AgBr Emulsion Research Articles

Transitions in Crystal Habit in Silver Bromide Emulsions

AbstractA series of AgBr emulsions has been prepared under controlled pAg conditions from a monodisperse “seed” emulsion, concentrating in those pAg regions where there is a transition from one crystal habit to another. The transition point between cubic and octahedral forms is defined as that tetradecahedron which has equal surface areas of (200) and (111) faces. The second transition point is that pag where precipitating AgBr is diverted to the formation of twinned crystal under the conditions of the experiment. A correlation was made between the observed transition points and the concentrations of the silver complexes in solution.The effect of crystal habit on sulphur sensitization was studied lIsing a set of cubic, tetradecahedral and octahedral emulsions having the same average grain volumes. The tetradecahedral emulsions were found to be intermediate in their behaviour between cubes and octahedra. The thiosulphate additions required for maximum speed were in the order: octahedral < tetradecahedralec...

The Influence of Iodide on Photographic Properties of Homogeneous AgBr Emulsions

AbstractIntroduction of iodide in AgBr emulsion grains results in several effects. One of them, a change of size distribution, can be prevented by preparing emulsions different in iodide content but equal in grain size and with a narrow size distribution. It is demonstrated that the number of photoelectrons captured in the mass of mixed crystals, prepared by introducing iodide at initial precipitation, is strongly increasing with increasing volume of the grains. The probability of surface latent image formation is asymptotically approaching zero with increasing I/Br ratio.It is assumed that the size and the composition of an iodide-containing core determine the internal latent image formation in these grains.

Formation and Properties of Sub-Image and Latent-Image Silver Specks Part IlI: Properties of Silver Sub-Specks Produced by Radiation

AbstractSub-image specks have been produced in monodisperse AgBr emulsions by a weak pre-exposure with y-rays, with electrons, and with light at 77 K as well as at room temperature. Coverage of the pre-exposed grains by precipitation of additional AgBr onto the grains or oxidation of the sub-specks at the crystal surfaces led to emulsions which now contained the sub-specks only in the interior of the grains. Upon an image-wise second exposure and surface development all these emulsions showed an increase of the sensitivity in the threshold region of the characteristic curve which can be explained only by an over-all increase of the quantum yield due to capture of holes by the sub-specks. These sub-specks consequently are not precursors of latent image specks and they do not influence latent image topography.Under certain conditions in addition to the former another type of sub-specks (presumably larger in size but still nondevelopable) can be found which do influence latent image topography, which, hence,...

Dielectric loss measurements of AgBr (100) emulsions

Dielectric loss measurements of AgBr (100) emulsions

Dependence of Light-induced ESR Spectra of Dyes Adsorbed by AgBr Emulsion Grains upon Emulsion Factors

Dependence of Light-induced ESR Spectra of Dyes Adsorbed by AgBr Emulsion Grains upon Emulsion Factors

The Mechanism of Sulfur Sensitization in Fine Grain AgBr Emulsions

The degrees of sensitization of octahedral AgBr grains by halogen acceptors (acetone semicarbazone and sodium nitrite) increased as the size of the grains decreased. In fine grain (0.2 μ) AgBr emulsions, the sensitization by the halogen acceptors and sulfur sensitization were competitive. These results have been thought to support the view that sulfur sensitization in fine grain AgBr emulsions is in part due to the halogen acceptance of Ag2S specks formed during digestion.

Effects of Dyes upon Amount of Developed Silver of Cubic and Octahedral AgBr Emulsions Fogged by Reducing Agents

Effects of Dyes upon Amount of Developed Silver of Cubic and Octahedral AgBr Emulsions Fogged by Reducing Agents

Determination of Energy Levels in AgBr Emulsion Crystals from Optical Measurements

AbstractThe width of the forbidden energy gap and the position of the top of the valence band cannot be determined as precisely for AgBr at room temperature as for many ionic crystals. Some choices for these parameters, which are necessarily arbitrary, are given here to provide good agreement with the variety of optical and photographic measurements made with small AgBr crystals. Changes of the energy levels with temperature, iodide incorporation, and the presence of surfaces were measured. Surface states located at lattice ions are too shallow to act as electron traps or to be detected in our optical absorption experiments. Luminescence of pure AgBr was investigated at 77°K. The luminescence centre is at an electron trap which is 0.75 eV below the bottom of the conduction band. This centre, which is stable when formed by exposures at 77°K, is the same as the unstable latent image centre at room temperature investigated by Webb and is thought to be a single electron trapped at two silver ions. The stable ...

