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On-Line Separation of Short-Lived Tungsten Isotopes from Tantalum; Hafnium and Lutetium by Adsorption on Ion Exchangers from Aqueous Ammonia Solution

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On-Line Separation of Short-Lived Tungsten Isotopes from Tantalum; Hafnium and Lutetium by Adsorption on Ion Exchangers from Aqueous Ammonia Solution Jointly I,ublished by Elsevier Scie.ce S. A~. Lausanne and J.Radioanal.Nucl.Chem.,Letters Akad?miai Kiod6, Bltdapest 214 (I) I-7 (I 996) ON-LINE SEPARATION OF SHORT-LIVED TUNGSTEN ISOTOPES FROM TANTALUM; HAFNIUM AND LUTETIUM BY ADSORPTION ON ION EXCHANGERS FROM AQUEOUS AMMONIA SOLUTION 1 1 1 1 D. Schumann , R. Dressler , St. Taut , H. Nitsche , Z. Szeglowski2, B. Kubica2~ L.I. Guseva 3, 4 G.S. Tikhomirova3, A. Yakushev~, O. Constantinescu , V.P. Domanov 4, M. Constantinescu 4, Dinh Thi Lien 4, Yu. Ts. Oganessian 4, V.B. Brudanin 4, I. Zvara 4, H. Bruchertseifer 5 I Institute of Analytical Chemistry, University of Technology Dresden, 01062 Dresden, Germany 2H. Niewodniczanski Institut of Nuclear Physics, Krakow, Poland ~Institute of Geochemistry and Analytical Chemistry, Moscow, Russia 4joint Institute of Nuclear Research, Dubna, Russia 5paul-Scherrer-Institute, Villigen, Switzerland Received 17 June 1996 Accepted I July 1996 The title goal was achieved using a DOWEX 50Wx8 cation exchange column saturated with La(OH) 3 and ammonia solution as eluent.>Hf, Ta and Lu were adsorbed on this column, where- as W remained in the solution. This chemical system may be used for fast on-line separa- tions of element 106. INTRODUCT ION Subgroup VI elements form oxo-anions in alkaline solu- tion I , whereas subgroup IV and V elements and lanthanides hydroiyze under these conditions. This might be of inter- 0236 -5 731/76/.[/S ~ J 2,0 Cops I"ight ~'9~6 Ak~ch~nlirli KicaM, Blldapr All t il.,ht$ rest'tied SCHUMANN et al.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES est for fast on-line separation of element 106 from heavy actinides and element 104 produced simultaneously in heavy ion reactions. It was shown in an earlier study that more than 95% of tantalum, hafnium and ytterbium tracers adsorb on Wofatit KPS from ammonia solution, whereas tungsten passes through the column without sorp- tion 2. For application of this chemical system in experi- ments with element 106, the decontamination factor must be increased, because element 104 is produced in consid- erable amounts both directly during the bombardment and as an e-decay product of element 106. Therefore, we improved the chemical separation proce- dure, especially the preparation of the columns, and tested this system with varying concentrations of ammonia in on-line experiments at the U-400 cyclotron (Flerov Laboratory of Nuclear Reactions, JINR). EXPERIMENTAL Short-lived isotopes of tungsten were produced by bombarding Sm (85% 144Smi 15% 147Sm) with a 24Mg beam: 144/147sm:(24M~,xn)164-169 W 112 MeV The recoiled atoms were transported with a KCI/Ar aerosol jet (I i/min) 3 The apparatus used for chemical separations consisted of a degasser system and two ion- exchange columns (first column: DOWEX 50Wx8, second col- umn DOWEX Ix8). Details of the chemical setup were de- 4 scribed earlier The cation and anion exchange columns were prepared as follows: The ion-exchange resins (DOWEX 50Wx8 and DOWEX SCHUMANN et al.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES Ix8, 200-400 mesh, 80 mg) were filled in teflon columns (size 4x15 mm). The anion-exchange column was pre-equi- librated for 12 h before the experiment with the cor- responding ammonia solution. The cation exchange column was saturated with La(OH) 3, subsequent washing with about 10 ml of 6M HCI, 2M HCI, H20 (to neutrality), 0.1M La(NO) 3, H20, 0.01M NaOH for complete precipitation of the lanthanium hydroxide onto the cation exchange column, H20 , and finally with ammo- nia solution of a concentration similar to the one used in the experiment (2._~ vol.%, 5 vol.%, 7.5 vol.%, 10 vol.%). Flow rates of 2-4 ml were used. The y-activity of the columns was measured with a HPGeX detector (ORTEC). RESULTS AND DISCUSSION Adsorption of carrier-free radionuclides on the sur- faces as glass, silica gel or paper can in some cases be used for their separation, especially for elements which show a strong tendency to hydrolyze 5. Particularly amor- phous precipitates such as hydroxides (Mn(OH)4 , Fe(OH) 3 , AI(OH) 3, Zr(OH) 4) are used to solve separation problems because of their large specific surface area and high sorption capability 6. The adsorption on amorphous hydrox- ides can be caused by physical (formation of an electric double layer, depending on the pH of the solution) or chemical effects (substitution of H + or OH within the -MOH-group). With the aim to get a large effective sur- face for the separation of subgroup IV/V and lanthanide hydroxides, we saturated the cation-exchange column (DOWEX 50Wx8) with La(OH)3 as described above. This col- SCHUMANN et al.