Curium

Electrochemical studies of curium are mostly limited to radiopolarography 

Lobanov et al. electroplated curium (ultimately converted to Cm02) in a series of electrodeposition steps from solutions of curium nitrate in isobutanol [158]. The electrochemical setup consisted of a Ti foil cathode, Ti or At foil anode, potential difference of 600 V, and a plating time of 10-15 min for each plating step. Between each deposition step the deposited curium was converted to Cm02. The multistep procedure allowed targets of curium with the desired thickness (300-400 pg cm ) to be obtained with a deposition yield of no less than 90%. Ramaswami and coauthors electroplated curium from isopropanol solution [159]. A 100 pL aliquot 

A common method for the electrodeposition of Am is from isopropanol solutions containing small quantities of dilute acid stock solutions of Am ions. Aqueous deposition methods have also been employed, but the organic electrolyte medium is more advantageous in that it tends to produce more uniform coatings [151[. Zhi etal. prepared relatively thick targets of Am from a mixture of isopropanol and dilute (0.1 N) nitric acid stock solutions pf [152]. The electrolysis 

There have been no solubility data reported for americium(VI) oxide/hydroxide phases or stability data for hydrolysis species. 

The thermodynamic values derived for americium phases and hydrolysis species are listed in Table 9.23. Again, data are given for all oxidation states of americium. 

Also given in the table are values for the thermodynamic parameters for Am and Am02, as listed by Guillaumont et al. (2003). The thermodynamic data derived in this review are also compared with those given by Guillaumont et al. (2003). 

Curium has a number of relatively long-lived isotopes, with the longest being Cm with a half-life of about 16 million years. Hydrolysis and solubility constant data are only available for trivalent curium. 

Two studies have reported solubility constants for Cm(OH)3(s) (Fanghanel et al., 1994 Morss and Williams, 1994), and the two values reported are in very good agreement. For reaction (2.13) (M = Cm, x = 0), the average of the two reported values has been retained  

---

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

In the actinides, the element curium, Cm, is probably the one which has its inner sub-shell half-filled and in the great majority of its compounds curium is tripositive, whereas the preceding elements up to americium, exhibit many oxidation states, for example -1-2, -1-3. -1-4, -1-5 and + 6, and berkelium, after curium, exhibits states of -1- 3 and -E 4. Here then is another resemblance of the two series. 

Thiols have a marked ten dency to bond to mercury and the word mercaptan comes from the Latin mer curium captans which means seizing mercury The drug dimercaprol is used to treat mercury and lead poisoning It IS 2 3 dimercapto 1 propanol... 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

Most chemical iavestigations with plutonium to date have been performed with Pu, but the isotopes Pu and Pu (produced by iatensive neutron irradiation of plutonium) are more suitable for such work because of their longer half-Hves and consequendy lower specific activities. Much work on the chemical properties of americium has been carried out with Am, which is also difficult to handle because of its relatively high specific alpha radioactivity, about 7 x 10 alpha particles/(mg-min). The isotope Am has a specific alpha activity about twenty times less than Am and is thus a more attractive isotope for chemical iavestigations. Much of the earher work with curium used the isotopes and Cm, but the heavier isotopes... 

In general, the absorption bands of the actinide ions are some ten times more intense than those of the lanthanide ions. Fluorescence, for example, is observed in the trichlorides of uranium, neptunium, americium, and curium, diluted with lanthanum chloride (15). 

EXTRACTANT CONCENTRATION GRADIENT IN THE AMERICIUM(III) / CURIUM(III) SEPARATION BY COUNTERCURRENT CHROMATOGRAPHY... 

---