Isotopes of thulium

Isotopes of thulium (₆₉Tm)
Standard atomic weight Ar°(Tm)
	168.934219±0.000005; 168.93±0.01 (abridged);
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Last updated September 06, 2025

Naturally occurring thulium (₆₉Tm) is composed of one stable isotope, ¹⁶⁹Tm, with 100% natural abundance. Thirty-nine radioisotopes have been characterized from ¹⁴⁴Tm to ¹⁸³Tm; with the most stable are ¹⁷¹Tm with a half-life of 1.92 years, ¹⁷⁰Tm with a half-life of 128.6 days, ¹⁶⁸Tm with a half-life of 93.1 days, and ¹⁶⁷Tm with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 3 days, with the majority less than 10 minutes. This element also has 26 meta states, with the longest half-lives being ^164mTm (5.1 minutes), ^160m1Tm (75 seconds) and ^155mTm (45 seconds).

The primary decay mode before the stable isotope, ¹⁶⁹Tm, is electron capture to erbium isotopes, and the primary mode after is beta emission to ytterbium isotopes. All isotopes of thulium are either radioactive or, in the case of ¹⁶⁹Tm, observationally stable, meaning that ¹⁶⁹Tm is predicted to be radioactive but decay has not been observed.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[4] ^{[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 4]}	Isotopic abundance
Nuclide ^{[n 1]}	Excitation energy^{[n 4]}			Half-life ^[1] ^{[n 4]}	Decay mode ^[1] ^{[n 5]}	Daughter isotope ^{[n 6]}	Spin and parity ^[1] ^{[n 7]}^{[n 4]}	Isotopic abundance
¹⁴⁴Tm	69	75	143.97621(43)#	2.3(9) μs	p	¹⁴³Er	(10+)
¹⁴⁵Tm	69	76	144.97039(21)#	3.17(20) μs	p	¹⁴⁴Er	(11/2−)
¹⁴⁶Tm	69	77	145.96666(22)#	155(20) ms	p	¹⁴⁵Er	(1+)
^146m1Tm	304(6) keV			73(7) ms	p	¹⁴⁵Er	(5−)
^146m2Tm	437(7) keV			200(3) ms	p	¹⁴⁵Er	(10+)
¹⁴⁷Tm	69	78	146.9613799(73)	0.58(3) s	β⁺ (85%)	¹⁴⁷Er	11/2−
¹⁴⁷Tm	69	78	146.9613799(73)	0.58(3) s	p (15%)	¹⁴⁶Er	11/2−
^147mTm	62(5) keV			360(40) μs	p	¹⁴⁶Er	3/2+
¹⁴⁸Tm	69	79	147.958384(11)	0.7(2) s	β⁺	¹⁴⁸Er	(10+)
¹⁴⁹Tm	69	80	148.95283(22)#	0.9(2) s	β⁺ (99.74%)	¹⁴⁹Er	11/2−
¹⁴⁹Tm	69	80	148.95283(22)#	0.9(2) s	β⁺, p (0.26%)	¹⁴⁸Ho	11/2−
¹⁵⁰Tm	69	81	149.95009(21)#	3# s	β⁺	¹⁵⁰Er	(1+)
^150m1Tm^{[n 8]}	140(140)# keV			2.20(6) s	β⁺ (98.9%)	¹⁵⁰Er	(6−)
^150m1Tm^{[n 8]}	140(140)# keV			2.20(6) s	β⁺, p (1.1%)	¹⁴⁹Ho	(6−)
