Berkelium separation

Berkelium may be purified by many methods that are also applicable to other actinide elements. Therefore, only those methods that specifically apply to berkelium separation and purification will be treated here. 

For additional discussion of berkelium separation procedures, the reader is referred to several reviews and comprehensive texts on the subject (51-58). 

The purification procedures outlined above provide separation of berkelium from all trivalent lanthanides and actinides with the notable exception of cerium. Since berkelium and cerium exhibit nearly identical redox behavior, most redox separation procedures include a Bk-Ce separation step (21, 27, 37-41). Separation of Bk(III) from Ce(III) and other trivalent lanthanide and actinide elements can also be accomplished without the use of redox procedures (37, 39-47). 

An innovative procedure for the rapid separation of berkelium from other actinides, lanthanides, and fission products has been reported... 

This collection of the state-of-the-art papers emphasizes the continuing importance of industrial-scale production, separation, and recovery of transplutonium elements. Americium (At. No. 95) and curium (At. No. 96) were first isolated in weighable amounts during and immediately after World War II. Berkelium and californium were isolated in 1958 and einsteinium in 1961. These five man-made elements, in each case, subsequently became available in increasing quantities. 

The separation column effluent is divided into about 15 fractions that are collected in small (250-mL) polyethylene bottles. The volume collected in each bottle is determined by the appearance of the alpha-emitting elements in the column effluent solution as indicated by the response from the flowthrough alpha detector a typical response curve is shown in Fig. 2. Normally/ two einsteinium fractions/ two intermediate fractions/ and three californium fractions are collected. The intermediate fractions are taken when the valley between the einsteinium and californium peaks occurs on the response curve and usually contain less than 5% of each element. Sometimes the alpha trace will show a small fermium peak just ahead of the einsteinium/ but usually there is not enough fermium alpha to make a response and the fermium is assumed to be in one or both of the two fractions taken just prior to the einsteinium. The berkelium is primarily a beta emitter and is not detected by either the alpha or neutron detectors thus, three fractions are usually taken after the californium alpha peak to isolate the berkelium. If there is a significant amount of 244Cm he feed (milligram quantities)/ the alpha trace will show a third major peak when americium and curium are eluted at the end of the run. 

Because of its promise, the pressurized ion exchange approach was applied immediately to transcurium element production at TRU, and Fig. 2 indicates the sort of separation that was obtained. This shows the relative alpha count rate given by an in-line detector, and it demonstrates good separation of Fm, Es, Cf, and Cm. Berkelium is also well separated, appearing between Cf and Cm, but it is not shown because it is not an alpha-emitter. 

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). 

Many of the actinoids are also separated by exploiting their redox behavior. Thorium is exclusively tetravalent and berkelium is chemically similar to cerium, so iodate precipitation of Th and extraction of Bk(IV) with bis(2-ethylhexyl)orthophos-phoric acid (HDEHP) are used to isolated these elements. The differing stabilities of the (III), (IV), (V), and (VI) states of U, Np, and Pu have be exploited in precipitation and solvent extraction separations of these elements from each other and from fission product and other impurities with which they are found. Because of its technical importance, the process chemistry to separate U and Pu in nuclear materials has been highly developed. Extraction of Bk(IV) with HDEHP is used to separate Bk from neighbouring elements. 

Plutonium is manufactured in megagram quantities neptunium, americium, and curium in kilogram quantities californium in gram amounts berkelium in 100-milligram amounts and einsteinium in milligram quantities. Chemical separations play a key role in the manufacture of actinide elements, as well as in their recovery, and analysis in the nuclear fuel cycle. This collection of timely and state-of-the-art topics emphasizes the continuing importance of actinide separations processes. 

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). 

The actinides, such as californium or berkelium, can be separated by a method which had been used successfully to separate the rare earth elements. It is known as the ion exchange absorption-elution method, a complicated name for something very simple. It can be demonstrated with other... 

The actual apparatus used to separate berkelium from californium, for example, is a dark column of resin surrounded by a glass jacket which serves merely to contain a vapor that warms the column so the process will go on faster at a high temperature. 

Ion-exchange chromatography is generally used for the separation of the transplutonium elements (americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, lawren-cium). Determinations are usually made directly by a-spectrometry with solid-state detectors. Some elements (americium, curium, berkelium, californium) also have long-lived isotopes and can be determined by chemical methods such ultraviolet-visible spectrophotometry. 

