Standardized High Current Solid Targets for Cyclotron Production of Diagnostic and Therapeutic Radionuclides

TECHNICAL REPORTS SERIES No. 432 COMPANION CD-ROM

STANDARDIZED HIGH CURRENT SOLID TARGETS FOR CYCLOTRON PRODUCTION OF DIAGNOSTIC AND THERAPEUTIC RADIONUCLIDES

UNEDITED REPORTS OF THE PARTICIPANTS OF THE THIRD RESEARCH COORDINATION MEETING

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 2004

CONTENTS

Development of a high current solid target, a novel radiochemistry for Tl-201 and Pd-103 production R. Strangis, C. Rocco, E. Guevara, G. Maslat, F. Corral, N. Gonzáles, R. Téramo, J. Lago, G. Casale

A plating/electrodissolution/recovery cycle for rhodium target material used for the industrial cyclotron production of palladium-103 P. van den Winkel, L. de Vis, R. Waegeneer, A. de Schrijver, H. Afarideh, M. Sadeghi, M. Haji Saeid

New technology for the industrial preparation of high quality Tl-203 cyclotron targets by constant current electroplating P. van den Winkel, L. de Vis, M. de Vreese, R. Wageneer, A. de Schrijver, A. Arzumanov, N. Gorodiskaya, P. Zheltov

Cyclotron production of iodine-123 and Pd-103 Zhou Wei, Wang Yongxian, Zhang Chunfu

Production of diagnostic and therapeutic radionuclides S. Takács

High current Tl-203, Rh-103 targets preparation for cyclotron production of Tl-201 and Pd-103 radionuclides A. Arzumanov, V. Berger, A. Borissenko, N. Gorodisskaya, I. Ilmatov, A. Knyazev, V. Koptev, S. Lyssukhin, A. Platov, G. Sychikov, D. Zheltov

Research and technological development for the production of Pd-103 at the U-120 cyclotron from Bucharest P.M. Racolta, D. Dudu

An operated solid target device design for iodine-123(124) production L.M. Solin, V.A. Jakovlev, A.I. Baranov, A.A. Timofeev, D.A. Zubov

Standardized high solid targets for cyclotron production of diagnostic and therapeutic radionuclides S. Al Jammaz, S. Al-Yanbawi, S. Melibari, Rahma

Useful concepts in solid state target technologies D.J. Schlyer, R.A. Ferrieri

DEVELOPMENT OF A HIGH CURRENT SOLID TARGET, A NOVEL RADIOCHEMISTRY FOR TL-201 AND PD-103 PRODUCTION

R. STRANGIS, C. ROCCO, E. GUEVARA, G. MASLAT, F. CORRAL, N. GONZÁLES, R. TÉRAMO, J. LAGO, G. CASALE Cyclotron Facility, Ezeiza Atomic Centre, Comisión Nacional de Energía Atómica, Argentina

Abstract

201

P Solid targets development aims to obtain large quantities of radionuclides from accelerators.P Tl is the most used radioisotope in nuclear medicine, which is produced in cyclotron. The scope of the research was to test another procedure of Tl-201 production as an alternative of the precipitation and extraction method used at present. Utilization of ionic exchange resins was studied. Pd-103 is increasingly used in brachytheraphy seeds. A high current solid target technique for cyclotron irradiation of electroplated metals was developed to produce Tl-201 and Pd-103. The design of the solid target set up and different procedures to obtain Pd-103 for seeds applications are presented.

1. INTRODUCTION

Tl-201 has wide utilization in cardiologic studies, renal, and in the last years as tumoural 103

P cerebral detector. P Pd has been used in treatment of various cancers such as eye, brain, neck, uterus, colon [1], but it is almost exclusively used for prostate cancer as the most common cancer and causing the highest death rate in men. These radionuclides are cyclotron-produced by irradiation of solid targets and the objective of this CRP is to develop procedures to obtain these targets.

2. DEVELOPMENT OF A NEW SOLID TARGET CARRIER

The solid target system installed in the Cyclotron Facility by Forschungszentrum Karlsruhe o

P (FZK), Germany, has the following characteristics: Tangent beam 7P , ISO-RABBIT pneumatic transport system; welded system, Al body + Ag face, Irradiation surface of 23 mm × 80 mm.

203

P Problems after 160 P Tl irradiations:

• High cost: US$1800 • Recovery needed: High dose (Ag-105) 6 month of decay to reuse. • 30 Targets for a weekly routine production +

• P AgP ions are introduced with Tl-203. Pitting of the silver surface reduce the life. • Cooling studies made by Prof. Van Den Winkel show that at 100 µA metallic thallium melts. • Ag+ traces are recovered with enriched Tl (same cationic group)

The proposed target has the following advantages:

• Screwed system, no weld needed. • Frontal face: 1mm Cu (not recycled) thickness • Two-pieces target. Al body (low dose, recycled) Cu face, (high dose, not recycled). • Low assembly dose. • 3-4 target body/weekly irradiation. • Low irradiation cost. 103

• P Allows Rh irradiation for P Pd production; better cooling.

FIG. 1. Ezeiza target.

TABLE I. DEFORMATION OF DIFFERENT CU SHEETS (MM)

Thickness Pressure 2 2 2

P P P 1 Kg/cmP 3 Kg/cmP 7 Kg/cmP 1 mm - 0.02 0.04 1.5 mm - 0.01 0.02 2 mm - - 0.01

3. NEW CHROMATOGRAPHIC TL/PB SEPARATION FOR TL-201 CYCLOTRON PRODUCTION

3.1. Analytical methods

+ 3+ 2+

P P P The distribution constants (Kd) of TlP , TlP and PbP were determined for the cation exchange resin BioRad AG-50W of different cross-linkages and particle sizes and different HCl and HNO3B B 201 2+ 210

P P P concentrations. To measure Tl tracer of P Tl, was used to detect PbP tracer of P Pb was involved. The concentrations of Tl measured in the Jarrell-Ash equipment by atomic emission (sensibility 1.0 ppm) at 3445 Å were correlated with Pb measured in the same equipment at 2170 Å (sensibility 0/01ppm).

The chromatographic separation was developed using preparative equipment constituted by a peristaltic pump, a GILSON fractions collector coupled to a NaI (Tl) detector and a home made data acquisition system.

3.2. Determination of Kd

1,000 g of cationic resin in 50 ml acid solution was equilibrated with 250 mg of Tl2B SO4B labeled 201 2+ 210

P P P with P Tl. For the PbP , a solution of Pb (NO3B )B 2B B (concentration 0.1mg/ml) spiked with P Pb was used. 201 3+ 201 +

P P P P The P TlP was obtained oxidizing the P TlP with a Cl 2B B generator (KMnO4B B + HCl) bubbling gently during one minute and then heating in order to eliminate the residual Cl2B .B Table II shows the Kd values obtained with AG50Wx12, 200-400 mesh resin for different concentration of HCl and HNO2.B

TABLE II. KD RESULTS

[HNO3B ]B 0.1 M 0.25 M 0.5 M 1.0 M 2.0 M 5.0 M 2+ 4

P P PbP 10P 1420 183 35 8.5 7.2 +

P TlP 173 91 41 22.3 9.9 7.6

[HCl] 0.1M 0.25 M +

P TLP 100 62 3+

P TlP 80 53 2+ 4

P P PbP 10P 3500

3.3. Optimization of the chromatographic Pb/Tl separation 201 210

P P Using a simulated target (700 mg of TlNO3B B and 1mg of Pb (NO)2B B labeled with P Tl and P Pb respectively) in a low pressure chromatographic equipment, separations involving different types of columns, resin bulks, gradients and solvent flows were tried.

The optimal conditions for the separation are, as follows: • Type of Resin: AG50WX12 200-400 • Solvent: HNO3B B 0.1M • Resin bulk: 1,20 g • Flow: 1.3 ml / min • Temperature: ambient

+ + 2+

P P P In these conditions, a high ratio of Kd PbP /TlP in HNO3B B 0.1M is found, allowing to keep PbP +

P adsorbed on the column during quantitative elution of Tl P .

3.4. Proposed method

The previous results allow to realize a new separation of 203Tl carrier from the carrier-free 201Pb after dissolution of the irradiated target in diluted HNO3 and adsorption on a small AG-50W X12 203

P (200-400 merk) column. The P Tl is quantitatively eluted with 0,1 MHNO3 and 0,1 MHCl. Upon a 32 hrs decay period, the 201Tl is eluted with 0,1 MHCl. The flow diagram is represented in Fig. 3.

HNO .1M HCL .1M HCL 2M 150

Tl Pb 100

0 0 50 100 150 200 250 300 350 400 450

FIG. 2. Chromatogrammes.

201 201

P P FIG. 3. Method of cyclotron produced P Tl using chromatographic withholding in P Pb column.

The solution obtained in the 203Tl recovery step is HNO3 0.1M, a medium allowing use as such in the recovery step of 203Tl.

The active residues from Pb obtained in the last step were used to study the percentage of Pb2+, remaining on the column and by the isotopic relationship, the energy range to which was irradiated the target.

3.5. Target irradiation 203 201 201

P P P P The main production reaction is: P Tl (p, 3n) P Pb Tl (t½=73hs)

4 and the secondary reactions are: 203 203

P P P Tl (p, n) P Pb (t½=52hs. ) 203 202 202

P P P P P Tl(p,2n)P Pb Tl(t½=12.2 d) 203 200 200

P P P P P Tl (p, 4n) P Pb Tl(t½ = 26.1hs)

From the ALICE code and according to literature (8, 9) it follows that the optimum irradiation +

P range with HP is 28 to 18Mev. This range minimizes the impurities produced by the secondary reactions, in order to produce a final product according the pharmacopoeia regulations.

A target thickness corresponding with such energy degradation was produced and sufficient surface area for the power dissipation of the cyclotron beam (3 kw) was realized.

P For solid targets, the proton beam target angle equals 7P . The target area consists of an ellipse 203

P (to 7 degree projection of a circle of 10 mm in diameter) of 80 * 10 mm with 700 mg of P Tl (98%), electroplated in basic medium according Van den Winkel’s recommendations in a double window cube.

3.6. Tests in the cyclotron and results

The method was tested in the cyclotron of the Ezeiza Atomic Centre, distant 30 km from the +

P city of Buenos Aires. This cyclotron accelerates HP up to 45 Mev with a current of 150 µA. Irradiation with different currents were performed in order to evaluate the quality of the electrodeposited target layer and the final product. Using natural thallium facilitates the study of the adsorption of Pb since 203

P large quantities of P Pb are produced by the reaction:

205 203

P P P Tl (p, 3n) P Pb (t½=52hs)

The following yields (EOB corrected) were obtained:

P o Recovery of PbP on column: 99.8% 201

P o Yield of P Tl (respect to the theoretical): 95% 203

P o Recovery of P Tl: 99.5%

The radionuclidic purity was determined by gamma spectrometry with HPGE detector coupled to the multichannel Canberra series 4100; (EOB corrected):

201 200 202 201 203

P P P P P P o Tl (reference): 100%; P Tl: 1.0%; P Tl: 0.4%; P Pb: 6.10-3%; P Pb: 0.21% o Radiochemical Purity: according to bibliography (7,8) obtaining: 201 + 201 3+

P P P P P o TlP : 100%; P TlP : 0%

3.7. Conclusions 201

P The method developed gives a good yield for the P Tl production. The quality control of the 201

P P Tl obtained complies with the regulations of the current pharmacopoeia requirements; even for the irradiation of natural thallium. The principal advantage of this method is that precipitation and/or extraction steps are avoided, steps that are difficult to do in hot cells.

P The ion exchange chromatography proposed for the separation of nanomoles of PbP from large +

P quantities of TlP , is simple and allows total automation of the entire process.

201

P 4. DIRECT PC P Tl PRODUCTION 201

P In order to complete our radiochemical P Tl processing presented in this workshop, an automated system was developed. The system is operated by Windows Visual Basic 3.0 software,

5 allowing multi task performance. Several electronic interfaces have been developed for operating the electromechanical component of the manifold, thus avoiding the industrial automation equipment such as PLCs. Though not frequently used for automation of industrial processes the operating system and software developed, proved to be 100% reliable.

The automation intends:

o To minimize the personnel's operative interventions involved in the production and consequently to reduce the risk of human error during the process. o To minimize the time of the operators’ radiation exposure. o To reduce the size of the hot cells.

4.1. PC software to obtain Tl-201

This software possesses a window of graphic interface (Image 1), in which one can control all electric and electro-pneumatics components integrated in the automatic system.

FIG. 4. Image 1 (Outline of the automatic process).

On the left part of the window there is a panel showing the process diagram, where each component can be checked by double clicking with the left button of the mouse.

On the right part of the window, the storage system of residual liquids is presented. The state of each of them can be checked as well.

203

P During the dissolution of the irradiated P Tl electrodeposited on the solid target carrier, one can obtain a potentiometric dissolution graph (V versus t) curve and a temperature versus time (T versus t) curve. These data sets allow optimization of the dissolution time as a function of temperature.

FIG. 5. Image 2 (Breakup curve).

There are two ways to use this software, manual or automatic. In the manual option, the operator controls each component of the system (electronic valves, bombs, ovens heaters, sensors, etc.). The automatic option runs the whole sequence of operations automatically. To implement this option, a micro language of programming of processes has been generated. It is composed of a series of commands allowing control of any of the components of the system. To use the micro language, a program that creates and edits the process performance is introduced. During the automatic operation of a process, a window will be visualized, indicating the data of the program in course. The automatic process could be interrupted at any time without waiting for the whole process program to be completed.

4.2. Editor programs for the process operations

Apart from the possibility of generating the operations in charge to carry out tasks involved in the process, the software provides a series of commands that allow generating messages to be visualized during the process.

FIG. 6. Image 3 (editor of process programs).

4.3. Conclusions

This automatic system has been used successfully in 200 process runs in a prototype hot cell in 3

P the Cyclotron Facility at the Ezeiza Atomic Centre. The mini hot cell has a volume of 0.25 mP and is fitted with 15cm thick lead walls. The electronic systems are simple parallel interfaces and eight channel analog-digital converters. All built into the PC box. Direct PC interfacing has the advantage that the microprocessor “knows” all the parameters of the radiochemical process and the whole system is very simple and safe.

103

P 5. CYCLOTRON P PD PRODUCTION

103

P Four ways to obtain P Pd for seed production are proposed, according to the type of cyclotron and radiochemistry.

5.1. Targets

Main reaction:

103 103

P P P Rh (p, n) P Pd Ep+B =18-0B MeV Yield= 398 uCi/uA.h

Proposed methods:

• Direct irradiation of Rh wires. • Rh foil irradiation & thermomigration of Pd. (Artyom Arzumanov Method) • Electrodeposited Rh target &thermomigration of Pd. • Electrodeposited Rh target & wet chemistry (Van den Winkel Method).

5.2. Direct irradiation of Rh wires

103

P This system was designed in order to produce directly P Pd by irradiation of Rh wires. The wires have appropriate dimensions to be put into the titanium tubes for brachytherapy seeds. 20 Rh wires (7x 0.5mm) can be assembled in a 7degree target to beam system separated by 4 mm. A graphite mask (1.5 mm) covers the wires, gives mechanical support and acts as energy degradation. Cooling is by direct contact of the backing with water.

Disadvantages:

• Direct irradiation produces Rh 102 (207d), Rh 102m(2.9y), Rh 101m(4.34d), at lower levels than pharmacopoeia accepts for Pd-103 (<2%) • Necessity to rotate the wires during irradiation (not rigorous) to obtain a more or less 103

P homogenous P Pd distribution. • The apparent activity is lower than real activity (due the self shielding). • It is not applicable in high current beams. (< 50µA).

Advantages:

• The stopping power of Rh is sufficient to degrade 18MeV –5 MeV in 0.5mm of Rh in a o

P 7P beam/target geometry. (Sparkly –Program) • Direct application in seeds.

FIG. 7. Direct production of Pd-103 by irradiation over Rh wires.

5.3. Rh foil irradiation & thermomigration of Pd

This method is based on the thermomigration of impurity atoms in a perfect metal lattice. For Rh it was first developed by N. Gorodisskaya and A. Arzumanov. It consists in direct irradiation of an Rh foil (99.99% purity) 50µm, in direct contact with the backing of the solid target that is water- cooled.

The high Rh melting point allows irradiation up to 100µA without damage in a 7° beam to 103

P target angle. Then the irradiated foil is put into a high temperature oven at 1200°C for 2-3 hours. P Pd is displaced out of the Rh metal matrix. Finally, the foil is washed with HCl 0.1M removing in part the 103

P P Pd from the surface of the foil.

5.4. Electroplated Rh target and thermodifussion of Pd

In this method, the Rh is electroplated from a chloride Rh bath on a target Cu sheet with a layer thickness of 50µA. This target tolerates more than 150 µA at 18 MeV. The irradiated target is disassembled and the copper sheet is dissolved in HNO3B B (c) + HCl (c) (50-60°C). The fragments of Rh obtained are washed with distilled water and then put into a high temperature oven at 1200°C for 2-3 103

P hours. P Pd is displaced out of the Rh metal matrix. Finally, the fragments are washed with HCl 0.1M 103

P removing the P Pd from the surface of the rhodium.

5.5. Electrodeposited Rh target and wet chemistry method

Van den Winkel has developed this method. The Rh is electroplated (50µm layer) from a sulphate bath on a target Cu carrier. This target supports much more than 150 µA at 18 MeV. The irradiated target is disassembled and the copper sheet is dissolved with HNO3B B (c) + HCl (c) (50-60°C).

The fragments of Rh obtained are dissolved by electrodissolution with bubbling of Cl2B B gas into the

9 solution of HCl(c) while applying a current of 10 Amp A.C. 60 Hz between two graphite electrodes. The solution obtained is used in the wet radiochemistry procedures.

5.6. Conclusions

All the systems proposed are suitable for Pd-103 production; the choice depends of the beam current on the target and type of solid target station. The direct method is for low current beams, up to 50 uA, Rh radionuclidic impurities obtained are below the pharmacopoeia limits if the energy of protons is below 18 MeV. The great advantage of this method is the direct application in seeds so that no radiochemistry is needed. The disadvantage is due to the self shielding of the wire; the apparent activity is less than the real one. The Rh foil irradiation method is simple, fast, and the target can be 103

P recycled, but the P Pd yield is 50–70% of the activity produced. The electroplated Rh method tolerates more current but needs recovery chemistry for the rhodium; the yield is 50–70%. The electrodeposited Rh method has high yield but needs a complete radiochemical procedure.

The CRP has provided the possibility to investigate and validate methods to produce Pd-103 from Rh targets. The target developed and improvement in Tl-201 production are the main achievements of the CRP The new technology adopted for Tl target electroplating and enriched thallium recovery gives excellent results in a very clean process with yields of 99.9%.

REFERENCES

[1] DEWI M LEWIS, Designing a Radioisotope Facility, Amersham Int. UK, 1996. [2] REDDY A. S.; Solvent Extraction Separation of Tl. J.Radioanalitical Nucl.Chem.Letters 87/6 [3] MALININ S.; Production of Tl-201, JARI Vol 37 No. 7. [4] BRITTO J.L.Q.; A New Production Method for Tl-201. J.Radioanalitical Nucl.Chem.Letters 94/6 1985. [5] BONARDI M., Tl-201 for Medical Use. Radiochem Radioanal. Letters 42/1/1980. 3+ +

P P [6] ASHOK RAO, Separation of TlP from TlP . J.Radioanalitical Nucl.Chem.Letters 94/6/ 1985. [7] FERNANDEZ L.; Quality Control of Tl-201 at IPEN. J.Radioanalitical and Nucl.Chem. Vol 172, Nr. 2, 1993. [8] LAGUNAS SOLAR M. Tl-201 Excitation Functions. JARI Vol 31, pp 117-121. [9] QAIM S.M. et al. Production of Tl-201 and Pb-203 via Proton induced nuclear reaction on natural thallium. JARI, v. 30 (2), p.85 (1979)

10 A PLATING/ELECTRODISSOLUTION/RECOVERY CYCLE FOR RHODIUM TARGET MATERIAL USED FOR THE INDUSTRIAL CYCLOTRON PRODUCTION OF PALLADIUM-103

P. VAN DEN WINKEL, L. DE VIS, R. WAEGENEER, A. DE SCHRIJVER, VUB- Cyclotron, Brussels, Belgium

H. AFARIDEH, M. SADEGHI, M. HAJI SAEID NRCAM — Cyclotron Department, Tehran, Islamic Republic of Iran

Abstract

103 103

P P The production of carrier-free Pd-103 solutions by the P Rh(p,n)P Pd threshold reaction involves three chemical steps. The first deals with the electroplating of a homogeneous 40-50 µm rhodium layer on a copper target carrier, ensuring to take full benefit of the excitation function during the irradiation in a 6° beam /target geometry. After irradiation the second step involves the dissolution of the irradiated rhodium, followed by step number 3, the separation of rhodium and carrier-free Pd-103. A cylindrical, graphite centrifugal electro-dissolution mini-reactor was developed. It allows time-controlled solution of rhodium fragments, powder and pieces of foils and wires. Feeding 12 N hydrochloric acid into the system operated at 85°C and 1000rpm rotation speed and applying a 30 amperes ac-current, up to 3 grams of metal are dissolved in 40 ml of acid at 99% solubilization level in less than 3 hours. Carrier-free Rd 103 was separated and extracted using the solvent-solvent method. Three different solvents, aqueous Rh2B OB 3B ,B Rh2B (SOB 4B )B 3B ,B RhCl3B ,B were tried for rhodium electroplating and recovery. The results indicate that aqueous Rh2B OB 3B B works best. To optimize the process, the experiment was repeated for different currents, temperatures, and pHs. With this method, a completely smooth, reflective, and crack-free electroplated layer with a thickness of 120 micrometers was obtained.

1. INTRODUCTION

The suitability of a given radionuclide for Brachytherapy is determined by its half-life, the type of radiation and its energy and the abundance (number per decay) of its emission.

Pd-103 with half-life of 17 days is a very low energy photon emitter (21 KeV) available for permanent interstitial implantation. Pd-103 has better energy and safety characteristics than as I-125. Its initial peripheral dose rate is approximately three times higher than that of I-125. Tis may provide improved control of rapidly proliferating tumours. Pd-103 has been used in treatment of various cancers such as eye, brain, neck, uterus, colon [1], but it is almost exclusively used for prostate cancer as the most common cancer and causing the highest death rate in men.

2. A PLATING/RECOVERY CYCLE FOR RHODIUM TARGET MATERIAL USED FOR THE INDUSTRIAL CYCLOTRON PRODUCTION OF PALLADIUM-103

The aim of the joint research concerned the plating/recovery cycle of rhodium targets. The ultimate purpose of the experimental work was the production of Cyclone-30 targets that can be used at the NRCAM in Karaj and that can be prepared from chemicals commercially available in Iran or from rhodium recovered from solutions obtained after centrifugal electro dissolution of irradiated targets and extraction of Pd-103. Moreover, attempts were made to obtain deposits showing acceptable qualities to fully exploit the beam current capacity of our accelerator.

2.1. Recovery of rhodium from irradiated target fragments

2.1.1. Introduction Preliminary experiments showed that high-quality rhodium targets could be obtained from commercially available plating solutions such as Rhodex (Enthone, USA). As the purchase of these baths may be a problem in developing countries and as the price of rhodium compounds suitable for the preparation of solutions for thick-target (40 µm) plating are rather high, the recovery of rhodium from dissolved (irradiated) targets and the preparation of home-made plating baths were studied.

The plating from Rhodex is taken as a reference as far as the surface granulometry and the thermal shock behaviour are concerned.

2.1.2. Reference quality criteria The simultaneous preparation of four Cyclone-30 rhodium targets (thickness 40 µm, surface 2

P plating area 11,69 cmP , rhodium weight 580 mg/target, 6° beam/target irradiation geometry) in the VUB plating set-up requires the presence of 2,32 g of Rh (116 ml Rhodex of 25g/1250 ml concentrate) in a 450 ml plating volume. The standard plating procedure is, as follows:

1. Dilute 116 ml Rhodex concentrate to 450 ml with 11% sulfuric acid ( pH = -0.34); 2. Heat up to 60°C and start a 24 hour plating at constant volume and temperature applying a DC-current of 150 mA per target carrier; 3. Discard the colorless solution (pH = -0.39) and rinse abundantly with water 4. Remove the targets from the plating vessel and rinse with demineralized water 5. Clean the rhodium surface area with CIF detergent, rinse with water and acetone and air- dry the targets.

The SEM (scanning electron microscope) picture at a 250 magnification factor is shown in Fig. 1.

FIG. 1. Rhodex Reference Rhodium target (SEM X 250).

The reference quality criteria for targets prepared from other plating solutions are:

1. Visual inspection and comparison of the granulometry of the X 250 magnification shot of a target with that of Fig. 1; 2. The thermal shock test – heating of the target for 1 hour at 500°C in air, followed by prompt immersion in cold water (15°C) should NOT give rise to crack formation nor to peeling off of the rhodium layer.

2.1.3. Procedures for recovery and plating bath preparation Upon centrifugal electrodissolution of (irradiated) rhodium fragments and extraction of the Pd- 103, a strong (up to 6N) hydrochloric acid solution containing the rhodium is used for the recovery. To prepare a new plating bath, combined recovery solutions holding the required amount of rhodium (2,32 g for the simultaneous preparation of 4 targets of 40 µm) should be involved.

Three procedures were tried :

12 -

P a. Recovery as RhCl3B B solution after evaporation to near dryness as such. The Cl P content of the plating solution will be relatively high;

b. Recovery as Rh2B (SOB 4B )B 3B B solution after addition of H2B SOB 4B B and subsequent evaporation to near dryness. The chloride content strongly reduced;

c. Recovery as solid hydrated Rh2B OB 3B B after evaporation to near dryness as such, followed by dilution with water and precipitation of Rh2B OB 3B .aqB upon addition of concentrated NaOH. The chloride content of the plating solution will be reduced to a mininum.

a. Recovery as RhCl3B B solution [2]

- Filter the recovery solution over a 0.45 µm filter (HVLP, Millipore) to remove any solid (Rh) particle present; - Evaporate under gentle stirring (350°C at the start, 150°C near the end) to near dryness; - Take up in 300 ml of water, heat (150°C) and stir for 30 minutes and then filter through a 0.45 µm filter; - Add the required quantity of plating additive (sulphamic acid, stress reducing agent);

- Adjust pH to the aimed at value by means of 10 N NaOH or 36N H2B SOB 4B ;B - Make up to 450 ml with water.

In Table I, the data of 11 recovery/plating bath preparations obtained according this procedure are summarized.

TABLE I. RECOVERY OF RH AS RHCL3

ExperimentNr pH WEIGHT RH SULPHAMIC VOLUME (G) ACID (G) (ML) C1 2.8 5 450 2.00 C2 3.5 5 450 2.00 C3 4.1 5 450 1.94 C4 4.2 5 450 2.43 C5 3.3 5 450 2.28 C6 3.1 5 450 2.65 C7 3.6 5 450 0.00 C8 3.1 5 450 0.00 C9 1.9 5 450 0.01 C10 2.5 5 450 3.60 C11 1.7 10 450 0.98

b. Recovery as Rh2B (SOB 4B )B 3B B solution[3]

P To further reduce the ClP content of a plating solution, the recovery solution should be taken to near dryness after the addition of concentrated sulfuric acid:

- Filter the recovery solution over a 0.45 µm filter to remove any solid (Rh) particle; - Evaporate under gentle stirring (350°C at the start, 150°C near the end); - Carefully add a suitable volume (2 to 20 ml) of 95% of sulfuric acid;

- Evaporate (350°C) until SO3B B fumes evolve and then continue heating and stirring for 30 more minutes; - Carefully add 300 ml water, stir and heat at 150°C for 30 minutes and then filter through a 0.45 µm filter; - Add bath additive (sulphamic acid, stress reducing agent) and adjust pH if desired with 10N NaOH: - Make up with demineralized water to the volume requested.

Details on the preparation of four recoveries are summarized in Table II.

TABLE II. RECOVERY OF RH AS RH2B (SOB 4B )B 3B B SOLUTION

Experiment Weight Volume Sulphamic Volume Acidity /

Nr Rh (g) H2B SOB 4B (ml)B acid (g) (ml) pH S1 12.5 20.2 10 900 2 N S2 8.2 8.1 5 450 1.9 N S3 5.7 2 5 450 pH=2 S4 1.5 2 5 150 pH=2

c. Recovery as solid Rh2B OB 3B .aqB

A two-step procedure allows the preparation of a new plating bath.

Step 1: Precipitation of Rh2B OB 3B .aqB

- Filter the recovery solution containing 2 to 6 grams of rhodium through a 0,45 µm filter (to remove any particle); - Evaporate the filtrate to near dryness (350°C at the start, 150°C near the end); - Take up in 350 ml of demineralized water and heat (150°C) and stir for 15 minutes - Filter through a 0,45 µm filter (2-10 mg of black (Rh) residue is obtained), cool down the filtrate to room temperature in a water bath; - Neutralize under vigorous stirring with 10N NaOH up to pH = 10 to 10.5. Use a combined glass electrode as pH sensor;

- To improve the filterability of the yellow Rh2B OB 3B .aqB precipitate, allow to digest for 24 hours at 50°C and gentle stirring; - Filter the precipitate on a Bleu Band filter paper (Schleich&Scheull 589) and wash at least -

P ten times with water to remove most of the adsorbed ClP anions. As some of the yellow precipitate leaks through the filter, the filtrate is applied to a 0.45 µm filter; - Allow both filters carrying the precipitate to dry at the air for 24 hrs. Then remove the rhodium oxide, grind the precipitate in an agate mortar and apply a 48 hrs vacuum-drying (350 mbar) at room temperature. - The results of 14 recovery experiments are shown in Table III.

TABLE III. RECOVERY OF RH AS RH2B OB 3B .AQB

Experiment Weight Rh Weight Rh2B OB 3B .aqB Rh in Rh2B OB 3B .aqB Nr (g) (Vacuum-dried) (g) (%) O1 3.6 5.77 62.3 O2 3.3 5.88 56.1 O3 1.9 3.02 61.2 O4 3.8 6.40 59.3 O5 2.5 4.24 58.9 O6 2.6 4.06 64.0 O7 3.4 5.67 60.0 O8 5.2 9.93 52.1 O9 2.6 4.70 55.3 O10 3.6 6.88 52.3 O11 3.6 6.71 53.6 O12 3.7 7.23 51.2 O13 2.5 4.77 52.4 O14 3.7 7.23 51.2 Mean 56.4 ± 4.4

14 The mean rhodium content of the precipitate amounts to 56.4 ± 4.4%. For the Rh2B OB 3B .5HB 2B OB compound referred to in literature, this percentage is 59.9. The difference with the experimental value together with the different colors of the precipitates observed (ranging from lemon-yellow over yellow, yellow-ochre to dark ochre Fig. 2) suggests the composition and/or water content of the precipitate do depend on slightly changing experimental parameters such as rate of neutralization, final pH and digestion conditions. The results imply that the percentage of rhodium in the hydrated oxide must be determined experimentally before the plating of targets. This is done in Section 2.2.3.4.

