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Thick tellurium electrodeposition on nickel-coated copper substrate for 124I production
ARTICLE IN PRESS
Applied Radiation and Isotopes 66 (2008) 1281–1286 www.elsevier.com/locate/apradiso
Thick tellurium electrodeposition on nickel-coated copper substrate for 124I production M. Sadeghia,b,, M. Dastanb, M.R. Ensafa, A. Abaspour Tehranib, C. Tenreiroc, M. Avilad a
Nuclear Medicine Research Group, Agricultural, Medical and Industrial Research School, P.O. Box 31485, 498 Karaj, Iran b Faculty of Engineering, Research and Science Campus, Islamic Azad University, Tehran, Iran c Faculty of Engineering, University of Talca, Talca, Chile d Cyclotron Department, Chilean Nuclear Energy Commission, Santiago, Chile Received 1 November 2007; received in revised form 14 February 2008; accepted 19 February 2008
Abstract Tellurium electrodeposition on a nickel-coated copper substrate was investigated for production of iodine-124. The electrodeposition experiments were carried out by the alkali plating baths. The optimum conditions of the electrodeposition of tellurium were as follows: 6 g l1 tellurium, pH ¼ 10, DC current density of ca. 8.55 mA cm2 and room temperature. r 2008 Elsevier Ltd. All rights reserved. Keywords: Thick electrodeposition; Tellurium target;
124
I; Production; TeO2
1. Introduction Due to its favorable nuclear properties, the 4.18 d radionuclide 124I (22.0% b+, E bþ ¼ 2:13 MeV, 78% E.C., Eg ¼ 603 keV) has great potential for application in nuclear medicine. The main research areas are the functional imaging of cell proliferation in brain tumors using [124I]iododeoxyuridine (Blasberg et al., 1996), the imaging of immunoreactions in tumors using 124I-labelled monoclonal antibodies (Wilson et al., 1991; Daghighian et al., 1993), the in vivo imaging of 124I-labelled tyrosine derivatives (Langen et al., 1990) as well as the classical imaging of thyroid diseases with [124I]iodide (Frey et al., 1986; Flower et al., 1990); all of those were demonstrated by positron emission tomography. Targets with isotopically enriched tellurium dioxide (TeO2) are often used in production of 121I (Helus et al., 1979), 123I (Van den Bosch et al., 1977; Michael et al., 1981; Oberdorfer et al., 1981; Zaidi et al., 1983; Beyer et al., 1988; Corresponding author at: Nuclear Medicine Research Group, Agricultural, Medical and Industrial Research School, P.O. Box 31485, 498 Karaj, Iran. Tel.: +98 261 4436395; fax: +98 261 4464055. E-mail addresses: [email protected], [email protected] (M. Sadeghi).
0969-8043/$ - see front matter r 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2008.02.082
Scholten et al., 1989) and 124I (Lambrecht et al., 1989; Firouzbakht, 1994; Weinreich and Knust, 1996; Knust et al., 1990) for medical purposes. Usually, the production process is performed according to the requirements formulated by Van den Bosch et al. (1977). This includes irradiation of solid TeO2 deposited on a platinum support and followed by volatilization of radioiodine after heating of the target to its melting point in a stream of oxygen for some minutes. Electroplated targets with enriched Te are used in 123,124I production by Van den Winkel, (2004). 124 I is routinely produced via the nuclear reaction 124 Te(d,n)124I in a cyclotron by irradiation of isotopically enriched 124Te, which is used either in metallic form (Lambrecht et al., 1988; Firouzbakht et al., 1994) or as TeO2 (Firouzbakht et al., 1994; Weinreich and Knust, 1996; Guenther et al., 1998). In the cited references, the energy of the deuterons is given as 15 and 14 MeV, respectively. Accelerator production of 124I is largely achieved via nuclear reactions 124Te(p,n)124I and 124Te(d,2n)124I which is well suited for medium to low-energy cyclotrons. The NRCAM (Agricultural, Medical and Industrial Research School) employs a Cyclone-30 while CCHEN, a Cyclone18/9 (both accelerators from IBA, Belgium). Solid targetry systems on these accelerators are made up of pure
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copper backings onto which target materials are electrodeposited. 2. Experimental The production of 124I is mainly achieved via nuclear reactions 124Te(p,n)124I or 124Te(d,2n)124I which is well suited to low-energy cyclotrons. To take full benefit of the excitation function and to avoid the formation of the radionuclide impurities, the proton entrance energy should be 14 MeV (Bastian et al., 2001; Scholten et al., 1995). The physical thickness of the tellurium layer is chosen in such way that for a given beam/target angle geometry the particle exit energy should be 8 MeV. According to SRIM code, the thickness has to be 470 mm for 901 geometry. To minimize the thickness of the tellurium layer (and hence lowering the cost price per target), a 61 geometry is preferred, In which case a 47 mm layer is recommended. Tellurium targets are prepared by DC constant current electrolysis of the metal from alkaline plating solutions. Copper plates coated with nickel are used as target carriers. TeO2 (7.3 g l1) was added to a 1000 ml beaker, followed by the addition of KOH (15.5 g l1) and deionized water (250 ml). The homogenized solution was filtered through fine glass filter (0.45 mm) to remove any residual particles, if necessary, to be ready for electroplating. The non-reactive plating vessels used were hollow Perspex cylinders (diameter 6 cm, height 20 cm) fitted with an axial Pt anode wire mounted at the bottom by means of a tube-end fitting though a perforated septum. Four symmetrical windows (22.36 or 11.69 cm2) on the vertical sidewalls allow positioning of up to four copper target backings. Each slot is sealed by an O-ring fitted-window. The