Mosaic Structure of Photographic Emulsion Crystals
CRYSTAL imperfections play an important part in present studies of the formation of the photographic latent image. In large silver bromide crystals it has been shown1 that silver prints out along individual dislocation lines. Little direct evidence has yet been given on defects within the small grains of photographic emulsions, since neither light microscopy nor electron microscopy has yet proved effective in this field.
Electrical Measurements on Photographic Emulsion Grains. II. Photoelectronic Carriers
Pulses of electric field applied to silver bromide grains of a photographic emulsion at short time intervals after the application of short light flashes cause displacement of photoelectrons and holes if their lifetimes are greater than the delay interval. The asymmetry in the location of the photoproducts—microscopically visible silver and bromine or developable latent‐image specks—is an indication of the fraction of carriers free at the time the electric field is applied. As the delay interval is varied, the decay of the number of free carriers may be followed. In the emulsion system studied, the number of photoelectrons was found to decay approximately according to a 1/(1+αt) law, falling to half the initial value in 0.25 μsec. The lack of a dependence on intensity or temperature is taken to indicate temporary trapping in a distribution of shallow traps, perhaps at the grain surface. The number of free holes decays by an exponential law, with a mean lifetime of about 15 μsec. Indications are that hole ...
Time behavior of gas pressure and PD activity in insulation cavities under AC voltage
In the framework of developing defect-based life models (i.e. the life model of partial discharge-induced damage growth from a micro-void in polymer matrix), ageing tests were performed on PE layered specimens with artificial cavities under constant gas pressure and constant gas volume conditions, respectively. Time behavior of the discharge repetition rate and amplitude were recorded and compared under these two conditions. Results show that pressure variation has little influence on PD activities at constant gas volume. Under constant gas pressure, the evolution of gas volume has similar characteristic to the product of discharge amplitude and repetition rate.