FIG. 2. Hue of vacuum-dried Rh2B OB 3B .aq.B

Step 2: Preparation of plating bath from Rh2B OB 3B .aqB

P To further reduce the ClP content of the plating solution, the latter is prepared by dissolution of an appropriate amount of rhodium oxide in boiling concentrated sulfuric acid thus expelling any chloride anion as HCl. For the simultaneous plating of four 40 µm Cyclone-30 targets and taking the mean rhodium percentage reported in Table III as a reference, the procedure is, as follows:

- Transfer 4,076g of hydrated rhodium-oxide into a 400 ml beaker provided with a magnetic stirring bar and carefully introduce 10 ml of 95% sulfuric acid. Cover the beaker with a watch-glass supported by glass hooks;

- Heat under gentle stirring (350°C) until SO3B B fumes evolve and continue for 15 more minutes. A dark yellow-brown concentrate is obtained; - - Carefully add 250 to 300 ml of water and continue heating (150°C) and vigorous stirring for 15 minutes; - Filter through a 0,45 µm filter and dilute to about 400 ml with water; - If required, adjust pH to the aimed at value with 10N NaOH after the addition of plating additives (sulphamic acid or magnesium sulphamate, stress reducing agent); - Make up to 450 ml.

2.2. Plating of rhodium targets from home-made plating solutions

2.2.1. Introduction The electrodeposition of rhodium targets from homemade plating baths (described in Section I) was carried out with VUB plating equipment that has been used previously for the preparation of Rh targets from the commercially available Rhodex (Enthone). A brief description of the equipment precedes the summary and discussion of the current results.

2.2.2. Description of the VUB-plating set-up The plating vessel (Fig. 3) is hollow perspex cylinder fitted with an axial Pt anode wire mounted in the bottom by means of a tube-end fitting with perforated septum. Four symmetrical windows in the vertical wall allow introduction and positioning of four Cu target carriers. Each slot is provided with an O-ring fitted window, the geometrical shape of which determines the electrodeposition area. Liquid-tightness is realized by stainless steel mechanical pestles mounted in a PVC ring surrounding the plating vessel and by pressing the Cu-carriers against the O-ring.

The external PVC ring is also fitted with four supporting pins to hold a motor-stirrer combination in position. The stirrer is a hollow perforated POM cylinder mounted on the axis of the motor and surrounding the platinum anode. The stirrer rotation speed is set at 1000 rpm while the direction of rotation is reversed after 8 seconds to improve the homogeneity of the deposit. To maintain the temperature at the required level, a series of six isolated 1Ω/1 W resistors through which an appropriate dc-current is forced (1.1A – 40°C up to 1.8A-60°C) are circularly mounted.

An insulated sensor is introduced through the stirrer support plate to monitor the temperature of the plating bath. As electrolysis to depletion requires long-time (up to 24 hrs) plating, evaporation of the plating solution occurs. To maintain the liquid at the required value (450 ml), a conductivity glass/graphite sensor monitors the solution level and actuates a peristaltic pump supplying distilled water at a rate to compensate for the evaporation losses.

FIG. 3. Plating set-up Rh-electrodeposition.

As constant current DC power supplies for plating and temperature control, two SM 7020-D (Delta Elektronoca) power supplies are used. The total cc-dc current through the plating vessel is measured by means of a DVM890 (Velleman) multimeter. Before the rhodium plating, the copper carriers are etched followed by copper plating on a 2

P surface area showing a perimeter that is about 4 mm larger (surface area per window 22,36 cmP ) as 2

P compared with that of the rhodium plating area (11,69 cmP ). A second plating vessel with appropriate windows is used therefore. The set-up involving the same cc-dc plating source is shown in Fig. 4.

FIG. 4. Copper etching/plating set-up.

2.3. Plating experiments

2.3.1. Pretreatment of copper carriers

The 1 mm copper plates used as target carriers during the experiments, are cleaned with abrasive wool, rinsed with water and acetone and air-dried. Next, four Cu plates are mounted in the plating vessel represented in Fig. 4. The vessel is then filled with 450 ml of Cu etching/plating solution (250 g CuSO4B .5aqB + 25 ml HNO3,cB B + 50 ml H2B SOB 4,cB madeB up to 2.5 L). Under vigorous stirring (1000 rpm / 8:8 seconds) and in the absence of any power supply, the thickness of the copper plate at the window area is reduced with a few µm after 3 hours. Next, a dc power supply is applied resulting in a 200 mA current per target: after 1 hour a 10 µm copper layer in excess is obtained. After removal of the etching/plating solution, the vessel is abundantly rinsed with water. Upon removal of the copper plates, the latter are rinsed with demineralized water and acetone, dried with soft adsorbing tissue and weighed.

2.3.2. Rhodium plating from RhCl3B B solutions (series C1 to C11)

The plating solutions referred to in Tables I and IV are heated up to 40°C or 60°C and then introduced in the plating set-up shown in Fig. 3. At the end of the experiment, the (pale yellow to colorless) solution is discarded and the plating vessel rinsed abundantly with tap water. Upon removal of the targets, the latter are rinsed with demineralized water and acetone, air-dried and weighed. From this weight, the thickness toB B of the layers is calculated. As Rh-plating to depletion always gives rise to a black coating of the deposit (Rh-black) near the end of the plating, the rhodium layers were cleaned with a scouring suspension (CIF) and a sponge. After rinsing with water and acetone and air-drying, the weight was determined again. From this weight, a thickness after cleaning tcB B was calculated.

TABLE IV. PLATINGT DATA FOR RHODIUM DEPOSITION FROM RHCL3 SOLUTIONS

Bath W(Rh) pH T ° I T toB tcB B L Comments Nr (g) (°C) (mA) (hrs) (µm) (µm) (%) C1 2.8 2.00 40 80 24 48.60 48.55 0.10 Reflective, smooth C2 3.5 2.00 40 80 24 59.48 * - Highly reflective, smooth C3 4.1 1.94 40 100 28.5 70.10 * - Highly reflective, smooth C4 4.2 2.43 40 125 24 71.59 71.25 .47 Reflective, smooth C5 3.3 2.28 40 150 24 56.30 53.75 4.53 Smooth, grey C6 3.1 2.65 40 200 22 53.60 46.05 14.08 Smooth, dark grey C7 3.6 0.00 40 200 15.5 61.40 58.95 4.00 Smooth, black C8 3.1 0.00 40 200 21 53.00 50.93 3.90 Smooth, black C9 1.9 0.01 60 150 5.5 33.00 31.10 5.76 Smooth, grey C10 2.5 3.60 40 150 17 100 Not adherent C11 1.7 0.98 40 125 5 28.6 27.02 5.59 Reflective, smooth (*) = Not determined

The plating data are summarized in Table IV, where:

- W(Rh) = weight rhodium present in the bath in grams °

P - T P = plating temperature in degrees Celsius - I = dc current applied per target in milliampere - T = plating time in hours

- toB B and tcB B = mean thickness of rhodium layers in micrometer - L = losses during CIF cleaning in percent

From the results it can be concluded:

- Plating rhodium targets from RhCl3B B solutions at pH = 1.9 to 2.5 applying a current of 80 to 125 mA per target at 40°C, results in (highly) reflective targets requiring no or limited scouring cleaning. Losses during scouring cleaning are then confined to less then 0.5%;

- Increasing the current per target to more then 125 mA in the same pH range and at the same temperature, gives rise to increasing losses ( up to about 15% at 200 mA per target) of rhodium during the the cleaning process; - At lower pH (< 1.0) cleaning losses are about 5% while plating at higher pH (>3.0) results in a non-adherent deposit that is completely removed from the Cu-carrier during the cleaning; - Though of acceptable quality at visual inspection, the granulometry of all deposits is poor as compared with that of the reference Rhodex plating. The x250 magnification SEM shots of the reference and of the C3 plating are represented in Figs 5 and 6, respectively. - As far as the thermal shock test is concerned, none of the deposits satisfies the 500°C test: quantitative peeling-off and powdering occurs. All deposits satisfy a 250°C thermal shock test; - When the copper backing of the Reference Rhodex target is dissolved in concentrated nitric acid in a flow-through stripper, the rhodium may be collected as real rhodium fragments that can be applied easily to the centrifugal electrodissolution unit (see Fig. 7)

- When the stripping procedure is applied to rhodium deposits obtained from RhCl3B B solutions, the target material disintegrates to a dark-grey black powder that blocks the stripper and that can be recovered difficultly from it.

FIG. 5. Rhodex Reference Rhodium target (SEM X 250).

FIG. 6. C3 Rhodium target granulometry (SEM X 250).

FIG. 7. Rhodium reference fragments after Cu stripping.

2.3.3. Rhodium plating from Rh2B (SOB 4B )B 3B B solutions (series S1 to S4) The solutions S1 to S4 were used for target plating at pH = 2 and in strong sulfuric acid (2N) acid containing 5 g sulphamic acid stress reducing agent.

The date is represented in Table V where:

- W(Rh) = weight rhodium present in the bath in grams °

P - T P = plating temperature in degrees Celsius - I = dc current applied per target in milliampere - T = plating time in hours

- toB B and tcB B = mean thickness of rhodium layers in micrometer - -L = losses during cleaning in percent

TABLE V. PLATING DATA FOR RHODIUM DEPOSITION FROM RH2B (SOB 4B )B 3B B SOLUTIONS

Bath W(Rh) Acidity T° I T t0B tcB L Comments Nr (g) or pH (°C) (mA) (hrs) (µm) (µm) (%) S1 2.24 N=2 60 150 22 38.60 37.62 2.52 Reflecting, smooth S1 4.63 N=2 60 150 24 79.83 74.70 6.43 Reflecting, smooth S2 5.92 N=1.9 60 150 15.5 102.02 91.70 10.12 Not adhering S3 5.0 pH=2 40 100 21.5 85.90 - Highly reflecting, smooth S4 1.5 pH=2 40 25* 16.5 108.08 106.32 1.63 Smooth,gray 2

P (*) Surface area 2.79 cmP

In Figs 8 and 9, the X 250 SEM pictures from deposits obtained at (pH = 2 / I = 100 mA) and (2N sulfuric acid / 150 mA) respectively, are represented.

FIG. 8. Plating at 2N/150 mA.

FIG. 9. Plating at pH=2/100 mA.

From the results, it can be concluded that as compared with the Rhodex reference (Fig. 1), the granulometry of the deposit is poor. As moreover none of the deposits satisfies the 500°C thermal shock test, no further experiments on this plating technology was done.

2.3.4. Rhodium plating from Rh2B (SOB 4B )B 3B B baths prepared from Rh2B OB 3B .aqB (series O1 to O14)

Using the Rh2B OB 3B .aqB precipitates reported in Table III a series of Rh2B (SOB 4B )B 3B B plating baths containing a minimum amount of chloride ions were prepared. A summary of the plating experiments and - conditions carried out with these solutions are represented in Tables VI, VII and VIII.

TABLE VI. INFLUENCE OF STRESS REDUCING AGENT PLATING CURRENT 150 MA/TARGET; PLATING TEMPERATURE 60°C

W(Rh2B OB 3B )B pH T S.A W(Rh) t0B tcB B L %Rh SEM (g) (hrs) (g) (g) (µm) (µm) (%) 2.4394(O1)° -0.36 19 0 1.2138 41.87 40.70 2.8 49.7 22 2.4394(O1,O2)° 1.00 17 5.0 1.2271 42.33 41.25 2.6 50.3 24 5.0552(O8) 0.72 6* 30 1.9946 34.40 33.90 1.4 - 34 2.4394(O1)° -0.39 20 54.1* 0.6773 23.36 23.05 1.3 - 23 4.8184(O14) 0.47 18 54.1* 1.8409 31.75 30.20 4.9 - --

TABLE VII. INFLUENCE OF PH, PLATING CURRENT 150 MA/TARGET; PLATING TEMPERATURE 60°C

W(Rh2B OB 3B )B PH T S.A W(Rh) t0B tcB B L %Rh SEM (g) (hrs) (g) (g) (µm) (µm) (%) 6.0985(O1 to O4) 0.52 19 5.6 2.8951 49.93 49.67 0.51 47.5 27 2.4394(O2) ° 1.00 17 5.0 1.0555 36.41 36.05 0.99 43.3 26 5.6700(O7) 2.09 18 5.0 2.8394 48.97 48.77 0.40 50.1 30 5.7200(O5,O6) 3.03 9 5.0 2.8643 49.40 48.31 2.21 50.1 31 (°) = Two target plating

TABLE VIII. INFLUENCE OF CURRENT PER TARGET, PLATING TEMPERATURE 60°C; SULFAMIC ACID 5G

W(Rh2B OB 3B )B PH I T W(Rh) t0B tcB B L %Rh SEM (g) (mA) (hrs) (g) (µm) (µm) (%) 2.4394(O2) ° 1.00 150 17 1.0555 36.41 36.05 0.99 43.3 26 4.8787(O3toO5) 1.00 200 5 2.2390 38.62 37.90 1.86 45.9 32 3.0337 1.92 100 24 1.5800 27.05 ------52.1 15 5.6700(O7) 2.09 150 18 2.8394 48.97 48.77 0.40 50.1 30 (°) = Two target plating

2.3.5. Influence of the presence of stress reducing agent A first set of experiments deals with the presence/absence of a stress reducing agent on the quality of the deposit. Solutions containing no stress reducing agents or containing sulphamic acid or magnesium sulphamate were prepared. The results are summarized in Table VI,

where :

- W(Rh2B OB 3B )B = weight of rhodiumoxide in grams with reference to its origin (O#); - (°) = two-target plating - pH = acidity of solution - T = plating time in hours; T* = not plated to depletion - S.A = weight sulphamic acid or magnesium sulphamate (*) in gram - W(Rh) = weight of rhodium deposited after plating to depletion

- toB =B thickness of the deposit in micrometer

- tcB =B thickness of the deposit in micrometer after CIF cleaning - L = loss in percentage due to cleaning

- %Rh = percentage rhodium in rhodiumoxide calculated from W(Rh2B OB 3B )B and W(Rh)

From Figs 10 and 11, it follows that the presence of sulphamic acid enhances the quality of the granulometry. Please note all SEM shots were taken at an X250 magnification factor.

FIG. 10. No stress reducing agent present.

22 Increasing the concentration of sulphamic acid up to 35 grams further improves the quality as can be seen from Figs 11 and 12. Substituting for sulphamic acid by magnesium sulphamate, results in an additional improvement of the quality (Fig. 13). Unfortunately, in the present experimental conditions, the magnesium sulphamate gives also rise to the formation of finely divided rhodium powder that sticks to the electromechanical stirrer and to the walls of the plating vessel such that about 50% of the rhodium present in the plating solution is lost. Experiment 5 for which no SEM shot as taken confirmed this behavior.

FIG. 11. Sulphamic acid (5g) present.

FIG. 12. Sulfamic acid (35g) present.

FIG. 13. Magnesium sulfamate (54g) present.

2.3.6. Influence of pH The influence of the pH of the plating solution on the quality of the rhodium layer was investigated in the range 0.5 up to 3 in the presence of 5 g sulphamic acid. The data are summarized in Table VII. The SEM shots (250 magnification factor) are represented in Figs 14 to 17.

FIG. 14. Plating at pH = 0.52.

FIG. 15. Plating at pH 1.00.

FIG. 16. Plating at pH = 2.09.

FIG. 17. Plating at pH = 3.03.

From the pictures it is obvious that plating should be carried out in the range pH = 1 to 2. Removal of the rhodium black layer by means of a scouring suspension (CIF) then results in a less than 1% loss of target material.

2.3.7. Influence of current density The effect of the current density was studied out in the 100 to 200 mA per target range. Taking 2

P into account the plating surface area (11.69 cmP ) this corresponds to a current density (j) 8.55 to 17.11 -2

P mA.cmP . The experiments were performed with solutions containing 5 g sulphamic acid stress reducing agent, pH was adjusted between 1 and 2 and temperature was set at 60°C.

The data are represented in Table VIII. The SEM data are shown in Fig. 18 up to Fig. 21.

FIG. 18. Plating current 150 mA/target.

FIG. 19. Plating current 200 mA/target

FIG. 20. Plating current 100 mA/target.

FIG. 21. Plating current 150 mA/target.

26 -2

P From the results it follows that 100 mA per target (j = 8.55 mA.cmP ) gives the optimum result. It should be noted that applying the same current density when plating at pH 1.00 or pH = 2.09 (Figs 18 and 21) gives comparable results, as expected.

From the above it can be concluded:

Optimum plating conditions for the simultaneous preparation of four 40 µm Cyclone-30 rhodium targets from Rh2B (SOB 4B )B 3B B solutions prepared from hydrated Rh2B OB 3B usingB the VUB plating equipment are :

- 1

P - Current 100 mA/target (j = 8.55 mA.cmP ) - Stress reducing agent: sulphamic acid 5 g/450 ml - Temperature 60°C - The granulometry of the deposit is comparable with that of the Rhodex reference as is shown in Figs 22 and 23; - Scouring cleaning (using CIF) to remove the shallow rhodium-black deposited near the end of the plating, results in losses of about 1%: - The deposit satisfies the 500°C thermal shock test as was the case for the Rhodex reference; - Application of the flow-through copper stripping procedure results in rhodium fragments as does the Rhodex reference (see Fig. 7);

The mean rhodium content of the vacuum-dried (48 hrs, 25°C, 350 mbar) Rh2B OB 3B .aqB precipitates amounts to 48.2 ± 3.1%. Calibration of the compound can be done by plating-to-depletion.

FIG. 22. Rhodex reference deposit.

FIG. 23. VUB/NRCAM deposit.

2.4. Conclusions 1. Recovery of rhodium from (irradiated) hydrochloric acid solutions obtained after centrifugal electrodissolution and extraction of Pd-103, and the preparation of new plating baths from recovered rhodium can be done in two ways:

1.1. Evaporation of the recovery solution (containing about 3 g of rhodium) to near dryness, uptake of the RhCl3B B concentrate in 300 ml hot water and filtration through a 0.45 µm filter to remove any solid particle, followed by the addition of sulphamic acid stress reducing agent (up to 35 g per bath) and adjustment of the pH to a value 1.9 to 2.5. Upon make up with water to 450 ml, the RhCl3B solutionB can be used for the simultaneous plating of four Cyclone-30 targets showing a thickness of 40 µm;

1.2. Evaporation of the recovery solution (containing up to 6 g of rhodium) to near dryness, uptake of the RhCl3B B concentrate in 300 ml hot water and filtration through a 0.45 µm filter to remove any solid particle, followed by addition of 10 N NaOH up to pH = 10 to 10.5. To enhance the filterability, the hydrated Rh2B OB 3B B suspension formed is allowed to digest (50°C, gentle stirring) for 24 hrs whereupon filtration through a blue band filter paper is performed. Any colloidal particle in the filtrate is recovered by filtration through a 0.45 µm filter. Upon 24 hrs of air-drying, the precipitate is ground in an agate mortar. The resulting yellow powder is vacuum-dried (room temperature, 350 mbar) during 48 hrs. The mean rhodium contents of the hydrated rhodium oxide powder amounts to 48.2 ± 3.1%.

A new plating solution for the preparation of 4 Cyclone-30 targets (40 µm layers) can be prepared by dissolution of 6.1 g rhodium oxide in 10 ml boiling sulfuric acid followed by uptake in 300 ml hot water and filtration through a 0.45 µm filter. After addition of 35 g sulphamic acid stress reducing agent, the pH is adjusted to a value between 1 and 2 and the solution made up to 450 ml. The resulting Rh2B (SOB 4B )B 3B B solution is ready for plating.

2. The simultaneous plating of 4 Cyclone-30 (40µm) rhodium targets using the VUB plating set up, can be done from the RhCl3B solutionB or from the Rh2B (SOB 4B )B 3B B solution described above. In either case, the copper target carriers are first etched in an acidic copper sulfate bath followed by plating of a 10µm layer in excess of copper.

2.1. For the preparation from the RhCl3B solution,B the latter is heated up to 40°C and then -2

P transferred to the plating vessel. An optimum current of 100 mA per target (j = 8.55 mA.cm P ) was determined. Upon plating to depletion (24 hrs), deposits showing a poor granulometry as compared with that of the Rhodex reference plating are obtained. As moreover the 500°C thermal shock test results in quantitative peeling off and powdering, the targets are not suited for high beam current irradiation;

2.2. When the Rh2B (SOB 4B )B 3B B solution is used, a 60°C plating temperature is applied. Again, a 100 mA plating current per target is to be preferred. The granulometry is comparable with that of the Rhodex reference and the 500°C thermal shock test is satisfied. As moreover the removal of the copper backing (using concentrated nitric acid) in a flow-through stripper gives rise to rhodium fragments, as does the reference, it may be concluded that the quality of the deposit is acceptable for high beam current irradiations.

3. CENTRIFUGAL ELECTRODISSOLUTION SYSTEM FOR FRAGMENTED ELECTROPLATED RHODIUM TARGETS USED FOR THE INDUSTRIAL CYCLOTRON PRODUCTION OF PALLADIUM-103

As it is well known from literature, the method to be preferred is the alternative current electrodissolution [4][5] in hydrochloric acid introduced Box [6]. Though applicable for foils, it

28 suffers from a serious limitation: due to fragmentation the maximum applicable current density (and 2

P hence the dissolution rate) is confined to 0.5 A/cmP and the recovery of Pd-103 is less than 90%.

Therefore, a centrifugal high-current density electrodissolution system was developed at VUB. Preliminary had shown that it allows fast dissolution of fragmented rhodium (up to several grams) within a few hours.

The present experimental work aims at the evaluation and optimization of the performances of the prototype system.

3.1. Brief description of the system

The homemade experimental set-up is shown in Fig. 24. The PVC frame (PVCF) supporting the mini-reactor is made up from four circular and parallel supporting-plates held together by cylindrical spacers.

Fig. 24 Schematic set up

The working-electrode (WE) consists of a cylindrical excavated electro-graphite receptacle 2

P (inner diameter 3.6cm, height 1.4cm, surface area vertical walls 15.8 cmP ) provided with a screwed-in perspex top-piece (TP, height 9cm ) to increase the total volume of the system. Liquid-tightness at the graphite/perspex junction is assured by means of a NBR O-ring .To limit upwards lead of small rhodium fragments to the graphite section, the perspex top-piece is fitted with a lower inside flange

(IF). A circular insulating Teflon disk (TD) covers the bottom of the working electrode. This entity is fixed onto a stainless steel pin (SSP) connected to the shaft (MS) of a dc motor–tacho-reductor (M/T) combination by means of an insulating Teflon bush (ITB). Home–made electronics allow continuous adjustment and measurement of the rotation speed. The cylindrical graphite rod counter–electrode (CE, diameter 2.6cm, height 16 cm) is mounted in the upper supporting plate such that the distance between the teflon disk and the lower end of the graphite rod equals about 1mm. Vibrations of the system at the current rotation speed are eliminated by high-quality bearings (HQB) clipped onto the motor shaft and fixed into a supporting-plate.

The electrical contact with the ac-power supply is made by inserting a plug (PL) into a notch in the top of the counter electrode and by two custom made, spring-loaded soft-bronze and parallel- circuited sliding brushes (SLSB) contracting the stainless steel pin supporting the rotating graphite/perspex receptacle. When filled with a rhodium fragments containing hydrochloric acid solution and by applying a 1000 rpm rotation speed, the design results in the fragments to be collected and current to flow mainly between the side wall of the working-electrode and the lower section of the vertical wall of the counter-electrode, thus ensuring a high current density.

As warming up and evaporation of the solution due to high-current flow and chemical reactions do result in a continuous decrease of volume of the solution present in the reactor, feed-back addition of hydrochloric acid is done by means of home-made conductivity electronics that actuates a peristaltic pump. Therefore a third mini carbon-glass auxiliary electrode (LS) sensing the liquid level (LL) is mounted in the upper supporting-plate. The conductivity measurements that trigger the pump are done between the counter- and the auxiliary electrode. The hydrochloric acid volume is about 40ml and the maximum rotation speed 1000 rpm.

The complete experimental set up is shown in Fig. 25 By means of an auto-transformer (Output 0 to 250V) the voltage applied to the primary coil of a transformer (1250 VA) is varied such that the output current applied to the reactor equals maximum 30 A. This current is monitored by means of a clamp meter.

FIG. 24. Experimental set up.

30 3.2. Performances of the system

From preliminary experiments, it follows that:

- The change of concentration of HCl due evaporation and chemical reactions as a function of time results in a constant concentration after a certain time of operation (for input concentration of 12 N HCl, the equilibrium concentration is about 7 N after about 1 hour at a current of 30 A); - The rhodium dissolution rate depends on the HCl concentration; - The dissolution rate depends on the applied current; - The dissolution rate depends on the weight of rhodium.

From the experimental data, it follows that the dissolution rate (dW(t)/dt , mg/min) is given by:

dW(t)/dt = K*[1-exp(-b.C(t))][1-exp(-c.∆I)][1-exp(-d.W(t))]

with:

- C(t) = CeqB (1-exp(-a.t))+CB °B .exp(-a.t)B (concentration HCl as function of time with a =

0.0727-0.00266 C0B )B

- C0B B = input concentration (max 12 N)

- CeqB B = C0B B (1 – 0.0178*I) (I = current in A) - ∆I = I – 4.75 - K =55.6; b=0.292; c=0.1105 ; d=0.804 - A, b, c and d are experimental constants.

Numerical integration of this equation can be done by any loop algorithm interrupted by an appropriate condition concerning the aimed at solubilization level, i.e. the fraction (99% level for instance) or weight W of rhodium fragments to be dissolved. The output is then the Time required (T99%) to obtain that solubilization level.

3.3. Experimental results

The goal of the experiments was to determine:

1. The maximum rhodium input weight that results in a T99% in agreement with the calculated value, i.e. the maximum allowable amount of Rh to be dissolved in a single run. 2. The applicability of the system to dissolve not only rhodium fragments, but Rh powder, wires and foils. 3. Technical limitations of the reactor prototype and forward suggestions for improvement of the performances.

The rhodium fragments were prepared by dissolution of the copper carriers of electroplated Rh targets in concentrated nitric acid – giving rise to Rh fragments, which were further grounded in an + 0

PB P agate mortar. All experiments were carried out at 80 P - B 2 P C.

From Fig. 26 it follows that the maximum single run capacity of the system is 3,0 g of rhodium dissolved in 40 ml of hydrochloric acid.

Dissolution Yield Rh versus weight Rh

110 ) 100

70 Dissolution Yield Rhodium (%

60 0123456

W eight Rhodium (gr)

FIG. 25. Maximum single run capacity of the system.

From Table IX it can be concluded that the technology is applicable to tune-controlled electrodissolution of rhodium fragments, cut wires and cut foils as well as to rhodium powder.

Suggestions to further improve the performances of the systems are introduction of coolmy and current sensor allowing feedback stabilizator of bath parameters.

TABLE IX. DISSOLUTION TRIALS WITH RHODIUM POWDER, WIRE, FOIL

Weight I (A) Yield Normality Normality T99% Remarks Rh (gr) % input output (min)

2.5067 25 99.8 12 8.3 167 CA80_POWDER 2.5053 25 99.66 12 6.6 167 CA80_POWDER 1.1269 25 99.7 12 6.2 145 CA80_WIRE 1.3340 25 99.8 12 6.7 149 CA80_FOIL

3.4. Conclusions 1. From Fig. 26 it follows that the single run capacity of the system operating at 25 A, 12

P hydrochloric acid input concentration P N and a reactor volume of 40 ml is limited to 3.0 gr irradiated rhodium.

2. The system can be used for rhodium powder, cut rhodium wires and foils, and for rhodium fragments (Table IX) obtained upon nitric acid dissolution of the Cu-target carrier of electroplated rhodium targets.

3. To avoid local boiling and current drops, a temperature sensor must be introduced into the system. A mini-diode integrated in a bridge circuitry proved to be an excellent temperature sensor. Coupled to a differential amplifier /comparator/current-booster/valve set-up, compressed air-cooling of the graphite limits the temperature to 80±2 C°. In this way the system proves to be very stable at 25 A a.c electrodissolution current.

32 REFERENCES

[1] M.S.PORRAZZO ET AL. “Permanent Interstitial Implantation using Pd-103: the New York Medical College Preliminary Experience “, Int. J. Radiation Oncology Biol. Phys. 1992, Vol 23 (5), pp. 1033-1036. [2] PLETCHER D., URBINA R.I. Electrodeposition of rhodium. Part 1. Chloride solutions. J. Electroanalytical Chemistry, v. 421 (1-2), (1997), pp.137-144. [3] PLETCHER D., URBINA R.I. Electrodeposition of rhodium. Part 2. Sulphate solutions. J. Electroanalytical Chemistry, v. 421(1-2), (1997), pp.144-151. [4] LAGUNAS-SOLAR M.C., ET AL. Targetry and radiochemical methods for the simultaneous cyclotron production of no-carrier-added radiopharmaceutical quality Pd-100, Ru-97 and Rh- sup.(101m). J. Appl. Radiat. Isot. 38 (2) (1987), pp. 151-157. [5] LAGUNAS-SOLAR M.C., ET AL. Cyclotron production of no-carrier-added 97Ru by proton bombardment of 103Rh target. J. Appl. Radiat. Isot. 34 (6) (1983), pp. 915-922. [6] GAITA R., AL-BAZI S.J. An ion-exchange method for selective separation of palladium, platinum and rhodium from solutions obtained by leaching automative catalytic converters. Talanta, v. 42 (2) (1995), pp. 249-255. [7] LAGUNAS-SOLAR M.C. ET AL. Cyclotron production of Rh-sup(101m) via proton induced reactions on Rh-103 targets. J. Appl. Radiat. Isot., v. 35 (8) (1984), pp. 743-748. [8] RAMLI M., SHARMA H.L. Radiochemical separation of Rh-101m via Pd-101 from a rhodium target. J. Appl. Radiat. Isot. v. 48 (3) (1997), pp. 327-331. [9] CHUNFU Z., ET AL. Cyclotron production of no-carrier-added palladium-103 by bombardment of rhodium-103 target. J. Appl. Radiation and Isot. v. 55 (4), (2001), pp.441-445. [10] TARAPCIK, P., MIKULA, J.V., Separation of Pd-103 from cyclotron irradiated rhodium targets. J. Radiochem. Radioanal. Letters., 48 (1) (1981), pp. 15-20.

