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
|-id=Thulium-144 | 144Tm | style="text-align:right" | 69 | style="text-align:right" | 75 | 143.97621(43)# | style="text-align:center" | 2026 | 2.3(9) μs | p | 143Er | (10+) | |-id=Thulium-145 | 145Tm | style="text-align:right" | 69 | style="text-align:right" | 76 | 144.97039(21)# | style="text-align:center" | 1998 | 3.17(20) μs | p | 144Er | (11/2−) | |-id=Thulium-146 | 146Tm | style="text-align:right" | 69 | style="text-align:right" | 77 | 145.96666(22)# | style="text-align:center" | 1993 | 155(20) ms | p | 145Er | (1+) | |-id=Thulium-146m1 | style="text-indent:1em" | 146m1Tm | colspan="3" style="text-indent:2em" | 304(6) keV | style="text-align:center" | (2005) Only published in a conference proceeding and not a refereed journal | 73(7) ms | p | 145Er | (5−) | |-id=Thulium-146m2 | style="text-indent:1em" | 146m2Tm | colspan="3" style="text-indent:2em" | 437(7) keV | style="text-align:center" | 2006 | 200(3) ms | p | 145Er | (10+) | |-id=Thulium-147 | rowspan=2|147Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 78 | rowspan=2|146.9613799(73) | rowspan=2 style="text-align:center" | 1982 | rowspan=2|0.58(3) s | β+ (85%) | 147Er | rowspan=2|11/2− | rowspan=2| |- | p (15%) | 146Er |-id=Thulium-147m | style="text-indent:1em" | 147mTm | colspan="3" style="text-indent:2em" | 62(5) keV | style="text-align:center" | 1993 | 360(40) μs | p | 146Er | 3/2+ | |-id=Thulium-148 | 148Tm | style="text-align:right" | 69 | style="text-align:right" | 79 | 147.958384(11) | style="text-align:center" | 1982 | 0.7(2) s | β+ | 148Er | (10+) | |-id=Thulium-149 | rowspan=2|149Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 80 | rowspan=2|148.95283(22)# | rowspan=2 style="text-align:center" | 1987 | rowspan=2|0.9(2) s | β+ (99.74%) | 149Er | rowspan=2|11/2− | rowspan=2| |- | β+, p (0.26%) | 148Ho |-id=Thulium-150 | 150Tm | style="text-align:right" | 69 | style="text-align:right" | 81 | 149.95009(21)# | style="text-align:center" | 1982 | 3# s | β+ | 150Er | (1+) | |-id=Thulium-150m1 | rowspan=2 style="text-indent:1em" | 150m1TmOrder of ground state and isomer is uncertain. | rowspan=2 colspan="3" style="text-indent:2em" | 140(140)# keV | rowspan=2 style="text-align:center" | (1988) Not clear that the isomer is different from the ground state, not included in discovery database | rowspan=2|2.20(6) s | β+ (98.9%) | 150Er | rowspan=2|(6−) | rowspan=2| |- | β+, p (1.1%) | 149Ho |-id=Thulium-150m2 | style="text-indent:1em" | 150m2Tm | colspan="3" style="text-indent:2em" | 811(140)# keV | style="text-align:center" | 1984 | 5.2(3) ms | IT | 150m1Tm | 10+# | |-id=Thulium-151 | 151Tm | style="text-align:right" | 69 | style="text-align:right" | 82 | 150.945494(21) | style="text-align:center" | 1982 | 4.17(11) s | β+ | 151Er | (11/2−) | |-id=Thulium-151m1 | style="text-indent:1em" | 151m1Tm | colspan="3" style="text-indent:2em" | 93(6) keV | style="text-align:center" | 1988 | 6.6(20) s | β+ | 151Er | (1/2+) | |-id=Thulium-151m2 | style="text-indent:1em" | 151m2Tm | colspan="3" style="text-indent:2em" | 2655.67(22) keV | style="text-align:center" | 1982 | 451(34) ns | IT | 151Tm | (27/2−) | |-id=Thulium-152 | 152Tm | style="text-align:right" | 69 | style="text-align:right" | 83 | 151.944476(58) | style="text-align:center" | 1980 | 8.0(10) s | β+ | 152Er | (2)− | |-id=Thulium-152m1 | style="text-indent:1em" | 152m1Tm | colspan="3" style="text-indent:2em" | −100(250) keV | style="text-align:center" | 1982 | 5.2(6) s | β+ | 152Er | (9)+ | |-id=Thulium-152m2 | style="text-indent:1em" | 152m2Tm | colspan="3" style="text-indent:2em" | 