Emulsion Thickness Research Articles

Experiments on technology and performance of Lippmann-Bragg phase holograms

For many technical applications, Lippmann-Bragg phase holograms are interesting because of their wavelength selectivity and the theoretical possibility of obtaining reconstruction efficiencies near 100%. We performed experiments on such holograms using photographic emulsions. With commercially available plates having 7μm emulsion thickness we obtained reproducible efficiencies above 10% and very low light scattering, optimum exposure conditions to achieve this are described. The dependence of the reflection factor on wavelength and emulsion thickness is in agreement with theory. With our results an efficiency of 50~ can be predicted for the same emulsion but with a thickness of 20~m. This indicates that despite their high spatial frequency requirements, Lippmann-Bragg holograms can be superior to the more conventional transmission holograms.

Resolution in electron microscope radioautography.

An analysis of grain distributions around a radioactive line source (consisting of polystyrene-(3)H) showed that the shape of the distribution was independent of the factors that influence resolution, i.e. section and emulsion thickness, silver halide crystal, and developed grain size. These factors did effect the spread of the distribution, however, and thus the distance from the line source within which 50% of the total developed grains fell. We called this distance "half distance" (HD) and determined it for a variety of specimens. When grain distributions were normalized in units of HD, one could plot universal grain distributions for specimens with radioactive sources of various shapes. The use of HD and the universal curves in interpreting radioautograms is discussed.

Die Abbildungseigenschaften autoradiographischer Systeme

In autoradiographic transfer two characteristic ranges can be distinguished which result from the composed kind of dose function (e−kR/R2). In “photographic region” of transfer, i. e. when thickness of emulsion and object are comparable with the maximum range of beta particles, the influence of absorption or beta energy is predominant and that of geometry can be neglected. The autoradiographic transfer properties are very similiar to those of photographic transfer. In the “crossfire region” of autoradiographic transfer i. e. when the thickness of emulsion and object are very small compared with the maximum particle range, the influence of geometric parameters is predominant. High crossfire causes blurred images, typical for microautoradiography with nuclides of high energies. In addition to linear transfer of periodic and nonperiodic distributions of radioactivity, the nonlinear transfer is considered. The influence of exposure on contrast transfer and grain density is also considered. Contrast measurements, made by using 131I- and 32P-labelled sine wave gratings, are in agreement with the calculated contrast transfer functions.

Alpha Track Autoradiography of Sub-micron Aerosol Particles with the Electron Microscope

THERE are many problems in aerosol work in the nuclear energy field in which it is important to be able to distinguish radioactive from non-radioactive particles. This has led to the development of methods1 for track autoradiography of particles by transmitted light microscopy. Nuclear emulsions can give better resolution than that attainable with an optical microscope, and extension of techniques to electron microscopy is logical. But the gelatine which remains after photographic processing absorbs the electrons and limits the thickness of emulsion which can be used.

Photographic Relief Images*

A systematic study has been made of the formation of photographic relief images for sinusoidal exposures in the spatial frequency range 0 to 200 lines/mm. It is found that, for a given process and emulsion, the differential height of the surface relief between minimum and maximum density points is strongly dependent on frequency. For a given peak-to-peak density swing, the relief height is very small at zero frequency, builds up to a maximum at a spatial frequency which is inversely proportional to the emulsion thickness, and then declines slowly with increasing spatial frequency. The effect is explained in terms of the differential tanning action of the developer between high- and low-exposure regions. The effect has been studied as a function of several emulsion parameters, processing, spatial frequency, peak-to-peak density swing, and emulsion thickness.

Influence of emulsion thickness and absorption in hologram reconstruction

It is shown that absorption must be taken account of when reconstructing a thick hologram.

Hologram Copying by Gabor Holography of Transparencies

The copying of holograms by constructing Gabor type holograms from the originals is discussed mathematically. The analysis is based on plane wave expansions, and the paraxial approximation is not used. Two sets of double images of the original scene appear in the reconstruction process with the copy hologram when emulsion thickness is not important. The separation of the double images is equal to twice the separation of the two photographic emulsions during the copying process. The importance of the extra images is discussed and ways to eliminate them are described. Double images are not produced by copies of wide angle holograms with interference fringe spacing that is small compared to the emulsion thickness.

