Hi there,
I have been playing around with electrochemical reactions using Cu64 but I can't seem to get it to behave like Cu when using a cold salt of CuCl2. As far as I am aware when it comes from the reactor it should be in the Cu2+state and there will be various other metals in solution like Fe, Co, Ni and Zn. These other metals may be the source of the problem (not having the Cu galvanically replace Au) but it is not clear to me what else could be interfering with the galvanic replacement. The quantities of all these metals are significantly smaller than the available Au surface area the solution is being given to react on, so if there is some sort of blocking going on I'm not sure of its source. What seems more likely to me is that the electrical state of the Cu64 is not compatible with the galvanic replacement reaction. Does anyone have any ideas regarding the electrical state of Cu64 as it comes fresh from the reactor?
Thanks in advance,
Dear Jos, I am not sure about your conditions but you havn''t mentioned the age of your solution. I & my colleague (Detlef) noticed on the nuclide table that the half-life of your Cu-64 is just 12.7h. This means that in 5 days (10 half-lives) , practically all your Cu64 is gone and will be replaced by the equivalent amount of Zn-64 (by positron (e+) ejection) and by Ni-64 (beta decay) plus substantial ionisation to radiolyse the water. I would think that your gold surface would also help catalyse the reduction of Ni2+ in solution to Ni deposit on the gold and help ensure the Zn remains in solution as Zn2+. Even with some Cu 64-2+ in the first 2 days, the Ni deposition could be blocking the Au for any Cu deposition. Try looking at the a) the solution composition and b) surface analysis (by SEM-EDS) to see how much Ni and Cu are at the surface.
Hi D. Bottomley,
That is a good point, I hadn't considered the change in product as the decay continues. We use the Cu pretty much straight from the reactor and we intend to only do two more subsequent simple steps before imaging, where the reactor to scanner time should only be a maximum of 10 h. When using cold Cu2+ the replacement reaction is complete within 30-40 seconds at room temp, but with the hot Cu64-2+ the reaction proceeds much more slowly.
We will run ICPMS and attempt some surface analysis to quantify the Cu/Ni surface loading. We had considered the potential for Ni to block the deposition of Cu but we thought that the sheer quantity of gold surface area present would be more than enough for both the Ni and Cu to deposit on to without allowing inhibition. If it is the case that the Ni is filling all the available deposition sites we will look into blocking or removing the Ni in solution prior to the reaction, there is also the potential to significantly increase the available Au sites.
Thanks for your thoughts on my question,
Jos
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