2455(250) keV | style="text-align:center" | 1986 | 301(7) ns | IT | 152Tm | (17+) | |-id=Thulium-153 | rowspan=2|153Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 84 | rowspan=2|152.942058(13) | rowspan=2 style="text-align:center" | 1964 | rowspan=2|1.48(1) s | α (91%) | 149Ho | rowspan=2|(11/2−) | rowspan=2| |- | β+ (9%) | 153Er |-id=Thulium-153m | rowspan=2 style="text-indent:1em" | 153mTm | rowspan=2 colspan="3" style="text-indent:2em" | 43.2(2) keV | rowspan=2 style="text-align:center" | 1989 | rowspan=2|2.5(2) s | α (92%) | 149Ho | rowspan=2|(1/2+) | rowspan=2| |- | β+ (8%) | 153Er |-id=Thulium-154 | rowspan=2|154Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 85 | rowspan=2|153.941570(15) | rowspan=2 style="text-align:center" | 1964 | rowspan=2|8.1(3) s | β+ (54%) | 154Er | rowspan=2|(2)− | rowspan=2| |- | α (46%) | 150Ho |-id=Thulium-154m | rowspan=2 style="text-indent:1em" | 154mTm | rowspan=2 colspan="3" style="text-indent:2em" | 70(50) keV | rowspan=2 style="text-align:center" | 1964 | rowspan=2|3.30(7) s | α (58%) | 150Ho | rowspan=2|(9)+ | rowspan=2| |- | β+ (42%) | 154Er |-id=Thulium-155 | rowspan=2|155Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 86 | rowspan=2|154.939210(11) | rowspan=2 style="text-align:center" | 1971 | rowspan=2|21.6(2) s | β+ (99.17%) | 155Er | rowspan=2|11/2− | rowspan=2| |- | α (0.83%) | 151Ho |-id=Thulium-155m | style="text-indent:1em" | 155mTm | colspan="3" style="text-indent:2em" | 41(6) keV | style="text-align:center" | 1990 | 45(4) s | β+ | 155Er | 1/2+ | |-id=Thulium-156 | rowspan=2|156Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 87 | rowspan=2|155.938986(15) | rowspan=2 style="text-align:center" | 1971 | rowspan=2|83.8(18) s | β+ (99.94%) | 156Er | rowspan=2|2− | rowspan=2| |- | α (0.064%) | 152Ho |-id=Thulium-156m | style="text-indent:1em" | 156mTm | colspan="3" style="text-indent:2em" | 400(200)# keV | style="text-align:center" | 1985 | ~400 ns | IT | 156Tm | (11−) | |-id=Thulium-157 | rowspan=2|157Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 88 | rowspan=2|156.936973(30) | rowspan=2 style="text-align:center" | 1974 | rowspan=2|3.63(9) min | β+ | 157Er | rowspan=2|1/2+ | rowspan=2| |- | α (7.5%) | 153Ho |-id=Thulium-157m | style="text-indent:1em" | 157mTm | colspan="3" style="text-indent:2em" | 100(50)# keV | style="text-align:center" | (2008) | 1.6 s
| 7/2−# | |-id=Thulium-158 | 158Tm | style="text-align:right" | 69 | style="text-align:right" | 89 | 157.936980(27) | style="text-align:center" | 1970 | 3.98(6) min | β+ | 158Er | 2− | |-id=Thulium-158m | style="text-indent:1em" | 158mTm | colspan="3" style="text-indent:2em" | 100(50)# keV | style="text-align:center" | (1981) Half-life later corrected to 20 ns, not included in discovery database | ~20 s
| 5−# | |-id=Thulium-159 | 159Tm | style="text-align:right" | 69 | style="text-align:right" | 90 | 158.934975(30) | style="text-align:center" | 1971 | 9.13(16) min | β+ | 159Er | 5/2+ | |-id=Thulium-160 | 160Tm | style="text-align:right" | 69 | style="text-align:right" | 91 | 159.935264(35) | style="text-align:center" | 1970 | 9.4(3) min | β+ | 160Er | 1− | |-id=Thulium-160m1 | rowspan=2 style="text-indent:1em" | 160m1Tm | rowspan=2 colspan="3" style="text-indent:2em" | 67(14) keV | rowspan=2 style="text-align:center" | 1983 | rowspan=2|74.5(15) s | IT (85%) | 160Tm | rowspan=2|(5+) | rowspan=2| |- | β+ (15%) | 160Er |-id=Thulium-160m2 | style="text-indent:1em" | 160m2Tm | colspan="3" style="text-indent:2em" | 215(52)# keV | style="text-align:center" | 1986 | ~200 ns | IT | 160Tm | (8) | |-id=Thulium-161 | 161Tm | style="text-align:right" | 69 | style="text-align:right" | 92 | 160.933549(30) | style="text-align:center" | 1959 | 30.2(8) min | β+ | 161Er | 7/2+ | |-id=Thulium-161m1 | style="text-indent:1em" | 161m1Tm | colspan="3" style="text-indent:2em" | 7.51(24) keV | style="text-align:center" | (1981) Half-life shorter than 100ns, not included in discovery database | 5# min
