allowed to form volatile compounds (by the addition of a reactive gas, if necessary). The element of interest could be separated by selective adsorption. Thermochromatography has also been used to separate the volatile products formed. A second approach is to form volatile compounds of elements of interest by allowing the recoiling products to chemically react with a reactive gas used in the gas jet; selective adsorption of the products by different traps could lead to the separation of the element of interest. The following sections give a summary of techniques used and specific examples of procedures used for some elements.

7.1 Production Outside the Target Chamber

Fission-product selenium and tellurium have been studied by Zendel and coworkers [Zen78] using volatile products generated outside the target chamber. An ethylene-nitrogen gas mixture thermalized and carried fission products from the target chamber of a gas-phase chemistry system that was in the beam port of a reactor. Tellurium was carried by clusters, while selenium, bromine, and iodine formed volatile products and were carried by the gas stream along with krypton and xenon. A schematic of the setup used for the continuous separation of tellurium from fission products is shown in Fig. 39. The gas stream from the target chamber was passed through a charcoal trap that retained selenium, bromine, and iodine. The gas mixture was then passed through a quartz spiral heated to 860°C. The clusters were decomposed at this temperature; tellurium formed volatile compounds that were carried away by the gas stream, and all other fission products were deposited in the spiral. The gas stream passed through a charcoal trap in front of a Ge(Li) detector that retained tellurium while krypton and xenon passed through.

Figure 39. Setup for the continuous separation of tellurium from fission products (not to scale). By replacing the first charcoal trap by two paper filters, the same setup can be used for the separation of selenium. [Zen78; reprinted with permission from Nucl. Instrum. Methods]



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