To identify the new nuclide, a rapid cation-exchange separation technique using ammonium citrate as an eluant was employed. Early experiments indicated that element 97 had two oxidation states 3+ and 4+. The actinide concept provided the guidance to search for these two oxidation states, by analogy with the homolog element, terbium (Tb). The chemically separated samples were subjected to the measurement of radiation. Characteristic Cm X-rays associated with the electron capture (EC) decay and low-intensity a particles with a half-life of 4.5 h were detected. Berkelium was named after the city of Berkeley, California where it was discovered, just as the name terbium derived from Ytterby, Sweden. 

As was the case for the previously discovered transuranium elements, element 97 was first produced via a nuclear bombardment reaction. In December 1949 ion-exchange separation of the products formed by the bombardment of Am with accelerated alpha particles provided a new electron-capture activity eluting just ahead of curium [1,2]. This activity was assigned to an isotope (mass number 243) of element 97. The new element was named berkelium after Berkeley, California, the city of its discovery, in a parallel manner to the naming of its lanthanide analog, terbium, after Ytterby, Sweden. The initial investigations of the chemical properties of berkelium were limited to tracer experiments (ion exchange and co-precipitation), but these were sufficient to establish the stability of Bk(iii) and the accessibility of Bk(iv) in aqueous solution and to estimate the electrochemical potential of the Bk(iv)/Bk(iii) couple [2,3]. 

Separation and purification Table 10.1 Nuclear properties of berkelium isotopes. 

Since berkelium can be readily oxidized to Bk(iv), it can be separated from other, non-oxidizable transplutonium elements by combining oxidation-... 

A procedure for the rapid separation of berkelium from other actinides, lanthanides, and fission products was developed in order to measure the decay properties of short-lived isotopes [54]. Bk and Ce were separated from other elements using solvent extraction with HDEHP followed by cation-exchange high-pressure liquid chromatography (HPLC) using a-hydroxyisobutyrate as the eluant. The elution curve, showing a clean separation of Bk from Ce, is shown in... 

Fig. 10.2. The total separation time was reported to be 8 min. The fast separation of berkelium from beryllium foil targets and gold catcher foils has been published [55].

A )8-diketonate compound of Bk(iii) has been prepared and reported to be stable when volatilized. The possibility of using this volatile compound in transport and subsequent separation of berkelium from other actinides has been proposed [177]. 

Knauer, J. B. and Weaver, B. (1968) Separation of Berkelium from Trivalent Actinides by Chromate Oxidation and HDEHP Extraction, US Atomic Energy Commission Document ORNL-TM-2428, Oak Ridge National Laboratory. 

For basic studies on weighable quantities of californium, the Cf isotope is used. Its alpha half-life of 351 4 years [2,3] makes it suitable for chemical/physical experiments, where weighable quantities of californium are required. The Cf isotope is available as an isotopically pure material from the decay of Bk (beta emitter, half-life of 320 days), the latter being the major berkelium isotope obtained from reactors ( Bk is also formed, but it has a 3.5 h half-life). To obtain Cf free of other californium isotopes, it is first necessary to separate berkelium chemically from the californium produced in a reactor, and then permit the Bk to decay to Cf, which can subsequently be chemically separated from the berkelium. Currently, up to 60 mg per year of Bk are produced in the HFIR at ORNL, which is sufBdent to provide multi-milligram amounts of Cf [4]. The only other known production of Bk, and hence isotopically pure Cf (excluding the use of a mass separator), is in the USSR. The quantity of these materials available in the USSR is believed to be less than that produced by the HFIR. 

It is also useful to note that berkelium and californium can be readily separated by extracting Bk(iv) away from Cf(m). This separation is important since isotopically pure is obtained from the beta decay of Bk. The Bk(iv) can be generated by oxidizing Bk(m) with a strong oxidant (NaBr03) in nitric acid solution. 

The citrate ion was the eluting agent used in the first isolation of berkelium and californium [189,190]. Soon afterwards, however, the lactate and tartrate ions were found to give considerably improved separations between americium(iii) and curium (ill) [191]. Lactate elution also proved superior to the classic citrate elution for the first isolation of einsteinium and fermium [188]. Later on, an even more selective eluant for actinide(iii) ions has been found in the a-hydroxyisobutyrate ion [192], With this ligand, very clean separations of the heavy actinide(iii) ions can be achieved, as illustrated in Fig. 21.12. The first isolation of mendelevium was achieved by this procedure [193]. 

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