PURPOSE: To semipermanently maintain the high-pressure and high-density state of the title aggregate by utilizing the physical and chemical characteristics of hydrogen isotope, etc., in the solid material such as the diffusion coefficient, solubility, and recombination of molecules due to a reactions between atoms for generating the internal pressure to realize the state.

CONSTITUTION: When the number density of the aggregate is increased, the aggregate is one-, two- or three-dimensionally arranged in order or irregularly distributed. When such a state is formed, an elastic stress field in the intermediate region between the aggregates is reduced, plastic deformation and rupture are hardly produced, and hence the internal pressure of the aggregate can be substantially increased. Accordingly, a high-strength solid material such as diamond and a thin film-shaped solid material mixed with a large amt. of hydrogen isotopes during the production process are used to control the temp., injection rate, injection amt, etc., of the solid material when the hydrogen isotope is injected. By this method, the internal pressure of the aggregate can be set at an optional value up to the upper value limited by the plastic strength or breaking strength.