Latent Image Formation Research Articles

Monte Carlo Simulation of Latent Image Formation— Modification of the Loss Processes

AbstractA detailed analysis of the Bayer-Hamilton model for computer simulation of latent image formation is carried out. It is shown that the model contains some tacit assumptions which seem to lack straightforward physical explanation. The problems associated with the properties of the holes and the process of their removal are particularly not clear.The above difficulties are avoided by the complemented simulation scheme offered here. It changes the loss channels and introduces bromine nucleation.The results obtained by the complemented simulation scheme are compared wtih experimental data. An attempt is made for their physical interpretation.

A Theory of Latent Image Formation Based on Thermodynamic Elastic Energy Considerations

AbstractThe main theories of Latent Image (L.I.) formation1-2 assume eoulombic forces to be the major (and only) forces in the production of the L.I. The present theory introduces the strong elastic forces in the silver halide crystal and their effect on LI. formation. L.I. formation is considered to be a two-stage process as follows:Stage 1. Photo-electrons produced by photon absorption are attracted electrostatically by interstitial silver ions so that isolated silver atoms (Ag°) are formed.Stage 2. The individual (neutral) Ag° atoms diffuse through the crystal (with a drift velocity determined by elastic interactions) and aggregate at locations of minimum elastic energy, where they form a stable aggregate Ag°n.The locations in which the Ag° atoms can aggregate are discussed in terms of the thermodynamics of second phase formation. The theory explains satisfactorily the important role of crystal imperfections such as dislocation lines, impurities and chemical sensitization.

Latent-image and fog formation in silver halide microcrystals by the action of a sequence of light and electric pulses

The effects due to the action of a 50 ns light pulse followed by a delayed 300 ns electric field pulse of high strength (1.5 to 3.5 MV/cm) are investigated in AgHal photographic emulsion microcrystals. Evidence is given that the latent-image amplification by field action results from avalanche multiplication of photogenerated carriers in AgHal. The limit of field efficiency is shown to be determined by rapid fog increase, due to field tunnelling of electrons from surface traps irrespective to light exposure. [Russian Text Ignored].

Trapping and recombination cross sections for electrons in silver halide

Abstract In a currently accepted model for formation of the photographic latent image, the photoefficiency is determined by the relative cross sections for electron capture at a silver site and at a bound hole. Comparison with sensitivity data shows that these cross sections are nearly identical. The two types of competing centers have sets of shallow coulombic levels with equal initial cross sections, but re-escape of the electron from these levels should be more probable than transition to the deep level, and it is not clear why the final capture probabilities should be equal for the two very different centers.

Influence of Temperature on Spectral Sensitization of AgBr Layers*

AbstractThe effect of temperature of exposure on the spectral sensitization of vacuum deposited AgBr layers was studied. A series of cyannine dyes with different reduction potentials ER. varying from -0.54 to -1.12V. was selected. It was found that on varying the temperature from 273 to 130°K the change of the efficiency of dye sensitized latent image formation does not show any significant difference between dyes with different ER(from -0.54 to - 1.12V).An attempt is made to correlate the experimental results with the theories of spectral sensitization.

Physics of latent image formation in silver halides

Physics of latent image formation in silver halides

Statistical time lag of gas discharge in electrostatic recording

AbstractElectrostatic recording is applied widely to facsimiles and printers because of its high speed and high resolution. the time lag in gas discharge formation causes dots to be missed, which must be improved for high‐speed, high resolution recording. We tested the latent image formation by using an aluminum drum coated with a dielectric film uniformly charged to positive potential and a pin electrode. the effects of the pin electrode material, the recording pulse repetition period, and the recording voltage on the statistical time lag on initiating discharges have been investigated. the following results were obtained: (1) A phosphor bronze electrode causes the smallest time lag, followed by nickel and tungsten. (2) the logarithm of the mean statistical time lag is proportional to that of the repetition period. (3) the logarithm of the mean statistical time lag is inversely proportional to the air gap electric field. (4) When the recording pulsewidth is larger than 15 μs for a gap field of 55 MV/m and a recording pulse period of 10 s, the dots missing probability becomes less than 1%.

A Computer Simulation of Latent Image Formation in Photographic Emulsion by a Monte Carlo Method

A digital computer analysis has been made of photon absorption, chemical sensitization and latent image distribution in a silver halide photographic emulsion, using the Bayer Hamilton model but with a different approach in treating the positive holes.In discussing the effect of sulphur sensitization it has been assumed that silver sulphide molecules can play a dual role in latent image formation, undergoing partial thermal dissociation to increase both the number of electron traps by providing more interstitial silver ions and that of positive hole traps by forming AgS-. The increased interstitial silver ion concentration has also been supposed to lead to an increase in the stability of single silver atoms. As to gold sensitization, it has been assumed that the main effect of gold is to enhance the developahility of latent image centres.Parameter values for simulation under various conditions of chemical sensitization have been calculated, based upon the above assumptions. The results have, as expected, reproduced in many respects those shown by experiments. Finally, a relation between the concentration of interstitial silver ions and the sulphur content in the emulsion grain has been derived.

