Naturally occurring terbium (65Tb) is composed of one stable isotope, 159Tb. Thirty-seven radioisotopes have been characterized, with the most stable being 158Tb with a half-life of 180 years, 157Tb with a half-life of 71 years, and 160Tb with a half-life of 72.3 days. All of the remaining radioactive isotopes have half-lives that are less than 6.907 days, and the majority of these have half-lives that are less than 24 seconds. This element also has 27 meta states, with the most stable being 156m1Tb (t1/2 = 24.4 hours), 154m2Tb (t1/2 = 22.7 hours) and 154m1Tb (t1/2 = 9.4 hours).
The primary decay mode before the most abundant stable isotope, 159Tb, is electron capture, and the primary mode behind is beta decay. The primary decay products before 159Tb are element Gd (gadolinium) isotopes, and the primary products after 159Tb are element Dy (dysprosium) isotopes.
|-| 135Tb| style="text-align:right" | 65| style="text-align:right" | 70|| 0.94(+33−22) ms||| (7/2−)||-| 136Tb| style="text-align:right" | 65| style="text-align:right" | 71| 135.96138(64)#| 0.2# s|||||-| 137Tb| style="text-align:right" | 65| style="text-align:right" | 72| 136.95598(64)#| 600# ms||| 11/2−#||-| rowspan=2|138Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 73| rowspan=2|137.95316(43)#| rowspan=2|800# ms [>200 ns]| β+| 138Gd| rowspan=2|| rowspan=2||-| p| 137Gd|-| 139Tb| style="text-align:right" | 65| style="text-align:right" | 74| 138.94829(32)#| 1.6(2) s| β+| 139Gd| 11/2−#||-| rowspan=2|140Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 75| rowspan=2|139.94581(86)| rowspan=2|2.4(2) s| β+ (99.74%)| 140Gd| rowspan=2|5| rowspan=2||-| β+, p (.26%)| 139Eu|-| 141Tb| style="text-align:right" | 65| style="text-align:right" | 76| 140.94145(11)| 3.5(2) s| β+| 141Gd| (5/2−)||-| style="text-indent:1em" | 141mTb| colspan="3" style="text-indent:2em" | 0(200)# keV| 7.9(6) s| β+| 141Gd| 11/2−#||-| rowspan=3|142Tb| rowspan=3 style="text-align:right" | 65| rowspan=3 style="text-align:right" | 77| rowspan=3|141.93874(32)#| rowspan=3|597(17) ms| β+ (96.8(4)%)| rowspan=2|142Gd| rowspan=3|1+| rowspan=3||-| EC (3.2(4)%)|-| β+, p| 141Eu|-| rowspan=2 style="text-indent:1em" | 142m1Tb| rowspan=2 colspan="3" style="text-indent:2em" | 280.2(10) keV| rowspan=2|303(17) ms| IT (99.5%)| 142Tb| rowspan=2|(5−)| rowspan=2||-| β+ (.5%)| 142Gd|-| style="text-indent:1em" | 142m2Tb| colspan="3" style="text-indent:2em" | 621.4(11) keV| 15(4) μs|||||-| 143Tb| style="text-align:right" | 65| style="text-align:right" | 78| 142.93512(6)| 12(1) s| β+| 143Gd| (11/2−)||-| style="text-indent:1em" | 143mTb| colspan="3" style="text-indent:2em" | 0(100)# keV| <21 s| β+| 143Gd| 5/2+#||-| rowspan=2|144Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 79| rowspan=2|143.93305(3)| rowspan=2|~1 s| β+| 144Gd| rowspan=2|1+| rowspan=2||-| β+, p (rare)| 143Eu|-| rowspan=3 style="text-indent:1em" | 144m1Tb| rowspan=3 colspan="3" style="text-indent:2em" | 396.9(5) keV| rowspan=3|4.25(15) s| IT (66%)| 144Tb| rowspan=3|(6−)| rowspan=3||-| β+ (34%)| 144Gd|-| β+, p (<1%)| 143Eu|-| style="text-indent:1em" | 144m2Tb| colspan="3" style="text-indent:2em" | 476.2(5) keV| 2.8(3) μs||| (8−)||-| style="text-indent:1em" | 144m3Tb| colspan="3" style="text-indent:2em" | 517.1(5) keV| 