SECURE Project

Deliverable 3.2

EXECUTIVE SUMMARY

The production and dissolution of W-186 metal targets were investigated. A W-186 target undergoes a double-neutron capture to produce W-188, a beta-emitting isotope used in nuclear medicine. Its daughter nuclide, Re-188, decays and is accompanied by a 155 keV predominant energy γ-emission, which could be used for γ-cameras, for imaging, biodistribution, or absorbed radiation dose studies. Additionally, its high beta emissions can penetrate and destroy abnormal tissue or cancer for therapy.

Both oxide and metallic W-186 have been reported in the literature. Oxide targets are preferred for their ability to dissolve and retrieve the W-186 product after irradiation. However, the ampoules of tungsten oxide targets have been reported to break, limiting the possibility of upscaling. Additionally, the lower W-density in the oxide form is unfavorable, given the limited availability in high-flux positions in research reactors. Although it is unclear why these ampoules break, a working hypothesis presumes it is due to the heat generated, the low thermal conductivity, and the thermal expansion of the material during irradiation. Therefore, W-metal targets are investigated to improve target performance during irradiation and increase production per irradiation cycle.

In this report, a feasibility study of W-metal targets was performed by making and dissolving W-metal target samples. Various metal targets were made by pressing, sintering, and cutting W-powder. The die and punch had a cylindrical cavity with a diameter of 9.8 mm. The applied force varied from sample to sample, from 4 to 6 tons in a hydraulic press. The samples were then sintered in a Hyptec 5 atmosphere at 1750°C for 2 and 24 hours. Following the production and characterization of these targets, they were then dissolved to study the time and conditions needed to extract medical isotopes.

To dissolve these targets, a single-step hydrogen peroxide method was used. The reaction was heated in a water bath up to 45°C and confirmed by weighing the residual W-mass. The reaction was observed to occur in three phases. Phase one—the initial dissolution phase—occurred over the first 12 minutes, with small hydrogen bubble formation. In phase two, a vigorous reaction was present between 12 and 16 minutes, where the target fell apart into a powder. After 60 minutes, it was found that around 91% of the initial target was dissolved. In phase three, the dissolution of the residual W-mass proceeded slowly until the reaction was stopped at 90 minutes. At 90 minutes, the residual W-mass was found to be between 1-2% of the initial target mass.

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.