US 2863061 A
Description (OCR text may contain errors)
Dec. l2, 1958 G, DESTRIAU 2,863,061
X-RAY FLUOROSCOPIC DEVICE Filed AMay 28, 1954 2 Sheets-Sheet 1 F/ELD IN VEN TOR. @E0/655 DEST/EMU Dec. 2, 1958 G. DEsTRlAu l 2,363,061
x-RAY FLUoRoscoPIc DEVICE:
Filed May 28, 1954 2 sheets-shea*h 2 i INVENToR. aimee-Es .aisne/,9a BY i7 4 PPL/Ep, HELP M M7W" nav/vnf.
United States Patent O France, assignor to West- Georges Destriau, Cauderan,
East Pittsburgh, Pa., a
inghouse Electric Corporation, corporation of Pennsylvania Application May 28, 1954, Serial No. 433,185 7 Claims. (Cl. Z50-80) This invention relates to X-ray devices and, more pan ticularly, to an X-ray device having improved luminescent response to an X-ray signal.
Heretofore it has been found that an electroluminescent cell, when irradiated with X-rays, will display a decreased brightness. This.electroextinctive effect, as `it has been known in the prior-art, has been published on numerous occasions, a recent publication being an article by G. Destriau in Journal of Applied Physics, vol. 25, No. 1, January 1954, page 66. Other references to this electroextinctive effect may be found in Journal of Applied Physics, vol. 23, No. 12, December 1952, page 1289, article by Theodore Miller, and Physical Review, vol. 92 (1953), page 1323, article by Keith W. Olsen.
Also known in the prior art is the Gudden and Pohl elect which may be described as a momentary luminescence induced by the application of an electric eld across a phosphor which has been previously excited.
It is the general object of this invention to provide an X-ray device which displays improved response to an X-ray signal.
It is a further object to provide an X-ray device which operates with increased brightness.
It is another obiect to provide an X-ray fluoroscopic `device which may be operated with decreased X-ray intensity while still obtaining a usable response, thus minimizing the hazards encountered in operating X-ray equipment.
It is still another object to provide luminescent materials which may be used in X-ray fluoro-scopic devices.
lThe aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing an X-ray device and luminescent material for use in combination therewith, wherein the luminescent material is irradiated by X-rays while under the influence of an electric field.
For better understanding of the invention, reference should be had to the accompanying drawings wherein:
Fig. 1 is a block diagram illustrating a fluoroscopic apparatus constructed according to this invention;
Fig. 2 is a plan view of a fluo-roscopic screen as used with the device shown in Fig. l;
Fig. 3 is a sectional elevational view taken on III- III of Fig. 2;
Fig. 4 is a sectional elevational view, corresponding to Fig. 3, illustrating an alternative embodiment;
Fig. 5 is a graph of screen brightness vs.fperiods of X-ray excitation for the electroluminescent cells of the prior art;
the line Fig. 6 is a graph of screen brightness vs.. 'periods of X-ray excitation for the X-ray device of this invention;
Fig. 7 is a graph representing the sensitization ratio vs. applied electric field for the preferred fluoroscopic screen as used with this invention;
Fig. 8 is another graph representing the sensitization ratio vs. applied electric held for the tluoroscopic screen as used with this invention.
Although the principles of the invention are broadly applicable to any application wherein phosphor material is to be irradiated by X-rays, the invention has particular application with reference to uoroscopic screens, and hence it has been so illustrated and will be so described.
ripice With particular reference to the form of the invention illustrated in the drawings, the numeral 10 in Fig. l indicates generally a .fluoroscopic apparatus which generally comprises a fluoroscopic screen 12, electric field Voltage supply 14, inspection table 16 and X-ray generating apparatus 18, which X-ray apparatus may be of kv., 3 ma. rated output, for example.
ln Figs. 2 and 3 are illustrated the preferred embodiment of the fluoroscopic screen 12 which comprises generally a substantially planar layer of luminescent material 20 in contact with a substantially planar layer of dielectric material 22, said luminescent material and dielectric being sandwiched between two thin transparent conducting layers or electrodes 24 and 26. A foundation-viewing plate 2S is placed over one of the conducting layers, for example layer 24, and an insulating layer 30 is placed over the other conducting layer in order to minimize shock hazard. Each of the conducting layers 24 and 26 are connected by separate electrical leads 32 and 34 to the field voltage supply 14, as shown in block diagram in Fig. l. A protecting and handling shield 36 is normally provided around the entire periphery of the cell in order to facilitate handling, storage, etc.
