Search for He-3 and He-4 in Arata-style palladium cathodes II: Evidence for tritium production

Measurements have been made of He-3, He-4, and H-3 in a sample containing 2 .7% of the gas from the interior of an Arata-style hollow palladium electro de charged with similar to5 g Pd-black that had undergone electrolysis in D 2O as a cathode for 90 days and then as an anode for a further 83 days. The re is no evidence for the much larger amounts of He-4 observed by Arata and Zhang in similar experiments. However, a very large concentration has been found of He-3, 2.3 +/- 0.5 X 10(12) atoms/cm(3) standard temperature and p ressure that apparently can all be attributed to the decay of tritium produ ced during electrolysis. No direct production of He-3 can be specified, a r esult that is also different from the conclusions of Arata and Zhang. The H e-3 and tritium measurements and the results of a gas analysis using a Finn igan-type mass spectrometer show that at the end of the anodic electrolysis , the electrode void contained 5.8 +/- 0.7 X 10(13) atoms tritium in the ga s phase as HT, DT and T-2, and 1.7 +/- 0.3 X 10(15) atoms tritium in the aq ueous phase as HTO, DTO, and T2O. At this stage, the gas phase pressure was similar to 18.8 atm in a free volume of 0.6 cm(3) and the total mass of wa ter was similar to5.7 mg. The gas phase tritium value is viewed as a lower limit for gaseous tritium produced inside the electrode because some of tha t tritium must have been removed into the D2O electrolyte during the anodic episode. The He-3 and He-4 measurements were also made in the two samples of the Pd- black and in sections cut from the walls of both Pd electrodes. The H2O ele ctrolyzed samples did not show any evidence of unusually high He-3 and/or H e-4, but all the D2O electrolyzed samples showed clear evidence of He-3 fro m tritium decay. A stepwise temperature heating experiment performed with a 24.9-mg sample of the D2O Pd-black showed that the diffusion process for H e-3 can be described by an equation of the form D = D-0 exp(-U/kT) with an activation energy U of 1.1 eV It is also apparent that the He-3 from tritiu m is quantitatively retained in the Pd-black at room temperature.