NEW TECHNOLOGY FOR THE INDUSTRIAL PREPARATION OF HIGH QUALITY TL-203 CYCLOTRON TARGETS BY CONSTANT CURRENT ELECTROPLATING

P. VAN DEN WINKEL, L. DE VIS, M. DE VREESE, R. WAGENEER, A. DE SCHRIJVER, A. ARZUMANOV, Vrije Universiteit Brussel, Cyclotron Department, Brussels, Belgium

N. GORODISKAYA, P. ZHELTOV Institute of Nuclear Physics, Almaty, Kazakhstan

Abstract

A new technology for the industrial preparation of high quality Tl-203 cyclotron targets was developed. It consists of ac-constant current electrodeposition of Tl-203 from an alkaline (pH> 12) EDTA plating solution containing appropriate amounts of an anodic depolarizer (hydrazine) and of non-incorporated neutral wetting agent (BRIJ-35). As plating waveform -2

P a bipolar chopped sawtooth (fSTB =100B Hz, fCHB B = 100 Hz) is applied while the optimum current density equals 2-3 mA.cmP . When plating up to 50% depletion is performed, the current efficiency is 100% allowing time-controlled plating of up to eight targets simultaneously. A single plating solution can be reused up to 10 times upon simple addition of the appropriate amount of Tl2B OB 3B B after each batch.

1. INTRODUCTION

To be up to standard, plated cyclotron targets must meet a set of requirements. First, the target layer should adhere strongly to the target carrier up to irradiation temperature. Secondly, it should be smooth (not spongy and dendrite-free), dense (no occlusions nor vacuoles), stress-free and homogeneous (+/- 5%) and show a well-defined thickness that may vary from a few tens up to several hundreds of µm, depending on the beam/target angle. Finally, the metal deposit and the carrier/layer interface should be free of traces of organic plating bath additives such as complexing agents, surfactants or stress reductants.

With reference to the upper requisites, “poor quality” of Tl-203 target layers means that one or more of these conditions are not satisfied.

The main causes that give rise to poor quality are:

- gas (hydrogen) evolution at the cathode during plating resulting in spongy and irregular deposits; - concentration polarization of the electro-active species (i.e. the hydrated or complexed target metal ion) giving rise to treelike structures called dendrites, requiring post-plating mechanical fashioning as rolling with enhanced risk of plating solution occlusions; - ill-considered choice of additives such as organic complexing agents and tensides bringing about peeling off of the target layer and/or target damage on irradiation; - unidirectional stirring and maladjusted plating temperature causing inhomogeneous layers and dendrites; - non-homogeneous electrical field and maladjusted plating voltage wave form causing inhomogeneous layers and dendrites.

In the frame of industrial routine production the plating solution, the electromechanical and electronic set-ups and the target carrier should currently meet a number of imperative additional requirements such as:

P - the plating solution must be free of toxic anions (especially CNP ) and well suited for repetitive plating (up to 10 batches per cycle) upon simple adjustment of the Tl-203 contents of the bath. At the end of a plating cycle any enriched material remaining in a partially depleted bath must be recovered quantitatively in a physico-chemical form so that it can be reused as such for the preparation of a new plating solution; - plating bath and set-ups must allow multi-target preparation (minimum 4 per batch) at room temperature with a duty cycle allowing finishing at least one batch per shift (= 7 hours); - the thickness of the layer must be time-controlled; - post-plating mechanical fashioning (rolling) of the target layer must be excluded.

In spite of excellent physico-chemical qualities of the Tl-203 deposit, the ultimate goal, the availability of a target showing a high maximum allowable target beam current load (> 300 µA, future 500-2000 µA) can not be reached in the absence of appropriate deposit and coolant channel geometry, linear coolant flow rate, beam diagnostics and beam wobbling. The optimization of beam parameters and cooling are not included in this work.

2. OPTIMIZATION OF THE PLATING TECHNOLOGY

2.1. Choice of the plating method

Fundamentally, one of the four available plating methods can be used.

In Constant Voltage Electrolysis (CVE), a fixed voltage is applied between the anode and the target carrier cathode immersed in the plating bath. As the electrolysis progresses the current decreases as a result of depletion of the electro-active species (hydrated or complexed metal ions) and the cathode potential shifts towards more negative values entailing an enhanced risk for hydrogen -

P evolution. This can be prevented by the addition of a suitable cathodic depolarizer (NO3B PB ) that fixes the +

P cathode potential at a constant value and that is reduced to a non-volatile species (NH4B PB ) in acid medium. Though this technique is frequently used in industrial coating and in analytical electro- gravimetry, the current efficiency (and hence the plating current density) varies during the plating process and is generally much less than 100%, making the method non attractive for time-controlled layer thickness plating.

In Constant Current Electrolysis (CCE) a fixed current is forced through the electrochemical cell and the applied plating voltage automatically adjusted (i.e. increased) such that the set current is kept up. Using concentrated solutions of appropriate composition that show a limited depletion ratio for the electro-active species (maximum 50%) at the end of the plating and applying an optimized plating current density, a 100% current efficiency can be easily obtained. For time-controlled layer thickness plating this technique must be preferred.

Controlled Cathode Potential Electrolysis (CCPE) involves the introduction of a reference electrode into the system. The potential of the cathode is set at a fixed value versus the potential of the reference electrode. This value corresponds to 99.99% depletion of the electro-active species, i.e. to the lower limit of its discharge interval. The current decreases exponentially as the process progresses and its reading may be used to monitor the depletion of the bath. CCCPE is well suited for quantitative separation of metals and is a very attractive tool in the frame of the recovery of enriched target material.

Internal Electrolysis (IE) does not involve the application of an external voltage or current source to the electrochemical cell build up from two non-indifferent electrodes. External short- circuiting of both electrodes results in a spontaneous current that decreases exponentially as a function of time. The anode dissolves and the electro-active species wanted is quantitatively plated out onto the

35 cathode. This method has limited number of applications and was frequently used in destructive neutron activation analysis in the sixties. It is not suited for thick target preparations. From the above it is obvious that CCE should be preferred for the preparation of high current beam cyclotron targets and that CCPE should be used for purification and recovery of enriched material.

2.2. Composition of the plating bath solution In general, thallium plating solutions contain a readily soluble inorganic Tl salt (sulphate, perchlorate…) and free acid (mostly sulphuric or perchloric acid) or base (sodium hydroxide). In most cases additives to improve the quality of the metal deposit are present: these compounds (complexing agents, surfactants, anodic depolarizers and stress reductants) mainly affect the tendency towards gas evolution, the maximum allowable plating current density and the oxidation of the Tl deposit.

Gas (hydrogen) evolution at the cathode can be prevented by adjusting the pH of the solution to a value higher than 12. This is feasible as TlOH is a strong base.

Concentration polarization linked up to plating current density and plating bath additives strongly affects the quality of the deposit. The higher the current density the smaller the crystal size and the better the physical properties of the metal layer: smooth, strong and adherent deposits are made up of very fine crystals obtained at higher current densities. Moreover, higher current densities result in a higher over voltage for hydrogen thus reducing the risk for gas evolution at the cathode. However, very high current densities do result in extremely high concentration polarization that leads to dendrite formation. From the foregoing, it follows that an optimum current density is to be expected. Its value may be increased and the plating time hence reduced by:

Plating from concentrated Tl-203 solutions such that the metal concentration at the end of plating procedure remains high, meaning that the depletion ratio (DR) of the plating bath is relatively low. From experiments, it follows that a DR up to 50% is acceptable for many plating vessel geometries and target windows. This implies that the Tl-203 contents of the plating solution equals at least twice the amount deposited on the target carriers;

Addition of complexing agents showing a low stability constant for monovalent thallium and for which the electron transfer rate at the solution/metal layer interface is high as compared with that of +

P the hydrated TlP cation. Experimentally it was found that out of eight complexing agents tried, only

EDTA 0,5M at pH>12 (pKsB =6.55)B is well suited for this purpose on the condition that no trivalent +3

P thallium is present. Indeed, TlP forms strong complexes with EDTA (pKsB =B 24.0) resulting in a large shift of the discharge interval of the metal towards more negative values with possible hydrogen generation as a consequence. The addition of an anodic depolarizer such as hydrazine prevents the oxidation of monovalent Thallium in solution and of the metallic deposit as well.

Addition of a tensio-active agent that causes a decrease of the surface tension of the solution resulting in a decrease of the thickness of the hydrodynamic layer at the metal/solution interface. Hence, the transfer rate of the electro-active species (i.e. complexed Tl ions) to the cathode surface is enhanced and the concentration polarization reduced. Though many organic surfactants of acceptable purity are commercially available, the practical choice is very limited because most of them tend to stick at copper/thallium interface or are incorporated in the thallium lattice.

Upon irradiation and heating up, the organic material is carbonized thus producing volatile decomposition compounds that lead to eruptions and crater formation resulting in the loss of enriched material and in a decrease of the irradiation yield. Out of 12 (anionic, cationic and neutral) compounds tried, a single one, BRIJ-35 (0,05% w/v) non-ionic polyoxyethylene ether, frequently used as wetting agent in automated continuous flow analyzers, met the requirements.

36 2.3. Electromechanical set-up, stirring system and plating temperature

Simultaneous multi-target plating that results in homogeneous Tl-203 layers requires an appropriate plating vessel design to ensure a homogeneous electric field all over the plating area and a well designed stirring system that avoids local concentration gradients -and hence local concentration polarization - of the electro-active species.

Plating vessel geometry: practically, the above requirements can be met by using a hollow perspex cylinder (maximum volume 500 ml), fitted with a single axial and grounded Pt anode wire mounted in the bottom and with four vertical slots in the outside wall allowing the introduction of four target carriers, as electrodeposition vessel. Appropriate choice of the diameter of the cylinder and shielding of the anode wire allows a quasi homogeneous electrical field to be realized at the surface of the four cathodes.

Stirring system: efficient homogenization of the plating solution can be achieved by introducing as a stirrer a hollow perforated perspex cylinder surrounding the Pt anode and mounted on the axis of a DC motor-tachogenerator combination with variable (up to 1200 rpm) rotation speed. The direction of rotation can be reversed after a predetermined time. Vigorous bi-directional stirring then reduces the thickness of the hydrodynamic layer and hence the concentration polarization. The geometry of the stirrer needs optimization for each target configuration.

Plating temperature: increase of the plating temperature may be an important quality parameter. At higher temperature the viscosity of the solution decreases and the mobility of the ions increase while in well-stirred conditions, the thickness of the Nernst layer is substantially reduced. Higher temperature hence reduces concentration polarization. On the other hand, over voltages are lowered at higher temperatures, even for heavy metals as Tl, with as a result an increased risk for gas evolution. Furthermore, the required electromechanical plating set-up should be much more sophisticated (heating elements and associated electronics for temperature control, solution level monitoring and feed back electronics to add water to compensate for evaporation) while the optimum temperature for a given electrolysis can be determined by experiments only. Weighing the pros and contras against each other, it was decided to develop a technology applicable at room temperature, a decision that was highly appreciated by industrial users.

2.4. Plating voltage waveform

In spite of the optimized conditions discussed above, a slight tendency towards dendrite formation is found when DC constant current electroplating is performed. This phenomenon can be suppressed completely by application of AC voltages and currents. During the cathodic part of the applied signal, deposition with micro dendrite formation takes place, during the anodic part the metal is redissolved. This redissolution rate is higher for fine treelike structures (showing a high surface area per unit of mass) than for real massive crystals. Appropriate choice of the wave form of the AC signal and of the amplitudes of the cathodic (icB )B and anodic ( iaB B) currents ( icB B > iaB B ) results in a net cathodic deposition with suppressed dendrite formation.

Out of four different wave forms tried, a bipolar chopped sawtooth gave optimum results in the case of Tl. The signal frequency equals 100Hz, the chopper frequency is 1000Hz and the chopper duty cycle amounts to 60%. The wave form is schematically represented in Fig. 1.

FIG. 1. Bipolar chopped sawtooth plating voltage.

2.5. Experimental

2.5.1. Preparation of the plating solution The following alkaline Tl-203 containing EDTA solution holding appropriate amounts of BRIJ- 35 surfactant and hydrazine depolarizer is used for the repetitive preparation of four IBA external beam Tl targets used in the Cyclone 30 accelerator. The metal layer is deposited on IBA’s finned copper carrier. 2.5.2. Reagents and products The chemicals used for the preparation of the plating bath are summarized in Table I. 2.5.3. Cleaning of target carriers (Cu backings) The Cu carriers are cleaned by rubbing the Tl deposition area with abrasive wool, followed by rinsing abundantly with demineralized water and acetone and paper drying.

1. rub the deposition area of the Cu backing successively with abrasive wool type 1 and type 2 for 1 min respectively;

2. rinse with water;

3. rinse with acetone;

4. dry the carrier with adsorbing paper and weigh the carriers;

5. introduce the backings in the four slots of the deposition vessel and turn the knobs of the mechanical pestles in pairs clockwise to ensure liquid tightness.

38 TABLE I. REAGENTS USED TO PREPARE A TL-203 PLATING SOLUTION

203

P Tl2B OB 3B B Enriched P Tl oxide, compound obtained by the purchase of the enriched material

203 3-

P P P TlEDTAP Final product obtained in the VUB-recovery cycle of the enriched material EDTA (ethylene-dinitrilo-tetra-acetic acid, di-sodium salt) – Titriplex III p.a. (Merck - 1.08418) NaOH Sodium hydroxide pellets p.a. (Merck - 6495) Hydrazine hydrate (55%) (Aldrich - 22.581-9) BRIJ-35 (30%) (Technicon Diagnostics - T 21-0110-17)

H2B SOB 4B B (95 - 97%) p.a. (Merck - 731) Perhydrol (30%) p.a. (Merck – 1.07209)

B B µ H2O Demineralized water - conductivity < 0.1 S/cm Acetone (purum) (Belgolabo 94-90013) Parafilm "M" American National Can pH indicator strips (Merck 9535) Abrasive wool Type 1: F12/002 very fine (Abrasive center) Type 2: F12/012 ultra fine (Abrasive center)

2.5.4. Preparation of the first electroplating bath

Though the volume of the plating bath is not very critical, it should be kept between 420 and 203

P 450 ml. The solution is 0,5 M EDTA showing a pH > 12.5 and contains 9 g of enriched P Tl together with 1% hydrazine hydrate and 0.2% of BRIJ-35.

• put 360 ml demineralized water in a 600 ml beaker (B1) fitted with a Teflon coated magnetic stirring bar;

• add 84 grams solid EDTA and 20 grams of NaOH pellets and stir until a colorless solution is obtained;

• add 10 ml hydrazine hydrate and 1 ml BRIJ-35 and homogenize (Solution-1);

• transfer quantitatively 9760 mg enriched 203Tl2O3 to a second 600 ml beaker (B2) also fitted with a magnetic stirrer bar;

• transfer Solution-1 by means of a peristaltic pump into beaker B2 at a flow-rate of 10 ml/min. Cover beaker B1 with Parafilm;

• reduce the stirring rate of the stirring bar in B2 and rinse the wall of this beaker with 1 ml hydrazine hydrate (If any yellow-brown color persists in the foam layer, gently swirl the beaker until the color disappears). Check pH by means of an indicator strip. The pH should be > 12,5;

• continue slow stirring of B2 for five more minutes.

Solution-2 (in B2) is now ready for electrodeposition.

2.6. Electromechanical set-up The electromechanical set-up is represented in Fig. 2.

The electrodeposition vessel is a hollow perspex cylinder fitted with an axial Pt anode wire mounted in the bottom by means of a tube-end fitting with perforated septum. Four vertical slots in the outside wall allow introduction and positioning of four Cu target carriers.

Each slot is provided with an O-ring fitted window, which geometrical shape determines the electrodeposition area. Liquid tightness is realized by stainless steel mechanical pestles mounted in a PVC ring surrounding the electrodeposition vessel and by pressing the Cu carrier against the O-ring.

The external PVC ring is also fitted with four supporting pins to hold the motor-stirrer combination in position. The stirrer is a hollow perforated cylinder mounted on the axis of a DC motor-tachogenerator combination and surrounding the Pt anode. The rotation speed is adjustable up to 1200 rpm while the direction of rotation can be reversed after a predetermined time (8sec/8sec).

FIG. 2. Electromechanical set-up.

2.6.1. Electronics

The schematic diagram of the home developed plating electronics is represented in Fig. 3. A stable multivibrator (AMV-1) generates a saw-tooth (ST) signal of appropriate frequency and duty cycle. The ST signal is amplified by a non inverting amplifier (NIA) and summed with a positive DC offset voltage (P-DC-O) by an inverting sum amplifier (ISA-1) which output forms the base for the positive alternation of the compound signal. The ST signal is amplified by an inverting amplifier (IA)

40 and summed with a negative DC offset voltage (N-DC-O) by an inverting sum amplifier (ISA-2) which output forms the base for the negative alternation of the compound signal.

A stable multivibrator (AM-2) generates a square wave (SW), with appropriate frequency and duty cycle, which chops the output of ISA-1 and ISA-2 in such a way that only one alternation is active at the same time. The outputs of the negative alternation chopper (NAC) and the positive alternation chopper (PAC) are summed in an inverting (ISA-3) which output delivers the compound signal. This signal is fed into four independent voltage-to-current (V/I) convertors with associated push-pull current boosters (IB) and grounded load. This circuitry allows the simultaneous deposition of four Tl targets at identical or at four different current densities using a single and grounded Pt- anode.

The electrodeposition electronics consists of a rack with eight Eurocards: two power supplies; one stirrer controller; one signal generator; four voltage-to-current (V/I) convertors with associated push-pull current boosters (IB).

FIG. 3. Schematic diagram of the electronics.

203

P 2.7. Electroplating of P Tl targets

Electrodeposition of four targets is carried out after the transfer of Solution-2 to the plating vessel fitted with four cleaned target carriers.

1. Pour Solution-2 into the plating vessel. Do not rinse the beaker but cover it with Parafilm;

2. connect the four outputs of the current boosters to the cathodes by introducing the four black male plugs into the wholes of the pestles;

3. introduce with care the electromagnetic stirrer such that the central Pt-anode wire fits into the hollow perforated stirring cylinder. Rotate the stirrer until an appropriate mortise and tenon joint between the stirrer assembly and the vessel is obtained;

4. connect the motor cable plug to the female connector at the top of the stirring motor housing. Start stirring motor (rotational speed: 1200 rpm; Period: 16 sec)

5. start the electrolysis by introducing the common (red) output plug of the I-boosters into the female connector at the bottom of the deposition vessel;

6. note the time; the four current indicators should give a 25.0 ± 0.2 mA reading after a few minutes of deposition. With a 100% current efficiency a Tl-203 deposition rate of 203

P 7,57 mg/mAh is obtained, for a 1092 mg P Tl deposit per target the plating time equals 5,77 hrs, i.e.: 5hrs 46min;

7. after 5hrs 46min of electrolysis, stop the stirring motor, disconnect the plug at the top of the motor housing and carefully remove the stirring assembly. Do not rinse the perforated hollow cylinder, but quickly introduce it into a 250 ml perspex holder;

8. pour the 50% depleted plating solution into beaker B2. Rinse the deposition vessel with 3 times 15 ml of demi-water and collect the rinsing liquid in a third 250 ml beaker (B3). Cover the beaker B3 with Parafilm;

9. unscrew the pestles, remove the pestle holder and collect the four targets. Rinse each of the targets extensively with hard water (waste), followed by rinsing with demi- water (waste);

10. dry the targets by means of adsorbing paper and weigh. Determine the current efficiency by calculating:

W i η = * 100 with : i 1092

ηiB B =current efficiency for target i

WiB B =weight (mg) of target i

The current efficiency should be 100 ± 0,2%

11. wipe off the surface oxide layer by means of adsorbing paper and store the targets in a 203

P vacuum desiccator or under nitrogen. Wiping off may result in a loss of a few mg of P Tl. If not acceptable, the adsorbing paper frotti's should be collected and later on destructed in

an HClO4B /HB 2B OB 2B B mixture. After catalytic elimination of H2B OB 2B B by introducing a Pt electrode, a bulk recovery of Tl can be carried out.

2.7.1. Preparation of the second .up to the tenth) plating bath using Tl2B OB 3B B As stated earlier, the partially depleted plating bath must be reusable as such upon simple adjustment of the Tl-203 contents. This can be done, as follows:

203

P 1. transfer quantitatively 4880 mg enriched P Tl2B OB 3B B to beaker B1 fitted with a magnetic stirring bar;

2. transfer the 50% depleted plating solution from beaker B2 to B1 by means of a peristaltic pump at a flow-rate of 10 ml/min. Cover beaker B2 with Parafilm;

3. reduce the stirring rate in B1 and rinse the walls of this beaker with 1 ml hydrazine hydrate (If any yellow-brown color persists in the foam layer, gently swirl the beaker until the color disappears);

4. continue slow stirring of B1 for five more minutes. Check pH by means of an indicator strip. The pH should be > 12, if not add a few drops of 10% NaOH;

5. proceed as described in 3.4.

The procedures 4 and 5 can be repeated up to maximum 10 times (due to degradation of the surfactant) where after a bulk recovery of the 50% depleted bath is necessary. This should be done by controlled cathode potential electrolysis.

3. RESULTS AND CONCLUSIONS

Constant current electrolysis (CCE) of Tl-203 from alkaline (pH>12), concentrated (i.e. holding an amount of Tl that is equal to twice the amount plated out) solutions of monovalent Tl, 0.5 M in EDTA and containing a non-incorporated surfactant (BRIJ-35) and a strong reducing anodic depolarizer (hydrazine hydrate) result in a plating technology that meets all metal layer quality requirements and all industrial demands. Indeed, by applying a bipolar chopped sawtooth (fSTB =B 100Hz; fCHB =B 1000 Hz; CDC=60%) to the cylindrical plating vessel, fitted with a single, grounded and axially mounted Pt anode and four slots that hold the Cu target carriers and by vigorous bi-directional stirring (1200 rpm) by means of a cylindrical perforated electromechanical stirrer surrounding the Pt anode and mounted on the axis of a DC motor-tachogenerator combination, the following results are obtained:

-2)

P - relatively high maximum allowable current density (2 to 3 mA.cmP ) allowing simultaneous time-controlled (plating current efficiency = 100%) production of 4 targets carrying more than 100 mg Tl-203 per square centimeter within less than 6 hours and requiring no post-plating mechanical fashioning;

- plating performed from cyanide free solutions that are well-suited for repetitive plating cycles (up to 10 batches) by simple adjustment of the metal contents of the plating bath and from which the remaining enriched material can be readily recovered by controlled cathode potential electrolysis;

- target layers are homogeneous (< 5%), smooth (dendrite free), dense neither occlusions nor vacuoles) and free of traces of organic bath additives (EDTA, BRIJ-35). The layer remains intact and strongly sticks to the copper target carrier up to 270°C, i.e. up to an irradiation temperature about 30°C below the melting point of the metal.

At present, the plating technology presented was successfully used for the preparation of twelve targets geometries used for routine production of Tl-201.

P P Up to now Tl-203 layers (surface area 11,6 cmP , total amount of Tl 1.1gram) P plated on IBA copper carriers withstand a non-loss 9 hours irradiation with a circularly wobbled 270 µA proton beam. Recent heat production and heat removal calculations resulting in a new target carrier and coolant channel geometry and in an optimum linear coolant flow rate show that a beam current burden up to 400 µA must be feasible. The new design that should fully make use of the Cyclone–30 external beam current output on a single target will be tested next year.

REFERENCES

[1] Electroplating, F. A. Lowenheim Editor, 3rd Edition, John Wiley & Sons, 1973 [2] Les Réactions Chimiques en Solution Aqueuse, G. Charlot, 7th Edition, Masson, 1983 [3] Chemical Analysis, H. A. Laitinen, Mac Graw-Hill, 1960

[4] The Canning Handbook on Electroplating, W. Canning Ltd, E.& F.N. Spon Ltd, 1977 [5] Electroplating Engineering Handbook, L. J. Durney, 4th Edition, Chapman & Hall, 1996

44 CYCLOTRON PRODUCTION OF IODINE-123 AND PD-103

ZHOU WEI, WANG YONGXIAN, ZHANG CHUNFU Shanghai Institute of Nuclear Research, Chinese Academy of Science, China

Abstract

The tellurium-124 target was prepared by electroplating of tellurium-124 on the Ni/Cu target carrier and was irradiated with a proton beam of 25 MeV energy. The loss of the target material was also determined. The overall 124

P radiochemical yield was typically greater than 92% and the recovery of P Te was greater than 99%. The layer of rhodium on the target was prepared by periodic reverse plating. After irradiation of the rhodium target, the electrodissolution and oxidation dissolution method were evaluated and the Molecular plating of Pd-103 onto silver rod was validated in this work.

1. INTRODUCTION

123

P The P I(T1/2B =13.2h,B Eγ=159keV) radioisotope has found wide application in diagnostic nuclear medicine. Of the many methods reported for the production of the medically important radioisotope 123

P P I, the two most important processes, according to the present state of knowledge, involve the 123 123 124 123

P P P P P Xe→P I generator method and the P Te→P I reaction. The latter method is more suitable for 124 124

P P production at low-energy cyclotrons. Precise excitation function measurements for the P Te(p, n)P I 124 123 124 123

P P P P and P Te(p, 2n)P I reactions showed that highly enriched P Te is necessary to produce P I containing 124

P relatively P I impurity. Considerable advances in targetry and chemical separation of radioiodine have 124

P been reported. Irradiation of 2π or 4π water –cooled P Te target at medium currents, followed by wet 124

P chemical separation of radioiodine and recovery of the enriched P Te-target material has also been reported.

Interstitial implantation of radiation-emitting materials has been long recognized as effective method for tumour therapy. The advantage of interstitial implants is an opportunity to concentrate the radiation at the tumour site while minimizing radiation exposure to normal tissue. Commonly used implantable materials include radioactive gold-198 and radon-222. Use of these radioactive sources is not without shortcomings, however, since the highly penetrating radiation that is emitted not only subjects normal tissues to more destructive radiation, but can also make it difficult to adequately shield personnel. Another important radioisotope commonly used for permanent implantation is iodine-125.

Palladium-103 has more favorable physical properties, including its low energy, rapid dose fall- off, short half-life, and total cumulative dose delivery at a higher dose rate than iodine-125 and is a promising radioisotope for localized tumour treatment. Production of palladium-103 can be accomplished by either cyclotron production or reactor production.

For nuclear reactor production, palladium-103 is produced by bombarding a target containing enriched palladium-102 with neutrons. In contrast to cyclotron production of palladium-103 where carrier-free palladium-103 can be produced, nuclear reactor production is not carrier free, and the product always contains palladium-102. In addition, palladium-109, palladium-111, and other palladium contaminants can also be present.

One drawback of reactor-produced palladium-103 is that the specific activity cannot be adjusted to provide for the production of a seed of predetermined therapeutic or apparent activity. A further possible disadvantage resides in the fact that large amounts of stable palladium-102 remain which may shield the low energy X-ray released when the palladium-103 nuclei disintegrate. Reactor-produced palladium-103 from enriched palladium-102 is also expensive because of the difficulty in enriching palladium-102 (only 1.02% natural abundance) from palladium metal. This paper discusses a method that can be used for commercial production of no-carrier-added palladium-103 with cyclotron.

2. METHOD

2.1. Iodine-123

2.1.1. Targetry

· B B B B· B B The Ni plating solution was prepared by dissolving 250g NiSO4B B 6H2O and 30g NiCl2 6H2O

in 500ml H2B O.B To which 35g H3B BOB 3B B was added and the final volume adjusted to 1.0L. The pH of the 2

- P solution should be 3 4. Ni surface of 200-300 ug/cmP was electroplated onto the Cu plate using a current of 200mA for 10 min. The current efficiency was 90%. A platinum electrode was used as the anode and the Cu plate as cathode. The dry weight of the Ni/Cu plate was determined after washing 0

CP the plate with distilled water, organic solvent and drying at 110P .

124

P The stock solution for electrodeposition of the enriched P TeO2B B was typically prepared by dissolving 1g tellurium-to-tellurium oxide in 50 ml concentrated HNO3B .B After evaporation to dryness, the tellurium oxide was dissolved by 30g KOH and 150 ml distilled water. The pH of the solution should be adjusted to 10―11.

124 2

P P The enriched P Te was electrodeposited on a 10 cmP area of electroplated Ni on a Cu plate. The Te cover was formed onto the Ni surface by electroplating with a current of 100mA for 60 minutes 2

― P and the thickness was 10 12mg/cmP . The plate was determined after rinsing the plate with distilled water and drying with acetone.

2.1.2. Irradiation The target was irradiated with a proton beam of 25 MeV energy. The loss of the target material was determined after bombarded with different beam current from 10uA up to 100uA. The loss of 124

P P Te was greater than 3% as the beam was above 80 uA. The loss of the target material on different Ni layers was also determined.

2.1.3. Separation of iodine-123 from tellenium 124

P After irradiation, the P Te coated on the Cu/Ni target plate was dissolved in a mixture of 1 ml 5 124

P M NaOH, 2ml of 30% H2B OB 2B andB the deionized water was needed to cover P Te deposit. After dissolution, the solution was transferred to a flask containing 250mg of aluminum power. The target plate and holder were rinsed three times with 5ml of water. Solution was heated gently until the reaction was complete and all H2B OB 2B wasB decomposed. Filtered carbon dioxide gas was bubbled through the solution for 5 min. The volume of the solution was reduced by heating gently on a hot plate. The solution was filtered through a glass frit and the iodine-123 solution was obtained.

2.1.4. Recovery of the enriched tellurium

The powder was dissolved in 10 ml of 7M H2B SOB 4B B and then 1.5ml of 30% H2B OB 2B B was added in small portions at which point a clear solution was obtained. 25ml of distilled water was added to cooled mixture and 25 ml was distilled off. This fraction contained the iodine-124. Then 10 ml of 50% hypophosphorus acid was added to cooled solution to precipitate the tellurium. The solution was filtered and the filtrate washed and dried.

2.2. Palladium-103

2.2.1. Targetry and irradiation The layer of rhodium on the target was prepared by periodic reverse plating. The target carrier was a ten centimeter long, one centimeter wide and 0.1 millimeter in depth copper support. Rhodium (ΙΙΙ) chloride hydrate (99.99% Merk product) is main component of the electroplating solution.

46 0 2

P P Electroplating temperature was 45P C. The negative electrode current density was 0.2A/cm P and 2

P the positive one was 0.15A/cmP . Time ratio of the two electrodes (tkB /tB AB )B was 15(s):5(s).

The irradiation of the rhodium-coated target was performed with a Cyclone 30 cyclotron manufactured by IBA. The irradiation lasted for 10 hours at the 21 MeV energy of proton and a beam current intensity is 200 µA, measured by integrating the charge collected on the target.

2.2.2. The dissolution of irradiated target We evaluated the electrodissolution and oxidation dissolution method in this work. All the targets were dissolved four days after the end of bombardment (EOB).

Electrodissolution. The dissolution of the target was performed using the improved electrolysis apparatus. The rhodium metal target with thin layer of copper on the back, which was peel off from the bulgy part of copper support by cutting machine, was placed onto the graphite plate (the positive “ ” 2

P P P electrode) and sealed by a rubber P OP ring and a 0.5A/cmP current density then applied. The fragmentation rate, referring to proportion of the weight of rhodium powder produced by electrodissolution to the weight of target, was determined by measuring the content of rhodium in the electrolyte using UV-240 Visible Recording Spectrophotometer, which was more accurate than weighting method. 2-(2-thiazolylazo)- 5-diethylaminobenzoic acid was used as the selective developer for rhodium and absorbency was determined at 674 nm. The improved eletrodissolution cell is more suitable for routine, large-scale production as well as more useful and considerably safer when handling a highly radioactive target in a remotely controlled processing system intend for this work.

