahn (December 2006). "Feasibility of Eliminating the Use of Highly Enriched Uranium in the Production of Medical Radioisotopes". Science & Global Security. 14 (2 & 3): 151–162. Bibcode:2006S&GS...14..151V. doi:10.1080/08929880600993071. S2CID 122507063.
  6. Ibrahim I, Zulkifli H, Bohari Y, Zakaria I, Wan Hamirul BWK. Minimizing Molybdenum-99 Contamination In Technetium-99m Pertechnetate From The Elution Of 99Mo/99mTc Generator (PDF) (Report).
  7. Richards, P. (1989). Technetium-99m: The early days. 3rd International Symposium on Technetium in Chemistry and Nuclear Medicine, Padova, Italy, 5-8 Sep 1989. OSTI 5612212.
  8. Richards, P. (1965-10-14). The Technetium-99m Generator (Report). doi:10.2172/4589063. OSTI 4589063.
  9. "Emerging leader with new solutions in the field of nuclear medicine technology". NorthStar Medical Radioisotopes, LLC. Retrieved 2020-01-23.
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