^150m2Tm	811(140)# keV			5.2(3) ms	IT	^150m1Tm	10+#
¹⁵¹Tm	69	82	150.945494(21)	4.17(11) s	β⁺	¹⁵¹Er	(11/2−)
^151m1Tm	93(6) keV			6.6(20) s	β⁺	¹⁵¹Er	(1/2+)
^151m2Tm	2655.67(22) keV			451(34) ns	IT	¹⁵¹Tm	(27/2−)
¹⁵²Tm	69	83	151.944476(58)	8.0(10) s	β⁺	¹⁵²Er	(2)−
^152m1Tm^{[n 8]}	−100(250) keV			5.2(6) s	β⁺	¹⁵²Er	(9)+
^152m2Tm	2455(250) keV			301(7) ns	IT	¹⁵²Tm	(17+)
¹⁵³Tm	69	84	152.942058(13)	1.48(1) s	α (91%)	¹⁴⁹Ho	(11/2−)
¹⁵³Tm	69	84	152.942058(13)	1.48(1) s	β⁺ (9%)	¹⁵³Er	(11/2−)
^153mTm	43.2(2) keV			2.5(2) s	α (92%)	¹⁴⁹Ho	(1/2+)
^153mTm	43.2(2) keV			2.5(2) s	β⁺ (8%)	¹⁵³Er	(1/2+)
¹⁵⁴Tm	69	85	153.941570(15)	8.1(3) s	β⁺ (54%)	¹⁵⁴Er	(2)−
¹⁵⁴Tm	69	85	153.941570(15)	8.1(3) s	α (46%)	¹⁵⁰Ho	(2)−
^154mTm^{[n 8]}	70(50) keV			3.30(7) s	α (58%)	¹⁵⁰Ho	(9)+
^154mTm^{[n 8]}	70(50) keV			3.30(7) s	β⁺ (42%)	¹⁵⁴Er	(9)+
¹⁵⁵Tm	69	86	154.939210(11)	21.6(2) s	β⁺ (99.17%)	¹⁵⁵Er	11/2−
¹⁵⁵Tm	69	86	154.939210(11)	21.6(2) s	α (0.83%)	¹⁵¹Ho	11/2−
^155mTm	41(6) keV			45(4) s	β⁺	¹⁵⁵Er	1/2+
¹⁵⁶Tm	69	87	155.938986(15)	83.8(18) s	β⁺ (99.94%)	¹⁵⁶Er	2−
¹⁵⁶Tm	69	87	155.938986(15)	83.8(18) s	α (0.064%)	¹⁵²Ho	2−
^156mTm	400(200)# keV			~400 ns	IT	¹⁵⁶Tm	(11−)
¹⁵⁷Tm	69	88	156.936973(30)	3.63(9) min	β⁺	¹⁵⁷Er	1/2+
¹⁵⁷Tm	69	88	156.936973(30)	3.63(9) min	α (7.5×10⁻⁴%)	¹⁵³Ho	1/2+
^157mTm^{[n 8]}	100(50)# keV			1.6 s			7/2−#
¹⁵⁸Tm	69	89	157.936980(27)	3.98(6) min	β⁺	¹⁵⁸Er	2−
^158mTm^{[n 8]}	100(50)# keV			~20 s			5−#
¹⁵⁹Tm	69	90	158.934975(30)	9.13(16) min	β⁺	¹⁵⁹Er	5/2+
¹⁶⁰Tm	69	91	159.935264(35)	9.4(3) min	β⁺	¹⁶⁰Er	1−
^160m1Tm	67(14) keV			74.5(15) s	IT (85%)	¹⁶⁰Tm	(5+)
^160m1Tm	67(14) keV			74.5(15) s	β⁺ (15%)	¹⁶⁰Er	(5+)
^160m2Tm	215(52)# keV			~200 ns	IT	¹⁶⁰Tm	(8)
¹⁶¹Tm	69	92	160.933549(30)	30.2(8) min	β⁺	¹⁶¹Er	7/2+
^161m1Tm	7.51(24) keV			5# min			(1/2+)
^161m2Tm	78.20(3) keV			110(3) ns	IT	¹⁶¹Tm	7/2−
¹⁶²Tm	69	93	161.934001(28)	21.70(19) min	β⁺	¹⁶²Er	1−
^162mTm	130(40) keV			24.3(17) s	IT (81%)	¹⁶²Tm	5+
^162mTm	130(40) keV			24.3(17) s	β⁺ (19%)	¹⁶²Er	5+
¹⁶³Tm	69	94	162.9326583(59)	1.810(5) h	β⁺	¹⁶³Er	1/2+
^163mTm	86.92(5) keV			380(30) ns	IT	¹⁶³Tm	(7/2)−
¹⁶⁴Tm	69	95	163.933538(27)	2.0(1) min	EC (61%)	¹⁶⁴Er	1+
¹⁶⁴Tm	69	95	163.933538(27)	2.0(1) min	β⁺ (39%)	¹⁶⁴Er	1+
^164mTm	20(12) keV			5.1(1) min	IT (~80%)	¹⁶⁴Tm	6−