Oxidization dissolution. The rhodium target, dissolving the thin layer of copper with HNO3B B on the back, was crushed down and put into 10 ml concentrate HCl with a stoichiometric level of KAuCl4,B heated, B and stirred for five hours.

2.2.3. Radiochemical separation of palladium-103 from rhodium solution Separation of palladium-103 was performed using anion-exchange chromatography. A 1.5 cm −

× P inner diameter glass column filled with Dowex 1 8(ClP ) 100-200 mesh resin to a height of 10cm was used. After preconditioning the resin with 6M HCl, the rhodium solution was loaded on to the column.

The eluants consisted of 0.03M HCl, 6M HCl and NH3B +NHB 4B ClB (1:1). The separation efficiency for palladium and rhodium was monitored by measuring the activity of palladium-103 and rhodium-102 in the eluant fractions using γ spectroscopy.

2.2.4. Molecular plating of Pd-103 onto silver rod The electroless-plating bath consists of palladium chloride, formic acid, formaldehyde and nitric acid. The silver rod (99.99%) is 3mm in length and 0.5mm in diameter. Reactor is a glass tube with 4mm inner diameter and 3 cm in length. The concentration of Pd-103 was about 120mCi/ml and the nuclide purity was greater than 99.95%. Silver rods were added and a NaI scintillation detector was used to measure the activity change of plating solution before and after electroless plating. The rods were washed by water and acetone three times, respectively.

3. RESULTS AND DISCUSSION

3.1. Iodine-123

124

P The Ni surface provided greatly increased adhesion for electrodeposited P Te. Ni did not interfere in the radiochemical separation. The relationship between the loss of Te and the beam current intensity was shown in Fig. 1, when the beam current intensity was less than 80 uA, the loss of the Te target material was less than 3%.

The relationship between loss of Te and the thickness of Ni layer was also shown in Fig. 2, as 2

P the Thickness of Ni layer was between 9-13 mg/cmP , the loss of Te was less than 3%.

The method for the separation of iodine-123 from tellurium was adapted from the reported methods. After dissolution of tellurium, aluminum power was added. Aluminum can reduce Te(+IV) to Te(0). During the reaction, a dark coloration was observed due to the formation of tellurides and tellurides were oxidized to Te(0) by stream filtered air. Aluminum was precipitated as the hydroxide. 124

P The overall radiochemical yield was typically greater than 92% and the recovery of P Te was greater than 99%.

3.2. Palladium-103 Metallic rhodium was selected as the target because of its favorable physical properties, such as high resistance to corrosion and high melting point. The advantage of periodic reverse plating is that we can obtain even rhodium plating layer with uniform in depth and little eyelet. The yield of palladium-103 was about 1250 mCi at the EOB.

The electrodissolution results of different mass rhodium target with rectangle shape are summarized in Table I. With the increase of current density, the fragmentation increased dramatically, but the time for dissolution decreased greatly. The optimal selection of the current density was 2

P between 0.4 and 0.6 A/cmP as the result of faster dissolution with less fragmentation. The measurement of content of rhodium in the electrolyte using visible spectrophotometer was more accurate than weighting method. Under the radiation conditions, the electrodissolution was judged as the most suitable method with regard to personnel safety and environmental protection.

KAuCl4B B was selected as the oxidant to dissolve rhodium target because it is simple and an easily manageable method. The chemical potential of the reaction is:

- - -

P P P E=0.572+0.0394lg[ClP ]+0.0197lg[AuCl4B PB ]/[RhCl6B PB ]

- - -

P P P At a given [ClP ], the last item- lg[AuCl4B PB ]/[RhCl6B PB ]-gives little contribution to the potential, which can also be seen from the experimental results (Table II). Temperature is the key factor 0

P affecting the reaction. Between room temperature and 60 P C, there was almost no dissolution of the 0

P target but at 100P C about 40% of the target dissolved. Using this approach with the residue under the same conditions did not dissolve the solid. Our inability to dissolve the residue in this way could result from formation of a layer of a compact insulation gold film on the surface of the target, which inhibits further reaction. In addition, rhodium was passivated at high temperature.

2- 3-

P P Based on the differences in the affinity of doubly charged PdCl4B PB and triply charged RhCl6B PB , an ion-exchange method was developed for the separation of palladium from rhodium. After eluting with 2+ 2+ 3+

P P P 100ml 0.03M HCl, which is intended to remove Cu P and micro-base metal ion such as ZnP , FeP , the resin was eluted with 120 ml with 6M HCl at a 4ml/min flow rate. As shown in Fig. 2, 99.82% of rhodium was released by 120 ml of 6M HCl solution. The amine complex of palladium behaves as a cation, so Pd is easily released from the anion resin with ammonia, but the efficiency of elution was about 73% (Fig. 4). When ammonium chloride was added to the ammonia solution palladium was eluted more rapidly with high efficiency. About 70% of palladium was washing out in the first 10ml and 95% of palladium was released from the resin with only 50ml mixture (Fig. 5).

Electroless-plating is a better method than electroplating for coating Pd-103 onto silver, because of more uniform-plated layer, stronger affinity of the plated layer to the substrate and simple technique used on micro scale. The optimum composition of the plating bath and ideal operating conditions are palladium chloride 0.1mol/l, formic acid 0.4mol/l, formalhyde 2mol/l, and nitric acid 1mol/l, 0

P temperature of electroless-plating bath at 30P C and the reaction time of 25 min.

48 6.0 Current integration:100 uAhr 5.5

5.0

4.5

4.0

3.5

3.0 loss of Te (%)

2.5

2.0

1.5

20 40 60 80 100 beam current intensity (uA) Fig.1 relationship between loss og Te and beam current intensity

14 beam current intensity:50uA current integration:200uAhr 12

6 loss of Te (%)

0 2468101214161820 2 thickness of Ni layer (mg/cm ) Fig.2 relationship between loss of Te and thickness of Ni layer

TABLE I. EXPERIMENTAL CONDITION AND DISSOLUTION RATES FOR ELECTRODISSOLUTION OF METAL RHODIUM TARGETS IN 6M HCL

Area Current Current density Fragmentation Time 2 2

P P (cmP ) (A) (A/ cmP ) (%) (h) 1×10 10 1 78 0.20 1×3.5 2.8 0.8 50.3 0.50 1×3 1.8 0.6 24.2 0.62 1×10 5 0.5 8 1.50 1×1.8 0.72 0.4 5.1 0.64

TABLE II. PERCENT OF DISSOLVED RHODIUM AT DIFFERENT TEMPERATURE

Temperature Molar ratio of KAuCl4B B to rhodium Percent 60 1:1 Very little 70 2:1 4.25% 80 1:1 15.26% 90 5:1 28.20% 100 5:1 40.00%

100

80 )

40 Pecent of Rhodium(% 20

0 0 20 40 60 80 100 120 V(ml) of 6M HCl Fig.3 Elution profile of rhodium with 6M HCl as eluant

40 percent of Pd-103 (%)

0 20406080100 V(ml) of conc. ammonia Fig.4 Elution profile of Pd-103 with ammonia as eluant

100

75 percent of Pd-103 (%)

65 10 20 30 40 50

V(ml) of NH3+NH4Cl(1:1) mixed eluant

Fig.5 Elution profile of Pd-103 with NH3+NH4Cl(1:1) as eluant

REFERENCES

[1] S.M.QAIM, G.STOCKLIN. Production of some medically important short-lived neutron- deficient radioisotopes of halogens. Radiochimica Acta. v. 34, pp. 25-40, 1983 [2] R. M. LAMBRECHT, M. SAJJAD, R. S. SYED, W. MEYER. Target preparation and recovery of enriched isotopes for medical radionuclide production. Nuclear Instruments and Methods in Physics Research, A282, pp. 296-300, 1989 [3] R. M. LAMBRECHT, M. SAJJAD, M. A. QURESHI, S. J. AL-YANBAWI. Production of iodine-124. J. Radioanal. Nucl. Chem., Letters, 127, pp. 143-150, 1988 103

P [4] P. TARAPCIK, V. MIKULAJ. Separation of P Pd from cyclotron irradiated rhodium targets. J. Radiochem. Radoanal. Letters, 48, pp. 15-20, 1981 [5]

52 PRODUCTION OF DIAGNOSTIC AND THERAPEUTIC RADIONUCLIDES

S. TAKÁCS Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary

Abstract

This work was done in the frame of the research program of “Standardized High Current Solid Targets for Cyclotron Production of Diagnostic and Therapeutic Radionuclides” co-ordinated by the International Atomic Energy Agency. The aim of the work was to collect, evaluate and calculate cross-section data for proton and deuteron induced reactions on stable isotopes of tellurium, rhodium and palladium in order to produce iodine, palladium and thallium radionuclide respectively for diagnostic and therapeutic purposes. A simple calculation tool was developed to estimate the amount of different radionuclide produced during proton or deuteron bombardment of targets with different enrichments. Using tabulated yield information absolute and relative activity can be calculated for any valid input parameters.

1. INTRODUCTION

Production of radioisotopes at a small cyclotron always requires optimization because of the limited bombarding energy and the interfering contaminating side-reactions. The needed radionuclide impurity level frequently requires highly enriched therefore expensive target materials. Knowing the excitation function of the contributing reactions, an optimization calculation can be performed. The optimization calculation is based on a database containing the relevant information about the nuclear reactions involved in the production process. The required experimental data are the cross-sections of the reactions and the stopping parameters of the target material used or integral yield as a function of energy. In order to be able to perform the necessary calculation experimental cross-section data were collected and measured to complete the required database. Where no experimental were available result of model calculation was used instead.

123

P 2. PRODUCTION OF P I RADIOISOTOPE

2.1. Nuclear data measurements 123

P Basic nuclear data regarding the production of P I was studied at our institute. Cross-section of 123 123

P P P Te(p,n)P I was measured [1] up to 18 MeV. Using the results, we could resolve and clarify the discrepancies between the reported experimental data. By measuring the excitation function of the 122 123

P P P Te(d,n)P I reaction we showed that the experimental data reported by Zaidi in 1983 is shifted by more than 2 MeV to higher energies [2]. With the correct cross-section data, it was concluded that 123 122 123

P P P production of P I radionuclide is possible via the P Te(d,n)P I reaction with important yield. Although 122 123

P P the yield of the (d,n) reaction is lower on P Te than the yield of (p,n) reaction on P Te it can be 122

P economical and more safe to use the (d,n) production route at small cyclotrons since the P Te enriched 123

P target material is much cheaper than the enriched P Te one [3]. The production technology uses TeO2B B targets on platinum backing. Therefore, we have also investigated the reactions of the platinum induced by proton and deuteron bombardment in order to be able to estimate the total activity level associated with an irradiated production target. The results will be published in Radiochimica Acta [4].

2.2. Production experiences 123 123

P P At the Debrecen cyclotron, we produced P I isotope using highly enriched P TeO2B B target material melted onto platinum target backing. The production details are given in [5]. Using a target 10 mm in diameter and vertical beam perpendicular to the target surface it was found that 8-10 µA beam current causes no problem to the target yet. A new target system was also developed to irradiate at a horizontal beam line at 30 degrees to the target surface. Using this arrangement the target surface increased the thickness of the TeO2B B layer can be decreased which resulted in better cooling parameters of the target and increased production yield.

2.3. Optimization of production using nuclear data Production of radioisotope with the needed radionuclide impurity level frequently requires highly enriched therefore expensive target materials. It is always recommended to make an apriori optimization calculation to determine the best target and irradiation parameters. Doing this calculation a database is needed containing the relevant information about the nuclear reactions (main and side reactions) involved in the production process. The required basic information is: the excitation function of the reactions, stopping parameters of the target material for the available bombarding particles and in the irradiation energy range.

2.3.1. Calculation of the total absolute activity A simple calculation tool was developed in EXCEL format to calculate the absolute activity and activity ratios of different radioactive products at any target enrichments and irradiation parameter combinations.

The required input parameters are:

- Target composition (absolute ratio of each of the stable isotopes in the target normalized to 1.) - Irradiation parameters o . type of the bombarding particle (proton, deuteron) o . irradiation time (in hours) o . bombarding beam current (in µA units) o . primary on-target bombarding particle energy (MeV) o . outgoing bombarding particle energy (MeV) o . cooling time (in hours)

2.4. Production of Iodine radioisotopes

The production of iodine radioisotopes with the needed radionuclide impurity level requires highly enriched and expensive Te-targets. The amount of produced activity and radionuclide impurity levels can be calculated from the relevant data of excitation functions, the thickness of the target or the energy range used at irradiation and finally the isotopic composition of the target. To fulfill this requirement experimental data were collected for proton and deuteron induced nuclear reactions on different stable isotopes of tellurium. In addition, theoretical calculation was made using the Alice- IPPE computer code.

123 124

P P For the proposed calculation in the case of P I and P I products, experimental data were evaluated and recommended cross-sections were given for the investigated reaction [6]. In those cases where only limited experimental data were available, only a spline fit was applied and a smooth curve was calculated over the experimental data. Reactions for which no experimental data were published the results of the Alice-IPPE theoretical model calculation were used. Based on the available cross- section data tabulated yield was calculated for all the contributing reactions and was applied to estimate the activity produced during production process.

By using a calculation tool it is easy to estimate the amount of main iodine isotope to be produced under realistic production circumstances as well as the amount of other iodine radionicludes produced in any side reactions. The amounts of produced radionuclide are given in MBq and in µCi activity units with correction for decay during irradiation and after irradiation during any cooling or waiting time. We have to note that in those cases when no experimental data were available the result of Alice-IPPE calculation was used. The theoretical calculation results in as a general tendency an excitation function having higher maximal value than the experimental one. The difference can be as high as a factor of two.

54 Tables I and II give information about the reactions take place on different Te isotopes for proton and deuteron bombardment respectively. The most probable contributing reactions are considered only. These are (p,n), (p,2n) and (p,3n) for proton irradiation, and (d,n), (d,2n), (d,3n) and (d,4n) for deuteron irradiation. In the last column of the tables the type of the data used in the calculation is given. Three different types of data were used, experimental, evaluated and theoretical. Explanation of the data types:

- Experimental evaluation: Evaluated experimental data. Several series of experimental data points exist, critical selection is made, and overall fit is calculated. Recommended cross-section data are given. - Experimental: Only limited amount of experimental data points exist but a statistical spline fit over the experimental points is possible to calculate. - Theoretical: The result of the Alice IPPE theoretical model calculation is used. - Experiment & theory: The result of theoretical calculation is normalized to experimental data. The fit of the experimental data points is completed with the normalized theoretical calculation.

Figs 1–24 show the excitation functions of the different possible contributing reactions used in our calculation for proton bombardment of tellurium target. Figs 25–53 show the excitation functions of the different possible contributing reactions used in the calculation for deuteron bombardment of tellurium target.

2.5. Production of Pd-103 radio isotope 103

P Production of P Pd radioisotope by accelerators can be made by proton and by deuteron bombardment of Rh target. Rhodium has one stable isotope on which the main reaction and some side reactions can take place during bombardment. Similarly to the iodine production a calculation tool was 103

P developed to calculate the activity of P Pd and the activity of the simultaneously produced other Pd and Rh radioisotopes. To estimate the level of the contaminating radioisotopes the cross-sections of the relevant reactions were used. The cross-sections were determined experimentally using stacked target activation technique. Results for proton and deuteron bombardment were published separately in Nuclear Instruments and Methods B [7] and [8] respectively. Statistical spline fit was applied over the experimental data and the result was used for calculating tabulated yield for each of the reactions. Tables III and IV summarize the investigated radioactive products, the contributing reactions, the Q- value of the reactions and the type of the data used in the calculation to estimate the total activity of the products.

Figs 54–60 show the excitation functions of the different possible contributing reactions used in the calculation for proton and deuteron bombardment of rhodium target.

2.6. Production of Tl-201 radioisotope High specific activity, carrier free Tl-201 radioisotope is produced in proton bombardment of thallium target followed by chemical separation of lead radioactive isotopes. The separated lead isotopes decay into thallium by electron capture or positron emission. In order to increase the 201

P radionuclide purity of the produced P Tl it is necessary to optimize the irradiation parameters. The (p,xn) reactions result in different radioisotopes of lead. The yields of the produced lead isotopes depend on the primary bombarding proton energy and the target thickness. For estimating the level of the contaminating radioisotopes the cross-section of the relevant reaction is used. The measured experimental cross-sections were collected and when there were enough data points available critical evaluation and selection of the data series were made and recommended cross-sections were determined using the selected experimental data [6]. Table V. gives information on the investigated radioactive products, the contributing reactions, the Q-value of the reactions and the type of the data used in the calculation to estimate the total activity of the products.

Figs 61–69 show the excitation functions of the different possible contributing reactions used in the calculation for proton bombardment of thallium target.

REFERENCES

[1] MAHUNKA I., ANDO L., MIKECZ P., TCHELTSOV A.N. SUVOROV I.A. Excitation 123 123 123

P P P function of P Te(p,n)P I reaction for direct production of P I by small cyclotron, Annales Universitatis Turkuensis, Ser. D. Medica – Ondotologica 88. Medical Application of Cyclotrons VI: Proceedings of the Sixth Symposium on the Medical Application of Cyclotrons, June 1-4, 1992. Turku, Finnland. Ed.: L.-M. Voipio-Pulkki, U. Wegelius, (1992) 11. [2] TAKÁCS S., AZZAM A., SONCK M., SZELECSÉNYI F., KOVÁCS Z., HERMANNE A., 122 123 123

P P P TÁRKÁNYI F., Excitation function of P Te(d,n)P I nuclear reaction: production of P I at a low energy cyclotron. Applied Radiation and Isotopes 50 (1999) 53. [3] SCHOLTEN B., TAKÁCS S., KOVÁCS Z., TÁRKÁNYI F., QAIM S.M.: Excitation function of deuteron induced reactions on 123Te: Relevance to the production of 123I and 124I at low and medium sized cyclotron. Applied radiation and isotopes 48 (1997) 267. [4] TÁRKÁNYI F., HERMANNE A., TAKÁCS S., SHUBIN YU, DITYUKA.I. Cross-sections for 198 199

P P production of therapeutic radioisotopes P Au and P Au in proton and deuteron induced 198

P reactions on P Pt, will be published in Radiochimica Acta. [5] TÁRKÁNYI F., ANDÓ L., SZŰCS Z., MAHUNKA I., KOVÁCS Z. Solid targets and Irradiation facilities for production of diagnostic and therapeutic radioniclides at the Debrecen st

P cyclotron. Report on the 1P RCM of the CRP on “Standardized High Current Solid Targets for Cyclotron Production of Diagnostic and Therapeutic Radionuclides”, 27-30 November 2000. Brussels, Belgium. [6] TÁRKÁNYI F., TAKÁCS S., GUL K., HERMANNE A., MUSTAFA M. G., NORTIER M., OBLOZINSKY P., QAIM S. M., SCHOLTEN B., SHUBIN YU. N., YOUXIANG Z. Beam Monitor reactions. IAEA TECDOC-1211. Charged particle cross-section database for medical radioisotope production: diagnostic radioisotopes and monitor reaction, chapter 4, IAEA,

Vienna, May 2001, p. 50. Web version at URL: http://www-nds.iaea.org/medicalT .T 103

P [7] HERMANNE A., SONCK M., FENYVESI A., DARABAN L. Study on production of P Pd 103

P and characterization of possible contaminants in the proton irradiation of P Rh up to 28 MeV. Nuclear Instruments and Methods in Physics Research B 170 (2000) 281-292. [8] HERMANNE A., SONCK M., TAKÁCS S., TÁRKÁNYI F., SHUBIN Y.: Study on alternative 103 103

P P production of P Pd and characterization of contaminants in the deuteron irradiation of P Rh up to 21 MeV. Nuclear Instruments and Methods in Physics Research B 187 (2002) 3-14.

56 TABLE I. THE IODINE RADIOACTIVE ISOTOPES PRODUCED IN PROTON BOMBARDMENT ON TE TARGETS, CONTRIBUTING REACTIONS, Q-VALUES AND TYPE OF DATA USED IN THE CALCULATION TO ESTIMATE THE TOTAL PRODUCED ACTIVITY

Product Half-life Contributing Q-value Used data Reaction (MeV) 118m,g 120 118g

P P P P P I 13.7 m Te(p,3n)P I -25.634 theory

119 120 119

P P P P P I 19.1 m Te(p,2n)P I -14.583 experimental

120g 120 120g

P P P P P I 81.0 m Te(p,n)P I -6.402 - experimental 122 120g

P P P Te(p,3n)P I 23.447

120m 120 120m

P P P P P I 53 m Te(p,n)P I -6.402 - experimental 122 120m

P P P Te(p,3n)P I 23.447 experimental

121 122 121

P P P P P I 2.12 h Te(p,2n)P I -12.876 - experimental 123 121

P P P Te(p,3n)P I 22.315 theory

122 122 122

P P P P P I 3.63 m Te(p,n)P I -5.016 - experimental 123 122

P P P Te(p,2n)P I 11.955 - theory theory 124 122

P P P Te(p,3n)P I 21.379

123 123 123

P P P P P I 13.27 h Te(p,n)P I -2.024 - eval. exp. 124 123

P P P Te(p,2n)P I 11.448 - eval. exp. theory 125 123

P P P Te(p,3n)P I 18.023

124 124 124

P P P P P I 4.176 d Te(p,n)P I -3.942 - eval. exp. theory 125 124

P P P Te(p,2n)P I 10.517 - theory 126 124

P P P Te(p,3n)P I 19.631

125 125 125

P P P P P I 59.408 d Te(p,n)P I -0.968 - theory theory 126 125

P P P Te(p,2n)P I 10.082

126 126 126

P P P P P I 13.11 d Te(p,n)P I -2.937 - theory theory 128 126

P P P Te(p,3n)P I 18.01

128 128 128

P P P P P I 24.99 m Te(p,n)P I -1.245 - experimental 130 128

P P P Te(p,3n)P I 16.53 theory

129 7 130 129

P P P P P P I 1.57 10P y Te(p,2n)P I -7.70 theory

130m,g 130 130g

P P P P P I 12.36 h Te(p,n)P I -1.21 experimental

TABLE II. THE PRODUCED IODINE RADIOACTIVE ISOTOPES IN DEUTERON BOMBARDMENT ON TE TARGETS, CONTRIBUTING REACTIONS, Q-VALUES AND TYPE OF DATA USED IN THE CALCULATION TO ESTIMATE THE TOTAL PRODUCED ACTIVITY

Product Half-life Contributing Q-value Used data reaction (MeV) 103 120 119

P P P P P I 19.1 m Te(d,3n)P I -16.82 theory

120g 120 120g

P P P P P I 81.0 m Te(d,2n)P I -8.62 - exp. + theory 122 120g

P P P Te(d,4n)P I 25.67 theory

120m 120 120m

P P P P P I 53 m Te(d,2n)P I -8.62 - exp. + theory 122 120m

P P P Te(d,4n)P I 25.67 theory

121 120 121

P P P P P I 2.12 h Te(d,n)P I +1.95 - theory 122 121

P P P Te(d,3n)P I 15.10 - experimental 123 121

P P P Te(d,4n)P I 22.03 theory

122 122 122

P P P P P I 3.63 m Te(d,2n)P I -7.24 - experimental 123 122

P P P Te(d,3n)P I 14.17 theory theory 124 122

P P P Te(d,4n)P I -23.59

123 122 123

P P P P P I 13.27 h Te(d,n)P I +2.69 - experimental 123 123

P P P Te(d,2n)P I 4.24 - exp. + theory 124 123

P P P Te(d,3n)P I 13.67 - exp. + theory 125 123

P P P Te(d,4n)P I 20.24 theory

124 123 124

P P P P P I 4.176 d Te(d,n)P I +3.26 - experimental 124 124

P P P Te(d,2n)P I 6.16 - experimental 125 124

P P P Te(d,3n)P I 12.74 - theory theory 126 124

P P P Te(d,4n)P I 21.86

125 124 125

P P P P P I 59.408 d Te(d,n)P I +3.38 - theory theory 125 125

P P P Te(d,2n)P I 3.19 - theory 126 125

P P P Te(d,3n)P I 12.31

126 125 126

P P P P P I 13.11 d Te(d,n)P I +3.95 - theory exp. 126 126

P P P Te(d,2n)P I 5.16 - + theory 128 126

P P P Te(d,4n)P I 2023 theory

128 128 128

P P P P P I 24.99 m Te(d,2n)P I -4.26 - exp. + theory 130 128

P P P Te(d,4n)P I 18.76 theory

129 7 128 129

P P P P P P I 1.57 10P y Te(d,n)P I +4.57 - theory 130 129

P P P Te(d,3n)P I 9.93 theory

130m,g 130 130

P P P P P I 12.36 h Te(d,2n)P I -3.43 exp. + theory

131 130 131

P P P P P I 8.02 d Te(d,n)P I +5.17 exp. + theory

58 103 TABLE III. P PDP AND CONTAMINATING RADIOISOTOPES PRODUCED BY PROTON 103

P BOMBARDMENT ON P RH TARGETS, Q-VALUES AND TYPE OF DATA USED TO ESTIMATE THE TOTAL PRODUCED ACTIVITY

Product Half-life Contributing Reaction Used data Q-value(MEV) 103 103 103

P P P P P Pd 16.97 d Rh(p,n)P Pd -1.33 experimental

101 103 101

P P P P P Pd 8.47 h Rh(p,3n)P Pd -19.52 experimental

103m 103 103m

P P P P P Rh 56.1 m Rh(p,n)P Rh 0.0 experimental

102m 103 102m

P P P P P Rh 2.9 y Rh(p,pn)P Rh -9.32 - experimental 103 102m

P P P Rh(p,d)P Rh 7.09

102g 103 102g

P P P P P Rh 207 d Rh(p,pn)P Rh -9.32 - experimental 103 102g

P P P Rh(p,d)P Rh 7.09

101m 103 101m

P P P P P Rh 4.34 d Rh(p,p2n)P Rh -16.76 - experimental 103 101m

P P P Rh(p,nd)P Rh 14.53 - 103 101m

P P P Rh(p,t)P Rh 8.27

101g 103 101g

P P P P P Rh 3.3 y Rh(p,p2n)P Rh -16.76 - experimental 103 101g

P P P Rh(p,nd)P Rh 14.53 - 103 101g

P P P Rh(p,t)P Rh 8.27

103 TABLE IV. P PDP AND CONTAMINATING RADIOISOTOPES PRODUCED IN DEUTERON 103

P BOMBARDMENT ON P RH TARGETS, CONTRIBUTING REACTIONS, Q-VALUES AND TYPE OF DATA USED TO ESTIMATE THE TOTAL PRODUCED ACTIVITY

Product Half-life Contributing Reaction Used data Q- VALUE(MEV ) 103 103 103

P P P P P Pd 16.97 d Rh(d,2n)P Pd -3.55 experimental

101 103 101

P P P P P Pd 8.47 h Rh(d,4n)P Pd -21.74 experimental

103m 103 103m

P P P P P Rh 56.1 m Rh(d,d)P Rh 0.0 - experimental 103 103m

P P P Rh(d,np)P Rh 2.22

102m 103 102m

P P P P P Rh 2.9 y Rh(d,p2n)P Rh -11.54 - experimental 103 102m

P P P Rh(d,dn)P Rh 9.32 - 103 102m

P P P Rh(d,t)P Rh 3.06

102g 103 102g

P P P P P Rh 207 d Rh(d,p2n)P Rh -11.54 - experimental 103 102g

P P P Rh(d,dn)P Rh 9.32 - 103 102g

P P P Rh(d,t)P Rh 3.06

101m 103 101m

P P P P P Rh 4.34 d Rh(d,p2n)P Rh -11.54 - experimental 103 101m

P P P Rh(d,dn)P Rh 14.53

101g 103 101g

P P P P P Rh 3.3 y Rh(d,p3n)P Rh -18.98 - experimental 103 101g

P P P Rh(d,d2n)P Rh 16.74 - 103 101g

P P P Rh(d,tn)P Rh 10.50

201

P TABLE V. THE P PB AND THE CONTAMINATING RADIOACTIVE ISOTOPES PRODUCED 203 205

P P IN PROTON BOMBARDMENT ON P TL AND P TL TARGETS, CONTRIBUTING REACTIONS, Q-VALUES AND TYPE OF DATA USED IN THE CALCULATION TO ESTIMATE THE TOTAL PRODUCED ACTIVITY

Product Half-life Contributing Reaction Q-value Used data (MeV) 203 203 203

P P P P P Pb 51.9 h Tl(p,n)P Pb -1.77 - experimental 205 203

P P P Tl(p,3n)P Pb 15.96

202m 203 202m

P P P P P Pb 3.62 h Tl(p,2n)P Pb -8.68 - experimental 205 202m

P P P Tl(p,4n)P Pb 22.88

201 203 201

P P P P P Pb 9.4 h Tl(p,3n)P Pb -17.41 experimental

200 203 200

P P P P P Pb 21.5 h Tl(p,4n)P Pb -24.52 experimental

204m 205 204m

P P P P P Pb Tl(p,2n)P Pb -7.56 experimental

202 nat 202

P P P P P Tl 12.23 d Tl(p,x)P TlP - experimental 203 202

P P Tl(p,d)P TlP 5.62 - separated curves 203 202

P P Tl(p,pn)P Tl 7.85 - 205 202

P P P Tl(p,2nd)P Tl 19.83 - 205 202

P P P Tl(p,3np)P Tl 22.05

201 nat 201

P P P P P Tl 73.1 h Tl(p,x)P Tl experimental 203 201

P P P Tl(p,t)P TlP -6.24 - separated curves 203 201

P P Tl(p,dn)P TlP 12.5 - 203 201

P P Tl(p,2np)P Tl 14.72 - 205 201

P P P Tl(p,2nt)P Tl 20.44 - 205 201

P P P Tl(p,3nd)P Tl 20.7 - 205 201

P P P Tl(p,4np)P Tl 28.92

60 600 800 122Te(p,3n)120I 120 118 700 Zweit 96 I-120 Te(p,3n) I Alice IPPE Hohn 97 I-120m 500 Hohn97 I-120g 600 Alice IPPE b) ) spline fit I-120m b 400 m 500

( spline fit I-120g ons i t

on (m 400 c e

300 s s

os 300 r C oss secti

r 200

C 200

100 100 0 0 20 30 40 50 60

20 30 40 50 60 Proton energy (MeV) Proton energy (MeV) FIG. 4. Excitation function of the FIG. 1. Excitation function of the 122 120m+g P P 120 118 P Te(p,3n)P I reaction calculated by using

P P P Te(p,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. 120m 120g P P Experimental data of P I and P I were fitted by using spline method. 1200 120Te(p,2n)119I 1400 1000 Alice IPPE 122Te(p,2n)121I Hohn 98 Hohn 97 spline fit 1200

) 800 Scholten 89 b

m Zweit 96 I-121 (

n 1000 o

i Alice IPPE b)

ct 600 spline fit s se

ns (m 800 s o o r

C 400 600 oss secti r

200 C 400

0 200 0 10203040506070 Proton energy (MeV) 0 FIG. 2. Excitation function of the 0 10203040506070 120 119

P P P Te(p,2n)P I reaction calculated by using Proton energy (MeV) Alice IPPE model code. Experimental data FIG. 5. Excitation function of the fitted by using spline method. 122 121 P P P Te(p,2n)P I reaction calculated by using Alice IPPE model code. Experimental data 1000 were fitted by using spline method. 120Te(p,n)120I 900 Alice IPPE Hohn 98 I-120m 800 1200 Hohn 98 I-120g 123 121 700 spline fit I-120g Te(p,3n) I Alice IPPE ) spline fit I-120m b 1000 m

( 600 n o i 500 )

b 800

ss sect 400 o r C on (m 300 600

200 oss secti r

C 400 100

0 0 5 10 15 20 25 30 35 40 200 Proton energy (MeV) FIG. 3. Excitation function of the 0 120 120m+g 0 10203040506070

P P P Te(p,n)P I reaction calculated by using Proton energy (MeV) Alice IPPE model code. 120m 120g FIG. 6. Excitation function of the

P P Experimental data of P I and P I were fitted 123 121

P P P Te(p,3n)P I reaction calculated by using by using spline method. Alice IPPE model code.

