Curium
Atomic Data
| Atomic Number | 96 |
| Symbol | Cm |
| Atomic Weight | 247 u |
| Density (STP) | 13.51 g/cm³ |
| Melting Point | 1339.85 °C (1613 K) |
| Boiling Point | 3109.85 °C (3383 K) |
| Electronegativity | 1.3 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f7 6s2 6p6 6d1 7s2 |
| Oxidation States | +3, +4 |
| Phase at STP | Solid |
| Category | Actinoid |
| Period / Group | 7 / None |
| CAS Number | 7440-51-9 |
Electron Configuration
[Rn] 5f7 6d1 7s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| O | 5 | 5f | 7 | 85 |
| P | 6 | 6s | 2 | 87 |
| P | 6 | 6p | 6 | 93 |
| P | 6 | 6d | 1 | 94 |
| Q | 7 | 7s | 2 | 96 |
| Total | 96 | 96 | ||
Isotopes of Curium
Curium has two naturally occurring stable isotopes. The most abundant is ²⁴⁴Cm, comprising None% of all naturally occurring Curium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Curium-244 | ²⁴⁴Cm | 96 | 148 | trace | Stable |
| Curium-247 | ²⁴⁷Cm | 96 | 151 | trace | Stable |
Abundance & Occurrence
Curium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Alpha radiation: Curium-244 (t½ = 18.1 years, alpha emitter) generates significant heat from radioactive decay: 2.8 W/g: creating both a radiation and thermal management hazard in larger quantities.
- Internal dose hazard: Curium concentrates in bone and liver; inhalation or ingestion of curium is acutely hazardous: handling requires negative-pressure glove boxes, air monitoring, and strict contamination controls.
- Neutron emission: Spontaneous fission of Cm-244 generates neutrons; shielding for both alpha and neutron radiation is required for bulk curium sources; dosimetry must include neutron dosimetry.
- Regulatory controls: Curium production and use are subject to nuclear regulatory licensing and safeguards; all sources must be inventoried and tracked under national and international controls.
Curium in the Real World
Real-World Uses
- Alpha particle X-ray spectrometers (APXS) on Mars rovers: Curium-244 (t½ = 18.1 yr) alpha sources on the APXS instruments of Sojourner, Spirit, Opportunity, Curiosity, and Perseverance Mars rovers irradiate rocks and soil with alpha particles and X-rays to determine elemental composition, characterising the geology of Mars.
- Thermoelectric power generation (research): Cm-244 generates heat through alpha decay at a specific power of approximately 2.8 W/g; it is studied as an alternative to Pu-238 for compact RTGs in scenarios where Pu-238 is unavailable, though its shorter half-life is a disadvantage for long missions.
- Production of californium: Cm-244 and Cm-248 irradiated in high-flux reactors (such as the High Flux Isotope Reactor at Oak Ridge) are the primary feedstock for producing californium-252, the most commercially important transuranium isotope.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is curium used for?
Curium-244 is used as an alpha-particle source in the Alpha Particle X-Ray Spectrometer (APXS) instruments on Mars rovers (including Pathfinder, Spirit, Opportunity, and Curiosity). The APXS bombards rock and soil samples with alpha particles and X-rays, and the resulting X-ray fluorescence pattern reveals the elemental composition of Martian rocks and soil. This is the primary practical application of curium.
Is curium extremely radioactive?
Yes, curium is intensely radioactive. Curium-244 (the most commonly produced isotope) has a half-life of 18.1 years and emits both alpha particles and spontaneous fission neutrons. It generates significant heat from its decay: enough to glow red-hot in the dark when a milligram-scale sample is assembled. All curium isotopes are radioactive, with half-lives ranging from fractions of a second to 15.6 million years (Cm-247).
How was curium discovered?
Curium was synthesised in 1944 by Glenn Seaborg, Ralph James, and Albert Ghiorso at the University of Chicago Metallurgical Laboratory. They bombarded plutonium-239 with helium ions (alpha particles) in a cyclotron to produce curium-242. The discovery was kept secret as part of the Manhattan Project until 1945. It was named after Pierre and Marie Curie in recognition of their pioneering research on radioactivity.
How does the APXS on Mars rovers use curium?
The APXS (Alpha Particle X-ray Spectrometer) on Mars rovers uses the alpha particles and X-rays emitted by curium-244 to probe the elemental composition of rocks. When these particles strike a surface, they excite atoms in the rock, which then emit characteristic X-ray fluorescence at energies specific to each element. A detector measures the energy spectrum of emitted X-rays, allowing scientists to identify which elements are present and in what proportions: essentially doing geochemistry on Mars remotely.