Isotopes of molybdenum

"Mo-99" redirects here. For MO99 Freon mix R438A, see refrigerant.

Molybdenum (₄₂Mo) has seven isotopes in nature, with atomic masses of 92, 94-98, and 100. All are stable except ¹⁰⁰Mo, which undergoes double beta decay with a half-life of 7.07×10¹⁸ years (the shortest known for this mode) to ¹⁰⁰Ru. ⁹²Mo and ⁹⁸Mo are also energetically able to decay in this manner, to zirconium and ruthenium respectively; the others are theoretically stable. There are also a total of 32 synthetic isotopes known, and at least 13 metastable nuclear isomers, ranging in atomic mass from 81 to 119.

Isotopes of molybdenum (₄₂Mo)

Main isotopes[1] Decay Isotope abun­dance half-life (t1/2) mode pro­duct 92Mo 14.7% stable 93Mo synth 4839 y[2] ε 93Nb 94Mo 9.19% stable 95Mo 15.9% stable 96Mo 16.7% stable 97Mo 9.58% stable 98Mo 24.3% stable 99Mo synth 65.932 h β− 99mTc 100Mo 9.74% 7.07×1018 y β−β− 100Ru
Standard atomic weight Ar°(Mo)
	95.95±0.01[3] 95.95±0.01 (abridged)[4]
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The isotopes with mass 93 or lower decay by electron capture or positron emission to niobium isotopes (or zirconium after delayed proton emission); those with mass 99 or higher by ordinary beta decay to technetium. The most stable of the former are ⁹³Mo, recently measured to have a half-life around 4800 years^[2], and ⁹⁰Mo at 5.56 hours. The most stable of the latter is the medically important ⁹⁹Mo, half-life 65.932 hours, and whose decay leads to the chief isotope of technetium. By far the most stable isomer is ^93m1Mo at 6.85 hours, decaying to its ground state.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[5] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope [n 6]	Spin and parity[1] [n 7][n 8]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion[1]	Range of variation
81Mo	42	39	80.96623(54)#	1# ms [>400 ns]	β+?	81Nb	5/2+#
					β+, p?	80Zr
82Mo	42	40	81.95666(43)#	30# ms [>400 ns]	β+?	82Nb	0+
					β+, p?	81Zr
83Mo	42	41	82.95025(43)#	23(19) ms	β+	83Nb	3/2−#
					β+, p?	82Zr
84Mo	42	42	83.94185(32)#	2.3(3) s	β+	84Nb	0+
					β+, p?	83Zr
85Mo	42	43	84.938261(17)	3.2(2) s	β+ (99.86%)	85Nb	(1/2+)
					β+, p (0.14%)	84Zr
86Mo	42	44	85.931174(3)	19.1(3) s	β+	86Nb	0+
87Mo	42	45	86.928196(3)	14.1(3) s	β+ (85%)	87Nb	7/2+#
					β+, p (15%)	86Zr
88Mo	42	46	87.921968(4)	8.0(2) min	β+	88Nb	0+
89Mo	42	47	88.919468(4)	2.11(10) min	β+	89Nb	(9/2+)
89mMo	387.5(2) keV			190(15) ms	IT	89Mo	(1/2−)
90Mo	42	48	89.913931(4)	5.56(9) h	β+	90Nb	0+
90mMo	2874.73(15) keV			1.14(5) μs	IT	90Mo	8+
91Mo	42	49	90.911745(7)	15.49(1) min	β+	91Nb	9/2+
91mMo	653.01(9) keV			64.6(6) s	IT (50.0%)	91Mo	1/2−
					β+ (50.0%)	91Nb
92Mo	42	50	91.90680715(17)	Observationally Stable[n 9]			0+	0.14649(106)
92mMo	2760.52(14) keV			190(3) ns	IT	92Mo	8+
93Mo	42	51	92.90680877(19)	4839(63) y[2]	EC (95.7%)	93mNb	5/2+
					EC (4.3%)	93Nb
93m1Mo	2424.95(4) keV			6.85(7) h	IT (99.88%)	93Mo	21/2+
					β+ (0.12%)	93Nb
93m2Mo	9695(17) keV			1.8(10) μs	IT	93Mo	(39/2−)
94Mo	42	52	93.90508359(15)	Stable			0+	0.09187(33)