^164mTm	20(12) keV			5.1(1) min	β⁺ (~20%)	¹⁶⁴Er	6−
¹⁶⁵Tm	69	96	164.9324418(18)	30.06(3) h	β⁺	¹⁶⁵Er	1/2+
^165m1Tm	80.37(6) keV			80(3) μs	IT	¹⁶⁵Tm	7/2+
^165m2Tm	160.47(6) keV			9.0(5) μs	IT	¹⁶⁵Tm	7/2−
¹⁶⁶Tm	69	97	165.933562(12)	7.70(3) h	β⁺	¹⁶⁶Er	2+
^166m1Tm	122(7) keV			348(21) ms	IT	¹⁶⁶Tm	(6−)
^166m2Tm	244(7) keV			2(1) μs	IT	¹⁶⁶Tm	(6−)
¹⁶⁷Tm	69	98	166.9328572(14)	9.25(2) d	EC	¹⁶⁷Er	1/2+
^167m1Tm	179.480(19) keV			1.16(6) μs	IT	¹⁶⁷Tm	7/2+
^167m2Tm	292.820(20) keV			0.9(1) μs	IT	¹⁶⁷Tm	7/2−
¹⁶⁸Tm	69	99	167.9341785(18)	93.1(2) d	β⁺ (99.99%)	¹⁶⁸Er	3+
¹⁶⁸Tm	69	99	167.9341785(18)	93.1(2) d	β⁻ (0.010%)	¹⁶⁸Yb	3+
¹⁶⁹Tm	69	100	168.93421896(79)	Observationally Stable ^{[n 9]}			1/2+	1.0000
^169mTm	316.1463(1) keV			659.9(23) ns	IT	¹⁶⁹Tm	7/2+
¹⁷⁰Tm	69	101	169.93580709(79)	128.6(3) d	β⁻ (99.87%)	¹⁷⁰Yb	1−
¹⁷⁰Tm	69	101	169.93580709(79)	128.6(3) d	EC (0.131%)	¹⁷⁰Er	1−
^170mTm	183.197(4) keV			4.12(13) μs	IT	¹⁷⁰Tm	3+
¹⁷¹Tm	69	102	170.9364352(10)	1.92(1) y	β⁻	¹⁷¹Yb	1/2+
^171m1Tm	424.9557(15) keV			2.60(2) μs	IT	¹⁷¹Tm	7/2−
^171m2Tm	1674.43(13) keV			1.7(2) μs	IT	¹⁷¹Tm	19/2+
¹⁷²Tm	69	103	171.9384070(59)	63.6(3) h	β⁻	¹⁷²Yb	2−
^172mTm	476.2(2) keV			132(7) μs	IT	¹⁷²Tm	(6+)
¹⁷³Tm	69	104	172.9396066(47)	8.24(8) h	β⁻	¹⁷³Yb	(1/2+)
^173m1Tm	317.73(20) keV			10.7(17) μs	IT	¹⁷³Tm	7/2−
^173m2Tm	1905.7(4) keV			250(69) ns	IT	¹⁷³Tm	19/2−
^173m3Tm	4047.9(5) keV			121(28) ns	IT	¹⁷³Tm	35/2−
¹⁷⁴Tm	69	105	173.942174(48)	5.4(1) min	β⁻	¹⁷⁴Yb	4−
^174m1Tm	252.4(7) keV			2.29(1) s	IT (>98.5%)	¹⁷⁴Tm	0+
^174m1Tm	252.4(7) keV			2.29(1) s	β⁻ (<1.5%)	¹⁷⁴Yb	0+
^174m2Tm	2091.7(3) keV			106(7) μs	IT	¹⁷⁴Tm	14−
¹⁷⁵Tm	69	106	174.943842(54)	15.2(5) min	β⁻	¹⁷⁵Yb	(1/2)+
^175m1Tm	440.0(11) keV			319(35) ns	IT	¹⁷⁵Tm	7/2−
^175m2Tm	1517.7(12) keV			21(14) μs	IT	¹⁷⁵Tm	23/2+
¹⁷⁶Tm	69	107	175.94700(11)	1.85(3) min	β⁻	¹⁷⁶Yb	(4+)
¹⁷⁷Tm	69	108	176.94893(22)#	95(7) s	β⁻	¹⁷⁷Yb	1/2+#
^177mTm^{[n 8]}	100(100)# keV			77(11) s	β⁻	¹⁷⁷Yb	7/2−#
¹⁷⁸Tm	69	109	177.95251(32)#	10# s [>300 ns]			1−#
¹⁷⁹Tm	69	110	178.95502(43)#	18# s [>300 ns]			1/2+#
¹⁸⁰Tm	69	111	179.95902(43)#	3# s [>300 ns]
¹⁸¹Tm	69	112	180.96195(54)#	7# s [>300 ns]			1/2+#
¹⁸²Tm^[5]	69	113	181.96619(54)#
¹⁸³Tm^[5]	69	114
This table header & footer: view

