FR2621773A1 - IMAGE RECORDING METHOD AND DEVICE FOR IMPLEMENTING SAID METHOD - Google Patents

Abstract

Device for recording successive images at high speed, comprising a generator 1 of X-ray pulses (IX) intended to be directed towards an object 2 to be radiographed behind which are arranged a scintillator screen 4 forming an X-ray converter into visible light and image recording means 5. Photomultiplier means 3 are interposed between the object to be radiographed 2 and the scintillator screen 4, in order to increase the intensity of the X radiation striking the scintillator screen. Use for the radiographic recording of a fleeting event animated at a high speed such as the detonation of an explosive or the impact of a projectile on a target.

Description

The present invention relates to a method for recording images

  succeeding at a high rate, notably to produce cinematography

  X-ray pulses or flash cineniography.

  The invention also relates to a device for

  implementation of the aforementioned method.

  The invention is more particularly intended to enable the radiographic recording of a fugitive event with a high speed, for example from 1000 to 10,000 m / s, such as the detonation of an explosive or

  the impact of a projectile on a target.

  Recording devices of the above kind are already known which comprise an X-ray pulse generator intended to be directed towards the object to be radiographed, behind which are arranged successively and coaxially at the output of the X-ray pulse generator a scintillator screen forming X-ray converter in visible light and means

image recording.

  The radiographic recording of a high-speed animated fugitive event can only be obtained with a negligible motion blur if the exposure time of the image-recording means is between 10 us and 100 ns. used as means

  image recording a fast electronic camera.

  However, given the characteristics of these cameras and the maximum intensity of the X-ray available at the output of the most advanced X-ray pulse generators, it is possible to obtain, with the aforementioned type of camera, only a definition or resolution on the particularly small impressed photosensitive film, of the order of 2 to 3 pairs of lines per millimeter. The quality of the recorded images is therefore considerably reduced. Moreover, the analysis of very

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  fast requires a separation of images. Thus, it is also not possible to consider retaining a scintillator screen having an excessively high fluorescence yield because correlatively obtaining a luminous persistence of the screen which exceeds the separation time of two successive pulses of X-rays. This inevitably leads to the superimposition of an image to the previous one, too little attenuated, and to a

blurred formation of these images.

  An object of the present invention is to provide a method and a device for recording images that make it possible to obtain several successive images of a fugitive phenomenon animated with a high speed, succeeding each other with a high frequency, the definition of which are excellent, and that use a pulse generator of

  X-ray of classic design.

  Another object of the invention is to ensure the spatial separation of the images of the phenomenon or the x-rayed object. The present invention thus provides a method of recording high-speed successive images which includes the steps of radiographing an object by bombarding X-ray pulses, transforming these X-ray pulses into visible light pulses, and sequentially impressing them. several photosensitive films or photosensitive film elements by means of the aforementioned light pulses to record distinct images of

the x-rayed object.

  According to the invention, this method is characterized in that prior to the transformation of the X-ray pulses into pulses of visible light, photomultiplication is intensified, which consists in transforming X-rays into electrons, said X-ray pulses. the intensification of the X-ray pulses, we

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  can obtain images of the x-rayed object having excellent definition even if the emission intensity of these pulses is relatively low. It is also possible to transform the X-ray pulses into visible light pulses without the risk of generating an overlap of two consecutive images by neglecting the fluorescence efficiency of the transformation means used at

  benefit from a low luminous persistence of these.

  According to another aspect of the invention, the image recording device for implementing the aforementioned method comprises an X-ray pulse generator intended to be directed towards an object to be radiographed behind which are arranged successively and coaxially. at the output of the pulse generator a scintillator screen forming an X-ray converter in visible light and means

image recording.

  According to the invention, this device is characterized in that photomultiplier means are interposed between the object to be radiographed and the scintillator screen, these photomultiplier means being intended to increase the intensity of the X-ray radiation that strikes the scintillator screen. The combination of photomultiplier means forming X-ray intensifiers, and a scintillator screen is a pulse-emitting X-ray pulse emitter transmitter emitting pulses

  light of great intensity and very short duration.

  Thus, it is possible to use an X-ray pulse generator of conventional design, that is to say whose output intensity is normally insufficient to obtain very short pulses of light and of high intensity after conversion, in a scintillator, X-rays in light. Consequently, by the use of a scintillator screen having a low luminous persistence,

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  for example, less than 10 ns, two successive x-ray pulses can be made to be separated by a very small time interval. It thus becomes possible to record several successive radiographies of very fast phenomena by means of the compliant device

to the invention.

