Berkelium preparation

Its stability then decreases progressively until we reach curium where aqueous solutions containing the tetra-positive state must be complexed by ligands such as fluoride or phosphotungstate. Even then, they oxidize water and revert to cur-ium(lll). The expected drop in I4 between curium and berkelium provides Bk" (aq) with a stability similar to that of Ce (aq), but the decrease in stability is then renewed, and beyond californium, the +4 oxidation state has not yet been prepared [2, 10, 15]. 

The actual situation with regard to the purity of most of the actinide metals is far from ideal. Only thorixun (99), uranium 11,17), neptunium 20), and plutonium 60) have been produced at a purity > 99.9 at %. Due to the many grams required for preparation and for accurate analysis, it is probable that these abundant and relatively inexpensive elements (Table I) are the only ones whose metals can be prepared and refined to give such high purities, and whose purity can be verified by accurate analysis. The purity levels achieved for some of the actinide metals are listed in Table II. For actinium (Ac), berkelium (Bk), californium (Cf),... 

This article presents a general discussion of actinide metallurgy, including advanced methods such as levitation melting and chemical vapor-phase reactions. A section on purification of actinide metals by a variety of techniques is included. Finally, an element-by-element discussion is given of the most satisfactory metallurgical preparation for each individual element actinium (included for completeness even though not an actinide element), thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. 

Americium, californium, and einsteinium oxides have been reduced by lanthanum metal, whereas thorium has been used as the reductant metal to prepare actinium, plutonium, and curium metals from their respective oxides. Berkelimn metal could also be prepared by Th reduction of Bk02 or Bk203, but the quantity of berkelium oxide available for reduction at one time has not been large enough to produce other than thin foils by this technique. Such a form of product metal can be very difficult to handle in subsequent experimentation. The rate and yield of Am from the reduction at 1525 K of americium dioxide with lanthanum metal are given in Fig. 2. 

Oxygenic photosynthetic organisms, [2Fe-2S] ferredoxins, 38 224-233 Oxygenyl ion, preparation of, 9 229 Oxyhalides, of berkelium, 28 49, 51-53 Oxyhalogeno cations, 9 276-279 Oxyhemerythrin, 40 373-374, 45 84 XAS, 36 325 Oxyhemocyanin, 40 363 m-peroxo dinuclear copper complexes as models for, 39 41-52 physicochemical properties, 39 47-48 Oxyhemocyanins, XAS, 36 326-327 Oxyhemoglobin, 21 135 Oxyiodonium cations, 9 277 Oxymanganese phthalocyanine, strucmre of, 7 31-35... 

The element berkelium was first prepared at the University of California at Berkeley in 1949 by a bombardment of Am. Two neutrons are also produced during the reaction. What isotope of berkelium results from this transmutation Write a balanced nuclear equation. 

The references given in Table I are those describing the preparation of a given compound the reference may or may not contain information on the behavior of the compound with time Note that the compounds have been synthesized in different oxidation states and different crystal structures where possible Not shown in the table are einsteinium, berkelium, and californium phosphates which have also been prepared and are being studied at present (11) ... 

The first bulk samples of berkelium metal were prepared in early 1969 by the reduction at about 1300 K of BkF3 with lithium metal vapor (119). The BkF3 samples were suspended in a tungsten wire spiral above a charge of Li metal in a tantalum crucible. A photomicrograph of the first isolated bulk (1.7 jug) sample of berkelium metal is shown in Fig. 7. 

Later berkelium metal samples of up to 0.5 mg each have been prepared via the same chemical procedure (120). Elemental berkelium can also be prepared by reduction of BkF4 with lithium metal and by reduction of Bk02 with either thorium or lanthanum metal. The latter reduction process is better suited to the preparation of thin metal foils unless multimilligram quantities of berkelium are available. 

During the handling of microgram-sized samples of berkelium metal, it was observed that the rate of oxidation in air at room temperature is not extremely rapid, possibly because of the formation of a protective oxide film on the metal surface (135). Berkelium is a chemically reactive metal, and berkelium hydride (123), some chalco-genides (123, 136, 137) and pnictides (138, 139) have been prepared directly from the reaction of Bk metal with the appropriate nonmetal-lic element. 

The berkelium monopnictides have been prepared on the multimicrogram scale by direct combination of the elements (138). In all cases, the lattice constants of the NaCl-type cubic structures were smaller than those of the corresponding curium monopnictides but comparable to those of the corresponding terbium compounds. This supports the semimetallic classification for these compounds. One additional report of BkN has appeared (139). The lattice parameter derived from the sample exhibiting a single phase was 0.5010 0.0004 nm, whereas that extracted from the mixed-phase sample of BkN resulting from incomplete conversion of a hydride was 0.4948 0.0003 nm. Clearly, additional samples of BkN should be prepared to establish more firmly its lattice constant. 

The only other crystallographic result reported for a berkelium chal-cogenide besides those summarized in Table II is a cubic lattice parameter of 0.844 nm for Bk2S3 (155). The microscale synthesis of the brownish-black sesquisulfide was carried out by treatment of berkelium oxide at 1400 K with a mixture of H2S and CS2 vapors. In later work (136,137), the higher chalcogenides were prepared on the 20- to 30-jug scale in quartz capillaries by direct combination of the elements. These were then thermally decomposed in situ to yield the lower chalcogenides. The stoichiometries of these compounds have not been determined directly. 

The preparation and characterization of intermetallic compounds and alloys of berkelium should be pursued, as well as the determination of the stability constants of Bk(IV) complexes. The range of oxidation states accessible to berkelium might be expanded by stabilizing Bk(II) and/or Bk(V) in highly complexing aqueous, nonaqueous, or even molten salt media and/or in appropriate solid-state matrices. 

The fermium, einsteinium, and berkelium are transferred from the main hot cells and are purified further and prepared for shipment in a small hot cell and in glove box facilities that are kept free from undesirable contaminants. The chemical processing (13) involves numerous additional cycles of ion exchange purification on the micro scale. 

Procedure. Aqueous phases were prepared from samples of cerium (IV), cerium (III), berkelium, and acid and diluted by distilled water to the proper concentrations. Samples of cerium were chosen in order to obtain dijSerent cerium (IV)/cerium (III) ratios. The solutions were allowed to stand for six hours to reach the oxidation equilibrium. A 2 cc. sample of the solvent was added to the same volume of aqueous solution and mixed for 15 minutes. After separation by a centrifuge, samples of both phases were taken for the beta counting of berkelium and the spectrophotometric determination of cerium (IV). In addition, one aliquot of the loaded solvent was taken for determining the distribution coefficient of berkelium (IV). 

Curium, berkelium, californium and einsteinium were separated from the americium samples irradiated by neutrons. For preliminary separation the anion exchange in hydrochloric acid and lithium chloride solutions was used as well as the HDEHP extraction. Mutual separation of the transamericium elements was made by using DIAION CK08Y cation exchange resin. Nuclides prepared and separation methods adopted are summarized in Table 1 (1-15). 

When these isotopes become available, chemical studies will be greatly simplified, and the complications introduced by the radioactivity of the actinide elements will be substantially minimized. The longest-lived isotopes of berkelium, californium, and einsteinium are still fairly short-lived substances, and macroscopic amounts have a tremendous associated radioactivity. Nevertheless, it should eventually be possible to prepare and study the solid halides of the actinide elements through the element einsteinium using weighable amounts of reactants. This remains for the future, however. The special experimental problems associated with highly radioactive substances are considered below. 

Although berkelium is available only in very small quantities, enough has been prepared to determine some stmctural parameters. 

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