670(60) ns||| (9+)||-| style="text-indent:1em" | 144m4Tb| colspan="3" style="text-indent:2em" | 544.5(6) keV| <300 ns||| (10+)||-| 145Tb| style="text-align:right" | 65| style="text-align:right" | 80| 144.92927(6)| 20# min| β+| 145Gd| (3/2+)||-| style="text-indent:1em" | 145mTb| colspan="3" style="text-indent:2em" | 0(100)# keV| 30.9(7) s| β+| 145Gd| (11/2−)||-| 146Tb| style="text-align:right" | 65| style="text-align:right" | 81| 145.92725(5)| 8(4) s| β+| 146Gd| 1+||-| style="text-indent:1em" | 146m1Tb| colspan="3" style="text-indent:2em" | 150(100)# keV| 24.1(5) s| β+| 146Gd| 5−||-| style="text-indent:1em" | 146m2Tb| colspan="3" style="text-indent:2em" | 930(100)# keV| 1.18(2) ms||| (10+)||-| 147Tb| style="text-align:right" | 65| style="text-align:right" | 82| 146.924045(13)| 1.64(3) h| β+| 147Gd| 1/2+#||-| style="text-indent:1em" | 147mTb| colspan="3" style="text-indent:2em" | 50.6(9) keV| 1.87(5) min| β+| 147Gd| (11/2)−||-| 148Tb| style="text-align:right" | 65| style="text-align:right" | 83| 147.924272(15)| 60(1) min| β+| 148Gd| 2−||-| style="text-indent:1em" | 148m1Tb| colspan="3" style="text-indent:2em" | 90.1(3) keV| 2.20(5) min| β+| 148Gd| (9)+||-| style="text-indent:1em" | 148m2Tb| colspan="3" style="text-indent:2em" | 8618.6(10) keV| 1.310(7) μs||| (27+)||-| rowspan=2|149Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 84| rowspan=2|148.923246(5)| rowspan=2|4.118(25) h| β+ (83.3%)| 149Gd| rowspan=2|1/2+| rowspan=2||-| α (16.7%)| 145Eu|-| rowspan=2 style="text-indent:1em" | 149mTb| rowspan=2 colspan="3" style="text-indent:2em" | 35.78(13) keV| rowspan=2|4.16(4) min| β+ (99.97%)| 149Gd| rowspan=2|11/2−| rowspan=2||-| α (.022%)| 145Eu|-| rowspan=2|150Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 85| rowspan=2|149.923660(8)| rowspan=2|3.48(16) h| β+ (99.95%)| 150Gd| rowspan=2|(2−)| rowspan=2||-| α (.05%)| 146Eu|-| rowspan=2 style="text-indent:1em" | 150mTb| rowspan=2 colspan="3" style="text-indent:2em" | 457(29) keV| rowspan=2|5.8(2) min| β+| 150Gd| rowspan=2|9+| rowspan=2||-| IT (rare)| 150Tb|-| rowspan=2|151Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 86| rowspan=2|150.923103(5)| rowspan=2|17.609(1) h| β+ (99.99%)| 151Gd| rowspan=2|1/2(+)| rowspan=2||-| α (.0095%)| 147Eu|-| rowspan=2 style="text-indent:1em" | 151mTb| rowspan=2 colspan="3" style="text-indent:2em" | 99.54(6) keV| rowspan=2|25(3) s| IT (93.8%)| 151Tb| rowspan=2|(11/2−)| rowspan=2||-| β+ (6.2%)| 151Gd|-| rowspan=2|152Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 87| rowspan=2|151.92407(4)| rowspan=2|17.8784(95) h[1] | β+| 152Gd| rowspan=2|2−| rowspan=2||-| α (7×10−7%)| 148Eu|-| style="text-indent:1em" | 152m1Tb| colspan="3" style="text-indent:2em" | 342.15(16) keV| 0.96 μs||| 5−||-| rowspan=2 style="text-indent:1em" | 152m2Tb| rowspan=2 colspan="3" style="text-indent:2em" | 501.74(19) keV| rowspan=2|4.2(1) min| IT (78.8%)| 152Tb| rowspan=2|8+| rowspan=2||-| β+ (21.2%)| 152Gd|-| 153Tb| style="text-align:right" | 65| style="text-align:right" | 88| 152.923435(5)| 2.34(1) d| β+| 153Gd| 5/2+||-| style="text-indent:1em" | 153mTb| colspan="3" style="text-indent:2em" | 163.175(5) keV| 186(4) μs||| 11/2−||-| rowspan=2|154Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 89| rowspan=2|153.92468(5)| rowspan=2|21.5(4) h| β+ (99.9%)| 