  According to a first advantageous embodiment of the invention, the photomultiplier means comprise a lead glass plate or the like whose surface is oriented substantially perpendicular to the incident X-ray, this plate being pierced with a multitude of microchannels whose surface is covered. of a semiconductor material layer behaving in photocathode under the effect

incident X-radiation.

  Thus, each microchannel acts as an individual photomultiplier so that the intensifying power of the photomultiplier means is

  multiplied by their number of microchannels.

  According to a second advantageous embodiment of the invention, the image recording means are designed to ensure spatial separation

  pictures of the x-rayed object.

  Preferably, the image recording means comprise a plurality of optical subassemblies each comprising a lens, a shutter and a photosensitive film, each optical subassembly being arranged to receive the light beam emanating from the scintillator screen. the opening of each shutter being synchronized with a voltage pulse of the X-ray pulse generator, which triggers, almost simultaneously, the emission of an X-ray pulse. Thus, the use of optical subassemblies of simple design, that is to say in particular

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  having no means of electronic image transformation as is the case of a fast electronic camera, makes it possible not to deteriorate the definition of the

recorded images.

  Other features and benefits of

  the invention will emerge again from the description which will

  to follow. In the accompanying drawings given by way of non-limiting examples: FIG. 1 is a block diagram of an image recording device according to the invention, FIG. 2 is a perspective view with tearing away. photomultiplier means according to the invention, - Figure 3 is an explanatory diagram in perspective with tearing of an individual photomultiplier channel means of Figure 2 and - Figures 4 to 7 are time diagrams illustrating respectively: trigger pulses of the generator of FIG. 1, the X-ray pulses of the aforementioned generator, the pulses of light emitted by the scintillator screen of FIG. 1, and the opening and closing sequences of the

  optical subassemblies of Figure 1.

  In the embodiment shown in FIG. 1, the image recording device according to the present invention, used to carry out X-ray cinematography or flash cineradiography, comprises a generator 1 of X-ray pulses IX whose barrel exit is directed to an object to

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  2. Object 2 represents, for example, a phenomenon of very short life such as the detonation of an explosive or the impact of a projectile on a target. Behind the object 2 are successively and coaxially arranged at the output 1a of the generator 1, photomultiplier means 3, a scintillator screen 4 and image recording means 5, the photomultiplier means 3 being intended to increase the intensity of the IX pulses that strike the screen

scintillator 4.

  In the example shown in FIG. 1, the generator i, which is of a type known in itself, is designed to deliver four successive pulses of X-rays emitted at a frequency of approximately 500 kHz and with a duration substantially equal to 40 ns. This generator 1 is for example the one that was presented by the authors of the present invention to the 1st European Congress of Cineradiography by photons or particles (May 18 to 21, 1981 in Paris) and which is the subject of the communication

  PROCEEDINGS (SPIE volume 312 - 1981- pages 164-167).

  The role of the microchannel wafer 3 and the scintillator screen 4, which is for example of circular section, is to convert the incident X-ray pulses into visible light pulses ILS

  operable by the image recording means 5.

  According to a preferred characteristic of the invention, the constituent material of the screen 4 is chosen so that its luminous persistence t (see FIG. 6) does not exceed the separation time of two successive pulses of X-rays, ie 2ps. In the opposite case, one would obtain a superposition of each image compared to the previous one and the images thus obtained would be fuzzy. Thus, according to the invention, is used for the screen 4, a plastic material, such as paterphenyl, whose persistence is lower

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  at 10 ns so that with an emission frequency of 500 kHz X-ray pulses which corresponds to a transmission period of 2 μs, there is no risk of superposition of two successive images. The thickness of the screen 4 is preferably between 0.1 and 0.5 mm

  to avoid image blur.

  According to an advantageous embodiment of the invention, the photomultiplier means 3 comprise a wafer shaped plate (see FIG. 2) made of lead glass or the like whose surface is oriented substantially perpendicular to the axis of the gun 1 of the generator 1 This plate 3 is pierced with a multitude of microchannels 3a (see FIGS. 2 and 3), the surface of which is covered with a layer of semiconductor material 3b which behaves like a photocathode under the effect of X-ray radiation. incident provided that the front and rear faces 3c and 3d of the plate 3, coated with an electrically conductive material, are connected to a DC voltage source V (see Figures 1 and 3). This metal coating of said faces 3c, 3d also provides an electrical connection of the parallel type between the different

channels 3a.

