Observation of the development process by positron annihilation

The effect of the free volume hole in photographic gelatin in the developin g process was studied by positron annihilation spectroscopy (PAS) in this p aper. A new mechanism was proposed to account for the formation of the silv er filament during the development. The application of PAS introduced a new research technology and method into photographic science. The results show ed that the average radius of free volume holes was maintained constant for the whole of the development. The free volume hole in gelatin restrained t he reduction process of the silver ion in the spaces with different electro n cloud densities. This might be one of the reasons for silver filament for mation. Because of the complexity of the structure and composition of the m acromolecule of photographic gelatin the free volume holes distribute in a disorderly and random manner in gelatin. It is probably the randomness and disorder that make the image silver become a loose spatial structure of sil ver filaments twining into balls.