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ULTRAFAST CHEMICAL SEPARATIONS
automation of part or all of the steps in the procedures. Often, classical techniques had to be modified or adapted so that the procedure could be handled conveniently by the automated system. For example, rapid exchange of ions in solution with preformed precipitate was used instead of precipitation from aqueous solution. Solvent extraction was performed by dispersing the solvent on an inert material and contacting the aqueous solution with this material.
A semi-automated system was used by Greendale and Love in their work on arsenic, tin, and antimony. They designed a system for rapidly transferring irradiated solution from the rabbit to a chemistry system in about 2 s [Gre63c]. The cap of the irradiation container had a Teflon and gum-rubber diaphragm. The irradiated rabbit impinged on two hypodermic needles; the solution was drawn through one of the needles by application of vacuum, while the second needle was used to let air or rinsing solution enter the rabbit. The solution was transferred to a vessel containing carrier solutions by manipulation of stopcocks. Again, by operating a few stopcocks and using nitrogen gas, they were able to generate hydrides of arsenic, tin, and antimony. Separated arsenic, tin, and antimony samples were available in about 10 s [Gre63a, Gre63b].
The first completely automated system for rapid radiochemical separation was reported by Schüssler and coworkers [Sch69]. The solution to be irradiated was sealed in polystyrene capsules. After irradiation using a pneumatic tube facility, the capsule containing the solution was transferred directly to the chemical separation apparatus. Impact on the wall of the apparatus broke the capsule, and the irradiated solution was sucked through a layer of preformed silver chloride. Fission halogens exchanged with chloride. Next, a washing solution was sucked through the silver halide. After the washing, a pneumatic system transported the separated fraction to a counter. The entire operation was performed with the use of syringes, valves, and stopcocks that were operated automatically by an electronic programmer. The entire sequence of operation was initiated by a signal received from photodiodes placed in the reactor, and was triggered by the Cerenkov radiation accompanying the neutron burst of the TRIGA reactor. Counting of the sample started 3 s after the end of irradiation. Schüssler and Herrmann used the system to study short-lived fission halogens [Sch72]. Similar systems used for the study of short-lived silver and technetium nuclides are described in Sec. 4.1 and Sec. 4.2.
Autobatch procedures based on solvent extraction using high-speed centrifugal contactors have been utilized to study short-lived palladium and silver nuclides [Mei80, Mei81]. The system is described in Sec. 4.3.
A microprocessor-based system was developed for the study of short-lived arsenic and antimony nuclides [Mey80]. The entire cycle of operations —from the loading of rabbits to counting of the sample—was controlled by the microprocessor. Details of the system are presented in Sec. 4.4.
Separations of individual lanthanides and actinides require complex ion-exchange chromatography; autobatch procedures based on such separations have been developed. Short-lived lanthanide nuclides were studied by the Idaho group using a combination of extraction and ion-exchange chromatography [Bak80, Bak81, Bak82]. A description of the technique is given in Sec. 4.5. Schädel and coworkers have reported autobatch procedures based on chromatography for the separation of transplutonium elements [Sch88b, Sch89]. Their microcomputer-controlled automatic rapid chemistry apparatus (ARCA) is described briefly in Sec. 4.6.
A large number of autobatch separation procedures are available. Table 10 gives a list of elements for which autobatch procedures are available in the literature. The table also lists the technique used in the separation, the time required for the separation, and the procedure number.
Several examples of autobatch chemical systems are described in the following sections. The systems are selected to illustrate the use of different types of batch techniques (solvent extraction, exchange, etc.).