Curium is intensely radioactive; it is about 3,000 times as radioactive as radium. It is also very toxic when absorbed into the body because it accumulates in the bones and disrupts the formation of red blood cells. Curium-242 and curium-244 are used in the space program as a heat source (from the heat they generate as they undergo radioactive decay) for compact thermionic and thermoelectric power generation.
Curium has not been found to occur naturally; it was the third transuranium element to be synthesized. Curium was first produced by the bombardment of plutonium-239 with alpha particles in a cyclotron at the Univ. of California at Berkeley. Identified in 1944 by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso, it was named for Pierre and Marie Curie, the noted pioneers in the study of radioactivity. The metal was first isolated in visible amounts as the hydroxide by L. B. Werner and I. Perlman in 1947.
A rare earth homolog, curium is somewhat chemically similar to gadolinium but with a more complex crystal structure. Chemically reactive, its metal is silvery-white in color and the element is more electropositive than aluminium (most trivalent curium compounds are slightly yellow).
Curium has been studied greatly as a potential fuel for radioisotope thermoelectric generators (RTG). Curium-242 can generate up to 120 watts of thermal energy per gram (W/g); however, its very short half-life makes it undesirable as a power source for long-term use. Curium-242 can decay by alpha emission to plutonium-238 which is the most common fuel for RTGs. Curium-244 has also been studied as an energy source for RTGs having a maximum energy density ~3 W/g, but produces a large amount of neutron radiation from spontaneous fission. Curium-243 with a ~30 year half-life and good energy density of ~1.6 W/g would seem to make an ideal fuel, but it produces significant amounts of gamma and beta radiation from radioactive decay products.
|Thermal neutron cross sections|
|LEU spent fuel 20 years after 53 MWd/kg burnup|
|3 common isotopes||51||3700||390|
|Fast reactor MOX fuel (avg 5 samples, burnup 66-120GWd/t)|
|Total curium 3.09%||27.64%||70.16%||2.166%||0.0376%||0.000928%|
The odd-mass number isotopes are fissile, the even-mass number isotopes are not and can only neutron capture, but very slowly. Therefore in a thermal reactor the even-mass isotopes accumulate as burnup increases.
The MOX which is to be used in power reactors should contain little or no curium as the neutron activation of 248Cm will create californium which is a strong neutron emitter. The californium would pollute the back end of the fuel cycle and increase the dose to workers. Hence if the minor actinides are to be used as fuel in a thermal neutron reactor, the curium should be excluded from the fuel or placed in special fuel rods where it is the only actinide present.