Introduction
Low melting point metals are often encapsulated in a hermetic container, irradiated and the container transferred to hot-cell for material removal and processing. An important process of this kind is the production of 82Sr from rubidium (melting point: 39.5 °C.)
This new concept departures completely form the encapsulated targets approach and allows an almost continues production by the irradiation of the bulk metal. As well, eliminated is the target transfer. By placing the target material dissolution chamber right in the target station, only the dissolution product is pumped to the hotcell for further processing.
Material and Methods
Some of the disadvantages of the encapsulated target are:
1. Complicated transfer system that is ex-pensive to install, slow and prone to failures.
2. Complex and expensive encapsulation procedure.
3. Loss of production time during the lengthy target changing.
4. Capsule geometry is constrained by the encapsulating process and transfer demands compromising heat transfer and beam power.
To avoid the difficulties of liquid metal handling, metal salts are often used instead (rubidium chloride is one example). This creates other problems and limits the beam currents and production yields.
In the system described, the liquid metal is transferred (by gravity) from a bulk container to an irradiation chamber. The chamber, made out of nickel-plated silver, holds the correct quantity of rubidium for one irradiation run. Because of the geometry of the chamber and the efficient cooling, up to 40KW of beam power can be delivered to the target. The chamber is equipped with thermocouples and a liquid-metal level detector and is entirely of welded/brazed construction. The alloy foil that forms the beam window is electron-beam welded to the chamber front ring.
At the end of irradiation the irradiated liquid metal is gravity fed into a reaction chamber situ-ated below the irradiation chamber, and a new load of fresh rubidium released into the irradia-tion chamber. The liquid-metal transfer and the irradiation components are shown on FIG. 1, and the sectional view on FIG. 2.
Appropriate chemicals (n-butanol in the case of rubidium) are delivered to the reaction chamber and the irradiated metal dissolved. The liquid dissolution product is transferred back to the hotcell. Since all steps of the reaction involve liquids, only small diameter tubes connect the target station with the hotcell. The transfer is fast and simple.
The bulk liquid-metal storage container can be constructed to hold enough material for 10 or more runs. When empty, it is replaced with a pre-loaded one. The container is connected to the target system with one coupling and the exchange takes a short time. A robotic bottle exchange can be implemented if desired.
The station is equipped with its own vacuum system, beam diagnostic (consisting of a four-sector mask) and a collimation. The target chamber and each of the beam intercepting components are electrically insulated to allow beam current monitoring.
Constructed entirely out of metal and ceramic the target core assembly does not suffer from radiation damage. The use of aluminum, silver and alumina reduce component activation.
Results and Conclusion
A large part of the station design is based on the well proven construction of high current solid target system and is using the same, or similar components.
Test was performed to optimize the liquid-metal transfer and the chamber filling with the correct volume, while leaving some room for expansion.
A process for niobium coating of sliver is investi-gated. Niobium is known to provide good corro-sion resistance against liquid metals.
Thermal modelling of the target and flow analysis of the cooling geometry is under way.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:d120-qucosa-165893 |
| Date | 19 May 2015 |
| Creators | Gelbart, W. |
| Contributors | Advanced System Design, Garden Bay, BC, Canada,, 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 | WTTC15 |
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