US2666144A - Electroradiography - Google Patents

Description

Jam 1954 R. M. SCHAFFERT ETAL 2,666,

ELECTRORADIOGRAPHY 2 Sheets-Sheat 1 Filed Feb. '2, 1950 FIGURE JNVENTORS Roland M. Schoffer'r Roberr C. McMqster BY WiHiomE. Bjixby MM. .%euem Ja AGENTS.

12, 1954 R. M. SCHAFFERT ET AL 2,666,

ELECTRORADIOGRAPHY Filed Feb. 2, 1950 2 Sheets-Sheet 2 FIGURE 3 FIGURE 4 INVENTORS Roland M. Schuffert Roberr C. McMclster BY William E. Bixby M, ymm 13 J4, AGENTS.

Patented Jan. 12 1954 UNITED stares *OlFlCE EDEGTRORADIOGRAPHY- Roland M...'Schaffr.t, Robert C..McMaster and William E. B'ixby, Columbus, Ohio, assignors,

by mesn'eassignments, to'The' Battelle Development Gorporation, Columbus, Ohio, a corporation of Delaware ApplicationFebruary 2, 1950, Serial No..142,0'24

3*01ai1'ns. (Cl. 250 -65 1 This invention relates to electroradiography; an electrical method for preparingradiographic images produced by penetrating radiation.

Ittis an object of this inventionto provide an electrical method for. producing radiographs which'is rapid and provides. forthe completionsidered in the light of the attached drawings resentative of the electroradiograph obtainediim such test.

Referring now more particularly toeach of. the drawings, it will be seen that in Figure 1 a sensitive plate i'l' isbeing electrostatically charged by corona discharge from asensitizingwire. l2. Such sensitizing or dischargewire I2 is shown supported by an insulating frame I3Lfixedto a 'supportingtable or bench 15. Also illustrated schematically is a high-voltage source 16 for en.- er'gizing the corona discharge wire 12;

In Figure Zis shown, for illustrative purposes, :a particular arrangement which may be used for exposing the sensitive plate to the X-ray radiations. In this particular set-up the sensitive plate; ll isshownin place in aplateeholder 2| which should be oisuch material as not to? absorb 'theX-rays. Plate22 is a lead plate for shielding purposes. A source 24 of X-rays is shown schematically while the remainder ofjthe drawing is in section. Anarticle; 215 being exam ined isrepresented here as a meta1' sandwich made up oi suc-cessive layersof metal as will be more fully'described in connection withfigure 4. Itwvill'beunderstcod, of course; thatthis article might be any object which it'isdesired to X-l'itY.

"Figure 3 illustrates two of" the waysxinwhich the-electrostatic imageproduced on plate M by an exposure processsuch as illustrated in Elgas illustrated in Figure 1.

2 1.11132 may bedevelopecl. In the examples shown the plate, I1 is placed in a tray til. Stops 3"l-'3l are-positioned in the bottom of the tray'to hold. plate I! inplace during the process. A suitable developer 33 is flowed. back and forth across theplate H by tipping tray 39 first; one wayand then the other; As will be pointed out. later the developer'particles 3-3 adhere to those areas of plate H which have. an electrical chargeresiding thereon. In (D) it is illustrated how plate H may be placed with its sensitive face down over a chamber in acontainer 35 wherein an atmosphere saturated with developer particles is maintained. An agitator 31, or similar. device, may be provided for the purpose of circulating and stirring up the developer particles. Agitator 3l'may be driven by a' suitable motor, not'sho'wn. Here. again developer particles striking charged areas will adhere thus making visible the image produced by the exposure step.

Figure ishows a specimen used in tests to determine contrast sensitivity for the process. The

specimen consisted of a metal sandwich made up of three layers of metal (alminum was used) 40, 4!, and 4.2. In the middle layer ti were circular hol'esoi, varying diameters as indicated at, M, 45, 45, 41, and 4%. In part (b) of thefigureis a pictorial representation of the electroradiograph obtained when using such specimen and illustrating how the regions of lesser thickness are, indicated by white, or lighter colored areas, on the 'electroradiograph.

In general, this invention relates to a dry, electrical method for producing images creatediby penetrating radiations.

An important factor in the present method is the sensitive plate which is used in carrying out the various steps of the invention. This. plateconsists of a conductive backing plate upon which a layer of semi-conductive material is coated. The manner of preparation of suchlplates forms no parttof the present invention and will not he described here except to mention some materialsL which. are" satisfactory as coating materials. These include selenium, sulphur; anthracenamixtures of sulphur and anthracene; mix-- tures of selenium and sulphur and other materials sensitive to penetrating radiations.