slot geometrical shape determines the actual target electrodeposition area. Windows liquid-tight sealing is realized by stainless steel mechanical pestles mounted on a PVC ring surrounding the plating vessel which press the copper backing against O-ring seal. An external PVC ring is fitted with four supporting pins, which hold a motor–stirrer combination in position. The stirrer is a hollow perforated POM cylinder mounted on the axis of a DC motor and surrounding the platinum anode. The stirrer rotation speed is set at 1000 rpm during the process and its rotating direction is reversed after 8 s, improving deposit homogeneity. To keep the desired temperature at a preset level, a heater (a series of six isolated 1 O/1 W resistors, through which an appropriate DC-current is forced (1.1 A—40 1C up to 1.8 A—60 1C), is mounted circularly at the bottom of the vessel. An insulated sensor, introduced through the stirrer support-plate, monitors the plating bath bulk temperature. As electrolysis to depletion requires long-time plating (up to 24 h), evaporation of the plating solution occurs. To maintain a constant liquid volume of 450 ml, a glass/graphite conductivity sensor monitors the solution level and actuates a peristaltic pump at the required rate, supplying distilled water to compensate evaporation losses. The rack-mounted home-made
electronics includes a motor/stirrer control, an adjustable DC voltage generator card and four V/I converters coupled to current boosters. The freshly prepared solution of tellurium was poured into the plating vessel. This refined procedure is a result of several repeated experiments with different concentrations of KOH and electroplating currents. All electrodeposited Te target layers were examined in morphology by a scanning electron microscopy (SEM) technique (using a Joel model JSM 6400 at an accelerating voltage of 20 kV). The thermal shock tests were also conducted which involve the heating of the target up to 250 1C (the temperature that the Te layer can experience during a high current irradiation) for 1 h followed by submersion of the hot target in cold water (15 1C). 3. Results and discussion In order to optimize the Te electrodeposition, the experimental conditions were investigated as follows. 3.1. Pretreatment of the Cu-backing prior to the tellurium plating To ensure a good adhesion, the copper plate was cleaned using 1000 grade sandpaper followed by rinsing the copper plate with deionized water. The copper plate was placed in the plating vessel with 450 ml of nickel sulfate plating solution. The copper plate was connected to the power supply as the cathode whiles the platinum electrode as the anode. The power supply was turned on and the current adjusted to 50 mA cm2 and allowed to plate for 3 min under vigorous stirring (1000 rpm, 8/8 cycle), giving a nickel-electroplated target. The nickel-electroplated copper plates were thoroughly rinsed with water followed by acetone and then paper-dried and weighed. The obtained layers had a thickness in excessive of the copper of approximately 10 mm. 3.2. Influence of the applied voltage The electrodeposition experiments were carried out with different applied voltages (DC, chopped sine (CS) and asymmetric square wave (SW) using a constant current at room temperature, 25 1C. All the electrodepositions were performed under vigorous stirring with a 11.29 mA cm2 current density. The voltages alternatives to DC were believed to reduce or eliminate dendrite formation in the deposits. The results are summarized in Table 1. Since the current efficiency (Z) obtained using DC current was the highest, it was therefore used for the remainder of the electrodeposition experiments. 3.3. Influence of current density Application of a very low current density results in a rather poor-quality deposit. Alternatively, a very high
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Table 1 Influence of applied voltage, current density 11.29 mA cm2, plating time 1.5 h, temperature 25 1C, pH ¼ 13 on the nickel-coated copper substrate
Table 4 Influence of current density, temperature 25 1C, pH ¼ 10 on the nickelcoated copper substrate
Applied voltage
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
DC CS SW
103 53 –
157 157 157
65 33 –
8.55 10.26 13.25
69 71 92
92 94 142
75 75 64
1.16 1 1.16
CS: chopped sine; SW: asymmetric square wave. Table 2 Influence of current density, temperature 25 1C, pH ¼ 13 on the copper substrate
Table 5 Influence of temperature, current density of 8.55 mA cm2, plating time 1.16 h on the nickel-coated copper substrate
J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
Temperature (1C)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
1.28 2.13 4.27 8.55 11.29 26.51
– – – 52 42 78
24 39 79 158 122 245
– – – 33 34 31
2 2 2 2 1.16 1
25 50 63
70 61 57
92 92 92
76 66 16
Table 6 Influence of pH, current density of 11.29 mA cm2, temperature 25 1C on the copper substrate pH
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
1 10 13
– 61 42
122 139 122
– 44 34
1.16 1.3 1.16
Table 3 Influence of current density, temperature 25 1C, pH ¼ 13 on the nickel coated copper substrate J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
2.13 4.27 8.55 11.29 12.83 17.10 21.72
– – 70 106 83 89 –
20 79 92 157 148 158 200
– – 76 67 56 56 –
1 2 1.16 1.5 1.25 1 1
current density reduces the overvoltage of hydrogen, which decreases the quality of the deposit as well as the current efficiency. Hence, an optimal value was expected and investigated. The current efficiency was determined at different current densities using DC current at room temperature (Tables 2–4). The optimum DC current density was found to be about 8.55 mA cm2 and should be applied.
