Isotopes of thulium

Naturally occurring thulium (₆₉Tm) is composed of one stable isotope, ¹⁶⁹Tm (100% natural abundance). Thirty-nine radioisotopes have been characterized, with the most stable being 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 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 26 meta states, with the most stable being ^164mTm (t_1/2 5.1 minutes), ^160mTm (t_1/2 74.5 seconds) and ^155mTm (t_1/2 45 seconds).

Isotopes of thulium (₆₉Tm)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 167Tm synth 9.25 d ε 167Er 168Tm synth 93.1 d β+ 168Er 169Tm 100% stable 170Tm synth 128.6 d β− 170Yb 171Tm synth 1.92 y β− 171Yb
Standard atomic weight Ar°(Tm)
	168.934219±0.000005[2] 168.93±0.01 (abridged)[3]
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The known isotopes of thulium range from ¹⁴⁴Tm to ¹⁸³Tm. The primary decay mode before the most abundant stable isotope, ¹⁶⁹Tm, is electron capture, and the primary mode after is beta emission. The primary decay products before ¹⁶⁹Tm are erbium isotopes, and the primary products after are 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 no actual decay has 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
	Excitation energy[n 4]
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−
					p (15%)	146Er
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−
					β+, p (0.26%)	148Ho
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−)
					β+, p (1.1%)	149Ho
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−)
					β+ (9%)	153Er
153mTm	43.2(2) keV			2.5(2) s	α (92%)	149Ho	(1/2+)
					β+ (8%)	153Er
154Tm	69	85	153.941570(15)	8.1(3) s	β+ (54%)	154Er	(2)−
					α (46%)	150Ho
154mTm[n 8]	70(50) keV			3.30(7) s	α (58%)	150Ho	(9)+
					β+ (42%)	154Er
155Tm	69	86	154.939210(11)	21.6(2) s	β+ (99.17%)	155Er	11/2−
					α (0.83%)	151Ho
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−
					α (0.064%)	152Ho
156mTm	400(200)# keV			~400 ns	IT	156Tm	(11−)
157Tm	69	88	156.936973(30)	3.63(9) min	β+	157Er	1/2+
					α (7.5×10−4%)	153Ho
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+)
					β+ (15%)	160Er
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+
					β+ (19%)	162Er
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+
					β+ (39%)
164mTm	20(12) keV			5.1(1) min	IT (~80%)	164Tm	6−
					β+ (~20%)	164Er
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+
					β− (0.010%)	168Yb
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−
					EC (0.131%)	170Er
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+
					β− (<1.5%)	174Yb
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

1. ^mTm – 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. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   p:	Proton emission

6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Order of ground state and isomer is uncertain.
9. Believed to undergo α decay to ¹⁶⁵Ho

Thulium-170

Main article: 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]