1000 1000 123 123 Mahunka96 122 122 900 Te(p,n) I Te(p,n) I Hohn 97 Scholten89 I-123 800 Alice IPPE 800 Van den Bosch77 I-123 Spline fit Hupf 68 I-123 b) 700 Barrall 81 I-123

b) Zweit 92 nat 600 m 600 ( Scholten 89 nat ons (m on i i

t 500 Acerbi 75 nat c

e Alice IPPE s

400 s 400 Spline fit of norm. Alice os r oss sect r C 300 C 200 200

100 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 35 Proton energy (MeV) Proton energy (MeV) 122 122

P P FIG. 7. Excitation function of the P Te(p,n)P I FIG. 10. Excitation function of the 123 123

P P reaction calculated by using Alice IPPE model P Te(p,n)P I reaction calculated by using code. Alice IPPE model code. Experimental data were fitted by using spline Experimental data were fitted by using spline method. method.

1200 2000 123 122 124 123 Van den Bosch77 Te(p,2n) I Sholten 89 1800 Te(p,2n) I 1000 Kondo77a I-123 Alice IPPE 1600 Kondo77b I-123 Scholten 95 I-123

b) 800 1400 Acerbi 75 I-123 ] m

b Alice IPPE norm. 1200

[m spline fit on ( n i

600 io

t 1000 ect

s 800 ss sec o os

400 r r

C 600 C 200 400 200

0 0 0 1020304050 5 10152025303540 Proton energy (MeV) Proton energy [MeV] 123 122

P P FIG. 8. Excitation function of P Te(p,2n)P I FIG. 11. Excitation function of the 124 123

P P calculated by using Alice IPPE model code. P Te(p,2n)P I reaction calculated by using Alice IPPE model code. Experimental data were fitted by using spline method.

1000 1200 124 122 125 123 900 Te(p,3n) I Alice IPPE Te(p,3n) I 1000 Alice IPPE 800 b) m 700 b) n ( 800 o m i 600 n ( ct o e 500 i 600 s S os

r 400 oss sect C r 400 300 C 200 200 100 0 0 0 10203040506070 0 10203040506070 Proton energy (MeV) Proton energy (MeV) FIG. 12. Excitation function of the FIG. 9. Excitation function of the 125 123

P P 124 122 P Te(p,3n)P I reaction calculated by using P P P Te(p,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

800 800 Van den Bosch77 124 124 125 125 700 Te(p,n) I Kondo77a I-124 700 Te(p,n) I Johnson58 Kondo77b I-124 Zweit 92nat Scholten95 I-124 600 600 Alice IPPE

Acerbi 75 I-124 ) b

) Acerbi 75 nat

b 500 500 (m

Zweit 92 nat s n (m

n Scholten 89 nat tio o 400 i c 400t Alice IPPE Spline fit ss se 300 o

300 r oss sec C r C 200 200 100 100 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 35 Proton energy (MeV) Proton energy (MeV) FIG. 16. Excitation function of the FIG. 13. Excitation function of the 125 125

124 124 P P P Te(p,n)P I reaction calculated by using P P P Te(p,n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. Experimental data were fitted by using spline method.

1200 1200 125Te(p,2n)124I 126Te(p,2n)125I 1000 1000 Alice IPPE Alice IPPE

) 800 800 b) V e (M on (m n 600 i 600 tio c s sect s s se o s r o 400 400 r C C

200 200

0 0 0 10203040 0 1020304050 Proton energy (MeV) Proton energy (MeV) FIG. 14. Excitation function of the FIG. 17. Excitation function of the 125 124 126 125

P P P P P Te(p,2n)P I reaction calculated by using P Te(p,2n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

1000 1200 128 126 900 126 124 Alice IPPE Te(p,3n) Te Te(p,3n) I 1000 800 Alice IPPE 700 800

600 b) b) m m

500 on ( 600 i on ( i 400

oss sect 400

300 r oss sect r C C 200 200 100 0 0 0 1020304050 0 10203040506070 Proton energy (MeV) Proton energy (MeV) FIG. 15. Excitation function of the 123 123 FIG. 18. Excitation function of the

P P P Te(p,n)P I reaction calculated by using 128 126 P P P Te(p,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

600 1200 126 126 130 128 Te(p,n) I Scholten 89nat Te(p,3n) I 500 Zweit 92nat 1000 Acerbi 75nat Alice IPPE )

b 400 Alice IPPE 800 b) (m s m n (

300 o i ction

ct 600 e s se s s o r

200 oss C r

C 400

100 200 0 0 5 10 15 20 25 30 0 Proton energy (MeV) 0 10203040506070 FIG. 19. Excitation function of the Proton energy (MeV) 126 126

P P P Te(p,n)P I reaction calculated by using FIG. 22. Excitation function of the 130 128

P P Alice IPPE model code. P Te(p,3n)P I reaction calculated by using Alice IPPE model code.

1200 1500 130 129 128Te(p,3n)126Te Te(p,2n) I Alice IPPE 1000 Alice IPPE

800 b)

) 1000 m b ( (m n ons o i

i 600 t c ect s ss se o 400 os r r C

C 500

200

0 0 10203040506070 0 Proton energy (MeV) 0 5 10 15 20 25 30 35 40 FIG. 20. Excitation function of the Proton energy (MeV) 128 126

P P P Te(p,3n)P I reaction calculated by using FIG. 23. Excitation function of the 130 129

P P Alice IPPE model code. P Te(p,2n)P I reaction calculated by using Alice IPPE model code. 350 500 128 128 130 130 Te(p,n) I Blaser51 Te(p,n) I 450 300 Blaser51 Johnson58 Daly64 400 Acerbi 75nat Johnson58 Zweit 92nat 250 Zweit 92nat 350 b] Scholten 89nat

b) Scholten 89nat Acerbi 75nat ns [m (m 300 Alice IPPE 200 s

o Alice IPPE i n

o Alice norm. to exp.

i Fit Alice norm to exp. 250 150 ... oss sect ss sect 200 r o r C C 150 100

100 50 50

0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 35 Proton energy (MeV) Proton energy [MeV} FIG. 21. Excitation function of the FIG. 24. Excitation function of the 128 128 128 128

P P P P P P P Te(p,n)P I reaction calculated by using Te(p,n) I reaction calculated by using Alice IPPE model code. Alice IPPE model code. Experimental data were fitted by using spline Experimental data were fitted by using spline method to Alice IPPE calculation normalized method to Alice IPPE calculation normalized to experimental data. to experimental data.

1200 700 120 119 120 121 Te(d,3n) I Te(d,n) I Qaim I-121 1000 600 Alice IPPE

500 b) 800 b) Alice IPPE 400 600 ion (m 300 oss section (m oss sect r

400 r C C 200 200 100

0 0 010203040 0 5 10 15 20 25 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 25. Excitation function of the FIG. 28. Excitation function of the 120 119 120 121 P P P P P P Te(d,3n) I reaction calculated by using P Te(d,n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

1400 1400 120Te(d,2n)120mgI Qaim I-120m 122Te(d,3n)121I 1200 Qaim I-120g 1200 I-120 Alice IPPE I-120 Alice IPPE norm. ) 1000 b) 1000 b

800 ns (m 800 o i Zaidi83 600 600 Shifted Zaidi83 oss section (m oss sect r r Alice IPPE C 400 C 400 Spline fit 200 200

0 0 0 10203040 0 10203040 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 26. Excitation function of the FIG. 29. Excitation function of the 120 120m+g 122 121

P P P P P Te(d,2n)P I reaction calculated by using P Te(d,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. The theoretical curve was normalized to Spline fit was applied to the experimental data. experimental data.

900 123Te(d,4n)121I 700 800 122Te(d,4n)120I 700 600

) 600 Alice IPPE 500 eV

b) Alice IPPE 500

400 on (M 400

300 300 oss secti r C oss section (m 200 r

C 200 100 100 0 0 102030405060 0 Deuteron energy(MeV) 0 102030405060 Deuteron energy (MeV) FIG. 30. Excitation function of the 123 121

P P FIG. 27. Excitation function of the P Te(d,4n)P I reaction calculated by using 122 120

P P P Te(d,4n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

1400 450 122Te(d,2n)122I 122Te(d,n)123I 1200 400

Zaidi83 350 Zaidi83 b) 1000 shifted Zaidi83 b) 300 Takacs97 800 Alice IPPE Shifted Zaidi83 250

ions (m AliceIPPE ctions (m Spline fit 600 200 Spline fit oss se r oss sect C

400 r 150 C 200 100 50 0 0 10203040 0 Deuteron energy [MeV] 0 5 10 15 20 25 30 35 FIG. 31. Excitation function of the Proton energy (MeV) 122 122 FIG. 34. Excitation function of the P P P Te(d,2n)P I reaction calculated by using 122 123

P P Alice IPPE model code. P Te(d,n)P I reaction calculated by using Spline fit was applied to the experimental data Alice IPPE model code. shifted in energy by 2 MeV down. Spline fit was applied to the experimental data.

1400 1400 123Te(d,2n)123I 123Te(d,3n)122I 1200 1200

1000 b) 1000 Scholten 97 Alice IPPE Alice IPPE b) 800 800 extrapolated fit

600 600 oss sections (m r

C 400

oss section (m 400 r C 200 200

0 0 0 5 10 15 20 25 30 35 0 10203040 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 35. Excitation function of the FIG. 32. Excitation function of the 123 123

P P 123 122 P Te(d,2n)P I reaction calculated by using P P P Te(d,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. Spline fit was applied to the experimental data extrapolated up to 40 MeV using the normalized Alice calculation.

900 1400 124 122 800 Te(d,4n) I 124 123 1200 Te(d,3n) I 700

b) 1000 600 Firouzbakht 93

b) Alice IPPE 800 Alice IPPE 500 ons (m (m Alice IPPE norm. 400 600 ction ss secti o r

300 C 400 oss se r

C 200 200 100 0 0 0 10203040 0 102030405060 Deuteron energy (MeV) Deuteron energy(MEV) FIG. 36. Excitation function of the FIG. 33. Excitation function of the 124 123 P P 124 122 P Te(d,3n)P I reaction calculated by using

P P P Te(d,4n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. The theoretical curve was normalized to experimental data.

1000 1400 125 123 125 124 900 Te(d,4n) I Te(d,3n) I 1200 800

b) 1000

700 b)

600 Alice IPPE (m 800 500 Alice IPPE 400 600 oss section (m oss section r r

C 300 C 400 200 100 200

0 0 0 102030405060 0 5 10 15 20 25 30 35 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 37. Excitation function of the FIG. 40. Excitation function of the 125 123 125 124 P P P P P P Te(d,4n) I reaction calculated by using P Te(d,3n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code.

140 1000 123Te(d,n)124I Scholten 97 126Te(d,4n)124I 120 Alice IPPE 900 fit of Scholten + Alice IPPE 800 Alice IPPE

b) 100

b) 700 80 600 ions (m 500 60 400 oss sect oss section (m r r C

40 C 300 200 20 100 0 0 0 5 10 15 20 25 0 102030405060 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 38. Excitation function of the FIG. 41. Excitation function of the 123 124 126 124 P P P P P P Te(d,n) I reaction calculated by using P Te(d,4n)P I reaction calculated by using Alice IPPE model code. Alice IPPE model code. Spline fit was applied to the experimental data extrapolated up to 22 MeV using the normalized Alice calculation.

300 1400 124 125 124 124 Te(d,n) I Te(d,2n) I Firouzbakht 93 1200 Bastian 01 250 Alice IPPE

b) 1000 Alice IPPE spline fit 200 b) ns (m

800 m

n ( 150 o 600 i ss sectio ect o s r s

C 400 100 os r 200 C 50 0 0 5 10 15 20 25 30 0 Deuteron energy (MeV) 0 10203040 FIG. 39. Excitation function of the Deuteron energy(MEV) 12 124 P P P Te(d,2n)P I reaction calculated by using Alice IPPE model code. FIG. 42. Excitation function of the 124 125

P P Spline fit was applied to the experimental data. P Te(d,n)P I reaction calculated by using Alice IPPE model code.

1400 1400 125Te(d,2n)125I 126 126 Te(d,2n) I Pement66 1200 1200 Alice IPPE 1000 Alice IPPE norm. b)

b) 1000 800 Alice IPPE 800 600 600 oss section (m r C 400 oss sections (m r

C 400 200 200 0 0 5 10 15 20 25 30 0 Deuteron enegy (MeV) 0 5 10 15 20 25 30 FIG. 43. Excitation function of the Deuteron energy (MeV) 125 125 FIG. 46. Excitation function of the P P P Te(d,2n)P I reaction calculated by using 126 126

P P Alice IPPE model code. P Te(d,2n)P I reaction calculated by using Alice IPPE model code. Theoretical curve was normalized to the experimental data.

1600 1200 126 125 128 126 1400 Te(d,3n) I Te(d,4n) I 1000 Alice IPPE 1200 ) Alice IPPE b

1000 b) 800 tion (m

800 on (m i 600

600 sect oss sec r C oss 400 r 400 C

200 200 0 0 102030405060 0 Deuteron energy (MeV) 0 102030405060 Deuteron energy (MeV) FIG. 44. Excitation function of the 126 125 FIG. 47. Excitation function of the P P P Te(d,3n)P I reaction calculated by using 128 126

P P Alice IPPE model code. P Te(d,4n)P I reaction calculated by using Alice IPPE model code.

1200 90 128Te(d,2n)128I 125Te(d,n)126I 80 1000 Pement 66 Pimentel 88 70

b) Alice IPPE

b) 800 60 Alice IPPE norm. 50 ion (m t 600 40 Alice IPPE oss sec r 30 400 ross sections (m C C 20 200 10 0 0 0 5 10 15 20 25 30 35 Deuteron energy (MeV) 0 10203040 Deuteron energy (MeV) FIG. 45. Excitation function of the 125 126 FIG. 48. Excitation function of the

P P P Te(d,n)P I reaction calculated by using 128 128

P P P Te(d,2n)P I reaction calculated by using

Alice IPPE model code.P Alice IPPE model code. Theoretical curve was normalized to the experimental data.

1200 1200 130Te(d,4n)128I 130Te(d,2n)130I Pement 66 Otozai 68 1000 1000 Nishi 69 Pimentel 88 Alice IPPE b) 800 800 Zaidi 83 nat

b) Alice IPPE 600 600 Alice IPPE norm. n (m o

400 oss sections (m secti r 400 C oss r C 200 200

0 0 0 102030405060 0 5 10 15 20 25 30 Deuteron energy (MeV) Deuteron energy (MeV) FIG. 49. Excitation function of the FIG. 52. Excitation function of the 130 128 130 130 P P P P Te(d,4n) I reaction calculated by using P P P Te(d,2n)P I reaction calculated by using

Alice IPPE model code.P Alice IPPE model code. Theoretical curve was normalized to the experimental data.

350 130 131 Te(d,n) I 300 Otozai 68 100 Nishi 69 128 129 Zaidi 83 nat 90 Te(d,n) I ) Alice IPPE b 250 Alice IPPE norm.

80 (m s 200 ) 70 b ction

(m 60 150 ss se o

Alice IPPE r

ction 50

C 100 40 ss se o

r 50

C 30

20 0 10 0 5 10 15 20 25 30 0 Deuteron energy (MeV) 0 10203040 FIG. 53. Excitation function of the Deuteron energy (MeV) 130 131

P P P Te(d,n)P I reaction calculated by using FIG. 50. Excitation function of the 128 129 Alice IPPE model code.

P P P Te(d,n)P I reaction calculated by using Theoretical curve was normalized to the

Alice IPPE model code.P experimental data.

1600 900 130Te(d,3n)129I 1400 103 103 800 Rh(p,n) Pd Harper 1200 Alice IPPE Albert 700 Johnson Hansen

1000 b) 600 Blaser b) Hermanne-X 800 500 Mukhamedov ion (m

on (m Sudár 600 400 spline fit oss sect

400 r oss secti 300 r C C 200 200

0 100 0 102030405060 0 Deuteron energy (MeV) 010203040 FIG. 51. Excitation function of the Proton energy (MeV) 130 129

P P P Te(d,3n)P I reaction calculated by using FIG. 54. Excitation function of the 103 103

P P P Alice IPPE model code. P Rh(p,n)P Pd reaction. Spline fit was made over the selected data as recommended cross- section.

500 1200 450 103Rh(p,3n)101Pd 103Rh(d,2n)103Pd 1000 400 Pd-103-x

b) 350 b) 800 300 spline fit on (m i 250 101Pd 600 sect 200 spline fit oss r ross section (m 400

C 150 C 100 200 50 0 0 0 10203040 0 5 10 15 20 25 Proton energy (MeV) Proton energy (MeV) FIG. 55. Excitation function of the FIG. 58. Excitation function of the 103 101 103 103 P P P P P P Rh(p,3n) Pd reaction. Spline fit was made P Rh(d,2n)P Pd reactions. Spline fit was made over the experimental data. over the experimental data. Experimental data were measured by using X-ray radiation.

600 1.0 103Rh(p,x)101m,gRh 0.9 103Rh(d,x)101m,gRh 500 0.8

b) 0.7 b) 400 m Rh-101m 101mRh 0.6 Rh-101g 101gRh on ( i 300 spline fit t 0.5 spline fit Rh-101m spline fit 0.4 spline fit Rh-101g oss sec r ross section (m 200 C

C 0.3 0.2 100 0.1 0 0.0 010203040 0 5 10 15 20 25 Proton energy (MeV) Proton energy (MeV) FIG. 56. Excitation function of the FIG. 59. Excitation function of the 103 101m,g 103 101m,g

P P P P P Rh(p,x)P Rh reactions. Spline fit was P Rh(d,x)P Rh reactions. Spline fit was made over the experimental data. made over the experimental data.

160 45 103 102m,g 103Rh(p,x)102m,gRh 40 Rh(d,x) Rh 140 35 120 b)

b) 30 Rh-102m 100 25 Rh-102g 102mRh spline fit Rh-102m 80 102gRh 20 spline fit Rh-102g spline fit 60 spline fit ross section (m oss section (m 15 r C C 40 10

20 5

0 0 0 10203040 0 5 10 15 20 25 Proton energy (MeV) Proton energy (MeV) FIG. 57. Excitation function of the FIG. 60. Excitation function of the 103 102m,g 103 102m,g P P P P P P P Rh(p,x)P Rh reactions. Spline fit was Rh(d,x) Rh reactions. Spline fit was made over the experimental data. made over the experimental data.

1600 140 203Tl(p,3n)201Pb 203 203 1400 Tl(p,n) Pb 120 Qaim79 norm. 1200

) 100 Spline fit b) b Bonardi (83)b 1000 Hermanne (92) n (m Lagunas-S. (78) 80 800 Qaim (79) fit Spline 60

ss sectio 600 o r oss sections (m r C 40

400 C

200 20

0 0 15 20 25 30 35 0 5 10 15 20 25 30 Particle energy (MeV) Particle energy (MeV) FIG. 61. Selected experimental cross-sections 203 201 FIG. 64. Experimental cross-sections for

P P for P Tl(p,3n)P Pb reaction and recommended 203 203

P P P Tl(p,n)P Pb reaction and statistical fit cross-section calculated by using spline . extended to higher energy by using spline method method.

180 140 203 202m Tl(p,2n) Pb 205 204m 160 Tl(p,2n) Pb 120 140

b) 100 b) 120 Bonardi (83)b Lagunas-Solar78 80 Hermanne (92) 100 Lagunas Solar (78) Hermanne 91 Qaim79 Qaim (79) 80 60 Lagunas-Solar80 oss section (m r fit Pade spline fit oss section (m C 60 40 r C 40 20 20 0 0 5 10152025 0 102030405060 Particle energy (MeV) Proton energy (MeV) FIG. 62. Selected experimental cross-sections 203 202m FIG. 65. Selected experimental cross-sections

P P for P Tl(p,2n)P Pb reaction and 205 204m P P for P Tl(p,2n)P Pb reaction and statistical fit recommended cross-section calculated by calculated by using spline method. using Pade method.

1200 1400 203Tl(p,4n)200Pb 205 203 1000 Tl(p,3n) Pb 1200

b) 800 Bonardi (83)b Hermanne (92) 1000

Lagunas-S. (78) ) Lagunas-Solar80 b

600 Qaim (79) m Hermanne 91 ( 800

fit Spline n

o Lagunas-Solar78 i t c spline fit

oss sections (m 400

r 600 ss se C o Cr 200 400

0 200 26 27 28 29 30 31 32 33 34 35 36 Particle energy (MeV) 0 10 20 30 40 50 60 FIG. 63. Selected experimental cross-sections Proton energy (MeV) 203 200

P P for P Tl(p,4n)P Pb reaction and recommended FIG. 66. Selected experimental cross-sections cross-section calculated by using spline 205 203 P P for P Tl(p,3n)P Pb reaction and statistical fit method. calculated by using spline method.

400 205Tl(p,4n)202mPb 350 Hermanne 91 Lagunas-Solar78 300 Lagunas-Solar80

) spline fit b 250 m on ( i t 200 c e s s

os 150 r C 100 50

0 20 25 30 35 40 45 50 55 60 Proton energy (MeV) FIG. 67. Selected experimental cross-sections 205 202m

P P for P Tl(p,4n)P Pb reaction and statistical fit calculated by using spline method.

80 natTl(p,x)202Tl 70 120 natTl(p,x)201Tl 60 Qaim79

b) 100 50 natTl(p,x)202Tl

203Tl(p,x)202Tl b) 80 40 205Tl(p,x)202Tl Qaim79 30 60 spline fit natural

oss sections (m 203Tl(p,x)201Tl r

C 20 205Tl(p,x)201Tl

oss sections (m 40 r 10 C 20 0 0 1020304050 0 Particle energy (MeV) 0 1020304050 FIG. 68. Experimental cross-sections for Particle energy (MeV) nat 202

P P P Tl(p,x)P Tl process and arbitrary separation FIG. 69. Experimental cross-sections for nat 202

P P into the two contributing processes using P Tl(p,x)P Tl process and arbitrary separation spline fitting method. into the two contributing processes using spline fitting method.

HIGH CURRENT TL-203, RH-103 TARGETS PREPARATION FOR CYCLOTRON PRODUCTION OF TL-201 AND PD-103 RADIONUCLIDES

A. ARZUMANOV, V. BERGER, A. BORISSENKO, N. GORODISSKAYA, I. ILMATOV, A. KNYAZEV, V. KOPTEV, S. LYSSUKHIN, A. PLATOV, G. SYCHIKOV, D. ZHELTOV. Institute of Nuclear Physics, National Nuclear Center, Kazakhstan

Abstract

The objectives of the present work are to increase thermal stability of cyclotron targets for production of Tl-201 isotope, increase Tl-203 regeneration rate at radiochemical reprocessing of the targets and develop production technology for radiochemical sources based on Rd-103 isotope. Electrochemical coating of copper substrate with Tl increased the beam current at target irradiation from 100 µA to 125 µA. Further increase of the beam current results in sharp decrease of target stability time at irradiation to 15 min at beam current 150 µA. Thermal calculations and tests at the electron-beam stand predict satisfactory stability at such currents. The discrepancy with the irradiation results has not been explained. More accurate specification of regimes for Tl-203 electrochemical recovery from irradiated targets and better matching of the electrolyte composition made it possible to increase the recovery rate up to 99.5%. Before the present Project, the INP had no experience in production of radioactive sources based on Pd-103. Thermo-diffusion extraction of Pd-103 from irradiated rhodium foil has been chosen as a technology-defining method. The process assures good extraction rate and high purity of extracted isotope. Production of Pd-103 sources based on this technology is much simpler compared to the same based on electrochemical processes

1. INTRODUCTION

The Project works were performed at the INP during 2000-2003 by a research group consisting of 12 people. The investigations were performed on the basis of isochronous cyclotron U-150M and the Laboratory of Radioactive Isotopes. Chronologically, the following tasks were solved:

Year 2001: Investigations of new electroplating techniques and testing of the targets at high beam current for production of Tl-201. Calculations of heat distribution and target recovery.

Year 2002: Continued works on optimization of the post irradiation chemistry and target recovery procedures for production of Tl-201 at beam current up to 150 µA. Initiation of designing and development of a solid target for production of Pd-103 from Rh, including the post irradiation chemistry.

Year 2003: Tl-203 target optimization for high current irradiation at cyclotron. Development of the thermal diffusion method for Pd-103 separation from Rh target. Therefore, the investigations were mainly focused on technology development for production of two medical radioisotopes Tl-201 and Pd-103.

2. RADIOISOTOPE PRODUCTION IN THE CYCLOTRON AT THE INP [1].

2.1. Status of the Cyclotron Kazakhstan’s variable energy isochronous cyclotron K=50 MeV is a 150 cm compact-pole 3 sector positive ion machine. It generates various beams of light ions: protons 6 – 30 MeV, deuterons 12.5 – 25 MeV, He-3-ions 18.5 – 62 MeV, and alpha-particles 25 – 50 MeV.

In the last years, the cyclotron is rather intensively used for radioisotope production to meet the needs of the Republic of Kazakhstan. Main users of radioisotope products are the institutes of the Ministry of Public Health and oil-chemistry, metallurgy, mining enterprises and scientific institutes.

The radioisotope production program shares the cyclotron facilities with the basic nuclear physics research program. For radioisotopes production both external and internal targets are used. Irradiation of external target is typically used during several years. The beam intensity on the external target is equal to 40 µA for protons. Extracted beam intensity is limited by power dissipation in the electrostatic deflector at the level of 1 – 2 kW.

For homogeneous target irradiation, the circular beam scanning system is used. Transversal rotating magnetic field is generated by the stator of an electro-motor and it shifts the beam from the transport channel axis for up to 12 mm. Swept beam spot can be adjusted to get uniformity of beam power distribution better than 80% inside the scanning circle of 30 mm diameter. High intensities, typically several hundred µA, are available at the internal target. In order to enlarge the beam spot on the target and, therefore, to reduce beam power density on the target, the target is declined with respect to the beam axis at the angle of 18º. Fig. 1 illustrate the technology of irradiation with the internal beam.

2.2. Target device.

Target design provides:

- Remote target insertion into the cyclotron tank through vacuum sluice;

- Target assembling between dees on final accelerating orbit R=646 mm under 18° to the beam axis, which ensures complete beam overlapping by target (beam width on final orbit is 15mm).

- Target’s head is a composite and it consists of a body and a changeable backing; the body is made of slightly activated aluminum alloy, which ensures its reuse. Backing is made of copper, a material with good thermal conductivity, and intended for single use. Irradiated material is plated on backing by electroplating. Backing is attached to the body by two screws that ensure head’s quick disassembling and reliable seal. Copper backing thickness is equal to 1 mm for water pressure 5 bar 2

P and 2 mm for 20 bars. Maximal water supplying and removal holes have the section of 28 mm P . Irradiated surface has dimensions 20 х 40 mm. View of the head of the target and its constituents are shown in the Fig. 2.

2.3. Electron beam stand

Trend to the commercial production of radioactive isotopes requires reliability of all kinds of work involved, their efficiency and safety, and this, for the first turn, refers to the process of target irradiation. Therefore, the problems related to the technology development for production of targets and their thermal testing are very topical. For this purpose, the electron beam stand has been created [2].

The stand’s vacuum tank is made of stainless steel and has the following dimensions: diameter 340 mm and length 600 mm. Electron gun and target device are installed in ends of the tank. Electron gun was chosen as heater because it is easy in operation with heat power taken up by the target and there is a possibility to displace the heating region across surface of the target.

Electron units for beam focusing and deflection in vertical and horizontal directions assure beam diameter of ∅ 1.5 mm and its scanning across target surface. Scanning frequencies are horizontal one – 50 Hz and vertical one – 1200 Hz what provides homogenous target heating. There is an opportunity of fixed beam spot moving at any point of the target surface.

. -4

P P There is a system of vacuum pumping (up to 5 P 10P Pa): vacuum monitoring is proceeded with ion and thermocouple converters. Electron beam has the following parameters: energy of electrons up to 25 keV, beam intensity up to 200 mA. The water pressure in cooling system is equal to 20 bar what provides water velocity in the cooling cannel equal to 30 m/s.

Target tests on the stand enable to determine maximal allowed heat flows that are fixed at melting point of the target material. Energy loss caused by reflected and second electrons are accounted on basis of known reference data. Electron beam density distribution influences the results of thermal endurance. Measurements, which were made using wire and pinhole methods, showed that the most acceptable beam has dimension of ∅ 5 mm and Gaussian distribution. It should be noted that irradiation at the stand is not exactly equal to irradiation at the cyclotron. At the last one, the energy absorption takes place in a deeper layer. Thus, the temperature distribution in the target because of irradiation with protons is different from the case with electron irradiation. This fact was taken into account by testing of the targets at the stand.

The electron-beam stand is used in the present work for development of electroplating technique and for final testing of the targets before their irradiation at the cyclotron.

2.4. Calculation of thermal properties for Tl target. Beam current density distribution for different irradiating modes is obtained by means of radiography technique and was used in the temperature calculations.

Cooling of the backing is carried out with forced convection. The cooling efficiency depends on cooling surface geometry, cooling channel geometry, physical properties and velocity of cooler. The heat transfer coefficient is determined on the basis of similarities theory by means of the Reynolds’s, the Prandtl’s and the Nusselt’s numbers. Usual water at 14°C is used as cooler. Parameters of backing and cooling system are, as follows: smooth cooling surface, water channel gap is equal to 0.5 mm; the water pressure in the cooling system is equal to 20 bar. All this provides the heat-transfer coefficient 2.