154Gd| rowspan=2|0(+#)| rowspan=2||-| β− (.1%)| 154Dy|-| rowspan=3 style="text-indent:1em" | 154m1Tb| rowspan=3 colspan="3" style="text-indent:2em" | 12(7) keV| rowspan=3|9.4(4) h| β+ (78.2%)| 154Gd| rowspan=3|3−| rowspan=3||-| IT (21.8%)| 154Tb|-| β− (.1%)| 154Dy|-| style="text-indent:1em" | 154m2Tb| colspan="3" style="text-indent:2em" | 200(150)# keV| 22.7(5) h||| 7−||-| style="text-indent:1em" | 154m3Tb| colspan="3" style="text-indent:2em" | 0+Z keV| 513(42) ns|||||-| 155Tb| style="text-align:right" | 65| style="text-align:right" | 90| 154.923505(13)| 5.32(6) d| EC| 155Gd| 3/2+||-| rowspan=2|156Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 91| rowspan=2|155.924747(5)| rowspan=2|5.35(10) d| β+| 156Gd| rowspan=2|3−| rowspan=2||-| β− (rare)| 156Dy|-| style="text-indent:1em" | 156m1Tb| colspan="3" style="text-indent:2em" | 54(3) keV| 24.4(10) h| IT| 156Tb| (7−)||-| style="text-indent:1em" | 156m2Tb| colspan="3" style="text-indent:2em" | 88.4(2) keV| 5.3(2) h||| (0+)||-| 157Tb| style="text-align:right" | 65| style="text-align:right" | 92| 156.9240246(27)| 71(7) y| EC| 157Gd| 3/2+||-| rowspan=2|158Tb| rowspan=2 style="text-align:right" | 65| rowspan=2 style="text-align:right" | 93| rowspan=2|157.9254131(28)| rowspan=2|180(11) y| β+ (83.4%)| 158Gd| rowspan=2|3−| rowspan=2||-| β− (16.6%)| 158Dy|-| rowspan=3 style="text-indent:1em" | 158m1Tb| rowspan=3 colspan="3" style="text-indent:2em" | 110.3(12) keV| rowspan=3|10.70(17) s| IT (99.39%)| 158Tb| rowspan=3|0−| rowspan=3||-| β− (.6%)| 158Dy|-| β+ (.01%)| 158Gd|-| style="text-indent:1em" | 158m2Tb| colspan="3" style="text-indent:2em" | 388.37(15) keV| 0.40(4) ms||| 7−||-| 159Tb[2] | style="text-align:right" | 65| style="text-align:right" | 94| 158.9253468(27)| colspan=3 align=center|Stable| 3/2+| 1.0000|-| 160Tb| style="text-align:right" | 65| style="text-align:right" | 95| 159.9271676(27)| 72.3(2) d| β−| 160Dy| 3−||-| 161Tb| style="text-align:right" | 65| style="text-align:right" | 96| 160.9275699(28)| 6.906(19) d| β−| 161Dy| 3/2+||-| 162Tb| style="text-align:right" | 65| style="text-align:right" | 97| 161.92949(4)| 7.60(15) min| β−| 162Dy| 1−||-| 163Tb| style="text-align:right" | 65| style="text-align:right" | 98| 162.930648(5)| 19.5(3) min| β−| 163Dy| 3/2+||-| 164Tb| style="text-align:right" | 65| style="text-align:right" | 99| 163.93335(11)| 3.0(1) min| β−| 164Dy| (5+)||-| 165Tb| style="text-align:right" | 65| style="text-align:right" | 100| 164.93488(21)#| 2.11(10) min| β−| 165mDy| 3/2+#||-| 166Tb| style="text-align:right" | 65| style="text-align:right" | 101| 165.93799(11)| 25.6(22) s| β−| 166Dy|||-| 167Tb| style="text-align:right" | 65| style="text-align:right" | 102| 166.94005(43)#| 19.4(27) s| β−| 167Dy| 3/2+#||-| 168Tb| style="text-align:right" | 65| style="text-align:right" | 103| 167.94364(54)#| 8.2(13) s| β−| 168Dy| 4−#||-| 169Tb| style="text-align:right" | 65| style="text-align:right" | 104| 168.94622(64)#| 5.13(32) s| β−| 169Dy| 3/2+#||-| 170Tb| style="text-align:right" | 65| style="text-align:right" | 105| 169.95025(75)#| 960(78) ms| β−| 170Dy|||-| 171Tb| style="text-align:right" | 65| style="text-align:right" | 106| 170.95330(86)#| 1.23(10) s| β−| 171Dy| 3/2+#||-| 172Tb| style="text-align:right" | 65| style="text-align:right" | 107| | 760(190) ms| β−| 172Dy| 6+#|