Radon transfer system

Fig. 13-4. Schematic of radon stripping and transfer system. The upper section is one of four channels used in this system the lower (transfer) section is shared by all four. In this upper section and the three others like it, four samples are degassed, purified of HjO and CO2 and trapped. The samples are then moved individually, via the transfer manifold, to the sample reduction trap, then on to counting cells (after Key et al. 1979).

Xenon is next eluted in Area 2. At the end of the sampling period, the main trap is valved off from the system and heated to 200° C to release the xenon. The outflow from the main trap is carried by ultrapure nitrogen (no CO2) through a MFC at 0.24 1/min. Desorption is timed to release most xenon flow is diverted when the remaining radon is expected to desorb. This slow flow takes the desorbed xenon gas with N2 carrier gas though one of a series of disposable chemical traps (NaOH + Al) to remove most CO2. The now purified gas is collected on a 0.2-15 A molecular sieve trap at -40 C, while the carrier N2 escapes. The trap is then heated to 200°C to desorb xenon and transferred to a tiny cold trap that is cooled to -120°C to sorb xenon in preparation for loading the counting cell. This step is necessary to transfer the gas into a scintillation cell, as shown in Area 3 of Fig. 15.7 and also in Fig. 15.8. 

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