P equal to 12.7 W/cmP K.

Numerical determination of the target thermal properties is based on solution of the thermal conductivity differential equation. The adiabatic equation was solved for a region with heat sources, and for a region without ones – the Laplace equation. The region with the sources consists of two layers – a target layer and that segment of the backing where complete stop of charged particles happens. Full temperature inflection in the target is calculated as:

q ⋅ a q ⋅b q ⋅b q ⋅ c q ∆T = 1 + 1 + 2 + + , (1) 2λ1 λ2 2λ2 λ2 h

where:

P q1B B and q2B B – heat flow density, emitted in the 1st and 2nd layers, correspondingly (W/cm P ); q – 2

P λB B λB B full heat flow density (W/cmP ); a, b, c, - widths of 1-st, 2-nd and 3-d layers (cm); 1; 2 – target and backing material thermal conductivity (W/cm K); h – heat transfer coefficient (from backing to water) 2

P (W/cmP K).

Temperature of cooling surface depends on amount of heat flow density and increases with its growth up to TbB ,B when bubble boiling forms (at water pressure in the cooling system equal to 20 bar ° TbB =215B C). All calculations for maximal allowed heat flows are carried out taking into account achievement this temperature or the melting point of target material (for easily melted materials). Verification of the temperature calculations was carried out at the cyclotron and at the electron beam stand by achieving the melting of different metals.

For that there were used Sn, Bi and Pb metals (melting points are equal to 232°C, 271°C and 327°C and flow temperature is equal 190°C, 206°C, 260°C, correspondingly.) Results of the experiments confirmed the calculations.

3. PREPARATION OF HIGH CURRENT TL-203 TARGETS FOR CYCLOTRON PRODUCTION OF TL-201 RADIONUCLIDES [3,4].

3.1. Electroplating technique for target preparation. Thickness of Tl layer is equal to 160 µm. It is determined for 6 MeV energy loss of incident 28 MeV proton beam. Target is inclined at 18° to the beam axis.

Two methods of electroplating were used:

1. Thallium electroplating from sulphurous electrolyte of the following content:

Thallium sulfate (refereed to metal) – 35 g/l, H2B SOB 4B B – 25 g/l, Phenol – 10 g/l, Gelatin – 1 g/l.

P Tl electroplating was carried out on copper plate S=8cm P , stable electrolyze mode with the use of direct current Pt anode was used. During the process of Tl plating cathode current density was varied and average rate of Tl plating was calculated. For current densities in the range from 5 up to 15 2

P µ mA/cmP , velocity of plating was changed from 20 up to 50 m/h, it must be noted that in the range 10 2

P – 15 mA/cmP plating rate changes very slightly. For noted above conditions, fine precipitation of Tl of grey color was obtained. But the detail examination of its structure by optical microscope (magnification x250) had shown that Tl precipitated in the form of fine plane crystallites slightly tightened with each other, i.e. precipitates have low density and therefore they are unlikely to be used for cyclotron irradiation. This forced us to look for new electrolytes for Tl electroplating.

2. Tl electroplating from ethylenedemintetracetic (EDTA) electrolyte of the following content: Tl – 20g/l, EDTA – 200 g/l, KOH – ≈80g/l, Phenol – 10 g/l, Hydrazine hydrate (55%) – 25g/l.

The use of noted above electrolyte provides very fine-grain density precipitates with thickness up to 50 µm and thick precipitates of average grain size are produced. Platinum anodes were used for the plating. Following thallium precipitation mode was experimentally chosen: cathode current density 2 o o

P P P ÷ 9-10 mA/cmP , tP =20-25P C, current reverse: ratio of the straight period to reverse one (7 8 s). Under the noted conditions Tl plating rate was equal to 15÷25 µm/h. No special preparation of copper backing was needed prior the electroplating. Precipitates testing with the use of net with fracture had shown good Tl adhesion with backing; testing of precipitates’ behavior at high temperatures has been carried on.

The used device for electroplating of Tl was supplied in frame of IAEA TC Project by Prof. Dr. P. Van den Winkel (Vrije Universiteit Brussel). An installment for electrodepositing of thallium is presented in the Fig. 3. Recovery of Tl-203 from the targets has been performed at the same installment with corresponding changes in electrolyte and regimes at the electrodes.

3.2. Irradiation of Thallium target at the cyclotron.

Production of the radiopharmaceutical “thallium-201 chloride” was achieved and it was delivered to medical institutions in Almaty. Several test irradiations have also been performed. At the initial stage of the project the available technology enabled to irradiate targets at the cyclotron with the beam current up to 100 µA. Developed technologies (mainly electroplating) made it possible to increase the irradiation current value up to 125 µA. Further increase in the beam current results in sharp worsening of target stability and at 150 µA current the target destructs after 15-min irradiation.

Thermal calculations and tests at the electron-beam stand predict satisfactory stability at such currents. The discrepancy between the irradiation results and the predictions has not been definitely explained yet.

Irradiation at the cyclotron was performed during 9 hours. Typical radioisotope yields are 3 – 201 201

P P 3.2 Ci of P Pb and about 300 mCi of P Tl. Targets irradiation modes are presented in the Table II.

3.3. Radiochemical reprocessing of the irradiated targets. The technology that implies thallium-201 production in two stages was chosen for the radiochemical separation and extraction of Tl-201 from a thallium target irradiated with protons of 28 MeV energy. The stages are:

1. Extraction of radioactive plumbum-201 by the co-precipitation and its optimal ageing (~26 hours) for thallium-201 accumulation.

2. Separation of the accumulated thallium-201 from the parent plumbum-201 radionuclide by means of the extraction method.

3. The produced thallium-201 chloride solution is corrected, analyzed according to the normative values (pH, content of NaCl, volume activity, radiochemical purity, content of radionuclides and non-active impurities).

4. The thallium-201 radionuclide production technology provides the radionuclide 203

P technological yield ~ 75%. Enriched P Tl in metal form is recuperated to the Tl target production cycle from the spent solutions and the electrolyte. The procedure implies electrolysis with controlled cathode potential (CCPE). The recovery rate is ≥99.5%.

103

P 4. DESIGN AND DEVELOPMENT OF CARRIER-FREE P PD CYCLOTRON PRODUCTION

Interstitial implantation of radiation-emitting materials has been long recognized as an effective 125 103 103

P P P method for tumour therapy. Currently P I and P Pd are used for this technique. P Pd has more 125

P favorable physical properties than P I, including low energy, rapid dose fall-off, short half-life and 103

P total cumulative dose delivery and it is predestine a promising beginning of P Pd for localized tumour 103

P treatment. P Pd was proposed by Harper in 1958. It was not used until 1987 when encapsulated sources became commercially available in the USA. There are some modifications of Pd-103 sources 103

P differing in fact in the matrix material that carries P Pd. High-molecular substance or carbon packing 103

P is to be in routine as carrying agents of P Pd. The gold compound as a rule is used for «marker» material.

4.1. Cross-section and evaluation data.

103

P Production with proton bombarding of P Rh is based on the data of Harper and Dmitriev on cross-section, thick target yields and possible contaminants (Fig. 4). In accordance with excitation function the optimum of energy for irradiation was determined in energy range of 7-20 MeV.

103

P Increase of incident energy above 18 MeV for production of medical P Pd is not acceptable due to two major reasons:

102m 102g 101g

P P P - the contamination with P ,P ,P Rh results in radiological hazard; - additional yield is negligible (less than 4% increase between 18 and 20 MeV).

The energy range 18-8 MeV is considered by convention to be optimal for irradiation of Rh at 103

P the cyclotron. There is no unitized method for P Rh-target preparation available due to baffling complexity of Rh plating and intractable problem of Rh dissolution. It is of general knowledge that 103

P separation of P Pd from rhodium with anion-exchange chromatography does not require special conditions; it is easy to separate these elements with high precision and yield. The main problem of 103

P P Pd radiochemical separation stage is dissolution of target material due to extremely low chemical reactivity of rhodium metal towards acid, alkaline and to other corrosive reagents. The most convenient technology used in developed countries such as the USA, Belgium, France, and China is electrodissolution of target and electroplating recovery of rhodium.

103

P 4.2. Study on alternative production of P Pd.

This work has been performed within the IAEA Research-project with primary accent on design and development of innovative technology. It is of common knowledge that production of any radionuclide consists of five general steps: target preparation; target irradiation; radiochemistry separation; preparation of isotope marketed form; recovery of target material. In all directions of investigation we try to find simple and effective scientific and engineering approaches.

4.3. Targetry and irradiation. First successful engineering approach was used in a new target construction. Rhodium foil was put on cooling side of the backing. The thickness and area of backing can be varied according to initial energy of irradiation and this technique of irradiation allows adjusting energy range and dose absorbed with rhodium foil. Direct cooling of target with water flow allows increasing proton energy in time of irradiation.

4.4. Radiochemistry separation (extraction of Pd-103). 103

P For radiochemistry separation and extraction of P Pd from irradiated Rh foils alternative method of thermal diffusion was used. The rhodium foils were put in tubular construction of vacuum furnace, heated at different temperatures within half an hour, hardened and treated with weak 103

P hydrochloric acid. As a result the P Pd was kept in the form of Pd chloride solution. Measurements for 103

P P Pd were done using the X-line as well as the EγB =357.7B keV line (Fig. 5).

103

P Increasing yield of P Pd activity is formal validation of the method of thermal diffusion acceptability for separation. Having experimental data on Pd-103 yield it is rather easy to calculate Pd- 103 diffusion coefficient. Like that the stage of radiochemistry separation by «dry» method of thermal diffusion allows simplifying essentially the technology since there is no need for: target preparation stage; target dissolution stage; target recovery stage. Purity of final product is 99.99.

4.5. Sealed sources. 103

P For the brachytherapy goals P Pd becomes really interesting in the form of sealed source. 103

P Equipment for P Pd labeling and packing of special compound is very expensive. The proposal of the 103

P technology consists in utilizing of silver wire as a basis for P Pd absorption and as a material for determination of localization into tissue simultaneously. As a «marker» silver can be detected with X- ray method (Fig. 6).

The high catalytic reactivity of Pd and the electrochemical properties of Ag have allowed using a method of metallic cementation for preparation of «active» part.

Due to coloring power of Pd salts the method of isotopic dilution was used for visual indication of deposition process and the method of UV-spectrophotometry – for quantitative estimation.

Series of experiments on a deposition of Pd on Ag from weak solution of Pd chloride have showed the following stable behavior:

- the process of cementation occurs evenly and rather at the dynamic conditions of deposition (shaking apparatus) than at the static ones; - the rate of Pd deposition linearly depends on concentration of Pd what allows calculating a cementation coefficient of process; - the coefficient of cementation (Kc, mg/cm2*min) linearly depends on concentration of Pd in range of concentrations 0.125-0.5 g/l according to the equation: Kc=14.06*CPd+0.95 (Fig.7); - the linear character of functional dependence of cementation coefficient on concentration of Pd allows calculating and varying most important conditions of the process such as:

o concentration of electrolyte; o volume of solution; o time of deposition.

The obtained results make it possible to propose a quite simple technology for production of radioactive sources based on Pd-103 for medical applications. A flow chart of the source production is presented at Fig. 8. Details of the technology obviously need further investigations stipulated by its simplicity.

5. CONCLUSION The works performed on the project made it possible to develop the production technology of radiopharmaceutical preparation “Tl-201 chloride” at the INP:

- target irradiation current has been increased from 100 µА at the beginning of the project up to 125 µА - there has been achieved the thallium target recovery rate of 99.5%.

103

P There has been proposed a new technique of P Pd extraction from irradiated Rh foil by the method of thermal diffusion without destruction of target matrix; the technique allows to:

- exclude the stage of target preparation; - exclude the stage of target recovery; - use Rh foils for multiple irradiation; - reduce quantity of radioactive waste to minimum; - reduce quantity of chemical reagents and materials used to minimum; - produce final product with 99.99% purity.

6. EQUIPMENT AND MATERIAL Power controller; 115 VAC, 60 Hz, temperature controller, flexible wire probes, infrared heating lamp, equipment for electrodeposition and recovery of Thallium target and Rhodium foil (0.25 mm thick, 99.8% (metal basis) 25 x25 mm) are provided by IAEA.

REFERENCES

[1] A.ARZUMANOV, V.BATISCHEV ET AL., “Status and development of the Kazakhstan isochronous cyclotron”, presented at the XV Int. Conf. Appl., East Lansing, Michigan, USA, 12-17 May, 2001. [2] A.ARZUMANOV, A.BORISENKO ET AL. – “Electron-Beam Stand for the Solid Isotope Targets Tests” paper in Russian at the International Conference “Nuclear and Radiation Physics”, Almaty, 2001. [3] A.ARZUMANOV, V.BATISCHEV ET AL. “Radioactive Isotopes Got on the Cyclotron” // Abstract in Russian at the International Conference “Nuclear and Radiation Physics”, Almaty, 1997. [4] A.ARZUMANOV, V.BATISCHEV ET AL. “Radioisotope production at the cyclotron in Almaty ”Proc. Int. Conf. Cycl. Appl. Caen, France, 14-19 June 1998, 58-61.

TABLE I. IRRADIATION MODES FOR DIFFERENT MATERIALS

Irradiated material Tl Tl Bi Sn Target thickness, µm 160 160 50 50 Proton energy (MeV) 28 28 22 22 Target current (µA) 100 150 420 390 Duration of irradiation, h 9 2

103

P TABLE II. SUMMARY OF THE P PD PRODUCTION

N Activity of Pd-103, kBq, before Temperature of Activity Pd-103, Yield of annealing annealing, ºC kBq, after Pd-103,% annealing 1 410 1050 330 19.5 2 297 1200 120 59.6 3 1250 1400 375 70

FIG. 1. Position of a target in the cyclotron tank. FIG. 2. Head of the internal target.

600 12

500 10 b h

m 400 8 , uA n o q/ i t B

c 300 6 M d, l

ss se 200 4 e i o r Y C 100 2

0 0 0 4 8 10 14 18 22

Partical energy, MeV

FIG. 3. An instalment for electrodepositing and FIG. 4. Excitation function and thick target yield 103 103

P P recovery of thallium targets. for the P RH(p,n)P Pd reaction.

FIG. 5. Gamma-spectrum of final product.

10.00

8.00 min 6.00 m2

/c y = 14,06x + 0,95 4.00 , mg

c 2.00 K 0.00 0.125 0.25 0.375 0.5

CPd,g/l

103

P FIG. 6. Proposed design of P PD sources. FIG. 7. Dependence of cementation coefficient on concentration of PD.

Rh irradiation

103Pd extraction Rh HCl (weak) with foils thermodiffusion

103Pd deposition with isotopic PdCl2(stab) dilution and cementation

Sources encapsulation

103

P FIG. 8. Flow chart of P PD sources production technology.

82 RESEARCH AND TECHNOLOGICAL DEVELOPMENT FOR THE PRODUCTION OF PD-103 AT THE U-120 CYCLOTRON FROM BUCHAREST

P.M. RACOLTA, D. DUDU Horia Hulubei National Institute for Research and Development on Physics and Nuclear Engineering; Bucharest, Romania.

Abstract

Research and development for the production of Pd-103 at U-120 Cyclotron in Bucharest was undertaken based on demand of two hospitals in Bucharest interested in brachytherapie of prostate cancer using Pd-103 seeds. The work done during three year project activity has been focused on design and adaptation of dedicated beam line at NIPNE-HH U-120 Cyclotron for experiments of Pd-103 production. Experiments were conducted to obtain nuclear data to find optimal parameters of target irradiation. Post irradiation characterization of the radionuclides activated in target was performed as well. The results obtained are promising and will be developed further in the next two years in the frame of a national research program for implementation of brachytherapie of prostate cancer with Pd-103 seeds.

1. INTRODUCTION

103

P Historically [3-9], P Pd, a short-lived isotope for permanent implant treatment of early stage 102 103

P P γ P prostate cancer, was generated via the P Pd(n, ) Pd reaction which relied on the availability of 1% 102

P naturally abundant P Pd in an enriched form and its moderately high neutron capture cross-section [1]. 103

P For the last 12 years, the accelerator production method for P Pd has been based on the irradiation of 103 103

P P the rhodium metal with rather low energy protons via the reaction P Rh(p,n)P Pd [1]. Big corporations from USA operate more than 10 dedicated accelerators to produce this nuclide. The prostate cancer market with 180,000 new cases reported annually justifies the effort for this radionuclide production. Recently, a manufacture in Europe also brought the USA patented type of 103

P P Pd seed implants on the world market.

Now, there are the initiatives to explore other uses of Pd-103 in non-oncologic disease states such as restenosis following coronary interventions, age-related macular degeneration as well as potential diagnostic applications.

Romania used irradiations with neutron fluxes at nuclear reactors (VVRS/NIPNE-HH Bucharest 32 60 131 192 197

P P P P P and Triga/SNC-Pitesti) to produce some radioisotopes (P P, P Co, P I, P Ir, P Au,etc.).

In NIPNE-HH from Bucharest, the U-120 Cyclotron is a classical, constant gradient, accelerator with variable energy, delivering internal beams up to 200µA and external beams up to 50µA of protons (up to 14MeV), deuterons (up to 13.5MeV) and alpha particles (up to 27MeV).

109 55 123

P P P We produced P Cd, P Fe for XRF applications, P I (only few hundred of mCi for experimental 67 22 48 68 103

P P P P P hospital applications) and as laboratory test procedures P Ga, P Na, P V, P Ge and P Pd.

After the appropriate irradiation of dedicated solid targets, these one were processed in the Center for Radioisotopes Production. This lab is licensed for some radionuclides separation and 131 125

P P radiopharmaceutical production as tritium labeled compounds, P I for endotherapy and diagnosis, P I labeled RIA kits, Technetium generators etc.

In spite of all these, there have not yet been finalized production lines for radiopharmaceutical products with short lived radioisotopes.

83 2. DESIGN AND ADAPTATION OF DEDICATED BEAM LINE AT NIPNE-HH U-120 CYCLOTRON FOR EXPERIMENTS OF PD-103 PRODUCTION. At the beginning of March 2000, we finished the rehabilitation of U-120 Cyclotron as a multipurpose facility dedicated for applications of accelerated ion beams. Our efforts were dedicated not only to repair, but also to upgrade or improve some associated systems or equipment as is:

- accelerating structure; - power RF generator; - vacuum system; - beam transport and diagnosis.

Consequently, we obtained an improved reliability of the accelerator as well as much stable and reproducible beam parameters. On the dedicated beam line for small scale radioisotope production, the main parameters of available beams are shown in Table I.

TABLE I. BEAM PARAMETERS OF U-120 CYCLOTRON FOR RADIOISOTOPES PRODUCTION

Energy FeB /2k+1B Beam current (µA) Transversal area PARTICLE 2

P No. (MeV) (kHz) Extracted On Target of the beam (cmP ) +

P 1 HP 14 15.400/1 50 1÷30 0,1÷2 2 +

P P P 2 HP 13,5 11.300/1 60 1÷30 0,1÷2 4 +2

P P P 3 HeP 27 11.300 40 1÷20 0,1÷2

The target system was designed to permit irradiation of metallic Rh in stacked foils of 25µm o

P thickness at normal incidence of the beam or 100µm Rh deposited on 2mm Cu backing at 30 P incidence of beam (Figs 1 and 2). Both target systems are provided with appropriate collimator, secondary electron suppressor and water cooling circuits as shown in Fig. 3.

FIG. 1. Control room of U-120 Cyclotron

FIG. 2.

FIG. 3. Beam line used in experiments for radioisotopeproduction.

Secondary electron Faraday-cup- suppressor Water like target cooled

Beam Rh foil Rh Water cooling In/Out

To current To negative DC To current meas. and digital supply integrator

FIG. 4. Schematic view of target systems.

85 2.1. Experiments to obtain home made nuclear data to find optimal parameters of target irradiation and post irradiation characterization of the radionuclides obtained in target. Experiments have been done using a stack containing 8 high purity 25µm Rh foils (Goodfelow) which has been irradiated in the external beam of U-120 Cyclotron with protons of 14MeV. All foils were irradiated in a Faraday-cup-like target holder equipped with a collimator (effective beam diameter on target is 6mm) and a secondary electron suppressor. The total charge on target was derived from the measured current on the target holder using a digital integrator. Beam current stability during the irradiation was 10%. The incident energy (14MeV) with an uncertainty of 0.5MeV was derived from earlier calibrations based on time-of-flight and activation techniques.

The irradiation was done with a total charge on the target of 20mC, which correspond to a mean beam current of 1.56µA and an irradiation time of 13000s. 103

P Measurements for the activity of produced P Pd were done in the X-line region as well as for gamma-lines as is published by Hermanne et al. [1] using high resolution X- and gamma-spectrometry (FHWM resolution of 200eV at 21keV respectively 1.9keV at 847keV). Each sample was measured (without any chemical treatment) several times at X-ray spectrometer from shortly after EOB up to 2 weeks, and for gamma spectrometry, the measurement was done after 11.67days after EOB. The activities derived in these two ways are in good agreement with the results and yields measured by Hermanne et al. [1] and by Dimitriev [2].

Fig. 4 shows the corresponding activity obtained on each foil measured with gamma spectrometer (Foil no. 8 is the first one seen by the beam).

7000

6000

] 5000 q B

[k 4000 ty i v ti c

A 3000

2000

1000 86420 Foil no.

FIG. 5. Measured activity of Rh foils.

According to published experimental data [1], in our experiments was not observed the presence 101 101m, 101g 102m, 102g

P P P of P Pd, P Rh and P Rh, due to the rather low energy of proton beam (14MeV). In addition, 56

P P Co contamination is observed, most probable in agreement with the Fe impurities in Rh foils. This 103

P contamination level with respect to the P Pd activity is negligible (less than 0.01%). In Table II are given the results of gamma spectrometry for Rh foils and in Fig. 5 a spectrum of gamma ray for one Rh foil.

86 1000 56Co Rh foil no. 6 103Pd 846.51 103Pd T=12.778 days after EOB 357.34 497.02 800

600 56Co s 10238.14

Count 400 56Co 1037.58 56Co 200 1771.67

0 200 400 600 800 1000 1200 1400 1600 1800 2000 Energy (keV)

FIG. 6. Gamma ray spectrum for the sixth Rh foil.

103

P The production of large amounts of P Pd is not a real task for this moment since the technology 103

P for the production of P Pd seeds is not yet available in Romania. However, the necessary parameters for irradiation of Rh targets were derived from the results presented above in correlation with other assumption as is following.

103

P According to published data concerning the use of P Pd seeds, the mean activity per patient is 103

P less than 37MBq (1mCi) distributed on 20÷30 seeds. Even for 50% efficiency of transferring the P Pd 103

P activity in seeds, 3.7GBq (100mCi) of produced P Pd in Rh target will cover at least 50 patients. 103

P Therefore, at 8.64MBq/µAh yield of P Pd production with 14MeV protons [1], it is necessary an integral charge of the beam on Rh target of 428 µAh (1.54C) to produce the required activity of 3,7GBq, respectively 4280 µAh for 37GBq (1Ci).

For the available external beams at U-120 Cyclotron, the possible irradiation parameters at normal incidence of the beam are summarized in Table III.

TABLE II. GAMMA-RAY SPECTROMETRY FOR RH FOILS

Pγ TB B[d] Eff. Λ[Bq] Λ[µCi] Λ[µCi] Elem E[keV] Tc[d] Tm[s AnetB B 1/2 57

P 121.78 11.667 8000 280.31 0.856 271.8 0.013157 3.205085807 0.000086626 0.00009 1 CoP 103

P 42.0 PdP 357.33 11.667 8000 10399.62 0.00022 16.96 0.0057459 1649004.058 44.57155545 103

P PdP 496.99 11.667 8000 1234.96 0.00004 16.96 0.0042581 1460364.366 39.46096488 56

P 0.003 CoP 846.48 11.667 8000 2252.87 0.999 78.8 0.0026552 117.6395703 0.003179448 56

P CoP 1237.77 11.667 8000 1216.53 0.67 78.8 0.0019128 131.4796328 0.003553504 56

P 1771.125 11.667 8000 176.54 0.155 78.8 0.0014139 111.5765053 0.003015581 CoP 57

P 121.78 11.788 8000 267.43 0.856 271.8 0.013157 3.058758622 0.000082669 0.00008 2 CoP 103

P 70.1 PdP 357.33 11.788 8000 17461.71 0.00022 16.96 0.0057459 2782522.621 75.20985817 103

P PdP 497.01 11.788 8000 2023.94 0.00004 16.96 0.0042581 2405213.586 64.99203286 56

P 846.5 11.788 8000 3985.32 0.999 78.8 0.0026552 208.3256462 0.005630423 CoP 0.006 56

P CoP 1037.58 11.788 8000 567.24 0.141 78.8 0.0022830 244.3341046 0.006603624 56

P CoP 1237.93 11.788 8000 1801.91 0.67 78.8 0.0019128 194.953482 0.005269013

P 1771.49 11.788 8000 347.51 0.155 78.8 0.0014139 219.8665594 0.005942339 CoP 103

P 357.33 11.993 8000 27654.06 0.00022 16.96 0.0057459 4463465.146 120.1117593 111.6 3 PdP 103

P PdP 497 11.993 8000 3184.5 0.00004 16.96 0.0042581 3988257.415 103.1198731 56

P 846.49 11.993 8000 5555.28 0.999 78.8 0.0026552 290.9140657 0.007862542 CoP 0.008 56

P CoP 1037.59 11.993 8000 745.85 0.141 78.8 0.0022830 321.8487843 0.008698616 56

P CoP 1237.97 11.993 8000 2720.76 0.67 78.8 0.0019128 294.8976226 0.007970206 56

P 1771.63 11.993 8000 427.71 0.155 78.8 0.0014139 271.0968147 0.007326941 CoP

87 103

P 148.5 PdP 357.32 12.118 8000 36721.24 0.00022 16.96 0.0057459 6013534.445 160.3107484 103

P PdP 497 12.118 8000 4197 0.00004 16.96 0.0042581 5055362.345 136.6025361 56

P 846.5 12.118 8000 6844.29 0.999 78.8 0.0026552 358.8133561 0.009697658 CoP 0.009 56

P CoP 1037.57 12.118 8000 655.58 0.141 78.8 0.0022830 283.206748 0.007654236 56

P CoP 1237.97 12.118 8000 3370.32 0.67 78.8 0.0019128 365.7039886 0.009883892 56

P 1771.51 12.118 8000 516.59 0.155 78.8 0.0014139 322.0745644 0.008704717 CoP 103

P 169.7 5 PdP 357 13.09 8000 15251.56 0.00022 16.96 0.0020224 7231582.687 196.8353083 103

P PdP 497.02 13.09 8000 1482.52 0.00004 16.96 0.0014986 5372424.078 142.6602264 56

P CoP 846.5 13.09 8000 2783.25 0.999 78.8 0.0009474 412.4482707 0.011147251 56

P CoP 1037.61 13.09 8000 298.31 0.141 78.8 0.0008016 370.1750373 0.010004731 56

P 0.01 CoP 1237.98 13.09 8000 1446.91 0.67 78.8 0.0006957 435.372356 0.01176682 56

P CoP 1771.49 13.09 8000 116.68 0.155 78.8 0.0005273 200.2272068 0.005411546 103

P 179.5 6 PdP 357.34 12.778 8000 15796.15 0.00022 16.96 0.0020224 7402846.895 201.2807168 103

P PdP 497.02 12.778 8000 1660.45 0.00004 16.96 0.0014986 5678525.502 157.7576159

P 846.51 12.778 8000 3280.83 0.999 78.8 0.0009474 484.8518995 0.013104105 CoP 0.012 56

P CoP 1037.58 12.778 8000 334.83 0.141 78.8 0.0008016 414.3542371 0.011198763 56

P CoP 1238.14 12.778 8000 15522.7 0.67 78.8 0.0006957 4657.948694 0.012589055 56

P 1771.71 12.778 8000 235.94 0.155 78.8 0.0005273 403.7721386 0.010912761 CoP 103

P 161.3 7 PdP 357.33 12.986 8962 16478.31 0.00022 16.96 0.0020224 6969585.57 189.034257

103

P PdP 497.02 12.986 8962 1562.38 0.00004 16.96 0.0014986 4784130.833 133.6374338 56

P 0.013 CoP 846.53 12.986 8962 3729.49 0.999 78.8 0.0009474 492.8950597 0.013321488 56

P CoP 1037.59 12.986 8962 430.04 0.141 78.8 0.0008016 475.9221511 0.012862761 56

P CoP 1238 12.986 8962 1875.79 0.67 78.8 0.0006957 503.3745995 0.013604719 103

P 126.5 8 PdP 357.33 12.887 8000 12185.10 0.00022 16.96 0.0020224 5792418.732 155.9605308

103

P PdP 497.01 12.887 8000 1017 0.00004 16.96 0.0014986 3581202.096 97.0555043

P 846.49 12.887 8000 3379.26 0.999 78.8 0.0009474 499.8772603 0.013510196 CoP 0.013 56

P CoP 1037.83 12.887 8000 358.06 0.141 78.8 0.0008016 443.5265558 0.011987204 56

P CoP 1237.83 12.887 8000 1655 0.67 78.8 0.0006957 497.0977918 0.013435075 56

P 1771.67 12.887 8000 262.76 0.155 78.8 0.0005273 450.101464 0.012164904 CoP 103

P 803.5 PdP 357.33 13.803 500 4532.14 0.00022 16.96 0.0020224 36349461.59 963.5347146

103

P PdP 497.02 13.803 500 405.87 0.00004 16.96 0.0014986 29733982.27 643.3756372

Stack 56

P 846.46 13.803 500 1066.96 0.999 78.8 0.0009474 2545.711455 0.068803012 CoP 0.065 56

P CoP 1037.49 13.803 500 138.21 0.141 78.8 0.0008016 2761.35697 0.074631269 56

P CoP 1237.92 13.803 500 549.33 0.67 78.8 0.0006957 2661.315838 0.071927455 56

P CoP 1771.73 13.803 500 61.34 0.155 78.8 0.0005273 1694.783431 0.045804958

TABLE III. IRRADIATION PARAMETERS FOR EXTERNAL BEAM AT U-120 CYCLOTRON

103

P Required activity of P Pd in the Rh target 3,7GBq (100mCi) 37GBq (1Ci) Integrated charge (µAh) 428 4280 Beam current (µA) 5 10 20 5 10 20 Irradiation time (h) 86 43 21 860 430 210 2

P Cross-section of the collimated beam (cmP ) 0,25 0,25 1 0,25 0,25 1 Beam power (W) 70 140 280 70 140 280 Density of dissipated power on the target for 280 560 280 280 560 280 2

P normal incidence of the beam (W/cmP )

As is shown in Table III, the corresponding irradiation time will be 86h, 43h, or 21h depending 103

P on the used beam current to produce 3,7 GBq of P Pd. For not long irradiation time, the preferred intensities are 10 or 20µA. Even for ten times more activity (37GBq) produced at 20µA beam current, the irradiation time is still convenient (below the saturation time of the yield).