95Mo[n 10]	42	53	94.90583744(13)	Stable			5/2+	0.15873(30)
96Mo	42	54	95.90467477(13)	Stable			0+	0.16673(8)
97Mo[n 10]	42	55	96.90601690(18)	Stable			5/2+	0.09582(15)
98Mo[n 10]	42	56	97.90540361(19)	Observationally Stable[n 11]			0+	0.24292(80)
99Mo[n 10][n 12]	42	57	98.90770730(25)	65.932(5) h	β−	99mTc	1/2+
99m1Mo	97.785(3) keV			15.5(2) μs	IT	99Mo	5/2+
99m2Mo	684.10(19) keV			760(60) ns	IT	99Mo	11/2−
100Mo[n 10][n 13]	42	58	99.9074680(3)	7.07(14)×1018 y	β−β−	100Ru	0+	0.09744(65)
101Mo	42	59	100.9103376(3)	14.61(3) min	β−	101Tc	1/2+
101m1Mo	13.497(9) keV			226(7) ns	IT	101Mo	3/2+
101m2Mo	57.015(11) keV			133(70) ns	IT	101Mo	5/2+
102Mo	42	60	101.910294(9)	11.3(2) min	β−	102Tc	0+
103Mo	42	61	102.913092(10)	67.5(15) s	β−	103Tc	3/2+
104Mo	42	62	103.913747(10)	60(2) s	β−	104Tc	0+
105Mo	42	63	104.9169798(23)[6]	36.3(8) s	β−	105Tc	(5/2−)
106Mo	42	64	105.9182732(98)	8.73(12) s	β−	106Tc	0+
107Mo	42	65	106.9221198(99)	3.5(5) s	β−	107Tc	(1/2+)
107mMo	65.4(2) keV			445(21) ns	IT	107Mo	(5/2+)
108Mo	42	66	107.9240475(99)	1.105(10) s	β− (>99.5%)	108Tc	0+
					β−, n (<0.5%)	107Tc
109Mo	42	67	108.928438(12)	700(14) ms	β− (98.7%)	109Tc	(1/2+)
					β−, n (1.3%)	108Tc
109mMo	69.7(5) keV			210(60) ns	IT	109Mo	5/2+#
110Mo	42	68	109.930718(26)	292(7) ms	β− (98.0%)	110Tc	0+
					β−, n (2.0%)	109Tc
111Mo	42	69	110.935652(14)	193.6(44) ms	β− (>88%)	111Tc	1/2+#
					β−, n (<12%)	110Tc
111mMo	100(50)# keV			~200 ms	β−	111Tc	7/2−#
					β−, n?	110Tc
112Mo	42	70	111.93829(22)#	125(5) ms	β−	112Tc	0+
					β−, n?	111Tc
113Mo	42	71	112.94348(32)#	80(2) ms	β−	113Tc	5/2+#
					β−, n?	112Tc
114Mo	42	72	113.94667(32)#	58(2) ms	β−	114Tc	0+
					β−, n?	113Tc
115Mo	42	73	114.95217(43)#	45.5(20) ms	β−	115Tc	3/2+#
					β−, n?	114Tc
					β−, 2n?	113Tc
116Mo	42	74	115.95576(54)#	32(4) ms	β−	116Tc	0+
					β−, n?	115Tc
					β−, 2n?	114Tc
117Mo	42	75	116.96169(54)#	22(5) ms	β−	117Tc	3/2+#
					β−, n?	116Tc
					β−, 2n?	115Tc
118Mo	42	76	117.96525(54)#	21(6) ms	β−	118Tc	0+
					β−, n?	117Tc
					β−, 2n?	116Tc
119Mo	42	77	118.97147(32)#	12# ms [>550 ns]	β−?	119Tc	3/2+#
					β−, n?	118Tc
					β−, 2n?	117Tc
This table header & footer: view

1. ^mMo – 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 y
10. Fission product
11. Believed to decay by β⁻β⁻ to ⁹⁸Ru with a half-life of over 1×10¹⁴ years
12. Used to produce the medically useful radioisotope technetium-99m
13. Primordial radionuclide

Molybdenum-99

Molybdenum-99 is produced commercially by intense neutron-bombardment (i.e. fission) of a highly purified uranium-235 target, followed rapidly by extraction.^[7] 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.^[8] 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.^[9][10] 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 current 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.^[11] 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.^{[citation needed]}

See also

Daughter products other than molybdenum

• Isotopes of technetium
• Isotopes of niobium
• Isotopes of zirconium