鐨的同位素
圖表

| 符號 | Z> 激發能量 | N> 激發能量 | 同位素質量（u） > 激發能量 | 半衰期 | 衰變方式 | 衰變產物 | 原子核 自旋 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 241Fm | 100 | 141 | 241.07421(32)# | 730(60) µs | SF(>78%) | (various) | 5/2#+ |
| 241Fm | 100 | 141 | 241.07421(32)# | 730(60) µs | α (<14%) | 237Cf | 5/2#+ |
| 242Fm | 100 | 142 | 242.07343(43)# | <4 μs | SF | (various) | 0+ |
| 243Fm | 100 | 143 | 243.07447(23)# | 231(9) ms | α (91%) | 239Cf | 7/2−# |
| 243Fm | 100 | 143 | 243.07447(23)# | 231(9) ms | SF (9%) | (various) | 7/2−# |
| 243Fm | 100 | 143 | 243.07447(23)# | 231(9) ms | β+ （不常見） | 243Es | 7/2−# |
| 244Fm | 100 | 144 | 244.07404(22)# | 3.12(8) ms | SF (99%) | (various) | 0+ |
| 244Fm | 100 | 144 | 244.07404(22)# | 3.12(8) ms | α (1%) | 240Cf | 0+ |
| 245Fm | 100 | 145 | 245.07535(21)# | 4.2(13) s | α (95.7%) | 241Cf | 1/2+# |
| 245Fm | 100 | 145 | 245.07535(21)# | 4.2(13) s | β+ (4.2%) | 245Es | 1/2+# |
| 245Fm | 100 | 145 | 245.07535(21)# | 4.2(13) s | SF (.13%) | (various) | 1/2+# |
| 246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | α (85%) | 242Cf | 0+ |
| 246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | β+ (10%) | 246Es | 0+ |
| 246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | β+, SF (10%) | (various) | 0+ |
| 246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | SF (4.5%) | (various) | 0+ |
| 247Fm | 100 | 147 | 247.07695(12)# | 31(1) s | α (>50%) | 243Cf | (7/2+) |
| 247Fm | 100 | 147 | 247.07695(12)# | 31(1) s | β+ (<50%) | 247Es | (7/2+) |
| 248Fm | 100 | 148 | 248.077186(9) | 35.1(8) s | α (93%) | 244Cf | 0+ |
| 248Fm | 100 | 148 | 248.077186(9) | 35.1(8) s | β+ (7%) | 248Es | 0+ |
| 248Fm | 100 | 148 | 248.077186(9) | 35.1(8) s | SF (.10%) | (various) | 0+ |
| 249Fm | 100 | 149 | 249.078928(7) | 1.6(1) min | β+ (85%) | 249Es | (7/2+)# |
| 249Fm | 100 | 149 | 249.078928(7) | 1.6(1) min | α (15%) | 245Cf | (7/2+)# |
| 250Fm | 100 | 150 | 250.079521(9) | 30.4(15) min | α (90%) | 246Cf | 0+ |
| 250Fm | 100 | 150 | 250.079521(9) | 30.4(15) min | ε (10%) | 250Es | 0+ |
| 250Fm | 100 | 150 | 250.079521(9) | 30.4(15) min | SF (6.9×10−3%) | (various) | 0+ |
| 250mFm | 1199.2(10) keV | 1199.2(10) keV | 1199.2(10) keV | 1.92(5) s | IT | 250Fm | (8−) |
| 251Fm | 100 | 151 | 251.081540(16) | 5.30(8) h | β+ (98.2%) | 251Es | (9/2−) |
| 251Fm | 100 | 151 | 251.081540(16) | 5.30(8) h | α (1.8%) | 247Cf | (9/2−) |
| 251mFm | 200.09(11) keV | 200.09(11) keV | 200.09(11) keV | 21.1(16) µs |  |  | (5/2+) |
| 252Fm | 100 | 152 | 252.082467(6) | 25.39(4) h | α (99.99%) | 248Cf | 0+ |
| 252Fm | 100 | 152 | 252.082467(6) | 25.39(4) h | SF (.0023%) | (various) | 0+ |
| 253Fm | 100 | 153 | 253.085185(4) | 3.00(12) d | ε (88%) | 253Es | (1/2)+ |
| 253Fm | 100 | 153 | 253.085185(4) | 3.00(12) d | α (12%) | 249Cf | (1/2)+ |
| 254Fm | 100 | 154 | 254.0868544(30) | 3.240(2) h | α (99.94%) | 250Cf | 0+ |
| 254Fm | 100 | 154 | 254.0868544(30) | 3.240(2) h | SF (.0592%) | (various) | 0+ |
| 255Fm | 100 | 155 | 255.089964(5) | 20.07(7) h | α | 251Cf | 7/2+ |
| 255Fm | 100 | 155 | 255.089964(5) | 20.07(7) h | SF (2.4×10−5%) | (various) | 7/2+ |
| 256Fm | 100 | 156 | 256.091774(8) | 157.6(13) min | SF (91.9%) | (various) | 0+ |
| 256Fm | 100 | 156 | 256.091774(8) | 157.6(13) min | α (8.1%) | 252Cf | 0+ |
| 257Fm | 100 | 157 | 257.095106(7) | 100.5(2) d | α (99.79%) | 253Cf | (9/2+) |
| 257Fm | 100 | 157 | 257.095106(7) | 100.5(2) d | SF (.21%) | (various) | (9/2+) |
| 258Fm | 100 | 158 | 258.09708(22)# | 370(14) µs | SF | (various) | 0+ |
| 259Fm | 100 | 159 | 259.1006(3)# | 1.5(3) s | SF | (various) | 3/2+# |
| 260Fm | 100 | 160 | 260.10281(55)# | 4 ms |  |  | 0+ |
1 2  畫上#號的數據代表沒有經過實驗的証明，僅為理論推測。
1 2 3  用括號括起來的數據代表不確定性。
↑  Heaviest nuclide produced via neutron capture
↑  Discovery of this isotope is unconfirmed
↑  Not directly synthesized, occurs as decay product of 260Md
| 0 | 1 | 2 |
| --- | --- | --- |

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