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES umn was used in on-line experiments for the isolation of short-lived tungsten nuclides from their daughter and granddaughter isotopes of hafnium, tantalum and lutetium. The y-spectra of the cation- and anion-exchange columns are shown in Fig. I. Five vol.% NH 3 aq. solution was used as eluent. The tungsten isotopes 166W (T = 18.9 s, 125.8 keV), 168W (T = 52 s, 178.7 keY) and 169W (T = 76 s, 169.2 keV) were found to adsorb only on the anion-ex- change resin. 164/165W (T = 5.8 s/5.2 s) could not be identified because their y-rays are unknown, but their daughters 164/165Ta were adsorbed only on the cation- exchange resin. This means that 164/165W decayed com- pletely during transport to the chemical setup and tan- talum is completely adsorbed on the La(OH) 3 saturated cation-exchange column. The non-observation of 164Hf (T = 111 s, 122.1 keV) and 165Hf (T = 75 s, 180.0 keV) on DOWEX Ix8 - these two isotopes are only found on DOWEX 50Wx8 - confirms this result and, furthermore, in- dicates that Hf is quantitatively separated from W by sorption on the first column. Taking into account the de- tection limit in the y-spectra of the second column, we calculated a decontamination factor of >5x102 for Hf. The tantalum and hafnium isotopes detected on the anion exchange resin (168Ta, 166Ta, 167Hf, 168Hf, 166Hf) are decay products of the corresponding tungsten isotopes which passed the first column without sorption. From the peak at 78.8 keV (166Hf/166Lu) we calculated the parti- tion of 166Hf (and 166W, respectively) between the two columns of DOWEX 50Wx8 : DOWEX Ix8 as 4 to I. Taking into account the half-life of 166W (18.9 s), this yields about 40 s for the transport time from the target chamber to the first column. This is the reason that the decay pro- ducts of 164/165W could not be observed on the second col- umn, as already mentioned above. Hence, the procedure 4 SCHUMANN et al.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES 40 C 0 35 % DOVYEX 50V~k8 5 vol.% NH3 3O - ~ = 14'v147Sm(24Mg,xn)W 25 - 1.6 .ll- . > I 20 o ~3 >'1 15 /L ::= ~ ,-r 10 l I I I I I I 100 150 200 250 300 350 Energy, keY 10 C: :3 o 9 DOV~E.X lx8 o 5 vol.% NI--I3 • 8 t~ 1~147Sm(24Mg,xn)W 7 I 6 5 4 3 2 1 0 I I I l I I 100 150 200 250 300 3~ Energy, keV Fig. I. y-spectra of the cation and anion exchange col- umn, solution containing 5 vol.% NH 3 aq., flow rate 2 ml/min SCHUMANN et ai.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES used in the present experiments is only suitable for iso- topes with half-lives longer than 10-15 s. Variation of the NH 3 aq. concentration (2.5 vol.%, 7.5 vol.%, 10 vol.%) did not change the results of sepa- ration. SUMMARY Ion-exchange experiments with dilute ammonia solution (2.5 - 10 vol.% NH 3 aq.) showed that a cation-exchange column (DOWEX 50Wx8) saturated with La(OH) 3 can be used for quantitative adsorption of short-lived tantalum, hafnium and lutetium radionuclides, whereas tungsten passes the column without sorption under these conditions. Therefore, this chemical system can be recommended for fast on-line separation of element 106. The transport time from the target chamber to the first column was estimated to be about 40 s. For experi- ments with element 106 the transport time must be lowered because the half-life for 264/265106 is expected to be 7 within 2-30 s This work was supported by BMBF, Germany. REFERENCES I. C.F. Baes, R.E. Mesmer, The Hydrolysis of Cations, John Wiley and Sons, New York (1976) p. 412. 2. H. Bruchertseifer, B. Eichler, J. Estevez, I. Zvara, Radiochim. Acta, 47 (1989) 41. SCHUMANN et al.: ON-LINE SEPARATION OF TUNGSTEN ISOTOPES 3. I. Zvara, V.P. Domanov, M.R. Shalaevsky, D.V. Petrov, Communication of the JINR 12-80-48, Dubna 1980. 4. D. Schumann, R. Dressler, S. Fischer, St. Taut, R. Binder, Z. Szeglowski, B. Kubica, L.I. Guseva, G.S. Tikhomirova, O. Constantinescu, V.P. Domanov, M. Constantinescu, Dinh Thi Lien, Yu.Ts. Oganessian, V.B. Brudanin, H. Bruchertseifer, Radiochim. Acta, 69 (1995) 35. 5. V. Majer, Grundlagen der Kernchemie, Johann Ambrosius Barth, Leipzig, 1982, p. 517. 6. M. Marhol, Ion Exchangers in Analytical Chemistry, Academia, Prague, 1982, p. 277. 7. R. Lougheed et al., J. of Alloys and Compounds, 213 (I 994) 61. .
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