Influence of emulsion thickness in hologram reconstruction

A method of calculation which involves the emulsion thickness is described which permits one to determine the influence of the various parameters of the recording setup.

On the Distribution of AgBr Grains in Photographic Plates for Ion Detection in Mass-Spectrometers

Investigations have been carried out on the distribution of AgBr-grains in unexposed photographic plates (type Q2, Ilford Ltd.) used for ion detection in mass-spectrometers. Electron micrographs show that a large fraction of the grains protrude about halfway out of the gelatine matrix and that these grains are covered by a very thin gelatine layer on the side facing the ions. The mean projection area of the unexposed grains, the percentage of the plate area covered with unexposed grains, and the emulsion thickness have been determined. The shape of unexposed as well as exposed and developed grains is discussed. A model of the distribution of the AgBr-grains in the emulsion is presented.

富士γ線用バッジフィルムのβ線感度とβ線の被曝線量の評価

The sensitivities of Fuji Badge Film to β-rays were investigated using the isotopes, 35S, 185W, 204Tl, 32P, 90Sr-90Y and natural uranium plaque.Plane sources for exposure were prepared, and the contact radiography showed the uniformity of the source was within ±10% over the whole area, 5.5cmφ.The flux of β particles was counted with a G-M counter calibrated by 4π flow counter. The surface doses were calculated about the mean energy of β spectrum by Bethe-Bloch formula.The particle sensitivity was found to have the peak around 0.2 MeV in maximum energy which can be explained considering the relation between the range of β-rays and the thickness of emulsion coating.The dosage sensitivity was found to increase with β-ray energy and to be almost in flat maximum above 1.5 MeV in maximum energy.By using the results above, an example was shown how to estimate the apparent energy of incident β-rays and to evaluate the skin dose and the lens dose of eye with three plastic filters of JAERI Film Badge, Model III.

Resolution in contact microradiography.

It has been pointed out (Combée, Houtman and Recourt, 1955; Ehrenberg and White, 1957; Blackett, 1958) that the resolution in contact micro-radiography has up to now been limited by the thickness of the photographic material. Whilst the separate grains of a maximum resolution emulsion cannot be resolved by the optical microscope, the thickness of conventional emulsions is much greater than the depth of focus (less than 0·5 μ) of an immersion objective of high aperture. This prevents the microscope objective making the best use of the radiograph.

Boron-loaded photographic plates as detectors of slow neutrons

The variations with position in the plate of the emulsion thickness and of the number of slow neutrons recorded per unit area have been determined for a 10 in. × 8 in. × 100 μ boron-loaded plate that had been irradiated uniformly with slow neutrons. The measurements were consistent with a constant concentration of boron throughout the plate and upper limits were placed on possible variations. Comparative slow neutron flux measurements with disks of stripped emulsion from the same sheet should have a standard error of 3% at most.

Transition Effect of the Star-producing Radiation

To prove the existence of the transition effect of the star-producing radiation suggested by G. Bernardini1, an experiment relating to this question was carried out in the High Tatras in the winter of 1950. Six batches of Ilford C 2 plates with emulsion thickness of 200 µ were exposed during 45 days at Lomnický Stit (2,640 m.). One batch of plates was exposed without any absorber, while the others were placed under different layers of lead of increasing thicknesses from 1 cm. to 5 cm.

Cross-Section for Nuclear Disintegration Produced by Cosmic Rays

IT has been suggested1 that the cross-section for star production is proportional to the geometrical cross-section of the nucleus. In order to establish this by direct experiment, we have exposed some 'gelatin sandwich' plates for fifty days at a height of 3,650 m. These plates consist of four layers of Ilford C.2 Nuclear Research emulsion, 30 µ thick, separated by three thin layers of plain gelatin. This sandwich emulsion, coated on an acetate base, was supercoated with a 5µ gelatin layer. A second batch of plates with emulsion layers of 25µ was exposed for forty days. In order to determine the thickness of the gelatin layers (excluding the super-coat) relative to the normal emulsion, we have measured the ratio of the projections in the plane of the emulsion of track length to gap length for those tracks which pass right through the sandwich emulsion. The gaps in the tracks occur when the ionizing particles pass through the gelatin layers. From these measurements on 300 tracks of length greater than 200µ we conclude that in the plates so far examined the mean gelatin thickness : mean emulsion thickness equals 9·2 per cent.