3.4. Influence of temperature Increasing the temperature of the solution increases the mobility of the ions and reduces the viscosity of the solvent. The mean current efficiency at 25 1C and a current density of 8.55 mA cm2 was found to be 76%, which the highest in the range investigated (Table 5).
Table 7 Influence of pH, current density of 8.55 mA cm2, temperature 25 1C on the nickel-coated copper substrate pH
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
1 10 13
– 69 70
79 92 92
– 75 76
1 1.16 1.16
3.5. Influence of pH Adjusting the bath acidity is an important effect for both the bath efficiency and the physical properties of the coatings. A large reduction in acidity causes hydrogen reduction and simultaneously deposit sediment of the base salts on cathode. After preparing the tellurium bath (the pH of bath was about 13) for studying the effects of solution acidity on electroplating quality, the acidity was changed from 13 to 1. It is clear that the higher current efficiency and better electrodeposited layers are obtained available in lower acidity than in comparison to electrodeposited layers using a higher acidity bath (Tables 6 and 7).
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3.6. Target quality control To estimate the quality of the electroplated tellurium targets, some criteria had to be taken into account such as homogeneity, morphology, visual appearance of the deposited tellurium and thermal shock test results. The homogeneity of the tellurium layer is important as it may seriously affect the production rate of 123,124I. This was determined by measuring the thickness of several parts of the layer by micrometer and calculation of the standard deviation of the data. All electrodeposited Te target layers were examined in morphology by a SEM technique. The evaluation of quality of the layers was achieved by comparison of the photomicrographs in terms of size and form of the Te nuclei and the extent to which they overlapped each other. Smaller, more spherical and the more overlapping nuclei were considered to be a good plating quality. The thermal shock tests involved the heating of the target up to 250 1C for 1 h followed by submersion of the hot target in cold (15 1C) water. Observation of the absence of crack formation or peeling off of the tellurium layers indicated a good adhesion for the deposit.
SEM photomicrographs show that granularity of electroplated targets with current densities of 4.27–11.12 mA cm2 were not as desired (Figs. 1–3). Hence, a current density of 8.55 mA cm2 was chosen and the SEM photomicrographs show a more suitable granularity (Fig. 4). After obtaining the optimum conditions (current density of 8.55 mA cm2 and temperature 25 1C), a series of electrodeposition procedures were conducted on four target backings. Using different concentration of Te in the bath, the experiments were carried out for the preparation of four targets (surface area of 11.69 cm2) with different thickness. The electrodepositions in these experiments were continued for depletion of Te (Z476%). At the end of the plating, the Te surface was observed to be black and shiny. The black appearance is probably from deposition of Te-black near the end of the plating due to excessive H2 evolution. The Te black was easily removed by simple rubbing of the surface using a print-board eraser followed by acetone cleaning in an ultrasonic bath. Neither crater formation nor peeling off was observed during a thermal shock treatment. Cracking occurred only after multiple bending.
Fig. 1. SEM of a tellurium deposit on the nickel-coated copper substrate grown at pH ¼ 13, 25 1C and a current density of (a) 4.27 and (b) 11.12 mA cm2 from the solution.
Fig. 2. SEM of a tellurium deposit on the nickel-coated copper substrate grown at a current density of 8.55 mA cm2 from the solution, pH ¼ 13: (a) 25 1C and (b) 63 1C.
