The radiation-chemical yield of the molecular hydrogen received under the influence of gamma quanta (60Co, P=22Rad/s, T=300K) to liquid water of constant volume (V=5 ml) in the process of a radiolysis of water at change of weight (m=0.01; 0.02; 0.06 and 0.12 g) and sizes of silicon particle (d=50 nanometers) is defined. It has been revealed that at increase in mass of the silicon added to water the radiation-chemical yield of the molecular hydrogen received in the process of a water radiolysis grows in direct ratio (m<0.02 g) and depending on the size of particle after a certain mass value (m>0.02 g) the stationary area is observed. In the Si+H2O system the maximum radiation-chemical yield of molecular hydrogen is equal to 10,9 molecules / 100eV at the sizes of silicon particle d=50 nanometer respectively. The mechanism explaining the received results is offered.