Fermium
Fermium is a synthetic, highly radioactive metal discovered alongside einsteinium in the fallout of the first hydrogen bomb test. It marks a turning point in how elements are made — everything heavier than fermium has had to be built by fusing two smaller nuclei together, rather than by simple neutron bombardment.
- Group · Period
- — · 7
- At room temp
- solid
- Melts at
- 1800 K
- Density
- Not yet available
- Discovered
- 1952
Uses
Fermium has no practical use outside of research. Like its neighbors on the periodic table, it’s made in quantities far too small and decays far too quickly to serve any commercial or industrial purpose. Its significance is almost entirely historical and scientific: it marks the practical limit of building elements through neutron bombardment, a technique that worked well for lighter transuranic elements but breaks down at this mass.
History
Fermium was discovered in the same radioactive debris from the 1952 Ivy Mike hydrogen bomb test that revealed einsteinium, produced when the explosion’s intense neutron flux was absorbed by uranium nuclei in rapid succession. As with einsteinium, the discovery was kept classified because of its ties to a weapons test, and it wasn’t announced to the public until 1955. It was named after Enrico Fermi, one of the towering figures of 20th-century nuclear physics.
Fun facts
- Fermium was discovered in the same 1952 hydrogen bomb debris as einsteinium, but its discovery wasn't announced until 1955 for security reasons.
- It's the last element that can be created by bombarding lighter atoms with neutrons — every element heavier than fermium has been made instead by fusing two nuclei directly together.
- It's named after Enrico Fermi, who built the world's first artificial nuclear reactor.
Frequently asked questions
Does fermium have any practical use?
No, fermium has no commercial or industrial application. It exists solely as a subject of nuclear physics and chemistry research, used to study how the actinide series behaves as it nears its end.
Why can't fermium be made by neutron bombardment, but everything before it can?
Building heavier elements by repeatedly adding neutrons to a nucleus works only as long as each intermediate isotope lives long enough to absorb another neutron before decaying. Just past fermium, the isotopes involved become too short-lived or too prone to fission for that chain to continue, so scientists switched to fusing two smaller nuclei together instead.
Who is fermium named after?
Enrico Fermi, the physicist who led the team that built Chicago Pile-1, the first human-made nuclear reactor, and whose work underpinned much of the nuclear science that followed.
Isotopes
19 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Fm-252 | — | 25.39 h | Alpha decay (99.9977%), Spontaneous fission (0.0023%) | 76,816.61 keV | 7,456.04 keV | 4.99 × 10-21 eV |
| Fm-253 | — | 3.00 d | Electron capture (88%), Alpha decay (12%) | 79,345.55 keV | 7,448.47 keV | 1.76 × 10-21 eV |
| Fm-257 | — | 100.5 d | Alpha decay (99.79%), Spontaneous fission (0.21%) | 88,590.14 keV | 7,422.19 keV | 5.25 × 10-23 eV |
Show all 19 isotopes
| Fm-241 | — | 0.73 ms | Spontaneous fission (78%), Alpha decay (14%), Electron capture (12%) | 69,220 keV | 7,459 keV | 6.25 × 10-13 eV |
| Fm-242 | — | 0.8 ms | Spontaneous fission (100%) | 68,400 keV | 7,465 keV | 5.70 × 10-13 eV |
| Fm-243 | — | 231 ms | Alpha decay (91%), Electron capture / beta-plus decay (10%), Spontaneous fission (9%) | 69,316 keV | 7,464 keV | 1.98 × 10-15 eV |
| Fm-244 | — | 3.12 ms | Spontaneous fission (97%), Electron capture (2%), Alpha decay (1%) | 68,964 keV | 7,468 keV | 1.46 × 10-13 eV |
| Fm-245 | — | 4.2 s | Alpha decay (100%) | 70,192 keV | 7,465 keV | 1.09 × 10-16 eV |
| Fm-246 | — | 1.54 s | Alpha decay (93.2%), Spontaneous fission (6.8%), Electron capture (1.3%) | 70,191.19 keV | 7,467.96 keV | 2.96 × 10-16 eV |
| Fm-247 | — | 31 s | Alpha decay (64%), Electron capture / beta-plus decay (36%) | 71,672 keV | 7,464 keV | 1.47 × 10-17 eV |
| Fm-248 | — | 34.5 s | Alpha decay (95%), Electron capture (5%), Spontaneous fission (0.1%) | 71,897.79 keV | 7,465.95 keV | 1.32 × 10-17 eV |
| Fm-249 | — | 2.6 m | Electron capture / beta-plus decay (67%), Alpha decay (33%) | 73,519.14 keV | 7,461.86 keV | 2.92 × 10-18 eV |
| Fm-250 | — | 30 m | Alpha decay (90%), Electron capture (10%), Spontaneous fission (0.0069%) | 74,072.19 keV | 7,462.09 keV | 2.53 × 10-19 eV |
| Fm-251 | — | 5.30 h | Electron capture / beta-plus decay (98.2%), Alpha decay (1.8%) | 75,958.81 keV | 7,457 keV | 2.39 × 10-20 eV |
| Fm-254 | — | 3.240 h | Alpha decay (99.9408%), Spontaneous fission (0.0592%) | 80,902.52 keV | 7,444.79 keV | 3.91 × 10-20 eV |
| Fm-255 | — | 20.07 h | Alpha decay (100%), Spontaneous fission (0.000024%) | 83,800.47 keV | 7,435.89 keV | 6.31 × 10-21 eV |
| Fm-256 | — | 157.1 m | Spontaneous fission (91.9%), Alpha decay (8.1%) | 85,484.8 keV | 7,431.79 keV | 4.84 × 10-20 eV |
| Fm-258 | — | 370 us | Spontaneous fission (100%) | 90,426 keV | 7,418 keV | 1.23 × 10-12 eV |
| Fm-259 | — | 1.5 s | Spontaneous fission (100%) | 93,704 keV | 7,407 keV | 3.04 × 10-16 eV |