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Fig. 3. SEM of a tellurium deposit on the nickel-coated copper substrate grown at, pH ¼ 10, 25 1C and a current density of (a) 11.12 and (b) 10.26 mA cm2 from the solution.
Enriched Te is a precious metal and it is therefore essential it be recovered from the processed solutions from the radiochemical separation to be re-used. The electrodeposition of Te using alkali baths gives a quite acceptable target quality for the irradiation purposes. References
Fig. 4. SEM of a tellurium deposit on the nickel-coated copper substrate grown at a current density of 8.55 mA cm2 from the solution, pH ¼ 10, 25 1C.
The layer thickness is no longer time-controlled, but governed by the amount of Te present in the plating bath. When hydrazine and H2O2 was used, metallic tellurium begins to precipitate. In addition, after some time, the electroplated targets started to dissolve and the whole solution turned dark in color using low acidity solution and low current density. This dark color originated from undissolved tellurium oxides. 4. Conclusions 124,123
I can be produced using electroplated tellurium targets on a nickel-coated copper substrate prepared from alkali solution. The electrodeposition experiments were continued for complete depletion of Te (Z476%) resulting in a deposited layer thickness of 46 mm and using an optimum amount of tellurium (6 g l1) in the bath. As the electrodepositions satisfy a thermal shock test, current beam irradiation of higher than 100 mA can be applied.
Bastian, T., Coenen, H.H., Qaim, S.M., 2001. Excitation functions of Te124(d,xn)I-124,I-125 reactions from threshold up to 14 MeV: comparative evaluation of nuclear routes for the production of I-124. Appl. Radiat. Isot. 55, 303–308. Beyer, G.J., Pimentel, G., Solin, O., Heselius, S.-J., Taka, T., Roeda, D., Virtanen, H., 1988. Production of 123I for medical use with small accelerators. Isotopenpraxis 24 (8), 297–303. Blasberg, R.G., Roelcke, U., Weinreich, R., Von Ammon, K., Crompton, N., Knust, E.J., Beattie, B., Finn, R.D., Leenders, K.L., 1996. [124I]Iododeoxyuridine imaging tumor proliferation. J. Nucl. Med. 37 (Suppl.), P59. Daghighian, F., Pentlow, K.S., Larson, S.M., Graham, M.C., Di Resta, G.R., Yeh, S.D.J., Macapinlac, H., Finn, R.D., Arbit, E., Cheung, N.K.V., 1993. Development of a method to measure kinetics of radiolabelled monoclonal antibody in human tumour with applications to microdosimetry: positron emission tomography studies in Iodine-124 labelled 3F8 monoclonal antibody in glioma. Eur. J. Nucl. Med. 20, 402–409. Firouzbakht, M.L., 1994. Practical yields of iodine-124 from different targets in the tellurium-124 (d,2n) iodine-124 reaction and improved recovery of tellurium-124. In: Duggan, J.L., Morgan, I. L. (Eds.), Proceedings of the 13th International Conference on the Application Accelerators in Research and Industry (Denton, TX, USA, 7–10 November, 1994), University of North Texas. Firouzbakht, M.L., Schlyer, D.J., Wolf, A.P., 1994. The yield of I-124 from different target materials in the 124Te(d,2n)124I reaction and an improved recovery method forTe-124. J. Lab. Comp. Radiopharm. 35, 257–259. Flower, M.A., Irvine, A.T., Ott, R.J., Kabir, F., McCready, V.R., Harmer, C.L., Sharma, H.L., Smith, A.G., 1990. Thyroid imaging using positron emission tomography a comparison with ultrasound imaging and conventional scintigraphy in thyrotoxicosis. Br. J. Radiol. 63, 325–330. Frey, P., Townsend, D., Flattet, A., DeGautard, R., Widgren, S., Jeavons, A., Christin, A., Smith, A., Long, A., Donath, A., 1986. Tomographic imaging of the human thyroid using 124I. J. Clin. Endocrinol. Metab. 63, 918–927. Guenther, I., Wyer, L., Knust, E.J., Finn, R.D., Koziorowski, J., Weinreich, R., 1998. Radiosynthesis and quality assurance of
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5-[124I]iodo-2-deoxyuridine for functional PET imaging of cell proliferation. Nucl. Med. Biol. 25, 359–365. Helus, F., Sahm, U., Silvester, D.J., Sinn, H.J., Maier-Borst, W., 1979. Production of I-121 on the Heidelberg compact cyclotron, and aspects of I-121 dosimetry. Radiochem. Radioanal. Lett. 39 (1), 9–18. Knust, E.J., Dutschka, K., Machulla, H.J., 1990. Radiopharmaceutical preparation of 3-123I-a-methyltyrosine for nuclear medical applications. J. Radioanal. Nucl. Chem. Lett. 144, 107–113. Lambrecht, R.M., Sajjad, M., Qureshi, M.A., Al-Yanbawi, S.J., 1988. Production of iodine-124. J. Radioanal. Nucl. Chem. Lett. 127, 143–150. Lambrecht, R.M., Sajjad, M., Syed, R.H., Meyer, W., 1989. Target preparation and recovery of enriched isotopes for medical radionuclide production. Nucl. Instrum. Methods Phys. Res. 282, 