The Effect of Light-Absorption on the Shape of the Photographic H and D Curve*

A theoretical treatment is first given to show how the gamma-value of the photographic H. and D. curve varies with the light absorption in an emulsion. The treatment is based on the idea that an emulsion can be subdivided into a number of layers and that the total H. and D. curve of the entire emulsion can be obtained by summation of the elementary H. and D. curves for the separate layers. The absorption of the emulsion is expressed in terms of the ratio, logIT/IB, where IT and IB represent the intensities of photographically active light in the top and bottom layers, respectively, of the emulsion. Theoretical curves giving γ/Dmax as a function of the ratio, logIT/IB, are given for several widely different types of blue-sensitive emulsions. The curves are compared with experimental measurements carried out by varying the wave-length of the exposing light. The experimental results are found to be in fair agreement with the theoretical curves.The quantity, logIT/IB, can be varied also by varying the emulsion thickness, keeping the absorption coefficient of the emulsion constant. Under these conditions, this theory gives curves for the variation of γ/Dmax as a function of emulsion thickness. The curves are accordingly tested, using different layer thicknesses of emulsion, and the results are again found to be in agreement with the theoretical curves.Finally, it is shown, by assuming that the maximum density of an emulsion varies linearly with emulsion thickness, that curves predicting gamma as a function of emulsion thickness can be obtained. Curves of this type are derived and tested by experiment.

Safeguarding the Storage of Photographic, Motion Picture, and X-Ray Films

This paper outlines briefly the hazards connected with the storage of photographic, motion picture, and X-ray film of the nitrocellulose variety, and suggests precautionary measures to be taken with these materials. The various kinds of film are described and the effect of heat is discussed, with particular reference to the toxicity and explosibility of the gases developed. Recommendations for proper storage and handling are made, including suggestions for location and construction of the vaults which should be used where any considerable quantity of film is to be stored. Description of film Photographic film consists of a base or support on which is coated a light-sensitive emulsion. This emulsion is a gelatin solution containing very small crystals of silver halide (usually the bromide with a small percentage of iodide), which are formed in the gelatin solution by the reaction of silver nitrate with potassium bromide and iodide. Potassium nitrate, also formed in this reaction, is removed from the emulsion before coating. Photographic processes following exposure in the camera convert the silver halide which has been affected by exposure to light to metallic silver in a very finely divided state and also remove all of the unused silver halide. The metallic silver image is all that remains in the gelatin after this process is completed. For the base either of two materials is used, a solid solution in camphor of nitrocellulose, which is highly flammable and gives off toxic gases on decomposition, or cellulose acetate, which has a flammability comparable to that of ordinary paper. Film made from cellulose acetate is called “safety film” and is not particularly hazardous in storage. Its use wherever possible is, therefore, to be highly recommended. Films for various uses differ in size, thickness, and amount of emulsion. Photographic film for amateur use is generally thin, small in size with a thin coat of emulsion on one side, and with or without gelatin on the other. Most large commercial photographic film is heavier and coated on both sides, to prevent curling. Motion picture film is generally of the same thickness (about .006 inch) and, except for some of the color films, is coated on one side only. Except for dental films, which are small, thin, and usually mounted, X-ray films are relatively thick and have heavy coats of emulsion on both sides. The latter may be as much as 10 per cent of the thickness of the film. The largest size of film generally used in X-ray work is about 14 by 17 inches and .008 inch or more in thickness. Effects of heat Nitrocellulose, which forms the base of “nitrate” films, is a substance prepared by treating cellulose made from cotton with sulfuric and nitric acids. It is thus essentially similar to celluloid and guncotton, being intermediate between these two in nitrogen content.