The firsttstcp in the process of the present invention is to provide an electrostatic charge on the surface of the sensitive plate. is preferably accomplished by subjecting theplate to a corona discharge from thin wires or-needles Other methods. are

by light.

terposed between the uniformly charged sensi tive surface and the source of the radiated energy. It will be understood that the'term penetrating radiation as herein employed relates to X-rays. gamma rays, Grenz rays and any other penetrating electromagnetic wave radiation capable of exciting suitable semi-conductors to a state of increased conductivity. The term may be further defined as radiation capable of penetrating a layer of matter, no matter how thin, which is opaque to ordinary visible light. The object to be radiographed may be suspended in any desired manner above the sensitive surface, or otherwise positioned between the radiation source and the sensitive surface during the exposure step. Arrangements may also be provided wherein the radiations pass; through a hole in the plate, strike the test object and are reflected back to the plate. According to well-known techniques provision may be made for either the object and/or the radiation source veloper powder with a granular carrier material produces a good combination for developing the radiographic images. Figure 3 illustrates two ways by which development may be achieved.

The visible image formed by the developing or dusting process may be inspected at once. However, a permanent copy of the image may be obtained in a few seconds and it is often desirable to obtain such a copy in addition to inond material.

spectingthe original image visually. The obtaining of. a copy may be accomplished in numerous ways. For example, an adhesive coated sheet may be pressed against the powder image bearing plate and transfer of the powder particles thus effected. Chemical transfer methods involving solvents, etc., are also convenient. A preferred method, however, comprises contacting the image bearing plate with a sheet or material to which the image is to be transferred and subjecting such assembly to a corona type discharge which will spray electrostatic charges onto the transfer material. By electrostatic action the powder image is transferred to the sec- This may be accomplished by the identical device shown in Figure 1. The transferred image may be rendered permanent by fusing or by chemically fixing to the transfer ma- I terial.

to move so as to provide clear images, to provide? two or more stereoscopic views, to permit radiographing the object from two or three mutually perpendicular directions, or to permit other desired views. Arrangements wherein the sensipossible. In case an extremely sensitive material is used, it may be necessary to perform the exposure step in the dark, since many charged It will be understood also that electrostatic scanning methods may be adapted to reproduce the electrostatic image pattern created during the exposure step. This may be accomplished by passing a scanning head over the sensitive surface bearing the charge pattern, whereupon semiconductive materials are readily discharged For example, a charged seleniumcoated plate should be exposed to the penetrating radiations in darkness, while a charged anthracene-coated plate may be so exposed in the light.

The step of exposing the charged, sensitive surface to penetrating radiation through the ob- I ject being tested, or radiographed, will produce a condition on the sensitive surface wherein those areas which have been subjected to high intensities of the radiations will become discharged, while other areas will be only partially discharged, in accordance with the amount'of penetrating radiation which has struck there.

Since the amount of energy reaching the plate will depend upon the amount absorbed by the object being radiographed, and since the amount so absorbed will be related to the thickness of the object at various points, to the composition of the object, etc., it will be apparent that a charge pattern will be formed on the sensitive surface wherein the charge pattern conforms to a positive image of the object being radiographed.

The next step in the process of the present invention is to develop this charge image and make it visible.

The development step in this process is preferably done by contacting the charge image with a suitable powder or other dry developer. This may be accomplished, for example, by flowing the developer powder back and forth across the charged surface. It will be found that the de veloper particles adhere to the charged areas on the plate. Various resinous powders have been found satisfactory for this developing process,

and it has also been found that a m ture of dethe image may be reproduced on a screen in response to the signals from the scanning head.

It will be apparent that a new, rapid and useful method for obtaining radiographs has been set forth in the description above. A further considerationof the requirements and properties of radiographic methods and images will serve to further demonstrate the advantages and desirabilities of the present method.

the lines per inch obtained under optimum conditions with a fine-grain industrial fluoro- An important property of all radiographs relates to their definition or resolving power, which can best be described in terms of the number of lines per inch of a high-contrast specimen which can be clearly shown by the X-ray image. In this respect, experimental images have been obtained of a U. S. Standard #30 sieve, wherein each of the 0.0l30-inch diameter ,wires, spaced 0.0232-inch apart, are clearly revealed. Similar images of U. S. Standard sieve show clearly wires of 0.0O3 l-inch diameter, spaced 0.0049-inch apart; while excellent images of ,200-mesh sieves establish the definition of the present electroradiographic method as at least I 200 lines per inch, which value is not intended to be limiting, but merely illustrative. This observed definition compares very favorably with scopic screen under laboratory observation conditions. These electroradiographs were obtained 'using a 20 second exposure to an industrial X-ray work and one per cent may be obtained under most conditions. In fluoroscopy, however, the

typical contrast sensitivity is of the order of 15 per cent. Even under optimum conditions industrial fluoroscopic images have seldom, if ever, shown contrast sensitivities better than six or seven per cent. A preliminary estimate of the large area contrast sensitivity of electroradiography has been obtained by using the process to produce electroradiographs of sandwiches made up to thick sheets of aluminum containing an. internal aluminum layer of nominal thickness with several drilled holes. For example, images have been obtained with a metal sandwich it-inch thick having a series of holes of different diameters in the middle fir-inch section. These are revealed clearly in the electroradiograph (see Figure l). Similar holes present in a i s-inch thick layer of aluminum sandwiched between two /2-inch layers of aluminum sheet containing no holes were equally detectable. This latter test corresponds to about six per cent contrast sensitivity and is only representative of the degree of constrast possible according to the present method, since optimum conditions have not yet been thoroughly investigated. These images were produced by a 60 second exposure to an industrial X-ray unit at 150 kilowatts peak and millianiperes.

