Production and chemical separation of 48 V radioisotope

The positron emitter 48 V isotope (T1/2=16 d, γ-lines: 511 keV (100%), 983.5 (100%), 1312 (97.6%)) is of interest in several fields of science. This is valid for transmitting scans in the validation process of PET-camera by positron emission. It can be used as an industrial monitoring isotope by its γ-photons having high energy and intensity. Also, it is suitable for biological study since it is the only radioisotope of the biological trace element vanadium which can be a radiotracer due to its longer half-life. The 48 V was produced by nat Ti (d,xn)48 V nuclear reaction in the U-120 cyclotron with activity of 6 mCi. The energy of irradiating beam was 13 MeV, its intensity was 5 μA and the metallic Ti target dimensions were 16 x 11 x 2 mm. For target cooling, the water circulation in the back side was used. After 3 cooling days, only 48 V, and some 46 Sc (T1/2 = 84 d), produced by the side nuclear reaction 48 Ti (d,α)46 Sc were found in the target. For the preparation of 48 V source, the Ti target was dissolved in HF and sulfuric acid. The ion exchange separation was developed for both dissolving methods. The dissolution of the chemically resistant Ti target is so violent in concentrated (3.5 % m/m) HF, that it is necessary to be carried out in polyethylene tube in order to avoid the splash of the dissolved target. An anion exchange column, Dowex 1-8 (size 100-200 mesh, length 12 cm, ID 10 mm, treated 1 day earlier, prepared fresh), was used for separation in HF media. The reduced ionic form of Ti bonds to resin, therefore the dissolved target was saturated with sulfur-dioxide produced in the Kipp-equipment by the following chemical reaction: Na2SO3 + 2 HCl → 2 NaCl + H2SO3. The treated solution was diluted to a concentration of 2 mol/l of HF and the same concentration of the HF was used as an eluent for separation. Flow rate of the elution was 1 ml/min. The eluate was cooled fractionally. The fractions were measured by γ-spectrometry, which detected only 48 V. The advantages of this method are the easy dissolution of the target and the quick, complete separation of 48 V. The disadvantage is glassware avoiding, all lab-equipment must be produced of HF-resistant plastic material and the final product is difficult to be used due to the aggressive HF media. The sulfuric acid with concentration of 6 mol/l can also dissolve the target, however it is much more difficult than in the case of HF use. It needs heating under reflux for 6 hours. During the dissolution, the solid salt of Ti was produced in high amount. Only 50 % of the stoichiometric necessary amount of sulfuric acid for fully dissolution was used in order to avoid the dissolution of the part of the target in which the nuclear reaction was not produced. After the dissolution, the liquid and solid phase were separated and the solid salts were dissolved in 0.01 mol/l sulfuric acid. This soft acidic condition is necessary for effective separation on the Amberlite CG-50 column. The higher oxidation stage and the peroxide-complex of Ti is a guaranty for Ti remaining on the cation exchange column. Therefore 1% H2O2 in 0.01 mol/l nitric acid was added to the sample. The orange color is a proof of successful chemical reaction. For ion exchange separation this solution was used. The elution was carried out by 1% H2O2 in 0.01 mol/l nitric acid as an eluent. The radio-chromatogram was determined by the same method which was mentioned in the case of the separation in HF media. The chemical yield of the separation was higher than 95%. The radionuclide impurity of 46 Sc was less 0.02 % determined by γ-spectrometry. The chemical purity of 48 V was 99.8% according to Ti determined by VIS-spectrophotometry using the absorbance of peroxide complex of Ti in 420 nm approximately. The advantages of this method are the softer chemical circumstances and the easy use of the final product. The disadvantages are the long dissolution time, the several hand-operated steps and the less separation ratio compared with the separation in HF media. For application of any methods in production of 48 V with high radioactivity some modifications are necessary to fit the method for manipulator operating in shielded box. (authors)