PNNL

Abstract

We made measurements of He-3, He-4 and H-3 in a sample with 2.7% of the gas from the interior of an Arata-style hollow palladium electrode charged with ~ 5 g Pd-black which had undergone electrolysis in D-2O as a cathode for 90 days and then as an anode for a further 83 days. There is no evidence for the much larger amounts of He-4 observed by Arata and Zhang in similar experiments. However, we found a very large concentration of 2.3 +/- 0.5 x 10^12 atoms/cc STP He-3 which we believe can be attributed to decay of tritium produced during electrolysis. We can?t specify any direct production of He-3, a result which is also different from the conclusions of Arata and Zhang. The He-3 and tritium measurements and the results of a gas analysis using a Finnigan-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 gas phase as HT, DT and T-2, and 1.7 +/- 0.3x10^15 atoms tritium in the aqueous phase as HTO, DTO and T-2O. At this stage, the gas phase pressure was ~18.8 atm. in a free volume of 0.6 cc, and the total mass of water was ~ 5.7 mg. The gas phase tritium value is viewed as a lower limit for gaseous tritium produced inside the electrode because some tritium must have been removed into the D-2O electrolyte during the anodic episode. He-3 and He-4 measurements were also made in the two samples of the Pd-black and in sections cut from the walls both Pd electrodes. The H2O electrolyzed samples didn?t show evidence of unusually high He-3 and/or He-4, but all the D2O electrolyzed samples showed clear evidence of He-3 from 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 He-3 can be described by an equation of the form D = D0 exp(-U/kT) with an activation energy U of 1.1 eV. It is also apparent that the He-3 from tritium is quantitatively retained in the Pd-black at room temperature.