Holographic gratings of arbitrary loss: Theory and experiment

Thick lossy dielectric gratings have been analyzed using a Raman-Nath formalism modified to incorporate losses. Four second order coupled-wave equations are retained for accurate computation of the zero; first-, and second-order diffracted beams for a multitude of practical cases. Significant differences are found in comparison to computations in which only two coupled waves are retained. The entire range of losses and thicknesses encountered for holograms in AgBr emulsions has been studied using this unified approach.

A Kinetic and Sensitometric Investigation of Sulphur Ripening

AbstractThe kinetics of Ag2S formation during thiosulphate digestion and the development of speed and fog have been investigated with monodisperse AgBr emulsions with either cubic or octahedric grain shape. Certain characteristic differences in the behaviour of the two different crystal types have been observed which are explained by application of general theories of crystal growth. According to these theories Ag2S formation proceeds at (100)-faces relatively slowly via two-dimensional nucleation processes. The reaction is rapid at (111)-faces and proceeds here according to a first order reaction scheme. A calculation model for the reaction at (100)-faces has been developed which agrees well with experimental results. The photographic properties upon thiosulphate digestion depend also on the crystallographic shape of the AgBr grains. The observed desensitization of AgBr octahedra and the increase of speed of AgBr cubes during ripening can be explained by differences in the dispersity of the sensitivity c...

Low-intensity reciprocity failure of a AgBr emulsion: effect of halogen acceptors.

Low-intensity reciprocity failure (LIRF) of a silver bromide emulsion was drastically reduced, but not eliminated, by the addition of a halogen acceptor, such as acetone semicarbazone, before coating. The remaining failure has a slope of approximately minus unity on an isodensity plot of log intensity vs log intensity × time. This is interpreted as exemplifying two types of LIRF, an intergranular type stopped by a sufficient amount of halogen acceptor, and an intragranular type caused by the thermal instability of a photolytically produced silver atom. A LIRF curve was also obtained in terms of the number of absorbed photons necessary to make a grain developable. These data suggest that considerable recombination occurs before nucleation of the latent image. The quantum efficiency of formation of print-out silver is 0.2 silver atom per absorbed photon. This value indicates that growth of the latent image after nucleation is efficient.

On the Crystal Habit and Particle Size Distribution of AgBr Emulsions Prepared in the Presence of Synthetic Colloids

AbstractAn account is given of the further experiments concerning the particle size distribution and crystal habit of AgBr particles in emulsions prepared in the presence of synthetic colloids such as polyacrylamide. paly-N-methylacrylamide and polr-N,N-dimethylacrylamide. The data have been obtained by examination of the emulsion with on electron microscope.

Radioactivity produced in Discoverer XVII by November 12, 1960, solar protons

Scintillation-spectroscopy measurements on a AgBr emulsion block from Discoverer XVII, which was flown during a period of high solar cosmic-ray activity on November 12, 1960, reveal a gamma spectrum attributable to 8.4-day Ag/ sup 106/. The disintegration rate, corrected to a probable production time of.2200 UT, November 12, 1960, is 14 dis sec/sup -1/. If one assumes a (p,pn) cross section of 100 mb, and applies the thin-target formula for production of radioactivity, this corresponds to a total proton dosage of about 1.6 x 10/sup 8/ protons cm/sup -2/ within the emulsion, and to a value of 16 rads radiation dosage. An attempt to measure the gamma spectrum of 40-day Ag/sup 105/ was unsuccessful, allowing the assignment of an upper limit on the disintegration rate of 1 dis sec/sup -1/ at the time of production. A search for 1.3-year Cd/ sup 109/ was unsuccessful. (auth)