Here are the results of another manganese activation experiment that I did a while ago. The purpose of this experiment is to show that the fusor's neutrons are fast--much like Jon Rosenstiel's very elegant experiment of moving a BF3 tube away from his fusor under water.
Two nearly identical MnO2 targets were prepared by filling little flat pastic boxes with 17.0 g each of the black powder. One target was exposed to fusor neutrons with 3" of water between it and the fusor, while the other had 3" of air. (For the former, the water was contained in a stack of VHS tape cases, while in the latter, the same VHS cases were used but had no water in them.) Both targets were "baked" at 60 mRem / hr for 15.0 minutes, and the data log shows that actually the sample behind 3" of air got a higher total neutron fluence by about 5%. After each sample was exposed, it was immediately counted as shown.
Anyway, the conclusion is that the Mn only activates when several inches of a good hydrogenous moderator are interposed between it and the fusor. Simply exposing Mn to fusor neutrons will not activate it. Since neutron capture essentially only occurs for thermal or epithermal neutrons in the Mn, we can see that the fusor must produce fast neutrons.
Of course we already know this is the case, but in the past there have been critics of the Farnsworth Fusor who claim that (with the aid of some unknown energy source) photoneutron or "stripping" reactions produce the neutrons. If this hypothesis were correct, a large fraction of the emergent neutrons should be slow--the photoneutron reaction has a negative Q-value to the tune of 2.2 MeV. So this little experiment just corroborates the other good evidence that a positive-Q-value, DD fusion reaction is taking place.
Just thought I'd toss this up here.
-Carl
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2003-04-17 22:58 Another manganese activation experiment 
(Carl Willis) [Latest: 2003-04-22 10:14]