From Fig. 5, result that an effective thickness of approximate 200µm for Rh target is necessary to obtain the mentioned yield.

Since the dissipated power on the target is rather high and the same is the superficial density of this power, it is more convenient to irradiate the target at a grazing angle of 30°or even 15° because the cooling of the target is considerably improved. Another advantage is that the effective thickness is increased two or four times and the Rh film deposited could be thinner.

We checked our target systems by irradiating metallic Zn targets at 10µA and normal incidence and 20µA at 30° grazing angle with an aperture of collimators of 6mm respectively 10mm. The Zn targets had 2mm thickness and a rectangular shape of 9mmx16mm respectively 15mmx30mm total area. Cooling was done by 2l/min. flow of distilled water. After 10h of irradiation, no visible damages of targets were observed.

2.2. Investigations and experiments for post-irradiation procedures; development of QC procedures.

103

P Two important steps in the technology of P Pd seeds are related to post-irradiation procedures and to QC procedures required by internal and international rules.

A team from our Center for Radioisotopes Production investigated the available data (published or collected from participants at this CRP) concerning post-irradiation procedures, which comprise 103

P separation of P Pd from Rh target, recovery of Rh after the separation of Pd and preparation of sealed sources for treatment of prostate cancer.

103

P Some experiments for dissolution of Rh target and separation ofP Pd were performed but no relevant results were obtained because of the absence of some technological facilities, as is ion exchange chromatography or special equipment for electro-dissolution and electroplating.

The same team was involved in developing QC procedures according to GMP requirements for 103

P some radiopharmaceutical products and it is possible to extend these procedures in future for P Pd sources.

3. CONCLUSIONS A dedicated beam line and appropriate irradiation systems were developed at U-120 Cyclotron 103

P for the production of P Pd by bombarding Rh targets with 14MeV protons beam.

Experiments for optimal irradiation parameters and post-irradiation characterization were performed.

The obtained results are in agreement with published data and are useful for routine production 103

P of P Pd in Rh targets in future.

The results obtained in this project are promising and will be developed in the next two years in the frame of a national research program for implementation of brachytherapie of prostate cancer with Pd-103 seeds.

REFERENCES

[1] A. HERMANNE, M.SONCK, A.FENYVESI, L.DARABAN, “Study on Production of Pd-103 and Characterisation of Possible Contaminants in the Proton Irradiation of Rh-103 up to 28 MeV”, NIM B 170 (2000) 281-292. [2] P.P. DMITRIEV, “Radionuclide Yield in Reactions with Protons, Deuterons, Alpha Particles and Helium – 3, INDC (CCP) –263/G +CN + SZ, Vienna, 1986.

89 [3] Z.FUKS, S.A.LERBEL, K.E.WALLNER ET AL. 1991, “The Effect of Local Control on Metastatic Carcinoma of the Prostate: Long Term Results in Patient Treated with I-125”, Int. J. Radiat. Oncol. Biol. Phys., 21, 537-547. [4] M.S.PORRAZZO ET AL. “Permanent Interstitial Implantation using Pd-103: the New York Medical College Preliminary Experience “, Int. J. Radiation Oncology Biol. Phys. 1992, Vol 23. pp.1033-1036. [5] D.M.LEWIS, “Production of Medical Isotopes for Therapy”, Synthesis and Applications of Isotopically Labelled Compounds 1997. Edited by J.R.Heys and D.G.Melilo, 1998 John Wiley &sons Ltd., 231-237. [6] IAEA TECDOC-1211. Charge-particle cross-section database for medical radioisotope production: diagnostic radioisotopes and monitor reactions, IAEA, Vienna, May 2001. [7] D.DUDU, V.POPA, P.M.RACOLTA, N.TETCU, DANA VOICULESCU, “Status and perspectives for the Pd-103 radioactive seeds production at the Cyclotron IFIN-HH from Bucharest”, poster presentation at the “International Symposium on Utilization of Accelerators”, held in Sao Paulo, Brazil, from 26 to 30 November 2001. [8] SHARKEY I ET AL. Outpatient ultrasound-guided Pd-103 brachytherapy for localized adenocarcinoma of the prostate. A preliminary report of 434 patients. UROLOGY 51: (5), 796- 803 May 1998 [9] WARETMAN FM, YUL N., CORN B.W., DICKER A.P. Edema associated with I-125 or Pd- 103 prostate brachytherapy and its impact on post-implant dosimetry: An analysis based on serial CT acquisition. International Journal of Radiation Oncology, Biology Physics 41:(5) 1069-1077 July 1998.

AN OPERATED SOLID TARGET DEVICE DESIGN FOR IODINE-123(124) PRODUCTION

L.M. SOLIN, V.A. JAKOVLEV, A.I. BARANOV, A.A. TIMOFEEV, D.A. ZUBOV V.G. Khlopin Radium Institute, Saint-Petersburg, Russian Federation

Abstract

The aim of the present work was to design and build a solid target device with remote control system to be used on the proton beam with the energy of about 15 MeV to produce iodine-123 (124) via p,n reaction with an enriched tellurium- 123 (124). It has a motor drive for target compressing. The control system is based on microcontroller and interface converter RS485. It is being used to control water and helium cooling, target compressing and dropping it into the container. The test of the system operation was successful.

1. INTRODUCTION

Radium Institute cyclotron MGC-20 is used since 1990. The main objective of the cyclotron is 123

P to provide radioisotopes for medicine. P I radionuclide is one of the most promising isotopes in nuclear medicine [1]. The iodine-labeled compounds are more natural for human organism, than many other radiopharmaceuticals. Huge advantages of iodine-123 are low radiation exposure to the patient and a high quality image.

123 123 123

P P P The production of P I via P Te(p,n)P I reaction is attractive because a small-size cyclotron with 14-16 MeV protons can be used. Iodine-123 is produced by proton bombardment of enriched tellurium-123 (in dioxide form) deposited on the platinum backing. After irradiation the target is heated and escaped iodine is absorbed and solved in NaOH solution. There are no principal limitations for achieving radionuclidic purity close to 100%.

The first radiopharmaceutical produced by Radium Institute was “sodium iodide solution, iodine-123”. We have started hospital deliveries in 1990. By now we have developed fast technology for four radiopharmaceuticals labelled by iodine-123. Besides “sodium iodide solution, iodine-123” there are sodium OIH, MIBG and BIMPP. It takes no more than 4 hours after EOB to prepare injection ready radiopharmaceuticals for application. Every week we provide about 20 Saint- Petersburg hospitals with radiopharmaceuticals labeled by iodine-123.

For ten years we have developed technology of iodine-123. Grave attention was paid to improve all stages of technology: target preparation, target irradiation, iodine extraction, tellurium regeneration, radionuclidic purity and radiation safety also. It is obvious that those stages are strongly connected with the target.

When target is being irradiated there is a problem to prevent melting of tellurium oxide under o

P proton beam bombardment. Tellurium dioxide has melting point about 733P C, but it is possible to have temperature above melting point at separate target spots because of low heat conductivity of tellurium dioxide and because of beam nonuniformity. In this case we may have a loss of iodine escaped from the target and a loss of target material, which is very expensive. To decrease this danger we have developed a special target device and a device to spread the beam on the target surface. Target device provides water cooling of platinum backing (back side of target) and helium cooling of tellurium dioxide (front side of the target).

91 2. STATEMENT OF PROBLEM

The first target device had a rather simple construction but it was sophisticated in operation. It took rather a long time to remove device from the beam line and to extract target from device. Therefore, employees received considerable doses. Moreover we used helium without flow in a small volume before target.

Next modifications of the device avoided disadvantages of the first target device. Nevertheless to take off the target it is necessary to make some operations with cooling systems (to close some valves and to open the others).

The main objectives of a new device design were:

- to reduce occupation dose by means of: - reduction induced activity of device elements, - introducing automatic operation of cooling system valves, - extraction of the target by remote-control mechanism - to guarantee appropriate cooling by means of the monitoring of water and helium flow, temperature and pressure. - to provide measurement of proton beam current simultaneously from the target and from the diaphragm before target

To perform these tasks the following steps were carried out:

- appropriate modification of the existing target device - improvement of the helium flux on the target. - installation of aluminum inner part of device - increasing of volume of platinum water cooling - providing the possibility of automatic operation - developing the automatic/manual device for target compression and throw down - developing target cooling system equipped with valves and sensors for automatic/ manual operation - developing software for monitoring and control of target device

3. MAIN PART OF THE ASSEMBLY

A target device operated by hand was designed and manufactured. In the design process for a new automated target device, particular importance has been attached to the simplicity, reliability and convenience of the system. As a basis, the previously designed manually operated target device was used. The following alterations and additions were introduced to the manually operated target device:

- Electromechanical drive with a system of contact stopping devices, marginal current sensor for the electric motor and a switch to the manual mode of operation. - The system of water and helium cooling is equipped with electromagnetic-driven faucets, duplicated by the corresponding stop-cocks to ensure the opportunity for transition to the manual operation of the system and also equipped with sensors of water flow and pressure.

In the design process for a target device, particular importance has been attached to the reduction of the induced activity level. Major part of the induced activity from the target device, if no special measures are undertaken, is contributed by the γ emission of Cobalt-56, formed through a reaction between the scattered protons of the beam and the inner walls of the target device.

To exclude this effect, all the inner walls of the target device are faced with a lining of chemically pure aluminum. Protective lining was mechanically attached to avoid the loss of mechanical durability due to inadequate firmness of aluminum.

A flowchart of the target device’s cooling system is shown in Fig. 1. The cooling of the target is performed using running water that washes the back side of the target backing, and a helium flow cooling the front side. The system of water cooling of the target includes a supplementary contour for blowing the channels and the volume behind the target with a compressed air using a compressor (pos. 3). The shutdown of the water cooling and the connection of the blowing contour are performed using four operated faucets (pos. 10 and 12) or manually using four stop-cocks (pos. 11 and 13). Water cooling system is equipped with the measuring instruments for pressure, flow and temperature on the inlet and on the outlet of the target.

The system of helium cooling consists of a cooling contour and a subsystem for filling. The cooling contour incorporates a ballast volume (pos. 7) filled with helium at the pressure of 1.0 – 1.5 atmospheres, an inner compressor (pos. 8) and tubes with faucets (pos. 15) and stop-cocks (pos. 15). The subsystem for filling consists of a highly pressurized container with helium (pos. 6), a reducer (pos. 5), and faucets (pos. 19 and 20). The cooling contour and the subsystem for filling are connected, through a system of pipes and faucets, to a common pre-vacuum pump (pos. 9). The cooling contour is equipped with helium flow and temperature measuring instruments on the inlet and the outlet of the target volume. To increase reliability of the target system at accidents a possibility of a fast switch to manual operation is provided for. To make it feasible, all the electromagnetic-driven faucets of water and helium cooling are duplicated by the corresponding stop-cocks.

A draft of the target assembly design is represented in Fig. 2. The target unloads by falling out into the container following the guides. The target volume is separated from the beam line of the cyclotron with an inlet window made of 0.1 mm thick aluminum foil (pos. 4).

Before the target unloading, water and helium cooling are switched off, water from pipes and the volume behind the target is removed with an air flow from the compressor. Further, the clamping part of the target device is withdrawn to its utmost backward position, using a motor (pos. 15) or in a manual mode (pos. 15). At that the guides (pos. 10) are detaching the target from a rubber sealing ring of water cooling (pos. 5), and the target is dropped into a lead protective container (pos. 8). In the automatic mode, clamping drive is positioned using a small roll (pos. 20) fixed on the drive gear (pos. 17), and three contact switches (pos. 19). The first contact switch fixes the position of the clamping drive at loading the target device with a target. The second contact switch serves to stop the drive at an utmost position at the tightening, in case when a marginal current sensor of the electric motor is out of order. The third contact switch restricts the drive’s motion at the target unloading.

The operation mode switch, from automatic to manual, is done by disengaging the gears (pos. 16 and 17), using an arm (pos. 18). While falling into the container, the target closes the electric contacts (pos. 12) of a system that controls fall-out of the target (at that a LED lightens up on the control panel). For loading the target and for eliminating the risk of its cocking at unloading in the target device, two locking bars (pos. 11), that ensure a stable centering of the target in the intermediate position of the clamping part of the target device.

4. TARGET DEVICE CONTROL SYSTEM FOR IODINE-123 PRODUCTION

The main task of the next step was a remote control of the target device. Target transfer by compressed air, make-and-break of water and helium cooling, removing the remaining water and dropping the target into the lead container are the tasks of the control system. The proposal and practical solution were realized at the Radium Institute Nuclear Medicine Laboratory.

93 4.1. Goals The target device control system is intended for control, visualization and storage of information on the operation of different elements.

It has the following functions:

- local and remote controls of the target compressor motor, water and helium supply valves; - beam current measurements from the target and from the diaphragm (before the target); - cooling water temperature, pressure and flow measurements; - information transmission to the controlling computer.

The connection of the control system to the computer is through RS-485 interface.

4.2. Performance specifications

Ac power supply - 220 ± 25 V, 50 ± 1 Hz

Measurements channel capacity for:

- temperature 2 - pressure 1 - water flow 1 - beam current 2

Measuring range:

- temperature 0 – 50 °С - pressure 0 – 4 bar - water flow 0 – 4 l/min - beam current 0 – 50 µA

Estimated error for all the channels is 0.2%.

Working conditions

- ambient temperature +10 - +40 °С - dust and moisture protection class - IP65 - relative air humidity at the temperature of +20°С is no more than 80%/

4.3. Control system structure chart. The control system structure chart is shown in Fig. 3. It consists of:

- microcontroller - keyboard controller - keyboard - display device - converters of input signals - commutator; - AD converter - buffer amplifier - 5 drive mechanism control units - interface converter RS485

The microcontroller is a principal controlling device of the system. It operates according to a developed algorithm. The keyboard controller provides the status poll of keyboard and the transmission on the keystroke to the microcontroller. The display device is responsible for the LED target device status. Six converters of input signals are used for sensor signal normalization and multiplication. Normalized signals go through the commutator to the AD converter input. Microcontroller control signals through the buffer amplifier go to the solid-state relays, which are used to control water and helium cooling systems, the compressor and the target compressor driver. Interface converter RS485 supplies conditioning between RS-485 and TTL levels.

4.4. Control system’s electrical scheme. The system is realized on the base of microcontroller AT89C52 from Atmel. It has resident data memory of 256K × 8, resident program memory of 8K × 8 and 32 in-out lines divided into 4 bi- directional ports. Ten unit ADC (Analog Devices Company) - AD7813YN is being used to register sensing devices signals. Commutation of input signals is realized with the help of analog signal commutator ADG608BN. Software for monitoring and control of target device was developed and tested at the Laboratory.

5. CONCLUSION

The solid target device with remote control system was designed and built. The target device was tested with the remote and local controls. It was used in iodine-123 production. The average beam current was 6.5 µA, proton energy of 15 MeV and irradiation run for 14 hours. All elements of the system were operating satisfactorily. Now the system is under routine operation for iodine-123 production.

FIG. 1. Flowchart of the cooling system of the target device.

1 – target device, 2 – the inlet and the outlet of water cooling, 3 – compressor for blowing the water volume, 4 – water drainage, 5 – reducer, 6 – highly pressurized container with helium (20 ATM), 7 – ballast volume with helium (1.5 ATM), 8 – compressors of helium cooling, 9 – the outlet of helium cooling system at the vacuum pump, 10 – electromagnetic faucets of the system for water supply, 11 – water stop-cocks for the water supply system, 12 - electromagnetic faucets of the system for water blowing, 13 - water stop-cocks for the water blowing system, 14 - electromagnetic faucets of the system for helium supply, 15 – gas stop-cocks for the helium supply system, 16 – helium compressor switch, 17 - water blowing compressor switch, 18 – exhaustion faucet of the target volume, 19 - exhaustion faucet of the system for filling the ballast volume, 20 – faucet of the system for filling the ballast volume, 21 – stop-cock for the high-pressurized container.

FIG. 2. Target device with a manual operation and with an operation from the panel.

1 – Tellurium target, 2 – tubes/pipes of water cooling, 3 – clamping/tightening ring and a disk/washer for the attachment of the outlet window, 4 – aluminum inlet window, 5 – rubber/elast(omer)ic tightening vacuum rings, 6 – protective aluminum insert, 7 - tubes/pipes for flooding and escape of helium, 8 - lead(en) container, 9 – sliding container cover/lid, 10 – guides for the target fall-out, 11 - locking device/stopper/ plug for the target fall-out, 12 – electric contacts of the alarm system for the target fall-out, 13-- cover of the inlet window for inserting the target 14 - arms for manual tightening and unloading the target, 15 – electromechanical motor, 16 – gear of the motor drive, 17 – gear of the clamping device drive, 18 – arm to switch from an automatic mode to a manual operation and inversely, 19 – contact switch, 20 – wheel for switching the contact switches (and, consecutively, for positioning the clamping device drive)

Input signals converters Keyboard

Commutator

ADC Keyboard controller

Microcontroller

Display

device

Buffer amplifier

Interface converter RS485

Water supply Target compression driver Water

compression

Helium supply Helium pump

To PC

FIG. 3. The control system structure chart.

REFERENCE

[1] BOURGUIGNON M.H., PAUWELS E.K.J., LOC'H C., MAZIIBRE B., Iodine-123 labelled radiopharmaceuticals and single-photon emission tomography: a natural liaison. European Journal Nuclear Medicine, 24 (3), (1997), pp. 331-344.

97 STANDARDIZED HIGH SOLID TARGETS FOR CYCLOTRON PRODUCTION OF DIAGNOSTIC AND THERAPEUTIC RADIONUCLIDES

S.T AL JAMMAZ, S. AL-YANBAWI, S. MELIBARI, RAHMAT King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia

Abstract:

Using the new technology described for electrodeposition of elemental thallium-203, zinc-68 and tellurium-124, it was possible to produce simultaneously four targets in each shift. These dense, smooth and homogeneous targets were being able to tolerate high beam currents without loosing or burning enriched material. As a result, radiochemical yields for Tl-201, Ga-67 and I-123 were increased by 22%, 17% and 31% respectively.

1. INTRODUCTION Cyclotron produced radiopharmaceuticals are being increasingly utilized in nuclear medicine for both research and routine clinical diagnosis of an extensive variety of diseases. Indium-111, Gallium-67 and Thallium-201 cyclotron produced metallic radionuclides are extensively used in a wide range of diagnostic nuclear medicine application. In addition to Iodine-123, Gallium-67 and Thallium-201 are enjoying spectacular use as Single Photon Emission Computerized Tomography (SPECT) radionuclides. Iodine-124, which can be used for Positron Emission Tomography (PET) studies as well as radiotherapy, is another radioisotope that shows great promise.

The most widely used radioactive tracer for myocardial perfusion imaging is Tl-201. Although, 201

P various methods have been proposed for the production of P Tl for injection, the method first reported by Lebowitz et al. [1] and worked out in detail by Lagunas-Solar et al. [2] and Qaim et al. [3] is still the most commonly used one.

In the early fifties, Gallium-67 was produced from enriched Zinc-68 using the nuclear reaction 68 67

P P P Zn (p,2n) P Ga [4-6]. Later, several nuclear reactions were reported for the production of Gallium-67 by either 8 MeV deuteron or 23 MeV alpha bombardment of natural zinc [7]. The finished product Gallium-67 citrate has been widely employed in the detection of inflammation, infections and tumours [8].

In the early sixties Meyers and Anger described the potential of iodine-123 (I-123) for use in diagnostic nuclear medicine due to favorable and almost ideal physical properties [9]. Since then, I- 123 is enjoying spectacular use as SPECT radionuclides. There are numerous different nuclear reactions leading to the production of I-123, many of which have been studied and reported. Among 123 123

P P these reported methods is the nuclear reaction P Te (p,n) P I suggested by Meyers and Anger. Later this was worked out by Hupf and et. al and Barrall et. al to produce hundred-millicurie amounts of I- 123 suitable for diagnostic procedures using isotopically enriched Te-123 [10,11]. This was followed by producing very pure I-123 through bombardment of different isotopically enriched tellurium isotopes with alpha and helium-3 particles from a low energy cyclotron [12,13].

In addition, one more nuclear reaction used for the production of pure I-123 in large quantities 127 123

P P have been developed in the last two decade using high energy cyclotron (> 60 MeV) is P I (p,5n) P I [14]. Nevertheless, the most widely used nuclear reaction to produce large quantities of I-123 with 124 123

P P high energy protons (25 MeV) is P Te (p,2n) P I [15-18]. Moreover and lately, it has been a routine practice in many centers to produce the ultra-pure iodine-123 in large amounts via highly enriched 124 123

P P Xenon-124 gas utilizing the following nuclear reaction P Xe(p,2n) P I [14].

123

P The finished product P I-sodium iodide is used most commonly for the measurement of thyroid uptake and thyroid imaging. In addition, radioiodinated compounds have been widely employed in the detection of cardiological, neurological and oncological diseases [14].

Recently, inadequate supply of Tl-201, Ga-67 and I-123 due to the limited capability of the solid targets of handling high beam current becomes a major obstacle in meeting the needs of nuclear medicine demands. Here, we report the development of Tl-201, Ga-67 and I-123 production utilizing new electroplating technology as member of the International Atomic Energy Agency’s co-ordinated meeting entitled: Standardized High Solid Targets for Cyclotron Production of Diagnostic and Therapeutic Radionuclides.

2. MATERIALS AND METHODS The chemicals used in this study were all purchased from Aldrich (USA), and were used without further purification unless stated. Enriched Tl-203, Zn-68 and Te-124 were purchased from Isotopes (Russia). Copper target plates, aluminum target holders, plastic target carrier and electroplating vessels were all fabricated at the precision machine shop attached to our cyclotron (Fig. 1). Each newly fabricated plates/holders/carriers and vessels were inspected and conditioned taking in consideration many critical steps [11].

FIG. 1. Copper target plate, aluminum target holder and electroplating vessel.

99 2.1. Thallium-203

2.1.1. New Thallium-203 Target Plating Solution Preparation In a 600mL beaker (B1) fitted with a Teflon coated magnetic stirring bar, 360 mL of deionized water was placed. To that EDTA (84 g), NaOH pellets (20g) were added and stirred until obtaining a colorless solution. In another beaker (B2) fitted with a Teflon coated magnetic stirring bar, hydrazine 203

P hydrate (10mL) and BRIJ-35 (1mL) were homogenized followed by the addition of P Tl2B OB 3B B (7.65 g) with continues stirring until yellow-brown color disappears. Solution in B1 finally added to B2 with continuous stirring to give the final electroplating solution with pH>12.5.

2.1.2. New Thallium-203 Target Electroplating The freshly prepared solution of a pH>12.5 was poured in the plating vessel. The four outputs of the current booster were connected to the cathodes by introducing the four block male plugs (copper targets, 1.5 cm thickness). This was followed by the introduction of the electromagnetic stirrer in a way that the central Pt-anode wire fits into hollow stirring cylinder. The rotational speed of the stirrer is 1200 rpm for a 16 second period. The electrolysis starts by introducing the common output plug of the boosters into the bottom of deposition vessel with 16 mA current. After 3.30 hours of electrolysis, which is needed for producing four thallium-203 targets (400 mg ± 10% each), the stirring motor stopped and the four electroplated targets were removed and rinsed extensively with deionized water then dried, weighed and finally stored in a vacuum desiccator.

2.1.3. New Thallium-203 Recovery from Depleted Plating Solution Pt-wire (Anode)/Pt-gauze (Cathode) electrodes connected to the current output of constant current source were introduced to the depleted plating solution which embodies almost 1 g of the enriched Tl-203 material in the plating vessel. The current was adjusted to 200 mA and the electrolysis continued for 15 hours. The amount of enriched Tl-203 in the depleted solution was checked and found to be less than 1 mg.

2.1.4. Irradiation and Extraction of Pb-201 from Enriched Tl-203 Lead-201 was produced by the bombardment of enriched Tl-203 targets (400 mg ± 10% each) 203 201 201

P P P P with 26 MeV protons from the CS-30 Cyclotron internal beamP using theP Tl(p,3n) P Pb(E.C.) P Tl nuclear process. The proton current was ranging between 70-105 µA and the irradiation time was 9.5 -3

P hours. The irradiated targets were dissolved in H2B SOB 4B B (2.5 mL, 4.0 mol dmP ) under a heating lamp. +3

P Aqua-regia solution (20 mL conc. HCl + 3 mL conc. HNO3B )B was added to maintain the TlP oxidation state. This was followed by addition of n-Butylacetate (50 mL) previously equilibrated with HCl (6 -1

P mol lP ) with continuous shaking. After several separations of the two phases the aqueous layer was collected in a flask containing concentrated HNO3B B (3 mL), then, left for 32 hrs, which is needed for Tl- 201 to grow. The enriched Tl-203 in organic layer was saved to be recovered using the previous method.

2.1.5. Extraction of radiochemical Tl-201 from Pb-201 After 32 hours, which is sufficient for the growth of Tl-201, the aqueous layer was extracted -3

P with Diisopropyl Ether (DIPE, 40 mL) equilibrated with HCl (6.0 mol dm P ). This was followed by -1

P washing DIPE layer (organic) twice with HCl (6.0 mol lP , 20 mL). Then, back extract Tl-201 from the +3

P DIPE with two portion of sterile water (10 mL) previously treated with SO2B B to reduce thallic (TlP ) to +

P thallous chloride (TlP ). Furthermore, the aqueous layer, which contains Tl-201, was evaporated to complete dryness and a calculated amount of sterile water was added. Then the activity transferred into pre-weighed sterile serum bottle. Finally, 0.8 mL of the Tl-201 bulk solution was given to quality control for radionuclidic purity, copper, iron and inactive thallium tests.

100

2.2. Zinc-68

2.2.1. New Zinc-68 Target Plating Solution Preparation 68

P In a 200 mL beaker, P ZnO (4.5 g) was added, followed by the addition of NaCN (3.2 g), NaOH (6.8 g) and deionized water (20 mL). Solution was filtered (if necessary) and the filtrate was diluted to 50 mL with another portion of deionized water to be ready for electroplating.

2.2.2. New Zinc-68 Target Electroplating The freshly prepared solution of Zn-68 was poured in the plating vessel. The four outputs of the current booster were connected to the cathodes by introducing the four block male plugs (copper targets, 1.5 cm thickness). This was followed by the introduction of the electromagnetic stirrer in a way that the central Pt-anode wire fits into hollow stirring cylinder. The rotational speed of the stirrer is 1200 rpm for a 16 second period. The electrolysis starts by introducing the common output plug of the boosters into the bottom of deposition vessel with 100 mA current. After four hours of electrolysis, which is needed, for producing four Zinc-68 targets (425 mg ± 10% each), the stirring motor stopped and the four electroplated targets were removed and rinsed extensively with de-ionized water then dried, weighed and finally stored in a vacuum desiccator. The same procedure was repeated with addition of hydrazine (10 mL) to the plating solution.

2.2.3. Irradiation and extraction of gallium-67 from enriched zinc-68 Gallium-67 was produced by the bombardment of enriched zinc-68 targets (325 mg old system

P and 425 mg new system ± 10%) with 26 MeV protons from the CS-30 Cyclotron internal beamP using 68 67

P P theP Zn(p,2n) P Ga nuclear process. The proton current was ranging between 40-65 µA and the irradiation time was ranging between 6-7.5 hours. The irradiated targets were dissolved in HCl (20 -3

P mL, 7.5 mol dmP ). This aqueous layer was extracted with Diisopropyl Ether (DIPE, 50 mL) -3

P equilibrated with HCl (7.0 mol dmP ). This was followed by washing DIPE layer (organic) three times -3

P with HCl (7.0 mol dmP , 20 mL) (first wash contain 1 ml of 20% titanium chloride solution). Then, back extract Ga-67 from the DIPE with three portion of sterile water (10 mL). Furthermore, to the aqueous layer, which contains Ga-67, sodium citrate (0.1 mL of 2.5%) was added and evaporated to complete dryness. The dried Ga-67 was transferred to a pre-weighed collection bottle using sodium citrate (2.9 mL of 2.5%) and sodium chloride (27 mL of 0.9%). Finally, 0.6 mL of the Ga-67 bulk solution was given to quality control for radionuclidic purity, titanium, copper, iron and gallium tests.

2.3. Tellurium-124

2.3.1. Nickel Target Electroplating Copper plate was cleaned using sandpaper (320-500) grade followed by rinsing copper plate with de-ionized water. The copper plate was placed in 1000 mL beaker containing nickel sulfate plating solution. Copper plated was connected to the power supply, as cathode while the platinum electrode is the anode. Power supply was turned on and the current was adjusted to 400–800 mA and allowed for 3 minutes, giving the nickel-electroplated target. After turning off the power supply electrodes were disconnected and rinsed with deionized water and acetone to accelerate drying.

2.3.2. New Tellurium-124 Target Plating Solution Preparation 124

P In a 500 mL flask, P TeO2 (3.0 g) was added, followed by the addition of KOH (7.5 g) and deionized water (250 mL). The homogenized solution filtered through fine glass filter (0.45 µm) to remove any residual particles if necessary to be ready for electroplating. 2.3.3. New Tellurium-124 Target Electroplating The freshly prepared solution of tellurium-124 was poured in the plating vessel. The four outputs of the current boosters were connected to the cathodes by introducing the four block male

101 plugs (copper-plated-nickel targets, 1.5 cm thickness). This was followed by the introduction of the electromagnetic stirrer in a way that the central Pt-anode wire fits into hollow stirring cylinder. The rotational speed of the stirrer is 1200 rpm. The electrolysis starts by introducing the common output plug of the boosters into the bottom of deposition vessel with 300 mA current. After one hour of electrolysis that is needed for producing four tellurium-124 targets (90 mg ± 10% each), the stirring motor stopped and the four electroplated targets were removed and rinsed extensively with de-ionized water then dried, weighed and finally stored in a vacuum desiccator. This refined procedure is a result of several repeated experiments with different concentrations of KOH and electroplating currents. 2.3.4. Irradiation and extraction of iodine-123 from enriched tellurium-124 Iodine-123 was produced by the bombardment of enriched tellurium-124 targets (90 mg ± 10%) with 26 MeV protons from the CS-30 Cyclotron internal beam using the 124Te(p,2n) 123I nuclear process. The proton current was ranging between 18-45 µA and the irradiation time was between 2.0- 2.75 hours. The irradiated targets were dissolved in a mixture of NaOH (1.0 mL, 5.0 mol l-1), H2O2 (3.0 mL, 30%) and Milli-Q water (6 mL). The dissolved Te-124 was transferred in 250 mL quarts reaction flask containing aluminum powder (160 mg) that was boiled until reaction is completed. Solution was bubbled with air for five minutes followed by bubbling with CO2 for additional five minutes. The bubbled solution was then carefully filtered through fine fritted glass and on-line AG50W-X8 column into pre-weighed serum vial. If necessary pH is adjusted in the range between 5-7 value with NaOH (0.01 mol l-1). Finally, 0.6 mL of the NaI-123 bulk solution was given to quality control for radionuclidic purity, specific concentration, pH, tellurium and aluminum tests.

