Curium tracer

First, the trivalent actinide and lanthanide elements are separated from the other elements in the waste. In the second step, americium and curium are then separated from the lanthanide elements. Experimental studies have largely been laboratory-scale in which synthetic waste solutions and tracer levels of radioactivity were utilized. A few laboratory-scale experiments were made in hot cells on the coextraction of trivalent actinides and lanthanides. The two most promising methods investigated for co-removal of trivalent actinides and lanthanides are ... 

The main radionuclides that are measured in this system are isotopes of thorium, uranium, and plutonium. Others are the longer-lived isotopes of heavy elements such as radium, protactinium, neptunium, americium, and curium. Conventionally, an isotopic tracer of known activity that emits alpha particles is added at the beginning of the radiochemical procedure (see Section 6.3.2). The solution from which the sample for counting will be deposited is thoroughly purified by the radiochemical procedure to remove interfering radionuclides and solids. 

Beyond einsteinium, the amount of chemical information becomes increasingly sparse but significant dataware obtained in exploratory studies at the tracer scale (see, e.g., Silva 1986) for elements up to the last actinide element, lawrencium (103), and the first transactinide elements, rutherfordium (104) and dubnium (105). From curium on, the chemical properties... 

As mentioned above, a very important point is the presence of seven 5f electrons in stable tripositive curium (element 96), making this element very actinium-like. A series of thoride elements, e.g., would imply stable IV oxidation states in elements 95 and 96 and the presence of seven 5f electrons and the IV state almost exclusively in element 97. A series of this type seems to be ruled out by the now-known instability of americium in solution in the IV state and by the apparent non-existence in aqueous solution of any oxidation state other than III in curium. Moreover, the III state of uranium would be surprising on this basis, because this element would be the second member of a thoride, or IV oxidation state , series. The fact that nearly a year was spent in an unsuccessful effort to separate tracer amounts of americium and curium from the rare earths, immediately following the discovery of these two elements, illustrates how unnatural it would be to regard them as members of a thoride, or IV oxidation state, group. 

The X-ray techniques have limited applications in actinide systems because the high concentration required for the measurements (ca. 2-3 M) does not allow study of elements for which only isotopes of high specific radioactivity are available. Beitz (1991) calculated the hydration number of some curium complexes using luminescence lifetime measurements and assuming a hydration number of nine of the free ion. Electrophoretic measurements using tracer concentrations (Lundqvist 1981, Lundqvist et al. 1981) have provided estimates of the hydrated radii (r ) for Eu, Am, Cm, Es, Fm and Md from Stokes law. The hydrated radii were used, in turn, to calculate hydration numbers, h, by dividing the volume of the hydrated sphere by the volume of a water molecule (si 30 A ). Since the volume occupied by the bare metal ion is small [2-5 A for Ln(III) and An(III)], it was neglected in comparison with the volume of the water molecules. The results are listed in table 3. 

Many systems using either HDEHP or Aliquat 336 as the stationary phase have been studied for extraction chromatographic separation of americium tracer. An Aliquat 336 (nitrate-form)-kieselguhr system has been used recently both in the USA and in Europe to separate milligram to gram amounts of americium from curium [70, 71]. 

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]. 

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