In the model two states for accumulated hydrogen (soluble and molecular) are suggested. Under ion irradiation three reactions (events) take place: recombination of soluble hydrogen on irradiated surface; accumulation of molecular hydrogen; molecular percolation. The first reaction describes recombination under and after irradiation. The second reaction describes molecular hydrogen accumulation as statistical packing of the “traps”. The third one describes molecular percolation as a capturing of one more incoming particle in already packed “trap”, that is accompanied by the reemission of H2, by the devastation of the “trap”, and by the increasing of the irradiated surface. Under steady state for molecular accumulation and surface formation, recombination flux approaches the value of incoming flux and no percolation acts take place. Molecular accumulation approaches the steady state prompter than surface formation. The cross sections for (helium/hydrogen) emission changing over hydrogen to helium beam and vice versa were calculated. Simulation of the model coincides with the experimental data of hydrogen retention, reemission, and post-implanted release.
