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ULTRAFAST CHEMICAL SEPARATIONS
irradiation. This procedure used the fact that the resin will not hold element 104 as strongly as the actinides. Similarly, short-lived mendelevium [Ghi55] has also been separated in a few minutes after irradiation from the recoil products collected from the target.
Figure 2.Elution of lanthanides from a Dowex-50 X-12 column (5 cm × 0.2 cm) with α-hydroxyisobutyric acid at 87°C. [Cho56b; reprinted with permission fromJ. Inorg. Nucl. Chem.]
The separation of individual lanthanides formed in fission is more complicated because of the large number of lanthanide nuclides formed and the variations in fission yields. A fast, autobatch procedure was used by Klein and coworkers in their study of 9.6-s 96Y [Kle75]. The procedure does not achieve separation of yttrium from lanthanides in the dysprosium-terbium region [Her82], but the fact that the low-energy fission yields of those nuclides are small compared to those of yttrium allowed a reasonably pure yttrium sample to be obtained 10 s after the end of irradiation. Table 5 gives a list of procedures that use ion-exchange techniques.
Recent developments in high-pressure liquid chromatography (HPLC) have an impact on fast radiochemical separation of lanthanides and actinides. The application of HPLC for the ion-exchange separation of fission-product lanthanides and actinides is discussed in Sec. 2.5.
2.4 Liquid-Liquid Extraction
Liquid-liquid extraction is one of the most common techniques used in all branches of chemistry. A few examples are its use
In analytical chemistry for separation and analysis of mixtures.
In organic chemistry for purification of reaction products.
For the separation of aromatics from aliphatics in the petroleum industry.
In the nuclear industry for the separation of uranium and for separation of plutonium from most of the fission products.
The technique has been frequently used in radiochemical separation procedures.
The first application of liquid-liquid extraction is credited to Peligot, who observed that uranyl nitrate can be recrystallized from diethyl ether [Pel42]. This extraction technique has been used from the time of the Manhattan Project to achieve rapid radiochemical separation. Levinger and coworkers [Lev51] separated iodine within 28 s after irradiation by extraction of molecular I2 with CCl4. A number of ultrafast procedures based on liquid-liquid extraction exist. The following subsections give information on the applications of this technique to ultrafast radiochemical procedures.