Ideally, nuclear-reaction products should be subjected to mass and charge separation for the study of the decay characteristics of a nuclide. Westgaard and coworkers [Wes69, Wes91] investigated thermochromatographic separation as a possible technique for providing a chemically separated gaseous beam that can be subjected to mass separation. The first such separation was reported by Grapengiesser and Rudstam [Gra73, Rud73]. They attached a thermochromatographic separation apparatus to the isotope separator facility OSIRIS, and achieved separation of short-lived bromine and iodine isotopes. Rudstam and coworkers [Rud81] achieved separation of neutron-rich isotopes of zinc and cadmium using thermochromatography after a mass separation by OSIRIS. Progress in coupling mass separation and chemical separation is imperative to improve the unique elemental identification of very short-lived species, especially for far-from-stability mass chains where the half-lives of several isotopes in a particular mass chain are nearly identical.

In the early decades, separations requiring several hours were used routinely [Mei49a, Kle54]. For example, fission yields of lanthanide nuclides were determined using ion-exchange procedures that took hours [Ste61a, Iye63]. In the 1960s and early 1970s, nuclear chemists turned their attention to the study of nuclides with half-lives in the range of minutes to tens of minutes, and to utilization of such nuclides in neutron activation analysis. A fast separation procedure for lanthanides using a small ion-exchange column was reported that was able to separate any specific lanthanide within 20 to 25 minutes [Ren64]. Multistep solvent extraction procedures requiring several minutes were used for the study of tin and antimony isotopes formed in fission [Hag62, Ren66]. On the other hand, volatilization procedures of a few seconds were available for elements such as bromine [Nuh72]. As attention turned to shorter-lived nuclides, faster multistep procedures, capable of providing separated products within a few seconds, had to be developed. Unfortunately, manual procedures tended to be slow. For example, multistep solvent-extraction procedures developed for selenium [Ren68] and yttrium [Ren76] were accomplished in about 150 s and 100 s, respectively. Obviously, such techniques are not useful for studying nuclides with half-lives in the range of a few seconds.

The first step in developing rapid separation techniques was to automate many or all of the steps involved in a procedure. By using automation, Kratz and coworkers [Kra70] developed a 5-s procedure for selenium. A 10-s ion-exchange procedure-was used by Klein and coworkers [Kle75] to study short-lived yttrium isotopes. Several “autobatch” procedures were developed for the study of short-lived nuclides [Mey80, Ren86a]. The separation time varied from 1.6 s for antimony to nearly 11 min for samarium. When the half-lives of nuclides of interest are less than a few seconds, the efficiency of production, isolation, and study by autobatch techniques decreases compared to continuous production and isolation of nuclides [Ste78, Lie81]. Again taking selenium as an example, continuous, gas-phase separation of selenium from fission products has been achieved in less than 2 s [Zen80, Ren82a]. In the last decade, nuclear chemists have developed a number of continuous-separation procedures for a variety of elements. Most of the procedures are based on solvent extraction, gas-phase chemistry, or thermochromatography.

A number of collections of radiochemical procedures have appeared, as well as reviews of techniques used in radiochemical separations. The earliest collection of procedures was published by Meinke [Mei49a] and was a compilation of procedures used at Lawrence Berkeley Laboratory. Another collection was published by Coryell and Sugarman [Cor51b] entitled Radiochemical Studies: The Fission Products; book 3 of this series was a collection of procedures. Kleinberg 's report [Kle54] also provided a collection of radiochemical procedures. As part of the Radiochemistry monograph series, Kusaka and Meinke published a volume on Rapid Radio-chemical Separations [Kus61]. In the first section, they describe the general procedures used for the sample preparation; the second section reviews the techniques used in rapid radiochemical separations. The last section gives a summary of procedures arranged according to elements. Herrmann and coworkers from the University of Mainz have been publishing periodic reviews of rapid radiochemical methods [Her69, Tra76a, Her82]. Rapid automated separations and