296–300. Langen, K.J., Coenen, H.H., Roosen, N., Kling, P., Muzik, O., Herzog, H., Kuwert, T., Stocklin, G., Feinendegen, L.E., 1990. SPECT studies of brain tumors with L-3-[123I]iodo-a-methyltyrosine: comparison with PET, 124IMT and first clinical results. J. Nucl. Med. 31, 281–286. Michael, H., Rosezin, H., Apelt, H., Blessing, G., Knieper, J., Qaim, S.M., 1981. Some technical improvements in the production of 123I via the 124 Te(p,2n)123I reaction at compact cyclotron. Int. J. Appl. Radiat. Isot. 32, 581–587. Oberdorfer, F., Helus, F., Maier-Borst, W., 1981. Experiences in the routine production of 123I via the 124Te(p,2n) 123I reaction with a low energy cyclotron. J. Radioanal. Chem. 65 (1–2), 51–56. Scholten, B., Kovacs, Z., Tarkanyi, F., Qaim, S.M., 1995. Excitation functions of the 124Te(p,xn)124,123I reactions from 6 to 31 MeV with
special reference to the production of 124I at a small cyclotron. Appl. Radiat. Isot. 46, 255–259. Scholten, B., Qaim, S.M., Stocklin, G., 1989. Excitation functions of proton induced nuclear reactions on natural tellurium and enriched 123 Te: production of 123I via the 123Te(p,n) 123I process at a low-energy cyclotron. Appl. Radiat. Isot. 40 (2), 127–132. Van den Bosch, R., De Goeij, J.J.M., Vander Heide, J.A., Tertoolen, J.F.W., Theelen, H.M.J., Zegers, C., 1977. A new approach to target chemistry for the iodine-123 production via the 124Te(p,2n) reaction. Int. J. Appl. Radiat. Isot. 28, 255–261. Van den Winkel, P., 2004. Standardized high current solid targets for cyclotron production of diagnostic and therapeutic radionuclides, Technical Reports Series No.432, IAEA, Vienna, pp. 25–35. Weinreich, R., Knust, E.J., 1996. Quality assurance of iodine-124 produced via the nuclear reaction 124Te(d,2n)124I. J. Radioanal. Nucl. Chem. Lett. 213, 253–261. Wilson, C.B., Snook, D.E., Dhokia, B., Taylor, C.V.J., Watson, I.A., Lammertsma, A.A., Lambrecht, R., Waxman, J., Jones, T., Epenetos, A.A., 1991. Quantitative measurement of monoclonal antibody distribution and blood flow using positron emission tomography and 124Iodine in patients with breast cancer. Int. J. Cancer 47, 344–347. Zaidi, J.H., Qaim, S.M., Stocklin, G., 1983. Excitation functions of deuteron induced nuclear reactions on natural tellurium and enriched 122 Te: production of 123I via the 122Te(d,n) 123I-process. Int. J. Appl. Radiat. Isot. 34 (10), 1425–1430.
Applied Radiation and Isotopes 66 (2008) 1281–1286 www.elsevier.com/locate/apradiso
Thick tellurium electrodeposition on nickel-coated copper substrate for 124I production M. Sadeghia,b,, M. Dastanb, M.R. Ensafa, A. Abaspour Tehranib, C. Tenreiroc, M. Avilad a
Nuclear Medicine Research Group, Agricultural, Medical and Industrial Research School, P.O. Box 31485, 498 Karaj, Iran b Faculty of Engineering, Research and Science Campus, Islamic Azad University, Tehran, Iran c Faculty of Engineering, University of Talca, Talca, Chile d Cyclotron Department, Chilean Nuclear Energy Commission, Santiago, Chile Received 1 November 2007; received in revised form 14 February 2008; accepted 19 February 2008
Abstract Tellurium electrodeposition on a nickel-coated copper substrate was investigated for production of iodine-124. The electrodeposition experiments were carried out by the alkali plating baths. The optimum conditions of the electrodeposition of tellurium were as follows: 6 g l1 tellurium, pH ¼ 10, DC current density of ca. 8.55 mA cm2 and room temperature. r 2008 Elsevier Ltd. All rights reserved. Keywords: Thick electrodeposition; Tellurium target;
124
I; Production; TeO2
1. Introduction Due to its favorable nuclear properties, the 4.18 d radionuclide 124I (22.0% b+, E bþ ¼ 2:13 MeV, 78% E.C., Eg ¼ 603 keV) has great potential for application in nuclear medicine. The main research areas are the functional imaging of cell proliferation in brain tumors using [124I]iododeoxyuridine (Blasberg et al., 1996), the imaging of immunoreactions in tumors using 124I-labelled monoclonal antibodies (Wilson et al., 1991; Daghighian et al., 1993), the in vivo imaging of 124I-labelled tyrosine derivatives (Langen et al., 1990) as well as the classical imaging of thyroid diseases with [124I]iodide (Frey et al., 1986; Flower et al., 1990); all of those were demonstrated by positron emission tomography. Targets with isotopically enriched tellurium dioxide (TeO2) are often used in production of 121I (Helus et al., 1979), 123I (Van den Bosch et al., 1977; Michael et al., 1981; Oberdorfer et al., 1981; Zaidi et al., 1983; Beyer et al., 1988; Corresponding author at: Nuclear Medicine Research Group, Agricultural, Medical and Industrial Research School, P.O. Box 31485, 498 Karaj, Iran. Tel.: +98 261 4436395; fax: +98 261 4464055. E-mail addresses: [email protected], [email protected] (M. Sadeghi).
