Here the"isotope effect" is referred to the heat generated by palladium systems in the presence of deuterium, not hydrogen. Some researchers have associated this heating with a nuclear reaction in the Pd lattice (D-D fusion that produces 24.5 MeV of energy and helium gas) [1,2]. While some earlier experiments showed a correlation between the generation of excess heat and helium production as possible evidence of a nuclear reaction, the results of that research have not been replicated by the other groups and the search for radiation was unsuccessful. Therefore, the unknown origin of the excess heat produced by these systems was of great interest.
Our goal was to explain the mechanisms of heat generation in those systems as a result of exposure to deuterium gas. In order to do so we built two custom-made isoperibolic calorimeters that could operate at the temperature range 40-390C with baseline stable within 0.01 C. Stainless steel vessels containing palladium nano-particle material was pressurized up to 2000 torr, with bleeding line through the residual gas analyser (RGA) to analyse the chemical reaction products. The palladium nanoparticles were dispersed over zeolite and alumina powder using ionic exchange and wet impregnation methods.
No radiation above the background or alpha-particle emission was observed from the gas loading of Pd-impregnated material. A hydrogen/deuterium (H/D) exchange chemical reaction through the "spillover" was proposed to explain the excess heat generation phenomenon. As the chemical reactions are generally reversible we focused on proving that not only heating, but also cooling (as a result of the reverse D/H exchange) can be observed in our system. We have successfully demonstrated the reaction's going both ways. Moreover, we were able to eventually "kill" the effect by baking out the reactants (H2O/D2O), thus proving theconventional chemical nature of the "isotope effect".
 Arata, Y. & Zhang, Y., 2008. Establishment of the "Solid Fusion" reactor. J. High Temp Soc., pp. 85-39 Hioki, T. et al., 2009. Hydrogen/deuterium adsorption property of Pd fine particle systems and heat evolution associated with Hydrogen/deuterium loading. Proceedings of 15th International Conference on Condensed Matter Nuclear Science, pp. 88-93