It has been found that electroradiography possesses a wide latitude range while retaining a good local contrast sensitivity. Latitude may be defined as the ability to obtain a usable image with widely varying exposure, or with widely varying thicknesses of material in a single exposure. Successful electroradiogra-phs of objects shown in Figure l have been made using X-ray voltages from 60 to 200 kilovolts peak.

Electroradiographic studies show increasing contrast with increasing exposure time, at least up to a definite optimum time. A decrease in background. density accompanies this effect. It is of interest that electroradiography produces direct positive images, whereas standard radiography on X-ray film gives negative images.

In connection with the present invention, it will be recognized, of course, that it is not required that an entire object be radiographed, but that ready provision may be made for radiographing any desired portion of any object and the word object in the claims should be so interpreted.

An alternative manner of practicing this in-- vention arises when the sensitive surface layer material. is sensitive to light as well as to penetrating radiations. As has already been noted, selenium is an example of such material. When a material having these characteristics is used it brings about the possibility combining light, or non-penetrating radiations, with any of the penetrating radiations in carrying out the exposure step. ixposure to the non-penetrating radiations and to the penetrating radiations may be made either simultaneously or separately.

The advantages and desirable features of the present method will be readily apparent to those skilled in the art in view of the above description. Numerous variations and equivalent procedures in carrying out the various steps have been pointed out and others will be apparent to persons skilled in the art, as will other advantages and properties not herein specifically pointed out.

For example, plates used in this process may be used repeatedly in the electroradiographic procedure. This requires only that any powder particles adhering to the plate be removed prior to repeating the steps of the process. Such cleaning may be readily effected by passing a granular material back and forth across the plate several times to pick up any adhering powder particles. Other cleaning procedures are also possible, of course.

It will be further apparent that the method of this invention may be used for other purposes than the production of electroradiographs of articles. For example, X-ray diffraction patterns, records of Xuay and other fields, or other patterns produced by the radiation source may be provided. The device may be used as a simple radiation detector or integrator.

In view of the above disclosure and description the present invention will now be more specifically described and its scope defined by the attached claims.

What is claimed is:

1. The method of electroradiography comprising the steps of charging the surface of a plate having a semiconductive selenium coating, exposins the charged plate to X-ray radiation while an object to be tested is positioned between the X- ray source and the charged selenium plate, dusting the surface of such exposed plate with a resinous material, transferring the image thus produced to a second surface, and fixing such transferred image to said second surface.

2. The method of electroradiography comprising the steps of charging the surface of a plate having a semiconductive selenium coating, exposing the charged plate to X-ray radiation while an object to be tested is positioned between the X-ray source and the charged selenium surface, dusting the surface of such exposed plate with a dry developer material, transferring the image thus produced to a second surface, and fixing such transferred image to said second surface.

3. The method of xeroradiography comprising the steps of charging the surface of a plate having a semiconductive selenium coating, exposing the charged plate to X-ray radiation while an object to be tested is positioned between the X-ray source and the charged selenium plate, and dusting the surface of such exposed plate with a dry developer material whereby such material is deposited on the plate to form an image in conformity with the electric charge remaining thereon.

ROLAND M. SCHAFFERT. ROBERT C. MCMASTER. WILLIAM E. BIXBY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,221,776 Carlson Nov. 19, 1940 2,297,691 Carlson Oct. 6, 1942 2,585,551 Hofstaclter Feb. 12, 1952 OTHER REFERENCES Xerogranhy, a New Industry, by C. F. Carlson. Photographic Age, March 1949, pages l0, l1 and 22.

Claims (1)

1. THE METHOD OF ELECTRORADIOGRAPHY COMPRISING THE STEPS OF CHARGING THE SURFACE OF A PLATE HAVING A SEMINCONDUCTIVE SELENIUM COATING, EXPOSING THE CHARGED PLATE TO X-RAY RADIATION WHILE AN OBJECT TO BE TESTED IS POSITIONED BETWEEN THE XRAV SOURCE AND THE CHARGED SELENIUM PLATE, DUST ING THE SURFACE OF SUCH EXPOSED PLATE WITH A RESINOUS MATERIAL, TRANSFERRING THE IMAGE THUS PRODUCED TO A SECOND SURFACE, AND FIXING SUCH TRANSFERRED IMAGE TO SAID SECOND SURFACE.

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