0969-8043/$ - see front matter r 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2008.02.082
Scholten et al., 1989) and 124I (Lambrecht et al., 1989; Firouzbakht, 1994; Weinreich and Knust, 1996; Knust et al., 1990) for medical purposes. Usually, the production process is performed according to the requirements formulated by Van den Bosch et al. (1977). This includes irradiation of solid TeO2 deposited on a platinum support and followed by volatilization of radioiodine after heating of the target to its melting point in a stream of oxygen for some minutes. Electroplated targets with enriched Te are used in 123,124I production by Van den Winkel, (2004). 124 I is routinely produced via the nuclear reaction 124 Te(d,n)124I in a cyclotron by irradiation of isotopically enriched 124Te, which is used either in metallic form (Lambrecht et al., 1988; Firouzbakht et al., 1994) or as TeO2 (Firouzbakht et al., 1994; Weinreich and Knust, 1996; Guenther et al., 1998). In the cited references, the energy of the deuterons is given as 15 and 14 MeV, respectively. Accelerator production of 124I is largely achieved via nuclear reactions 124Te(p,n)124I and 124Te(d,2n)124I which is well suited for medium to low-energy cyclotrons. The NRCAM (Agricultural, Medical and Industrial Research School) employs a Cyclone-30 while CCHEN, a Cyclone18/9 (both accelerators from IBA, Belgium). Solid targetry systems on these accelerators are made up of pure
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copper backings onto which target materials are electrodeposited. 2. Experimental The production of 124I is mainly achieved via nuclear reactions 124Te(p,n)124I or 124Te(d,2n)124I which is well suited to low-energy cyclotrons. To take full benefit of the excitation function and to avoid the formation of the radionuclide impurities, the proton entrance energy should be 14 MeV (Bastian et al., 2001; Scholten et al., 1995). The physical thickness of the tellurium layer is chosen in such way that for a given beam/target angle geometry the particle exit energy should be 8 MeV. According to SRIM code, the thickness has to be 470 mm for 901 geometry. To minimize the thickness of the tellurium layer (and hence lowering the cost price per target), a 61 geometry is preferred, In which case a 47 mm layer is recommended. Tellurium targets are prepared by DC constant current electrolysis of the metal from alkaline plating solutions. Copper plates coated with nickel are used as target carriers. TeO2 (7.3 g l1) was added to a 1000 ml beaker, followed by the addition of KOH (15.5 g l1) and deionized water (250 ml). The homogenized solution was filtered through fine glass filter (0.45 mm) to remove any residual particles, if necessary, to be ready for electroplating. The non-reactive plating vessels used were hollow Perspex cylinders (diameter 6 cm, height 20 cm) fitted with an axial Pt anode wire mounted at the bottom by means of a tube-end fitting though a perforated septum. Four symmetrical windows (22.36 or 11.69 cm2) on the vertical sidewalls allow positioning of up to four copper target backings. Each slot is sealed by an O-ring fitted-window. The slot geometrical shape determines the actual target electrodeposition area. Windows liquid-tight sealing is realized by stainless steel mechanical pestles mounted on a PVC ring surrounding the plating vessel which press the copper backing against O-ring seal. An external PVC ring is fitted with four supporting pins, which hold a motor–stirrer combination in position. The stirrer is a hollow perforated POM cylinder mounted on the axis of a DC motor and surrounding the platinum anode. The stirrer rotation speed is set at 1000 rpm during the process and its rotating direction is reversed after 8 s, improving deposit homogeneity. To keep the desired temperature at a preset level, a heater (a series of six isolated 1 O/1 W resistors, through which an appropriate DC-current is forced (1.1 A—40 1C up to 1.8 A—60 1C), is mounted circularly at the bottom of the vessel. An insulated sensor, introduced through the stirrer support-plate, monitors the plating bath bulk temperature. As electrolysis to depletion requires long-time plating (up to 24 h), evaporation of the plating solution occurs. To maintain a constant liquid volume of 450 ml, a glass/graphite conductivity sensor monitors the solution level and actuates a peristaltic pump at the required rate, supplying distilled water to compensate evaporation losses. The rack-mounted home-made