Effects of µs Pre-Exposure on Latent Image Formation in 103, 103a and I-N Kodak Spectroscopic Plates: Results and Limits

AbstractThe sensitizing effects of pre-exposure and their relationship with the formation, in the pre-exposed emulsion, of a sub-developable stable latent image have been examined. Having as a general scheme the theories of latent image formation, the authors have checked the possibility of improving the ratio of sub-developable to developable stable latent image by using a us pre-flashing technique.Experiments made on some types of Kodak plates have shown that this improvement can be attained at least for small increments in density, but only with “non-a” emulsions. In particular 103-O plates can reach almost the same sensitivity as l03a-O.No “non-a” emulsions type has been found which, using this technique, could surpass the sensitivity of the “a” plate with similar characteristics.

Study on the Initial Stages of Latent Image Formation by Multi-Flash Method

Study on the Initial Stages of Latent Image Formation by Multi-Flash Method

Latent-Image Formation: The Contribution of the Research Division, Kodak Limited, Harrow

AbstractA review is presented of work concerned with the problems of latent-image formation in silver halide systems which has been published by members of the Research Division,Kodak Limited, Harrow, over a period of more than 40 years.

Photothermochemical process in ammonium perchlorate crystals: I

It is shown that during uv irradiation of ammonium perchlorate (AP) crystals through an opaque stencil a latent photographic image of the stencil arises in their volume. This image can be developed on a crystal surface by heating at 230°C. The induction period of low-temperature decomposition (LTD) of polycrystalline AP depends linearly on the dose of preliminary uv irradiation: τ LTD = τ 0 − A log ( I · t irr). It is suggested that the mechanism of latent image formation consists of generation in the crystal volume of the chlorine oxidic products of AP photolysis—mainly ClO − 3 ions. Based on these considerations one is able to explain in a consistent way all the experimental data obtained: τ LTD dependence on dose, dependence of thermal development time on the concentration of proton-active additives, dependence of the image optical density on crystal depth, etc.

About the Nature and the Role of the Sensitivity Speck Formed during Gold Ripening

AbstractAfter a critical survey of recent literature about the present state of the mechanism of gold sensitization, there are presented new experimental results obtained by tracer techniques using 1,8Au, which lead us to believe that during a gold + sulphur ripening in addition to gold sulphide or silver gold sulphide metallic gold specks are formed. These specks are to be considered as real sensitivity specks.It seems likely that the function of gold in latent image formation is more related to better catalytic properties and better stability of the latent silver specks than to an increasing efficiency of the electron trapping at the grain surface.

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.

The Change in the Concepts and Outlook of the Photographic Scientist : 1928-1978

In a lecture to mark the 50th anniversary of the founding of the Research Division of Kodak Ltd., at Harrow, the author reviews the changes in the state of the photographic sciences between 1928 and 1978. The topics considered include: sensitometry, tone reproduction and image structure, sensitivity and latent image formation, spectral sensitization, and development.-Editor.

Chemical Sensitization of Evabrated Silver Bromide Layers

AbstractIt is demonstrated that evaporated silver bromide layers can be topologically chemically sensitized by conventional emulsion methods. These lead to a considerable increa e in toe ensitivity and even more in contrast for the formation of superficial latent image, in particular for long-time exposures. The so-called chemical sensitization by Ir-Au dips at RT does not change the topography of the latent image: it still forms in the interior of the crystals, very inefficiently for long exposures at low intensity.

PQ Synergism in Physical Development

AbstractIt is demonstrated that evaporated silver bromide layers can be topologically chemically sensitized by conventional emulsion methods. These lead to a considerable increa e in toe ensitivity and even more in contrast for the formation of superficial latent image, in particular for long-time exposures. The so-called chemical sensitization by Ir-Au dips at RT does not change the topography of the latent image: it still forms in the interior of the crystals, very inefficiently for long exposures at low intensity.

Studies on Formation of Latent Image and Print-out Image (I)

Studies on Formation of Latent Image and Print-out Image (I)

On the formation of silver specks in silver halide crystals

This theoretical study summarizes ionic and electronic processes in AgBr crystals and the influence of its results on photographic process. It deals with the importance of surface generated interstitials which Gurney and Mott left untouched because of the non-availability of sufficient data at that time. The magnitude of various parameters,e.g., mean intra-electron-ion distance in a latent image site, the rate of neutralization of Ag+ ion with trapped electron and capture cross-section for combination of Ag+ ion with the trapped electron, etc. (as desired for understanding the theory of photographic process) are calculated at different temperatures. The results when used in our earlier papers (Singh and Sharma, 1974 and 1975, and Singh 1975) for calculating charged particle track characteristics theoretically were found to give good agreement with the published experimental data (Della Corteet al 1953 and Dyer and Hechman 1967). A model for the mechanism of latent image formation (silver speck) is discussed.

The Role of Gold in Sulphur-Plus-Gold Sensitization

Experimental data are reviewed which show that the internal-image speed of an emulsion optimally sensitized by sulphur-plus-gold is usually lower than that of the same emulsion optimally sensitized by sulphur alone. This demonstrates that one function of gold sensitization when combined with sulphur is to increase the probability of trapping of electrons at the grain surface, and thus to improve the efficiency of formation of surface latent image.