Introduction
The Comecer ALCEO Metal system is intended to be a comprehensive solid targetry system, capable of all steps necessary to produce copper isotopes (60Cu, 61Cu & 64Cu) from enriched nickel: plating, transfer to/from cyclotron, irradiation, and dissolution/purification. To develop plating and chemistry methods, we plate natural nickel, and irradiate with deuterons to produce 61Cu. This alleviates the need for expensive enriched nickel isotopes, but gives a lower activity yield. We report a few issues with the ALCEO system, and some of our modifications.
Material and Methods
BRIEF DESCRIPTION OF SYSTEM: The ALCEO system uses cylindrical shuttles (dia 28 mm, height 35 mm) comprised of an Al body with a Pt well, onto which the Ni is plated. Shuttles are transferred pneumatically from the hot cell to the irradiation module, on the end of the cyclotron beamline.
The plating and dissolution are both done at the electrochemical cell, located in the hot cell. This cell is connected by capillary tubes to the electrolytic solution reservoir (for plating), or the acid reservoir (for dissolution). These tubes form a recirculation loop, through which the fluid is propelled by an inline micropump throughout plating and dissolution.
The platinum well is 16 mm in diameter, while an O-ring is used to plate only the center (6 mm in diameter). A constant DC voltage is applied.
PLATING: We dissolve natural nickel nitrate (99.999% pure) into an electrolytic solution comprised of deionized water, ammonium hydroxide and ammonium chloride (pH = 9.3). We use 30–100 mg of natNi in a 10mg/mL solution. We have varied the ALCEO electrochemical cell voltage between 2.25–3 VDC, and tried to maintain a low pump flow rate between 1–2 mL/min.
The electrochemical cell uses a fixed metal tube as the anode (~3mm above the plating surface). This tube also delivers the electrolytic plating solution to the Pt surface, forming part of the recirculating loop. The Pt surface is in contact with a gold-plated cathode.
Due to issues discussed below, we have built a custom plating rig for the ALCEO shuttles, which does not use the pump/recirculation loop, but leaves the reservoir of electrolytic solution in place, atop the plating surface. A graphite rod is used for the anode, rotating offcenter ~2mm above the plating surface. We use the same size O-ring to plate only the center 6 mm of the Pt surface, and apply a constant DC voltage.
TRANSFER TO/FROM CYCLOTRON: The pneumatic transfer tube is 50 ft long between the hot cell and the cyclotron vault, and has a rise of
14 ft from under the floor to the ceiling of the cyclotron vault.
IRRADIATION: The ALCEO irradiation module holds the plating surface orthogonal to the beam path. The module has a 10-mil-thick (0.010”) Al front foil, supported by a hex-grid. Once we realized the thickness, we replaced this with a 1-mil-thick Al foil, followed by a 1-mil-thick Havar foil.
The foil is cooled by a flow of helium, while the shuttle and grid are cooled by a flow of water. The helium and water are cooled in heat ex-changers by chilled water. As initially plumbed, the chilled water flowed through the heat ex-changers in series, cooling the helium first, then the water. After initial runs, we plumbed the heat exchangers in parallel, teeing the chilled water to the supply of each heat exchanger, and teeing the returns together.
Irradiation is performed with a PETtrace 800 accelerating deuterons to 8.4 MeV on target. The beam current limit is 20 μA for the ALCEO Metal target. A set point of 19 μA is used to avoid the system tripping off.
DISSOLUTION/PURIFICATION: The ALCEO system circulates 5 mL of 6M HCl, while heating the shuttle to 100 ⁰C for 40 min. This solution is loaded onto a column containing 10 g of 200–400 mesh chromatographic resin in chloride form.
A separation is performed yielding three solutions: The column is washed with 40 mL of 6M HCl to obtain the Recovered Nickel Solution, then 20 mL of 4M HCl to obtain the Cobalt Solution, then 10 mL of 0.5M HCl to obtain the Cop-per Product Solution.
Results and Conclusion
PLATING: Using the ALCEO method, the platings obtained had a tendency to mound, (up to 0.75 mm thick for 50 mg) giving a lower density of 3–4 g/cm3. This was attributed to the anode tube being fixed in place over the center of the plating surface. Using the custom rig, almost no mounding was observed, (0.25mm thick for 50 mg) giving a density of 7 g/cm3, closer to nickel’s nominal density of 8.9 g/cm3.
FIGS. 1 and 2 attempt to show the mounding from the ALCEO method, and relative flatness from the custom rig. Both methods give a rough, or “fuzzy” plated surface. FIG. 2 shows that the custom rig exaggerates this “fuzziness”. Using the ALCEO method, a slower pump speed (~1 mL/min) gives a smoother plating surface, but the pump has a tendency to lock up at this lower set point, stalling the plating.
Using the ALCEO method, slight increases in the voltage (2.65 V instead of 2.25 V), can form thin stalagmites of nickel, electrically connecting the anode and the plating surface, ending the chance for a useable plating. Using the custom rig, no stalagmites are seen, adjusting the voltage from 2.3 to 3.0 V. This leads to the potential for a faster plating.
Both the ALCEO method and the custom rig have obtained plating efficiencies of 95 %.
TRANSFER TO/FROM CYCLOTRON: The shuttle typically transfers without issue in < 15 seconds. Once or twice it has remained in the transfer tube, but been retrieved by cycling the com-pressed air/vacuum a couple of times.
IRRADIATION: During initial testing, the temperature of the return water rose rapidly during irradiation. This was attributed to the chilled water already gaining heat from the helium heat exchanger. Once the parallel chilled water plumbing was implemented, the water temperature rose much more slowly.
Initial testing with the 10-mil Al foils gave a very poor activity yield. The 1-mil Al foil ruptured under the 20 psi helium pressure before beam was applied. The 1-mil Havar foil produced 1.57 mCi of 61Cu at EOB, giving an activity yield of 0.308 mCi/μAh (results summarized in TABLE 1). This compares to yields of 1.4 obtained by [1], and 0.29 obtained by [2] for deuterons on natNi.
DISSOLUTION/PURIFICATION: The dissolution in 6M HCl is close to 100% efficient by weight.
After purification, the three solutions were assayed by dose calibrator as summarized in TABLE 2. The purification is very efficient at removing the starting material, and long-lived Co isotopes from the Copper Product Solution, as seen with the 57-hour EOB measurements. However, much of the desired 61Cu is removed as well, with only 32% remaining in the product.
The lack of nuclide impurities in the Copper Product Solution was confirmed by gamma spectroscopy using a HP-Ge detector.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:d120-qucosa-166465 |
| Date | 19 May 2015 |
| Creators | Erdahl, C. E., Bender, B. R., Dick, D. W. |
| Contributors | Department of Radiology, University of Iowa, Iowa City, IA, USA,, Helmholtz-Zentrum Dresden - Rossendorf, |
| Publisher | Helmholtz-Zentrum Dresden - Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:conferenceObject |
| Format | application/pdf |
| Source | MTTC15 |
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