The key properties of pool materials have been studied for intense implosion of cavitation bubble in order to give rise to the nuclear emission. The past studies treated this "bubble fusion" for a couple of special cases, while this paper takes the systematic searches, and clarifies the important roles of absorption efficiency of ultrasound wave, compressibility, surface tension, viscosity, number of D-ions, ionization energy. It is pointed out also that the dipole moment, the molecular structure (mass and size), and the vapor pressure are essential. The selection principles as well as the candidacies for the better materials are proposed. The reason why heavy water does not give rise to the nuclear emission is discussed. It is concluded that the phenomenon of "bubble fusion" is very rare to observe unless the matching contrivance between the irradiated ultrasound wave and the adiabatic bubble growth is undertaken. (C) 2003 International Association for Hydrogen Energy: Published by Elsevier Ltd. All rights reserved.