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ULTRAFAST CHEMICAL SEPARATIONS Figure 46. Experimental setup for the continuous separation and on-line measurement of germanium isotopes from fission products (not to scale). By placing the detector at the arsenic absorption position, the same setup can be used to measure arsenic isotopes. [Zen81; reprinted with permission from Radiochim. Acta] Continuous gas-phase separations have been utilized in a variety of applications in the study of short-lived fission products. Its potential usefulness in the measurement of fission yields has been demonstrated [Ren82d]. Ground-state decay branchings for short-lived selenium isotopes have been measured using this technique by Lin and coworkers [Lin 82]. The decontaminations obtained, especially using thermochromatographic techniques, are often not as high as those obtained with continuous solvent-extraction techniques. However, gas-phase separations, especially those based on volatile species produced in the target chamber, provide a very important opportunity for chemists to study the chemical reactions taking place in a radiation environment. 8. Future of Ultrafast Chemistry On-line isotope separators have been used in accelerators as well as in reactors to obtain isobaric separation of nuclear-reaction products. Recent developments in ion-source technology have extended the range of accessible elements by use of selective chemistry within the ion source of an on-line mass separator. Piotrowski and coworkers [Pio84], as well as Brüggar and coworkers [Brü85], have reported development of high-temperature sources that provide beams of alkaline earth and lanthanide elements. Gill and Piotrowski [Gil85] have developed a new FEBIAD-type ion source for use with on-line sources used in reactors. Figure 47 shows a survey of yields obtained from the ion source. The near-complete chemical suppression of elements such as selenium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, and
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ULTRAFAST CHEMICAL SEPARATIONS Figure 47. Survey of yields of some elements with the TRISTAN FEBIAD ion source. The results are based on g-ray spectra and are corrected to saturation activities. [Gil85; reprinted with permission from Nucl. Instrum. Methods Phys. Res.] tellurium is notable [Gil85]. The yields reported from the high-temperature ion sources also show low or no yield for many elements [Pio84]. For study of short-lived nuclides of these elements, either new ultrafast ion-source techniques or ultrafast chemical techniques are essential. Isotope separators provide isobaric beams; ideally, an additional separation will provide the best possible sources for far-from-stability spectroscopy studies. Rudstam and coworkers have investigated the possibility of subjecting the isobaric beam obtained from an isotope separator to thermochromatographic separation [Wes69, Gra73, Rud73]. They utilized such a combination to study neutron-rich zinc and cadmium isotopes [Rud81]. In the future, gas-phase chemical separations can be expected to provide Z separation following A separation provided by on-line isotope separators. In addition, production of volatile species in target chambers with a variety of reactive gases may be studied to understand the chemical reactions taking place with energetic nuclear-reaction products.
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