Curium
This article is about the chemical element Curium; for the ancient city also called Curium (located in Cyprus), see KourionCurium is a
synthetic element in the
periodic table that has the symbol
Cm and
atomic number 96. A
radioactive metallic
transuranic element of the
actinide series, curium is produced by bombarding
plutonium with
alpha particles (
helium ions) and was named for
Marie Curie and her husband
Pierre.
The
isotope curium-248 has been synthesized only in milligram quantities, but curium-242 and curium-244 are made in multigram amounts, which allows for the determination of some of the element's properties. Curium-244 can be made in quantity by subjecting
plutonium to
neutron bombardment. Very small amounts of curium may exist in
uranium ore as a daughter product of natural decay. There are few commercial applications for curium but it may one day be useful in radioisotope thermoelectric generators. Curium
bio-accumulates in
bone tissue where its radiation destroys
bone marrow and thus stops
red blood cell creation.
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 . Curium-242 can generate up to 120
watts of thermal
energy per gram (W/g); its very short half-life though makes it undesirable as a power source for long-term use. Curium-242 is the precursor 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.
Compounds include: curium dioxide (Cm
O2), curium trioxide (Cm
2O
3), curium bromide (Cm
Br3), curium chloride (Cm
Cl3), curium tetrafluoride (Cm
F4) and curium iodide (Cm
I3).
Curium was
first synthesized at the
University of California, Berkeley by
Glenn T. Seaborg, Ralph A. James, and
Albert Ghiorso in
1944. The team named the new element after
Marie Curie and her husband
Pierre who are famous for discovering
radium and for their work in
radioactivity. It was chemically identified at the Metallurgical Laboratory (now
Argonne National Laboratory) at the
University of Chicago. It was actually the third transuranium element to be discovered even though it is the second in the series. Curium-242 (
half-life 163 days) and one
free neutron were made by bombarding
alpha particles onto a
plutonium-239 target in the 60-inch
cyclotron at Berkeley. Louis Werner and Isadore Perlman created a visible sample of curium-242
hydroxide at the
University of California in
1947 by bombarding
americium-241 with neutrons. Curium was made in its elemental form in
1951 for the first time.
19
radioisotopes of curium have been characterized, with the most stable being Cm-247 with a
half-life of 1.56 × 10
7 years, Cm-248 with a half-life of 3.40 × 10
5 years, Cm-250 with a half-life of 9000 years, and Cm-245 with a half-life of 8500 years. All of the remaining
radioactive isotopes have half-lifes that are less than 30 years, and the majority of these have half lifes that are less than 33 days. This element also has 4
meta states, with the most stable being Cm-244m (t
½ 34 ms). The isotopes of curium range in
atomic weight from 233.051
u (Cm-233) to 252.085 u (Cm-252).
The
MOX which is to be used in power reactors should contain little or no curium as the neutron activation of this element 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.
*
Los Alamos National Laboratory - Curium*
Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
*
It's Elemental - Curium*
Human Health Fact Sheet on Curium*
WebElements.com - Curium
