Curium is a synthetic transuranic element produced and identified in 1944 by group of Glenn. T Seaborg. It is a radioactive element and is present in used nuclear fuel. Curium is used to make heavier actinides.
History and Discovery
Curium was synthesized by the team of Glenn. T Seaborg at University of California, Berkeley in 1944. It was produced by the bombardment of alpha particles on plutonium Pu-239 using the 60 inch cyclotron [1]. Due to on-going World War at that time, the discovery of curium was not announced to public until after the war, i.e. in November 1947. Curium was discovered before the lighter element americium making it the third transuranic element to be discovered. The sample of curium isolated by the group of Glenn T Seaborg was barely visible and was identified only by its radioactivity. The first sample in ample amount was created by Louis Werner and Isadore Perlman in 1947. The sample was made by bombarding americium with neutrons. Curium was made in metallic form in 1951. Curium was named after the discoverers of radioactivity, i.e. Madam Marie Curie and Pierre Curie, following the naming of the element above curium in the periodic table, gadolinium (belongs to lanthanide series of periodic table), which was named after the discoverer of rare earth elements.
Curium
| Periodic Table Classification | Group n/a Period 7 |
|---|---|
| State at 20C | Solid |
| Color | Silvery metallic, glows purple in the dark |
| Electron Configuration | [Rn] 5f7 6d1 7s2 |
| Electron Number | 96 |
| Proton Number | 96 |
| Electron Shell | 2, 8, 18, 32, 25, 9, 2 |
| Density | 13.50 g.cm-3 at 20°C |
| Atomic number | 96 |
| Atomic Mass | 247.00 g.mol -1 |
| Electronegativity according to Pauling | 1.30 |
Occurrence
Curium is a synthetic radioactive element that was first produced in laboratory. It can be found in spent nuclear fuel. It is present in nature in areas where nuclear tests were conducted. Curium isotopes, curium-245, curium-246, curium-247, curium-248 and curium-249, were found at the testing site of hydrogen bomb in U.S. It also occurred naturally in natural nuclear fission reactor at Oklo. Curium is formed in nuclear reactors in a series of nuclear reactions from uranium-238. For research purposes it is obtained by irradiating plutonium.
Physical Characteristics
Curium is dense hard metal that appears silvery white in colour. It belongs to actinide series of the periodic table. Its physical and chemical properties resembles to the element above it in lanthanide series. It has high melting point of 1340 degree centigrade. It is less dense than its preceding transuranic element but heavier than most other metals. Curium shows an increase in electrical resistivity with the increase in temperature. It is represented by symbol Cm and has atomic number 96.
Chemical Characteristics
Curium is a highly radioactive element and can be isolated in pure or elemental form. Curium readily oxidizes forming oxides. The most stable oxidation state for curium is +3 [2]. Curium ion forms most stable complexes with hard bases. Chemical behaviour of curium resembles americium and many lanthanides.
Significance and Uses
- Curium is used in alpha particle X-ray spectrometers (which are used in space probes to analyse the structure and composition of the surface) as a source of alpha particles.
- Curium is used to produce heaver actinides.
- Pu-238 is also produced from curium which in turn is used to make artificial pace makers [3].
Health Effects
Because of its high radioactivity curium should be handled with care. Curium if consumed or inhaled can eventually accumulate in bones, liver and lungs where its radioactive decay will cause cancer in human body. Its radiation destroys bone marrow preventing red blood cell production. Curium should be neutralized from the spent nuclear fuel before its disposal because of its hazards.
Isotopes of Curium
Curium has 20 known radioisotopes with no stable isotope. Amongst the isotopes of curium, curium-247 has the longest half-life, having a half-life of 15.6 million years. The relatively short half-life of curium isotope indicates any primordial curium would have decayed by now [4]. The presence of curium that would have existed and decayed can be detected by the abundance of its nearly stable daughter U-235 (an isotope of uranium). Curium isotopes exist between mass number 233 and 252. Curium-250 is a distinct isotope as it primarily decays via spontaneous fission .
REFERENCES
[1]. Seaborg, Glenn T.; James, R. A.; Ghiorso, A. (1949). “The New Element Curium (Atomic Number 96)” (PDF). NNES PPR (National Nuclear Energy Series, Plutonium Project Record). The Transuranium Elements: Research Papers, Paper No. 22.2. McGraw-Hill Book Co., Inc., New York,. 14 B
[2]. Domanov, V. P.; Lobanov, Yu. V. (October 2011). “Formation of volatile curium(VI) trioxide CmO3“. Radiochemistry. SP MAIK Nauka/Interperiodica. 53 (5): 453–6.
[3]. Hall, Nina (2000). The New Chemistry: A Showcase for Modern Chemistry and Its Applications. Cambridge University Press. pp. 8–9
[4]. Emsley, John (2011). Nature’s Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press