Kd-Value Determination for Rf (Element 104) with the Multi-Column Technique

After online experiments with Hf (t1/2 = 76 s, decaying into Lu) at GSI [1] we performed two experiments with the multi-column-technique [2] with Rutherfordium. Rf was produced in the Cm(O, 5n) reaction at the PSI Philips Cyclotron. A 730 μg/cm Cm target was bombarded with a 0.5 μApart O beam. The KCl aerosols transporting the activities was continuously dissolved in a degasser with a yield > 80% at a tolerable pressure in the target chamber of 1.7 bar at a gas-flow rate of 1.6 – 1.7 L/min and a distance between the target chamber and the degasser of approximately 50 m. The hold-up time of the activity in the degasser was about 2 s. A solution-level of 50 to 150 μL was kept at the bottom of the degasser through control by a light barrier which caused, if activated, an adjustment of the flow rate from the HPLC pump that pumped the solution into the degasser. The active solution leaving the degasser was pumped by a double-piston HPLC pump at a flow rate of 1 mL/min through a capillary of 0.3 mm inner diameter to three columns connected sequentially: A cation filter followed by the true chromatographic column filled with an anion-exchange resin, the latter followed by another cation filter. Two experiments were performed, one using 0.5 M HF/0.1 M HNO3 as the mobile phase, another one using 0.01 M HF (without any HNO3). The running time was 24 hours in both cases. In the first case, the cation-exchange columns were filled with 330 mg of DOWEX 50WX8, minus 400 mesh. These filters were used for 3 hours and were then replaced by new ones. This ensured that there was no break-through by any of the descendants of Rf, i.e. No, Fm, and Es. The anion-exchange column was filled with 50 mg of DOWEX 1X8, minus 400 mesh in the nitrate form. 17 mg of DOWEX 1X8 in the fluoride form was used in the experiment with 0.01 M HF. In this experiment, 68 mg of DOWEX50WX8 were used as cation filters for running times of 4 hours. The effluent from the final cation filter was collected in a reservoir (activity AE). After the end of the experiment, the final cation filter was stripped with 5 M HNO3 (activity AD). The solutions AE and AD were spiked with Am. After adjusting its pH to 2, the solution containing AE was passed over a cationexchange column where Fm and Es were sorbed. This column and the cation-exchange columns containing AD were stripped with 5 M HNO3 and the solutions were evaporated to dryness. The residues were dissolved in 8 M HCl and iron (from the steel capillary of the gas jet) was extracted into Aliquat 336 in chloroform. After evaporation to dryness of the aqueous phases, the residues were dissolved in 10 μl of 0.1 M HNO3 and transferred into isopropanol for molecular plating. The latter was performed with 1200 V onto thin Ti foils of 430 μg/cm thickness. These were subject to α spectroscopy in 4-πgeometry for more than 60 days, three half-lives of Es. Overall chemical yields determined via the Am activity (Eα=5.5 MeV) were 65% on the average. The background in the relevant energy window near 6.6 MeV was 1.5 α events per week.