↑ ^mTm – Excited nuclear isomer.
↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
↑ Modes of decay:
EC: Electron capture
IT: Isomeric transition
p: Proton emission
↑ Bold symbol as daughter – Daughter product is stable.
↑ ( ) spin value – Indicates spin with weak assignment arguments.
1 2 3 4 5 6 Order of ground state and isomer is uncertain.
↑ Believed to undergo α decay to ¹⁶⁵Ho

Thulium-170

Thulium-170 has a half-life of 128.6 days, decaying by β⁻ decay about 99.87% of the time and electron capture the remaining 0.13% of the time.^[1] Due to its low-energy X-ray emissions, it has been proposed for radiotherapy^[6] and as a source in a radiothermal generator.^[7]

References

1 2 3 4 5 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.
↑ "Standard Atomic Weights: Thulium". CIAAW. 2021.
↑ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (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.
↑ 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.
1 2 Tarasov, O. B.; Gade, A.; Fukushima, K.; et al. (2024). "Observation of New Isotopes in the Fragmentation of ¹⁹⁸Pt at FRIB". Physical Review Letters. 132 (072501). doi:10.1103/PhysRevLett.132.072501.
↑ Polyak, Andras; Das, Tapas; Chakraborty, Sudipta; Kiraly, Reka; Dabasi, Gabriella; Joba, Robert Peter; Jakab, Csaba; Thuroczy, Julianna; Postenyi, Zita; Haasz, Veronika; Janoki, Gergely; Janoki, Gyozo A.; Pillai, Maroor R.A.; Balogh, Lajos (October 2014). "Thulium-170-Labeled Microparticles for Local Radiotherapy: Preliminary Studies". Cancer Biotherapy and Radiopharmaceuticals. 29 (8): 330–338. doi:10.1089/cbr.2014.1680. ISSN 1084-9785. PMID 25226213 – via Academia.edu.
↑ Dustin, J. Seth; Borrelli, R.A. (December 2021). "Assessment of alternative radionuclides for use in a radioisotope thermoelectric generator". Nuclear Engineering and Design. 385: 111475. doi: 10.1016/j.nucengdes.2021.111475 .{{cite journal}}: CS1 maint: article number as page number (link)

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[4] Tm – Excited nuclear isomer.

[6] ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.

[TMS-7] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[TNN-8] 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[9] Modes of decay:
EC: Electron capture
IT: Isomeric transition
p: Proton emission

[10] Bold symbol as daughter – Daughter product is stable.

[11] ( ) spin value – Indicates spin with weak assignment arguments.

[order-12] 1 2 3 4 5 6 Order of ground state and isomer is uncertain.

[13] Believed to undergo α decay to ¹⁶⁵Ho

[NUBASE2020-1] 1 2 3 4 5 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.

[CIAAWthulium-2] "Standard Atomic Weights: Thulium". CIAAW. 2021.

[CIAAW2021-3] Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (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.

[AME2020_II-5] 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.

[PRL132.7-14] 1 2 Tarasov, O. B.; Gade, A.; Fukushima, K.; et al. (2024). "Observation of New Isotopes in the Fragmentation of ¹⁹⁸Pt at FRIB". Physical Review Letters. 132 (072501). doi:10.1103/PhysRevLett.132.072501.

[polyak2014-15] Polyak, Andras; Das, Tapas; Chakraborty, Sudipta; Kiraly, Reka; Dabasi, Gabriella; Joba, Robert Peter; Jakab, Csaba; Thuroczy, Julianna; Postenyi, Zita; Haasz, Veronika; Janoki, Gergely; Janoki, Gyozo A.; Pillai, Maroor R.A.; Balogh, Lajos (October 2014). "Thulium-170-Labeled Microparticles for Local Radiotherapy: Preliminary Studies". Cancer Biotherapy and Radiopharmaceuticals. 29 (8): 330–338. doi:10.1089/cbr.2014.1680. ISSN 1084-9785. PMID 25226213 – via Academia.edu.

[dustin2021-16] Dustin, J. Seth; Borrelli, R.A. (December 2021). "Assessment of alternative radionuclides for use in a radioisotope thermoelectric generator". Nuclear Engineering and Design. 385: 111475. doi: 10.1016/j.nucengdes.2021.111475 .{{cite journal}}: CS1 maint: article number as page number (link)

[1]

[2]

[3]

[n 1]

[4]

[n 2]

[n 3]

[n 4]

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[n 6]

[n 7]

[n 8]

[n 9]

[5]

[6]

[7]

Isotopes of thulium

Contents

List of isotopes

Thulium-170

See also

References