I just looked into some details concerning the scenario presented in slide 9 of Michael McKubre's recent presentation in Brussels to get a sense of what might be causing the tritium they were seeing.
The slide summarizes an Arata/Zhang replication. In their replication, they saw excess heat and, apparently, primarily tritium. This is unusual, because when tritium has been present in many experiments, it has usually been found only in small amounts, suggesting that it is the result of some kind of side reaction. But the slide indicates that they saw 2-5 * 10^15 atoms. If you consider that 1 W excess heat from the generation of 4He from d+d (however this happens) will yield on the order of 10^11 atoms, it is apparent that 10^15 atoms is a lot of tritium. Presumably the experiment ran for a while, but nonetheless one gets the impression that the tritium is more than simply the result of some side reaction, and it looks like the main daughter in this case. The possibility of excess heat arising primarily from tritium generation poses some interesting questions: What were some candidate exothermic reactions that might produce the tritium? Is some kind of neutron capture required to explain the result? What else can be gleaned from the slide? For the quick analysis that follows, here are relevant details: - The experiment involved palladium black and LiOD electrolyte in an electrolytic setup. - They saw excess heat from LiOD but not LiOH. - They saw no 4He. - They saw no 3He above what can be expected from the decay of tritium. This suggests that the 3He was not a daughter product of whatever reaction was causing the heat. - The 3He they saw diffused from a source within the hollow cathode, which had the palladium black within in it. I think palladium black is in the form of powder. After looking at a number of reactions, I found only two exothermic reactions that produce tritium with precursors that would have been present: - 6Li + d → t + 5Li + 594 keV - - 3He + n → p + t + 1.27 MeV I saw no other reactions involving stable isotopes of H, Li, O, or Pd that were exothermic, although it is possible the heat was generated by a reaction I missed or by one involving a different element. At a minimum it seems that deuterium was needed, because they saw excess heat with LiOD and not LiOH. Assuming for the moment that the reaction was one of these two, neutron capture cannot be ruled out, but neither is it necessary. If the 3He really was a byproduct of tritium decay, then neutron capture would appear to be unlikely as the primary source of heat in this instance, leaving the 6Li+d reaction. Another reason the 3He+n reaction seems unlikely as the primary source of heat is that it does not involve deuterium. Since 6Li is 7 percent of naturally occurring lithium, the amount of if that will have been present in the electrolyte is non-negligible. But it's not clear that it would make it into the hollow cathode, where the tritium diffused from; perhaps it was able to enter the cathode through a crack in a ligation that was used to seal in the palladium black. Another possibility is that tritium was generated at the exterior of the cathode and then migrated through the cathode into the center, where palladium black was. In this case the reaction would have been in the electrolyte or at the interface between the exterior of the cathode and the electrolyte. If this is what happened, it is not clear what would have been driving the 6Li(d,t)5Li reaction. Perhaps there were d's shooting out into the electrolyte sufficiently fast for this purpose. I am not sure what the cross section for this reaction is, which could tell us how fast the d's would need to be going. To summarize some interesting details: - The possibility of tritium as the main daughter product giving rise to excess heat is unusual and is worth thinking about. - It looks like the tritium and excess heat could be arising in this case from reactions with the electrolyte that involve lithium and deuterium. - Alternatively, neutrons from an unknown source could be causing the tritium and excess heat by way of 3He(n,p)t reactions, but if that is the case, you would need a way to get neutrons from the presence of LiOD and not LiOH, and you would need the presence of 3He prior to that of the tritium. - If the lithium in the electrolyte is involved, it seems like you would need fast particles to keep things going; fast enough, anyway, to make the 6Li(d,t)5Li reaction a likelihood. I would be interested in seeing the paper that the slide is based off of. Has anyone seen it? Eric