3. RESULTST AND DISCUSSION T

The new electroplating technology has produced high quality Tl-203, Zn-68 and Te-124 targets. These targets and through microscopic inspection appear to be dense, smooth and homogeneous (Figs 2 and 3). Prior to that, the solid state targets in general were mainly prepared by constant voltage electrolysis from rather intricated plating solutions, which mostly results in dendrite formation and non-uniformed plates due to gases evolution making mechanical rolling (smoothing) post electroplating a general requirement. Such rolling produces non-homogeneous layers. As a result, crater formation and peeling-off of such layers when bombarded with high beam current. This will decrease the radionuclide yield and more importantly loss of very expensive enriched materials inside the cyclotron, which raise the multi-pacting effect that consequently decreases the vacuum.

The new electroplating simultaneously allows preparation of four dense, smooth and homogeneous targets within acceptable shift taking in consideration three important parameters. These parameters are 1- composition of plating solution, 2- stirring and 3-the current density range. The new +

P plating solution for thallium contains EDTA as complexing agent for Tl P at pH more than 12 to lead to smoothly electroplating of Tl-203 on the cathode. In addition, hydrazine as an anodic depolarizer that is oxidized faster than water, this prevents oxygen evolution at the anode and the cathode, which may +1 +3 o

P P P oxidize TlP to TlP or TlP to Tl2B OB 3B B respectively. In addition, a non co-deposited tenside BRIJ-35 should be introduced to the electroplating solution to reduce or to prevent to some extent dendrite formation.

When hydrazine is introduced to the zinc plating solution, oxygen evolution at the anode and the cathode was prevented. As a result, the electroplating efficiency was increased to nearly 100% without affecting electroplating quality.

Unlike the old electroplating solution, the electroplating efficiency of the new basic electroplating solution of tellurium which contains potassium hydroxide as complexing agent for tellurium has increased the to nearly quantitative. While not more than 85% was obtained in the old system. In addition, the new system produced 20 high quality plated targets from each electroplating solution bath taking in consideration the depletion of the solution does not go more than 40%.

102

When the same amount of NaOH solution was used to dissolve the proper amount of tellurium instead of KOH, electroplating progresses smoothly. However, after sometime, the electroplated targets started to dissolve and the whole solution turned to dark color. This dark color is originated from undissolved tellurium oxides. This could be attributed to the high dissolution and complexing capacity of KOH as compared with NaOH [19]. In addition, when hydrazine was used, metallic tellurium begins to precipitate.

Ultimately, the higher the current, the faster the electrodeposition, however, each metal should have optimum current since the increase in current density may result in increasing gases evolution which consequently reduces the electroplating uniformity. The optimum currents for Tl-203, Zn-68 and Te-124 were found to be around 16, 100 and 75 mA respectively.

Moreover, these high quality (dense, smooth and homogeneous) electroplated Tl-203, Zn-68 and Te-124 targets did not require any post electroplating mechanical smoothing. Accordingly, beam currents up to 125 uA for Tl-203, 65 uA for Zn-68 and 45 uA for Te-124 were tolerated without loosing or burning natural material.

Several targets prepared by the new techniques were irradiated with 26 MeV protons using

P internal beam withP current ranging between 70-105, 40-65 and 20-45 µA for Tl-203, Zn-68 and Te- 124 respectively.

The yield, target weight, current and irradiation time for the new target irradiated plates for Tl- 203, Zn-68 and Te-124 are illustrated in Tables I, II and III, respectively.

The results in Tables I, II and III elucidate an increase in the yield while increasing the current, however, when exceeding 95, 45 and 24 uA beam currents for Tl-203, Zn-68 and Te-124 respectively; yield tends to declines, which make 95, 45 and 24 uA currents to be the optimum for such internal target design. This decrease might be attributed to the high heat generated from the high beam currents that necessitate new development on the cooling parameters. This development included electroplating of natural Tl-203 on a thin copper plates (0.5 mm), modifying the target holder by introducing a narrow coolant channel and optimizing the geometry of inlet and outlet coolant channel (Fig. 4). Results in Table IV proved that such development was ineffective in improving final yield. Thus, more elaborate development on the beam position, density, distribution and cooling parameters is required. Such development will include harmonic coil settings and their influence on beam position on internal targets.

Nevertheless, by using the new electroplating, we were able to increase Tl-201, Ga-67 and iodine-123 final yields to nearly 22%, 17% and 31% respectively.

On the other hand, the new electroplating technique has shown superiority by recovering more than 99.9% of the enriched Tl-203 from the depleted solution in a simple manner when compared with the laborious old method. Yet, quality control tests regarding radionuclidic purity, copper, iron and in active thallium were found to be the same.

As part of the development on beam position and distribution, several radiograms of thallium, gallium and iodine targets were taken. These radiograms were found to be different from plate to plate. Accordingly, radiograms were scanned to obtain a digitized image and treated using an in-house developed computer program called TargetIMX to normalize all images to a graphical presentation of target’s beam position. After normalization, images scanned in vertical direction from top and bottom to pre-defined homogenous beam density. The same process was repeated changing from vertical to horizontal direction and the centerline of beam position was calculated as will as sensible picture was generated (Fig. 5).

103 Using the information generated from the TargetIMX program, beam’s intensity distributions were determined when beam hit either the upstream or the downstream sides of the target. In the former, the angle of incandescence is larger resulting in very short and intense beam spot (Fig. 6). Whereas some of the beam does not hit the target material in the latter (Fig. 7). By using the above settings and interpolating to the center of these settings, intensity distribution in Fig. 8 was obtained. This study will allow us to have a better control on the beam position and intensity helping to eliminate the target’s hot spots that contribute to the evaporation of the radioactive products and consequently reduces the yield.

4.T CONCLUSIONSTT

Differences between the old and the new electroplating methods in terms of yield when a similar beam current is used were not observed. However, the new electroplating technologies that have been transferred under this CRP produced high quality electroplates. That has allowed the increase of beam current without damaging or burning the targets, resulting in a dramatic increase in the final yields as well as ensuring reliability of radiopharmaceuticals’ production. In addition, the new electroplating technique has shown superiority by recovering enriched material in a simple manner as compared with the laborious old methods.

TABLE I. DATA GENERATED FROM USING THE NEW THALLIUM-203 ELECTROPLATING TECHNOLOGY Current (uA) Time (hour) Weight (mg) Activity (mCi) 1 77 9.5 388.4 ± 19.8 283.7 ± 8.2 2 85 9.5 392.5 ± 14.1 308.4 ± 15.5 3 90 9.5 408.6 ± 23.3 340.8 ± 35.5 4 95 9.5 403.1 ± 18.7 368.5 ± 10.6 5 100 9.5 404.3 ± 21.1 321.8 ± 28.4 6 105 9.5 425.0 ± 2.0 318.2 ± 3.5

TABLE II. DATA GENERATED FROM USING THE NEW ZINC-68 ELECTROPLATING TECHNIQUE Current (uA) Time (hour) Weight (mg) ± 10% Yield (mCi/uA.h) 1 40 6.5 405 3.97 2 42 7.5 328 4.33 3 45 7.5 321 4.68 4 50 7.0 522 3.62 5 60 6.0 391 3.37

104

TABLE III. DATA GENERATED FROM USINF THE NEW TELLURIUM-124 ELECTROPLATING TECHNIQUE Current Time (hour) Weight (mg) ± Yield (mCi/uA.h) Yield (mCi) (uA) 10% 1 20 2.75 86.3 12.75 ± 1.93 136.02 ± 43.1 2 22 2.75 86.8 13.72 ± 2.61 175.63 ± 26.9 3 24 2.75 91.5 16.61 ± 0.78 234.50 ± 22.4 4 25 2.75 89.3 13.19 ± 0.34 178.42 ± 15.6 5 30 2.25 100.4 8.50 ± 1.31 126.39 ± 31.4 6 35 2.0 105.8 7.33 ± 1.05 119.86 ± 26.8

TABLE IV. DATA GENERATED FROM USING THE NEW NATURAL THALLIUM ELECTROPLATING TECHNIQUE WITH OPTIMIZED TARGET DESIGN Current (uA) Time (hour) Weight (mg) ± 10% Yield (mCi/uA) 1 100 0.5 408 6.47 2 105 0.5 171 5.20 3 110 0.5 186 4.80 4 115 0.5 157 4.68 5 120 0.5 156 2.97

A B C

FIG. 2. Microscopic inspection of zinc targets, A old, B new and C new with hydrazine.

105

FIG. 3. Microscopic inspection of tellurium targets, old and new.

FIG. 4. Developmental work on target plate and target holder.

106

FIG. 5. Centerline picture of the calculated beam position.

FIG. 6. Intensity distribution of beam hitting down streamside of the target.

FIG. 7. Intensity distribution of beam hitting up streamside of the target.

107

FIG. 8. Intensity distribution of interpolated position. REFERENCES

[1] LEBOWITZ, E., GREENE, M. W., FAIRCHILD, R., BRADLEY, R., MOORE, P. R., ATKINS, H. L., ANSARI, A. N., RICHARDS, P., BELGRAVE, E. Thallium-201 for medical use. J. Nucl. Med., v. 16 (2), p. 151 (1975). [2] LAGUNAS-SOLAR, M. C., JUNGERMAN, J. A., PEEK, N. F., THEUS, R. M. Thallium-201 yields and exication functions for the lead radioactivity produced by irradiation of natural thallium with 15-60 MeV protons. Int. J. Appl. Radiat. Isot. 29 (3), p. 159 (1978). [3] QAIM, S. M., WEINREICH, R., OLLIG, H. Production of Tl-201 and Pb-203 via proton induced nuclear reactions on natural thallium. Int. J. Appl. Radiat. Isot. v. 30 (2), p. 85 (1979). [4] GRUVERMAN J. AND KRUGER P. Cyclotron produced carrier free radioisotopes. Int. J. Appl. Radiat. Isotopes, v. 5, p. 21, 1959. [5] SUBRAMANIAN G, RHODES B., COOPER J. AND SODD V. Production and use of I-123. International Symposium on radiopharmaceuticals, Atlanta, Georgia, USA, Feb.1974. Radiopharmaceuticals, New York. Society of Nuclear Medicine. Inc. 1975, p.125. [6] DAYANIKLI B.F., WEISSMAN A. AND WAHL R. Successful Gallium-67 Imaging of North American Pulmonary Blastomycosis. J. Nuc. Med., v. 34 (6), p. 958, 1993. [7] MEYERS W. AND ANGER H. Radioiodine – 123. J. Nucl.Med. v. 3, p.183, 1962. [8] HUPF H., ELDRIGE J. AND BEAVER J. Production of Iodine-123 for Medical Applications. Int. J. Appl. Radiat. Isotopes, v. 19, p. 345, 1968. [9] BARRAL R., BEAVER J., HUPF H. AND RUBIO F. Production of Curie Quantities of High Purity I-123 with 15 Mev Protons. Eur. J. Nucl. Med. v. 6 (9), p.411, 1981. 122 4 123 + 123

P P P P P [10] LAMBRECH R. AND WOLF A., P Te(P He, 3n) P Xe betaP , EC/2.1 hr, P I generator. Radiat. Res. 52 (1), p.32, 1972. [11] HOMMA Y. AND MURAKAMI Y. The Production of Xe-125 for Medical Use by the He-3 Bombardment of Natural Tellurium. Int. J. Appl. Rad. Isot. 1977, v. 28 (8), p.738. th

P [12] SAHA G., Fundamentals of Nuclear Pharmacy, 4P Edition, New York, 1977. [13] LEBOWITZ E., GREENE M. AND RICHARDS P. On the production of I-123 for medical use. Int. J. Appl. Radiat. Isot. v. 22 (8), p. 489, 1971. [14] ZIELINSKI F., MacDONALD N. AND ROBINSON G. Radiopharmaceutical Development. J. Nucl. Med., 18, 1, 67, 1977. [15] VAN DEN BOSCH R., GOEIJ J., VAN DER HEIDE J., TERTOOLEN J., THEELER H. AND ZEGERS C. A new approach to target chemistry for the iodine-123 production via the 124

P P Te(p,2n) reaction. Int. J. Appl. Radiat. Isotopes, v.28 (3), p. 255, 1977. [16] KONDO K., LAMBRECH R. AND WOLF A. Iodine-123 production for radiopharmaceuticals. Int. J. Appl. Radiat. Isotopes, v. 28 (4), p.395, 1977. [17] LEDDICOTTE G., The Radiochemistry of Tellurium, Nat. Acad. of Scie. NAS-NS 3038, USA 1971.

108

USEFUL CONCEPTS IN SOLID STATE TARGET TECHNOLOGIES

D.J. SCHLYER, R.A. FERRIERI Brookhaven National Laboratory, New York, United States of America

Abstract

This paper presents some common characteristics of all solid targets. The effect of power density in solid targets is explored. The transfer of heat from the target to the water cooled target carrier is examined in terms of the laws of heat transfer which will allow transfer out of the target and into the cooling water. Some common types of solid targets are explored including both internal and external targets. Some possibilities for the extraction of the radioisotopes from the target matrix are presented including physical extraction, chemical extraction or extraction using supercritical fluids. Methods of recovery for the enriched target materials are also presented.

1. INTRODUCTION In general, radioisotopes fall into two basic groups, those which are neutron rich and those which are neutron deficient. Those that are neutron rich are usually made in a nuclear reactor while those that are neutron deficient are produced by bombarding a suitable target with protons, deuterons or helium particles. Particle accelerators and in particular cyclotrons, were very important in the preparation of radioisotopes during the years of 1935 to the end of World War II. The amount of radioactive material which could be produced in an accelarator was many times greater than the amount which could be produced using the alpha particles from naturally occurring radioactive elements.

After World War II, reactors were used to produce radioactive elements and the use of accelerators for this purpose became less common. However, as the techniques for using radiotracers became more sophisticated, it became clear that reactor produced radionuclides could not satisfy the growing demands and therefore accelerators were needed to produce new radioisotopes which could be used in new ways.

There are three major reasons the accelerator produced radioisotopes are used more widely that reactor produced radionuclides. These are:

1. The radioisotopes produced in a reactor may have unfavorable decay characteristics (particle emission, half-life, gamma rays, etc.) for a particular application. 2. The radioisotope cannot be produced in a reactor with high specific activity 3. Access to a reactor is limited. The number of reactors available has become many fewer than the number of cyclotrons available to the scientific community, or the radioisotope has too short a half-life to be transported to the site where it is needed.

There are wide varieties of nuclear reactions which are used in an accelerator to produce the artificial radioactivity. The bombarding particles are usually protons, deuterons, or helium particles. The energies which are used range from a few MeV to hundreds of MeV. There is a minimum energy required to overcome the Coulomb barrier. Particles with energies below this barrier have a very low probability of reacting.

1.1. Number of isotopes with solid targets

Table I in the appendix is a list of the isotopes which have value in medical applications or which seem promising for development. The radioisotopes which can be made using solid targets are marked with an “X”.

109 2. GENERAL CONSTRAINTS

2.1. Power deposition One of the main concerns in solid targets is the deposition of power in the matrix during irradiation. If the power deposited exceeds the ability of the target to remove the heat, the targe will eventually be destroyed or the target material will be melted or volatilized. The power deposited in the material is very simple to calculate. It is the beam current in microamps multiplied by the energy in MeV and the result is the number of watts deposited. The exact position of the heat deposition will of course depend on the dE/dx (stopping power) of the beam in the target material with most of the heat being deposited near the end of the particle range in the Bragg peak. A simple approximation for the stopping power is given by the relation [1]:

24 2 dE 42πze ℑ Z mV0 −= 2 ln dx mV0 A I

where: - dE/dx = energy loss per unit length - z = the atomic number of the projectile -10 1/2

P P - e = elementary charge 4.803 x 10P (erg-cm)P

- m0B B = the electron rest mass - V = relativistic projectile velocity 0

P - AP = Avogadro’s number - Z = atomic number of the target material - I = adjusted ionization potential of the target material

Some additional helpful approximations are that the relativistic velocity is given by the relation:

E V =−1.s384 1091cm ec− m

where: - E = particle energy in MeV - m = particle atomic mass number

The other useful approximations for the adjusted ionization potential are [2]:

I = 13 Z eV if Z < 13

-0.19

P I = 9.76 Z + 58.8 ZP if Z > 13

The stopping powers of particles other than protons are given by the relationships:

- deuterons SdB (E)B = SpB (E/2)B

- tritons StB (E)B = SpB (E/3)B 3

P P - He SB (E)B = 4SpB (E/3)B 4

P P - He S(E)B = 4SpB (E/4)B

2.2. Heat transfer in Solids Heat transfer in solids is somewhat simpler than in other media since the heat usually flows through the target matrix mainly by conduction. The heat will be conducted form the hotter region of a material to the cooler region according to Fourier's Law which is in one dimension:

110

QcondB B = -kA dT/dx

where: o Qcond = heat transferred by conduction (watts) o A = cross-sectional area (cm2) o k = thermal conductivity (watts/cm-°C) o dT = temperature differential (°C) o dx = distance differential (cm)

If this equation is integrated holding k, A and q constant, then the result is the heat transfer equation in one dimension given by:

QcondB B = -kA(T1-T2)/x (7)

where: o k = coefficient of thermal conductivity (watt/cm-°C) o A = cross-sectional area (cm2) o x = distance (cm) o T1 = temperature of the hotter part (°C) o T2 = temperature of the cooler part (°C)

Once the heat has been transferred to the cooled surface of the target, the heat will usually be removed by a fluid such as water flowing against the back of the target. This convective heat transfer is another topic which will not be discussed.

A picture of the target material points up several design considerations for solids. This is shown in Fig. 1.

Target Material Backing Material

Water Cooling

FIG. 1. Schematic diagram of solid target configuration.

The transfer of the heat through the target material and through the backing material is straightforward. The real surprises in designing solid targets come in the interfaces where the target material meets the backing material. This is where many problems arise and the more secure one can make this interface, the better the heat transfer will be and the less likely one is to have problems with loss of target material or damage to the target during the irradiation.

3. TARGET PREPARATION

3.1. Solids By far the easiest target preparation is that for a solid metal. The metal target is merely mounted on a water cooled backing plate and placed in the particle beam. There are several examples of targets such as this. One such target is the one fro making Cd-109 which consists of a silver plate mounted on an aluminum backing plate which is water cooled. An example of such a target is shown in Fig. 1.

111 3.1.1. CompressedT solids T A typical method for making targets composed of oxides or other compounds that are not amenable to electroplating is to place the material in a depression and then press the material under high pressure in order to obtain a uniform layer. An example of this is the tellurium oxide target, which is used for the production of Iodine-124. The tellurium oxide is pressed into a depression under 15,000 psi. It is also possible to add some metal to help with the heat conduction out of the target oxide.

3.1.2. ChemicalT Vapor Deposition T Chemical vapor deposition (CVD) is the process in which a film is deposited by a chemical reaction or decomposition of a gas mixture at elevated temperature at the wafer surface or in its vicinity, see Fig. 2 for a schematic view of the CVD process.

FIG. 2. Schematic diagram of the typical chemical deposition process. The solid film is produced concurrently with the formation of a gaseous product.

4. TYPICAL TARGETS

4.1. Perpendicular Incidence For some targets where the material is a good conductor, the matrix is not sensitive to heat, the quantities required are small or the isotope being used as the target is very rare, a perpendicular target may be used. A schematic diagram of such a target is shown in Fig. 3.

Thin Window Target Material

Target for Irradiation of Solid Powders

FIG. 3. Schematic diagram of a solid powder target used for radioisotope production.

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4.2. Inclined Incidence Internal - A schematic diagram of the inclined plane internal target is shown in Fig. 4.

Alpha beam

Target Material Leading Monitor Base Plate

Trailing Monitor

RAM

FIG. 4. Schematic diagram of an inclined plane target used internally in the cyclotron. The target uses glancing incidence of the beam to spread out power density of the beam.

External – A schematic diagram of an external inclined plate target is shown in Fig. 5.

FIG. 5. Schematic diagram of an inclined plane target, which is used external to the cyclotron.

5. RADIOISOTOPE RECOVERY

5.1. Dissolution A common method for the recovery of the radioisotope is to dissolve the target and then extract the desired radioisotope from the solution. This is often done by solvent extraction or by ion chromatography. An example of this method is given in the following example for Tl-201. In a typical procedure, the thallium target is dissolved in 4MU U H2B SOB 4B B and then transferred to a cation exchange column. The thallium can then be eluted off the column with 1 MU U H2B SOB 4B B and saved for recovery. The column is then rinsed with sterile water. The Pb-201 is eluted off the column with 2 MU U HCl. The thallium-201 is then allowed to grow in. After the grow-in period, the Tl-201 can be separated from the Pb-201 by extraction with di-isopropylether in a separatory funnel.

The aqueous phase that contains the Pb-201 is separated and saved for later processing. The organic phase is washed and then the thallium-201 is back extracted from the organic phase into water

113 that has been treated with sulfur dioxide. The solution is evaporated to dryness and then dissolved in enough normal saline to give the desired final concentration.

5.2. Distillation

5.2.1. During irradiation

To Radiochemistry Laboratory Quartz Holder

Graphite Secondary Holder

Proton Beam

.0 03" Mo lybdenum Foil

C-13 Powder

Spring Loading

Helium Inlet

FIG. 6. Solid carbon-13 powder target.

In certain situations, it is possible to distill the radioisotopes out of the solid matrix by using the heat of the beam to aid in separating the radioisotope from the solid matrix where it is contained. This technique is successful only if the radioisotope being produced can be volatilized and carried out of the target. An example of this type of target is given by the carbon-13 powder target for the production of nitrogen-13. A diagram of this type of target is given in Fig. 6. Temperatures inside the matrix can o

P easily exceed 600P C.

5.2.2. Post-irradiation The most common method for the removal of radioisotopes from a solid target matrix is a post- irradiation distillation. In this technique, the target plate is removed from the target holder and placed in a furnace. The temperature is increased until the radioisotope is released. In some targets this occurs when the target melts while in other targets, the volatilization of the material occurs at a temperature below the melting point of the matrix. An example of this type of distillation is shown in Fig. 7. This is the distillation of I-124 from the tellurium dioxide matrix, which is irradiated. The I-124 is volatilized and transported into a base solution [3].

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O + He Gas Inlet 2 TeO Target Holder 2

I-124 Out

Thermocouple Probe Fur nace

124

P FIG. 7. Furnace for the distillation of I-124 from the solid [P Te]TeO2B B matrix of the target.

5.2.3. Supercritical extraction Supercritical fluids are attractive as media for both chemical reactions, as well as process extraction since their physical properties can be manipulated by small changes in pressure and temperature near the critical point of the fluid. Such changes can result in drastic effects on density- dependent properties such as solubility, refractive index, dielectric constant, viscosity and diffusivity of the fluid. This suggests that pressure tuning of a pure supercritical fluid may be a useful means to manipulate chemical reactions based on a thermodynamic solvent effect. It also means that the solvation properties of the fluid can be precisely controlled to enable selective component extraction from a matrix. In recent years, there has been a growing interest in applying supercritical fluid extraction to the selective removal of trace metals from solid samples. Much of the work has been done on simple systems comprised of inert matrices such as silica or cellulose. Recently, this process as been expanded to environmental samples as well. However, very little is understood about the exact mechanism of the extraction process. Of course, the widespread application of this technology is highly dependent on the ability of scientists to model and predict accurate phase equilibrium in complex systems [4].

6. TARGET MATERIAL RECOVERY

6.1. Precipitation

One of the ways of the radionuclide production increasing on present cyclotrons is the use of the targets from enriched stable isotopes for irradiation. This allows to raise the productivity in two or more times in some cases and to increase a radionuclidic purity. Enriched stable isotopes are very expensive; therefore, it is advisable to recycle such raw materials as many times as possible. As an example of this process, the recovery of zinc-67 or zinc-68 is given below.

Depending on gallium-67 production method, (deuteron or proton bombardment) the targets from zinc-67 or zinc-68 are used. The target represents a copper block with a thin nickel layer covered with stable zinc by electrodeposition. Its treatment includes the dissolution of irradiated zinc in hydrochloric acid and following organic solvent extraction of gallium-67.

The remaining solution contains some quantities of copper, nickel and cobalt-57 besides the zinc. The technique is based on the well-known anion-exchange behavior of the relevant elements in hydrochloric acid. During zinc target irradiation, the zinc-65 (T½B B / = 244 d) is obtained. These procedures do not provide for the zinc isotope separation.

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FIG. 8. Scheme of zinc-67, 68 recovery.

This type of scheme results in a recovery of the enriched isotope of greater than 95%.

7. CONCLUSIONS

As can be seen from these examples and the table, most of the radioisotopes can or are being produced by irradiation of solid targets. The targets have a wide variety of designs, but can be grouped into three basic groups that are perpendicular external targets, inclined external targets and inclined internal targets. The target type being used is dependent on a number of factors, which include the amount of isotope being produced, the sensitivity of the target material to heat, the cost of the target material and the type of cyclotron available for the irradiation.

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TABLE I. LIST OF RADIONUCLIDES PRODUCED WITH A CYCLOTRON

Product Solid Half Nuclear Nominal Demand Other Reactions Impurity Nuclide Target Life Reaction Energy mCi/yr for Impurities Half-life 7 Be-7 X 53.3 d P Li(p,n)P 20 15

22 Na-22 2.6 y P Ne(p,n)P 15 1500

25 X P Mg(p,a)P 20

27 27 26

P P P P P Mg-28 X 21 h Al(a,3p) 45 Al(g,n)P Al 73,000 y

48 49 46

P P P P P V-48 X 16 d Ti(p,n) 11 50 Ti(p,a)P Sc 83.8 d

49 49

P P P Ti(p,n)P V 337 d

47 44m

P P P Ti(p,a)P Sc 2.44 d

50 47

P P P Ti(p,a)P Sc 3.3 d

47 48 49

P P P P P X Ti(d,n)* 10 Ti(d,n)P V 337 d

55 55 54

P P P P P Fe-55 X 2.73 y Mn(p,n) 20 100 Mn(p,pn)P Mn 312 d

56 56 56

P P P P P Co-55 X 17.5 h Fe(p,2n) 25 1000 Fe(p,n)P Co 77.3 d

60 Co-57 X 271 d P Ni(p,a)P 25 15000

55 X P Mn(3He,n)P 40

61 61 58m

P P P P P Cu-61 X 3.35 h Ni(p,n)* 12 50 Ni(p,a)P Co 9.1 h

64 X P Zn(p,a)*P 22

67 67 67

P P P P P Cu-64 X 12.7 h Zn(p,a)* 20 50 Zn(p,n)P Ga 3.3 d

66 66

P P P Zn(p,n)P Ga 9.5 h

66 66 67

P P P P P X Zn(d,a)* 20 50 Zn(d,n)P Ga 3.3 d

66 66

P P P Zn(d,2n)P Ga 9.5 h

63 65 65

P P P P P Zn-62 X 9.2 h Cu(p,2n) 22 2000 Cu(p,n)P Zn 244 d

65 64

P P P Cu(p,pn)P Cu 12.7 h

69 71 71

P P P P P Ge-68 272 d Ga(p,2n)* 30 2000 Ga(p,n)P Ge 11.4 d

74 74 74

P P P P P As-73 X 80.3 d Ge(p,2n)* 11 100 Ge(p,n)P As 17.8 d

74 74 73

P P P P P As-74 X 17.8 d Ge(p,n)* 15 100 Ge(p,2n)P As 80.3 d

78 80 77

P P P P P Br-77 X 2.37 d Se(p,2n) 20 100 Se(p,a)P As 38.6 h

77 74

P P P Se(p,a)P As 17.8 d

88 88 87

P P P P P Y-88 X 106.6 d Sr(p,n) 11 100 Sr(p,2n)P Sr 3.3 d

89 89 88

P P P P P Zr-89 X 3.27 d Y(p,n) 15 100 Y(p,2n)P Zr 83.4 d

96 96 96

P P P P P Tc-95m X 61 d Mo(p,2n)* 25 10 Mo(p,n)P Tc 4.3 d

96 96 95m

P P P P P Tc-96 X 4.3 d Mo(p,n)* 15 100 Mo(p,2n)P Tc 61 d

95 3

P P P Ru-97 X 2.89 d Mo(P He,n) 45

109 Cd-109 X 462 d P Ag(p,n)P 20 5000

117 124 124 123

P P P P P I-124 X 4.2 d Te(p,n)* 26 500 Te(p,2n)P I 13.1 h

121 123 126

P P P P P X Sb(a,n)* 30 Sb(a,n)P I 13.0 d

122 122 123

P P P P P Xe-122 X 20.1 h Te(3He,3n)* 50 Te(3He,2n)P Xe 2.0 h

127 127 126

P P P P P Xe-127 36.4 d I(p,n) 20 300 I(p,pn)P I 13.0 d

126 Ba-128 2.43 d P Xe(3He,n)*P 30 139 Ce-139 X 137.6 d P La(p,n)P 11 10

180 180 177

P P P P P Ta-179 X 1.8 y Hf(p,2n)* 22 1000 Hf(p,4n)P Ta 2.4 d

181 W-178 X 21.6 d P Ta(p,4n)P 38 100

192 Pt-195m X 4.02 d P Os(a,n)P 40

197 197 197

P P P P P Hg-195m X 1.67 d Au(p,3n) 30 100 Au(p,n)P Hg 2.7 d

194 194 193m

P P P P P X Pt(3He,2n)* 40 Pt(3He,a)P Pt 4.3 d

203 Pb-203 X 2.2 d P Tl(p,n)P 20 200

207 Bi-205 X 15.3 d P Pb(p,3n)*P 30

206 X P Pb(p,2n)*P 22

207 Bi-206 X 6.2 d P Pb(p,2n)*P 22

206 X P Pb(p,n)*P 15

209 At-211 X 7.2 h P Bi(a,2n)P 46 200 40 hr

237 Pu-237 X P Np(p,n)*P 25 10 10 hr

* Uses isotopically enriched target material.

REFERENCES

[1] JANNI, J. “Stopping Power and Ranges”. Air Force Weapons Laboratory Report AFWL-TR- 65-150, 1965. [2] DECONNINCK, G. Introduction to Radioanalytical Physics, Nuclear Methods Monographs No.1, Elsevier Scientific Publishing Co., Amsterdam, 1978. [3] FIROUZBAHKT, M.L; SCHLYER, D.J; FINN, R.D; LAGUZZI, G; WOLF, AP. Iodine-124 production: excitation function for the 124Te(d,2n)124I and 124Te(d,3n)123I reactions from 7 to 24 MeV. Nucl. Inst. Meth. In Physics Research B, v.79 (1-4), (1993), pp. 909-910. [4] ERKEY, C, Supercritical carbon dioxide extraction of metals from aqueous solutions: a review. Journal of Supercritical Fluids, (2000), 17, pp. 259–287.

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