  Thus, as seen in FIG. 3, the incident radiation IX which strikes the surface 3b of the microchannel 3a generates the emission of a first series of photons which in turn each generate the emission of a

  second series of photons by striking said surface 3b.

  This phenomenon is repeated up to the output of the microchannel 3a so that by photomultiplication effect, the intensity of the radiation emanating from the plate 3 is equal to that of the incident radiation multiplied by a factor depending in particular on the structure of the plate 3 and the voltage value of the source V. The photomultiplier plate 3 that has just been described is for example of the type manufactured by

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  the American company GALILEO ELECTRO-OPTICS CORP. and distributed in France by TEKNIS. This plate and its use are described in detail in the article "MICROCHANNEL PLATE DETECTORS" from Nuclear Instruments and Methods, Volume 162, 1979, pages 587 to 601. The use of the photomultiplier plate 3 allows in particular to intensify the ILS visible light radiation intended to be operated by the image recording means 5 so as to obtain an excellent resolution or definition of these images while using an X-ray pulse generator of known and non-specific design. Thus, according to the invention, with the image recording means used that will be described, a definition greater than 100 line pairs per mm is obtained, whereas the known devices only provide a definition of

a few pairs of lines per mm.

  According to an advantageous embodiment of the invention, the image recording means 5 comprise four optical subassemblies 5a, each having an objective 6, a control shutter 7

  electric, and a photosensitive film 8, each sub -

  5a optical assembly being arranged to receive the visible light pulse beam ILS emanating from the scintillator screen 4. Thus, this ILS beam is returned to the objective 6 of each optical subassembly 5a respectively by means of a semi mirror -transparent 9 (see Figure 1) disposed along the axis of the gun 1a of the generator 1 and suitably sized and oriented relative to the screen 4 to ensure optimal reflection towards the objectives 6. Given the partial reflection introduced by each mirror 9, it is understood that the intensity of the ILS beam received by an optical subassembly 5a is even lower than the mirror 9 which reflects it is away from the scintillator screen 4. By

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  Accordingly, the opening of each shutter 7 should be suitably adjusted to the position relative to the screen 4 of the optical subassembly 5a to which this shutter belongs, that is to say to the intensity of the beam ILS received. Of course, the last mirror 9a of the series

can be total reflection.

  In order for this arrangement to ensure the spatial separation of the images of the x-rayed object, the invention provides for the opening of each shutter 7 to be synchronized with a voltage pulse ID of the pulse generator i of radii. X causing substantially simultaneous emission of an X-ray pulse IX. Thus, the generator 1 comprises means Ib, known in themselves, connected to the optical subsets 5a to send to them pulses of synchronization IS and to simultaneously deliver the voltage pulses ID each triggering selectively and sequentially the generation of an opening and closing sequence OF of the shutter 7 of an optical subassembly 5a to separately and consecutively record the four images corresponding to the four X-ray pulses X emitted by the generator 1. The four aforementioned images thus materializing for example

  the evolution of the X-rayed phenomenon.

  The time diagrams of FIGS. 4 to 6 where the time t has been plotted on the abscissa respectively give the appearance and the synchronization of a train of four triggering pulses ID, of X-ray pulses, IX, and visible light pulses ILS at the output of the scintillator screen 4. The corresponding periods of opening O and closing F sequentially activated shutters 7a, 7b, 7c, 7d are shown in FIG. 7. These diagrams illustrate the

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  mode of operation described above which corresponds to

  the implementation of the method of the invention.

  The selective remote control of the shutters 7 by means of the pulses IS will for example be obtained by interposing in the control circuit 1c of the shutters 7 a switching device 10 of a type known in itself, comprising for example four doors each assigned to a shutter 7 and whose opening is synchronized with one of the pulses IS controlling the opening sequence

  and closure of the shutter 7 considered.

  According to the invention, since there is at the output of the scintillator screen 4 of visible light pulses of increased intensity thanks to the photomultiplier means 3, it is therefore possible to use image recording means 5 of simple design. that is to say in particular not including electronic image processing means such as those of a fast electronic camera used in known devices. It is known that these electronic transformation means deteriorate the definition of the images. Thus, with the device described with reference to the appended figures, it is possible to obtain an excellent definition of images that can exceed 100 pairs

of lines per mm.