electronics includes a motor/stirrer control, an adjustable DC voltage generator card and four V/I converters coupled to current boosters. The freshly prepared solution of tellurium was poured into the plating vessel. This refined procedure is a result of several repeated experiments with different concentrations of KOH and electroplating currents. All electrodeposited Te target layers were examined in morphology by a scanning electron microscopy (SEM) technique (using a Joel model JSM 6400 at an accelerating voltage of 20 kV). The thermal shock tests were also conducted which involve the heating of the target up to 250 1C (the temperature that the Te layer can experience during a high current irradiation) for 1 h followed by submersion of the hot target in cold water (15 1C). 3. Results and discussion In order to optimize the Te electrodeposition, the experimental conditions were investigated as follows. 3.1. Pretreatment of the Cu-backing prior to the tellurium plating To ensure a good adhesion, the copper plate was cleaned using 1000 grade sandpaper followed by rinsing the copper plate with deionized water. The copper plate was placed in the plating vessel with 450 ml of nickel sulfate plating solution. The copper plate was connected to the power supply as the cathode whiles the platinum electrode as the anode. The power supply was turned on and the current adjusted to 50 mA cm2 and allowed to plate for 3 min under vigorous stirring (1000 rpm, 8/8 cycle), giving a nickel-electroplated target. The nickel-electroplated copper plates were thoroughly rinsed with water followed by acetone and then paper-dried and weighed. The obtained layers had a thickness in excessive of the copper of approximately 10 mm. 3.2. Influence of the applied voltage The electrodeposition experiments were carried out with different applied voltages (DC, chopped sine (CS) and asymmetric square wave (SW) using a constant current at room temperature, 25 1C. All the electrodepositions were performed under vigorous stirring with a 11.29 mA cm2 current density. The voltages alternatives to DC were believed to reduce or eliminate dendrite formation in the deposits. The results are summarized in Table 1. Since the current efficiency (Z) obtained using DC current was the highest, it was therefore used for the remainder of the electrodeposition experiments. 3.3. Influence of current density Application of a very low current density results in a rather poor-quality deposit. Alternatively, a very high
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Table 1 Influence of applied voltage, current density 11.29 mA cm2, plating time 1.5 h, temperature 25 1C, pH ¼ 13 on the nickel-coated copper substrate
Table 4 Influence of current density, temperature 25 1C, pH ¼ 10 on the nickelcoated copper substrate
Applied voltage
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
DC CS SW
103 53 –
157 157 157
65 33 –
8.55 10.26 13.25
69 71 92
92 94 142
75 75 64
1.16 1 1.16
CS: chopped sine; SW: asymmetric square wave. Table 2 Influence of current density, temperature 25 1C, pH ¼ 13 on the copper substrate
Table 5 Influence of temperature, current density of 8.55 mA cm2, plating time 1.16 h on the nickel-coated copper substrate
J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
Temperature (1C)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
1.28 2.13 4.27 8.55 11.29 26.51
– – – 52 42 78
24 39 79 158 122 245
– – – 33 34 31
2 2 2 2 1.16 1
25 50 63
70 61 57
92 92 92
76 66 16
Table 6 Influence of pH, current density of 11.29 mA cm2, temperature 25 1C on the copper substrate pH
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
1 10 13
– 61 42
122 139 122
– 44 34
1.16 1.3 1.16
Table 3 Influence of current density, temperature 25 1C, pH ¼ 13 on the nickel coated copper substrate J (mA cm2)
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
2.13 4.27 8.55 11.29 12.83 17.10 21.72
– – 70 106 83 89 –
20 79 92 157 148 158 200
– – 76 67 56 56 –
1 2 1.16 1.5 1.25 1 1
current density reduces the overvoltage of hydrogen, which decreases the quality of the deposit as well as the current efficiency. Hence, an optimal value was expected and investigated. The current efficiency was determined at different current densities using DC current at room temperature (Tables 2–4). The optimum DC current density was found to be about 8.55 mA cm2 and should be applied.
