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ULTRAFAST CHEMICAL SEPARATIONS
A gas-jet system at the University of Mainz has been used with a number of continuous fast chemical separation systems. Various fissioning nuclides have been used as target material. The target chamber was located in one of the beam holes close to the core of their TRIGA reactor. Plugs filled with boric acid and paraffin provided the shielding. The fission products from the target chamber were transported through 7 m of capillary tubing. A transport time of 1 s from the target chamber to the end of the capillary was observed at a flow rate of 20 cm3/s [Tra75].
Figure 28 shows the schematic of the gas-jet system installed in the beam port of Ford Nuclear Reactor at the University of Michigan [Ren86b]. The target was 1 mg of 235U chemically plated on an aluminum backing. The target was covered with aluminum foils of total thickness 2.75 mg/cm2. This arrangement, as reported by Zendel and coworkers [Zen87], provided an enhancement factor of 100 for light-fission fragments. The target chamber is located inside an aluminum tube. A series of modular (60 cm or 30 cm) concrete cylinders, with spiral conduits, was inserted in the aluminum tube for shielding, and three tubes, passing through the conduits, were connected to the target chamber. The aluminum tube housed in the beam port could be withdrawn about 1 m when the gas jet was not being used. The aluminum tube is surrounded by water, which provides the necessary shielding. In its nonirradiation position, the target chamber was shielded by a 1-m thickness of water.
Figure 28.Schematic of the target chamber and its location relative to thereactor core; a) sketch of gas-jet system in irradiation position,b) sketch of gas-jet system in non-irradiation position, c) targetchamber. [Ren86b; reprinted with permission fromJ. Radioanal. Nucl. Chem.]
Gas targets have been used for study of short-lived materials. For such studies, gas-target systems and circulation systems have been developed. Details of these systems will not be