| (1/2+) | |-id=Thulium-161m2 | style="text-indent:1em" | 161m2Tm | colspan="3" style="text-indent:2em" | 78.20(3) keV | style="text-align:center" | 1981 | 110(3) ns | IT | 161Tm | 7/2− | |-id=Thulium-162 | 162Tm | style="text-align:right" | 69 | style="text-align:right" | 93 | 161.934001(28) | style="text-align:center" | 1963 | 21.70(19) min | β+ | 162Er | 1− | |-id=Thulium-162m | rowspan=2 style="text-indent:1em" | 162mTm | rowspan=2 colspan="3" style="text-indent:2em" | 130(40) keV | rowspan=2 style="text-align:center" | 1974 | rowspan=2|24.3(17) s | IT (81%) | 162Tm | rowspan=2|5+ | rowspan=2| |- | β+ (19%) | 162Er |-id=Thulium-163 | 163Tm | style="text-align:right" | 69 | style="text-align:right" | 94 | 162.9326583(59) | style="text-align:center" | 1959 | 1.810(5) h | β+ | 163Er | 1/2+ | |-id=Thulium-163m | style="text-indent:1em" | 163mTm | colspan="3" style="text-indent:2em" | 86.92(5) keV | style="text-align:center" | 1975 | 380(30) ns | IT | 163Tm | (7/2)− | |-id=Thulium-164 | rowspan=2|164Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 95 | rowspan=2|163.933538(27) | rowspan=2 style="text-align:center" | 1960 | rowspan=2|2.0(1) min | EC (61%) | rowspan=2|164Er | rowspan=2|1+ | rowspan=2| |- | β+ (39%) |-id=Thulium-164m | rowspan=2 style="text-indent:1em" | 164mTm | rowspan=2 colspan="3" style="text-indent:2em" | 20(12) keV | rowspan=2 style="text-align:center" | 1971 | rowspan=2|5.1(1) min | IT (~80%) | 164Tm | rowspan=2|6− | rowspan=2| |- | β+ (~20%) | 164Er |-id=Thulium-165 | 165Tm | style="text-align:right" | 69 | style="text-align:right" | 96 | 164.9324418(18) | style="text-align:center" | 1953 | 30.06(3) h | β+ | 165Er | 1/2+ | |-id=Thulium-165m1 | style="text-indent:1em" | 165m1Tm | colspan="3" style="text-indent:2em" | 80.37(6) keV | style="text-align:center" | 1967 | 80(3) μs | IT | 165Tm | 7/2+ | |-id=Thulium-165m2 | style="text-indent:1em" | 165m2Tm | colspan="3" style="text-indent:2em" | 160.47(6) keV | style="text-align:center" | 1968 | 9.0(5) μs | IT | 165Tm | 7/2− | |-id=Thulium-166 | 166Tm | style="text-align:right" | 69 | style="text-align:right" | 97 | 165.933562(12) | style="text-align:center" | 1948 | 7.70(3) h | β+ | 166Er | 2+ | |-id=Thulium-166m1 | style="text-indent:1em" | 166m1Tm | colspan="3" style="text-indent:2em" | 122(7) keV | style="text-align:center" | 1996 | 348(21) ms | IT | 166Tm | (6−) | |-id=Thulium-166m2 | style="text-indent:1em" | 166m2Tm | colspan="3" style="text-indent:2em" | 244(7) keV | style="text-align:center" | 1996 | 2(1) μs | IT | 166Tm | (6−) | |-id=Thulium-167 | 167Tm | style="text-align:right" | 69 | style="text-align:right" | 98 | 166.9328572(14) | style="text-align:center" | 1948 | 9.25(2) d | EC | 167Er | 1/2+ | |-id=Thulium-167m1 | style="text-indent:1em" | 167m1Tm | colspan="3" style="text-indent:2em" | 179.480(19) keV | style="text-align:center" | 1964 | 1.16(6) μs | IT | 167Tm | 7/2+ | |-id=Thulium-167m2 | style="text-indent:1em" | 167m2Tm | colspan="3" style="text-indent:2em" | 292.820(20) keV | style="text-align:center" | 1965 | 0.9(1) μs | IT | 167Tm | 7/2− | |-id=Thulium-168 | rowspan=2|168Tm | rowspan=2 style="text-align:right" | 69 | rowspan=2 style="text-align:right" | 99