3.4. Influence of temperature Increasing the temperature of the solution increases the mobility of the ions and reduces the viscosity of the solvent. The mean current efficiency at 25 1C and a current density of 8.55 mA cm2 was found to be 76%, which the highest in the range investigated (Table 5).
Table 7 Influence of pH, current density of 8.55 mA cm2, temperature 25 1C on the nickel-coated copper substrate pH
Mean weight Te (mg)
Theoretical weight Te (mg)
Current efficiency (%)
Time (h)
1 10 13
– 69 70
79 92 92
– 75 76
1 1.16 1.16
3.5. Influence of pH Adjusting the bath acidity is an important effect for both the bath efficiency and the physical properties of the coatings. A large reduction in acidity causes hydrogen reduction and simultaneously deposit sediment of the base salts on cathode. After preparing the tellurium bath (the pH of bath was about 13) for studying the effects of solution acidity on electroplating quality, the acidity was changed from 13 to 1. It is clear that the higher current efficiency and better electrodeposited layers are obtained available in lower acidity than in comparison to electrodeposited layers using a higher acidity bath (Tables 6 and 7).
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3.6. Target quality control To estimate the quality of the electroplated tellurium targets, some criteria had to be taken into account such as homogeneity, morphology, visual appearance of the deposited tellurium and thermal shock test results. The homogeneity of the tellurium layer is important as it may seriously affect the production rate of 123,124I. This was determined by measuring the thickness of several parts of the layer by micrometer and calculation of the standard deviation of the data. All electrodeposited Te target layers were examined in morphology by a SEM technique. The evaluation of quality of the layers was achieved by comparison of the photomicrographs in terms of size and form of the Te nuclei and the extent to which they overlapped each other. Smaller, more spherical and the more overlapping nuclei were considered to be a good plating quality. The thermal shock tests involved the heating of the target up to 250 1C for 1 h followed by submersion of the hot target in cold (15 1C) water. Observation of the absence of crack formation or peeling off of the tellurium layers indicated a good adhesion for the deposit.
SEM photomicrographs show that granularity of electroplated targets with current densities of 4.27–11.12 mA cm2 were not as desired (Figs. 1–3). Hence, a current density of 8.55 mA cm2 was chosen and the SEM photomicrographs show a more suitable granularity (Fig. 4). After obtaining the optimum conditions (current density of 8.55 mA cm2 and temperature 25 1C), a series of electrodeposition procedures were conducted on four target backings. Using different concentration of Te in the bath, the experiments were carried out for the preparation of four targets (surface area of 11.69 cm2) with different thickness. The electrodepositions in these experiments were continued for depletion of Te (Z476%). At the end of the plating, the Te surface was observed to be black and shiny. The black appearance is probably from deposition of Te-black near the end of the plating due to excessive H2 evolution. The Te black was easily removed by simple rubbing of the surface using a print-board eraser followed by acetone cleaning in an ultrasonic bath. Neither crater formation nor peeling off was observed during a thermal shock treatment. Cracking occurred only after multiple bending.
Fig. 1. SEM of a tellurium deposit on the nickel-coated copper substrate grown at pH ¼ 13, 25 1C and a current density of (a) 4.27 and (b) 11.12 mA cm2 from the solution.
Fig. 2. SEM of a tellurium deposit on the nickel-coated copper substrate grown at a current density of 8.55 mA cm2 from the solution, pH ¼ 13: (a) 25 1C and (b) 63 1C.
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Fig. 3. SEM of a tellurium deposit on the nickel-coated copper substrate grown at, pH ¼ 10, 25 1C and a current density of (a) 11.12 and (b) 10.26 mA cm2 from the solution.
Enriched Te is a precious metal and it is therefore essential it be recovered from the processed solutions from the radiochemical separation to be re-used. The electrodeposition of Te using alkali baths gives a quite acceptable target quality for the irradiation purposes. References
Fig. 4. SEM of a tellurium deposit on the nickel-coated copper substrate grown at a current density of 8.55 mA cm2 from the solution, pH ¼ 10, 25 1C.
The layer thickness is no longer time-controlled, but governed by the amount of Te present in the plating bath. When hydrazine and H2O2 was used, metallic tellurium begins to precipitate. In addition, after some time, the electroplated targets started to dissolve and the whole solution turned dark in color using low acidity solution and low current density. This dark color originated from undissolved tellurium oxides. 4. Conclusions 124,123
I can be produced using electroplated tellurium targets on a nickel-coated copper substrate prepared from alkali solution. The electrodeposition experiments were continued for complete depletion of Te (Z476%) resulting in a deposited layer thickness of 46 mm and using an optimum amount of tellurium (6 g l1) in the bath. As the electrodepositions satisfy a thermal shock test, current beam irradiation of higher than 100 mA can be applied.
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