Nuclear Instruments and Methods in Physics Research A250 (1986) 573-575 North-Holland, Amsterdam
Letter to the Editor PREPARATION OF RADIOACTIVE 44 Ti TARGETS D. GRZONKA, R. SANTO and L. WALLEK Institut für Kernphysik, Universität Münster, FRG
Received 29 October 1985 and in revised form 28 April 1986 The experimental conditions for a reproducible high yield electrodeposition of titanium in the jug range have been investigated . A plating cell for the use of carbon foils as backings was constructed, so that the target production of rare titanium isotopes became possible with high efficiency . During 1977 we produced 44 Tî by the 45 Sc(p, 2n) reaction at the Jitlich isochronous cyclotron . The reaction was induced by a 5 pA defocussed proton beam of 45 MeV on a 2 ,ug/cmz 45 SC target . After chemical separation of the titanium from scandium [1,2] a total amount of about 1 jig 44 Ti was left for the target preparation . For our investigations of titanium deposition we prepared a test solution of 3M nitric acid containing natural titanium nitrate in a concentration of 1 mg Ti per ml solution . We tested the deposition from pure organic solutions ("molecular plating" [3-16]) and from mixtures of nitric acid solutions with organic solvents, where the process of cathodic hydroxide deposition should be dominant . The deposition yield of titanium was investigated as a function of various factors such as organic solvent, voltage, duration of the deposition and backing material. The elemental composition of the target layer and the deposition efficiency were investigated by several methods. For qualitative analysis of the target layer we applied X-ray fluorescence and electron microscopy, which also yielded information about structure and homogeneity of the layer. The amount of deposition was determined by elastic proton scattering and the total yields by tracer analysis. To study the deposition yields a conventional "molecular plating" cell [2,16], consisting of a teflon funnel, a brass block as support for the backing foils and a brass ring which fastened the funnel on the backing, was used . The area to be plated was confined by a teflon ring of 5 mm in diameter . Because of chemical inertness thick tantalum foils served as backing material for most of the deposition runs . For the use * Supported in part by the Bundesminister Für Forschung und Technologie . 0168-9002/86/$03 .50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
of thin (50-100 pg/cmz ) carbon foils as target backing, a special deposition cell (shown in fig. 1) was constructed. In this cell the carbon foil is surrounded by fluid on both sides, so that mechanical stress on the foil is minimized. The balance tube and the support were filled with pure organic solvent while the plating tube contained the plating solution. Filling and removal of the solution were performed with a double-pipette . To get better sealing between plating solution and organic solvent below the carbon foil we painted the edge of the foil with Mowital *, a polyvinylacetate . A platinum wire dipping in the plating solution served as anode while a clip was connected with the cathode. The plating solutions were prepared by adding 1-10 pl of our test solution to the organic solvent mixed with some nitric acid of variable molarity . Using pure organic solvents, i.e . the region of "molecular plating", in most cases no visible target layers were built up, although voltage and plating duration corresponded to values Balance -Tube
Gasket rings- L- LZI
Fig. 1. Sketch of the electrodeposition cell for the use of thin carbon backing foils. * Mowital is a trademark of Hoechst AG .
44 D. Grzonka et al /Preparation of radioactive Ti targets
Table 1 Composition of the 44 Ti target and a natural titanium target [in ttg/cm2] Element
Ti target Natural titanium target 44
cited in the literature for other elements . When adding some nitric acid solution we observed a drastic rise in the deposition yield combined with a strong hydrogen evolution. For all tested organics, isopropyl-alcohol (2propanol), isobutyl-alcohol and acetone, titanium depositions with yields above 50% were obtained . Concerning the yields no important differences between the various organics appeared, but looking at the homogeneity and plating duration a clear dependence on the organic solvent is obvious. The best homogeneity was reached with isopropanol solutions. The backing material (C, Al, Ni, Ta and Au) had no remarkable influence on the deposition yield. The grain size of the deposit lies in the range of 1 pin and is comparable with target layers prepared by vacuum evaporation . The optimum experimental conditions for the preparation of a Ti target are as follows: solution : 0.6 ml isopropanol, 30 P1 H 2 O, 2 lil 65% HN03 ; current: 25 mA/cm2; voltage: 25 V; target material : 1 jig titanium in the form of Ti(N0 3 ) 4 ; deposition time : 30-60 min. Under this experimental condition yields larger than 90% were reached. For the preparation of the 44 Ti target a yield of 67% was obtained . The target composition, determined by elastic proton scattering, is listed in table 1. In comparison to a natural titanium target prepared in the same way, a high degree of impurities is present. But this is a general problem in chemical separation of such low quantities . Additional information about the absolute 44 Ti amount was gained by activity measurements, which also yielded important information about activity losses during the plating process. The measured activity of the target was 44 /ACi. This corresponds to a layer of 1 .5 Wg/cm2 and was in accordance to proton scattering experiments . The investigation of the cell components showed no measurable activity, i.e . no measurable diffusion of the plating solution into the pure organic solution . The experimental results indicate that the principal plating mechanism is based on the electrolytical hydrol-
ysis, although in comparison to the conventional cathodic hydroxide deposition [17-20] our plating solutions contained only small amounts of aqueous phase. To what extent molecular plating contributes to the deposition is an open question . Proton analysis has shown that in some cases nitrogen was present, probably due to deposition of titanium nitrate, but careful analyses of the target layers, concerning the content of hydrogen, oxygen and titanium, are consistent wilt a hydroxide deposition .
Acknowledgements The authors are very grateful to N. Trautmann for the careful and very successful chemical separation of the 44 Ti . We also thank D. Frekers for his help and advice in the first stages of the 44 Ti investigations . The support of the technical staff at the Jillich cyclotron during the irradiation is gratefully acknowledged .
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