  It will be noted that according to a practical embodiment, the object & radiograph 2 is disposed at a preferential distance from the output end of the barrel 1 substantially equal to 3 m and at a preferential distance from the assembly formed by the photomultiplier means 3 and the scintillator screen 4

substantially equal to 0.3m.

  The invention is not limited to the examples described and shown. Thus the generator I and the image recording means 5 could be designed to record more than four successive images. The image recording means 5 could also be a fast electronic camera at the cost of a loss of definition.

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Claims (11)

  1. A method of recording images succeeding each other at a high rate, in particular for performing X-ray cinematography or flash cineradiography, said method comprising the steps of radiographing an object (2) by bombarding X-ray pulses (IX), transforming said X-ray pulses into visible light pulses (ILS) and sequentially impressing a plurality of photosensitive films or photosensitive film elements by means of the aforementioned light pulses to record distinct images of the x-rayed object, characterized in that that prior to the transformation of the X-ray pulses (IX) into visible light pulses (ILS), said X-ray pulses are intensified by photomultiplication. 2. Method according to claim 1, characterized in that synchronizes the recording of the images of the x-rayed object with the emission of the X-ray pulses (IX).   3. Method according to one of claims 1   or 2, characterized in that the X-ray pulses (IX) are emitted at a frequency substantially equal to 500 kHz and at consecutive time intervals substantially equal to 2 Us. 4. Image recording device for implementing the method according to one of the   preceding claims, this device comprising a   generator (1) of X-ray pulses (IX) intended to be directed towards an object (2) to be radiographed behind which are arranged successively and coaxially at the output of the pulse generator (1) a scintillator screen (4) forming X-ray converter in visible light and image-recording means (5), characterized in that photomultiplier means (3) are interposed between the object to be radiographed (2) and 13 2 6 2 1 7 7 3   the scintillator screen (4), these photomultiplier means (3) being intended to increase the intensity of the X-radiation   which strikes the scintillator screen (4).   5. Recording device according to claim 4, characterized in that the photomultiplier means comprise a lead glass plate or the like (3) whose surface (3c, 3d) is oriented substantially perpendicular to the output (la) of the generator (1), this plate (3) being pierced with a multitude of microchannels (3a) whose surface is covered with a layer of semiconductor material (3b) behaving in photocathode under the effect of X-radiation incident so that each microchannel (3a) behaves in individual photomultiplier.   Recording device according to claim 4 or 5, characterized in that the scintillator screen (4) is made of a material with a low luminous persistence (t) such as a plastics material.   having a luminous persistence of less than 10 ns.   7. Device according to one of the claims   4 to 6, characterized in that the image recording means (5) are designed to ensure separation   spatial images of the x-rayed object (2).   8. Recording device conforming to one   Claims 4 to 7, characterized in that the   X-ray pulse generator (1) is adapted to deliver a plurality of pulses (IX) with a duration substantially equal to 40 ns and separated by a time interval substantially equal to 2ps.   Recording device according to claim 8, characterized in that the means   image recording (5) include several sub-images   optical assemblies (5a) each having a lens (6), a shutter (7a, 7b, 7c, 7d ...) and a light-sensitive film (8), each optical subassembly (5a) being 14 2621773   arranged to receive the light beam (ILS) emanating from the scintillator screen (4) and in that the opening of each shutter (7) is synchronized with a voltage pulse (ID) of the generator (1) of X-ray pulses triggering substantially   simultaneously the emission of an X-ray pulse (IX).   Recording device according to claim 9, characterized in that the X-ray pulse generator (1) comprises means (1b) connected to said optical subassemblies (5a) for sending thereto synchronization pulses (IS) and for simultaneously outputting voltage pulses (IDs) each triggering the generation of an X-ray pulse, each synchronization pulse (IS) selectively triggering an opening (O) and closing sequence   (F) of the shutter (7a, 7b, 7c, 7d ...) of one of the sub- optical assemblies (5a).   11. Device conforming to one of the   claim 9 or 10, characterized in that the beam   light (ILS) emanating from the scintillator screen (4) is returned to the objective (6) of at least one subset   optic (5a) by means of a semi-transparent mirror (9).