Curium has a few long-lived isotopes, some of which are strong a-emitters (particularly 242Cm and 244Cm). Their formation in U-Pu nuclear fuel, there­fore, increases the radiotoxicity of the waste. How­ever, even after a few years of irradiation at burnups >100 GWdton—1, the total Cm concentration in MOX was observed to be very low, ^10—3 at.%.228 In this scenario, the rare literature studies on Cm carbides have an essentially academic profile.

The substantially covalent (a) Cm-C bonding in gaseous curium-carbon complexes obtained by laser metal-polymer coablation was studied in the late 1990s.229

More recently, Radchenko et a/.230 prepared the first samples of curium carbides by high-vacuum high-temperature condensation of metallic 244Cm onto an iridium support coated with amorphous car­bon. Cm2C3 and Cm3C, isostructural to Am2C3 and Sm3C, respectively, were identified by XRD. Cm2C3 has a bcc crystal lattice of the 143d space group with a = 839.04 ± 0.05 pm. Cm3C has fcc Fe4N-like lattice (already observed for some lanthanides) with a = 517.2 ± 0.2 pm.

Since no other carbides were detected at any carbon concentration, these authors concluded that Cm2C3 and Cm3C are the only existing Cm carbides.