I have still been working on neutron activation, with a tiny bit more success. I am now confident that I can activate gold, although the long half-life (~2.7 days) of Au-198 and the very small quantity (0.4 g) that I have make detecting it quite challenging. Below are two spectra plotted together--one (blue) is a background taken over 16 hours with the non-irradiated gold foil target, while the black plot is taken after irradiation at my fusor. The spectra pretty much overlap, but looking carefully, we can see that there is one area of significant difference where the black spectrum has a peak centered on 418 keV. The dotted red line illustrates where the expected Au-198 peak should be centered, and it matches up. Finally, I have labelled the prominent naturally occuring peaks in both spectra. (The one marked 515 keV is from annihilation radiation and the K-40 peak shows up at 1453 keV). These results are certainly not as striking as my earlier ones with manganese, iodine and vanadium. However, I have repeated this gold experiment several times now and the Au-198 peak, however weak, has shown up every time. I am working on improving the signal-to-noise, and so tonight I irradiated a gold target in a prolonged run at some of the highest fusion rates my equipment can do (around 60 mRem / hr at the target), for the longest time it has been continuously operated: nearly 40 minutes. Right now, the gold target is being counted--this time, I am counting for 18 hours rather than 16 and have the counter set up vertically rather than horizontally, and wrapped in several layers of lead sheet. The only thing that bums me out is that it is raining now, and this probably means a higher background. By the way, the gold I use is the 23 kt leaf packs sold by Monarch for gilding, putting in confections, etc.
On another subject, I have also tried to activate silver. The problem with it is that the activation isotopes (Ag-110 and Ag-108) do not release gamma rays frequently during decay, and the predominant activation product Ag-110 has a very short half-life of only 24 seconds. Silver would be easier to detect using a pancake GM tube. I don't have any definitive gamma spectra yet from a silver acetate target, although I have been trying.
-Carl
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2003-04-07 01:15 More activation experiments 
(Carl Willis) [Latest: 2003-04-07 15:05]