Improved version of the wetted-paper 81Rb/81mKr generator. Influence of porous capillary spreading and diffusion on the performance

The performance of the Rb/Kr generator based on sorption of ⁸¹Rb solution in paper was investigated for various design modifications. Replacement of the ridged copper-foil separator between adjacent paper layers by ridged paper resulted in a more rapid attainment of the equilibrium elution efficiency and a more compact geometry. This is explained by the nature of the spreading process of water via the pores in the paper. Also the influence of the water concentration in the paper on equilibrium efficiency, drying rate, and pressure drop is related to this mechanism. A range of water concentrations (0.1–0.8 mL/g of paper) could be indicated where the equilibrium efficiency (>90%) is not limited by diffusion out of the larger pores (>0.9 mL/g) and where the “run-dry” phenomenon does not occur (<0.1 mL/g).