The luminescent material 20 is preferably positioned next to the foundation-viewing plate 23 in order to improve screen perception and minimize parallax, although for so-me applications it might be preferable to place the dielectric material 22 next to the viewing plate. The luminescent material 20 will be more thoroughly considered in the following paragraphs and for such an application as the the instant one may have a thickness of about V0.2 mm., although this thickness is no way critical. Where the phosphor and dielectric materials are included in separate layers, as illustrated in Fig. 3, the dielectric may consist of any material which has a high dielectric constant, is transparent to X-rays and will not deteriorate under the action of X-rays. Such materials are well known and, as an example, the dielectric material may consist of a mica sheet about 0.05 mm. thick although this thickness is in no way critical and may be increased or decreased as dictated by the application.
The thin transparent conducting electrodes 24 and 26 may be any conducting transparent materials which may readily be coated as a thin sheet, are transparent to visible light in the case of the upper layer 24 and transparent to X-rays in the case of the lower layer 26, and will not deteriorate appreciably under the action of X-rays. As an example, the coating 24 may be of tin oxi-de and may be applied as described in Patent No. 2,522,531 to Mochel. Alternatively the coating 24 may be of an oxide of Zinc, cadmium, aluminum or bismuth. The thin transparent conducting coating 26 may be of tin oxide, or may be a thin reflecting coating of aluminum which may be .applied by the well-known vacuummetallizing techniques, a representative thickness of such Al coating being 0.001 cm. The thin protective layer 30, which is intended to insure against shock hazard and to facilitate handling, may be of any X-ray transparent material which has a relatively high dielectric constant, an example being a polystyrene compound as sold by Dow Chemical Co. under the trademark Styron Another example 'of a satisfactory material is a methyl methacrylate compound, such as sold by E. l. du Pont under the trademark Lucite This protective coating 30 may be dispensed with if desired as it in no way affects the operation of the device. Shock hazard may then be eliminated by grounding thev electrode 26.
The foundation glass-viewing plate 28 may be fabricated of any glass which contains heavy atoms which will absorb the X-rays and thus protect the viewer. As an example, any ofthe well-known lead or cerium glasses may be used. The protecting shield 36 may be of any suitable plastic material such as the aforementioned polystyrene compound. This protecting shield is in no way necessary to the operation of the device and may be dispensed with if desired.
The electrical leads 32 and 34 may be directly connected to the electrodes 24 and 26 respectively or preferably are connected to the electrodes through bus bars 38 and 40 as described in Patent No. 2,628,299 to Gaiser.
The field voltage supply may Aconsist of a transformer having an output which is variable between 100 and 2,000 volts, 60 cycles, for example, in order that the eld applied across the electrodes may be adjusted to optimum conditions, as hereinafter explained.
In Fig. 4 is represented an alternative embodiment of the liuoroscopic screen, as illustrated in Fig. 3, and'all parts of this alternative embodiment are identical with the embodiment as illustrated in Fig. 3 except that the phosphor is embedded throughout the dielectric, to form a homogeneous phosphor-dielectric layer 40. In such an embodiment the dielectric in which the phosphor is embedded may consist of any material which is relatively transparent to visible light and X-rays, is stable under the action of X-rays and has a high dielectric constant, a dielectric constant about 4 being generally satisfactory. This requirement of high dielectric constant for the dielectric, however, is one of preference rather than necessity since the fields which are utilized in the instant application are relatively small as compared to the fields which are normally desirable in the usual electroluminescent cell or lamp applications Where the cell brightness is dependent upon the field applied. As examples of a dielectric in which the phosphor is embedded, either of the heretoforementioned polystyrene or methyl methacrylate compounds will be satisfactory. An X-ray transparent glass such as a boro-silicate glass having a phosphor embedded throughout can also be used .and the glass-dielectric layer may be fabricated as described in copending application of Eugene Etzel, Serial No. 419,232, tiled March 29, 1954, entitled Phosphor Embedded Glass and Method of Making. In the embodiment of the invention of Fig. 4, an equivalent amount of phosphor may be embedded in the dielectric as would form a phosphor layer about 0.2 mm. thick, as described in the preferred embodiment of Fig. 3. This amount of phosphor, however, is only one of choice and the amount may be varied as dictated by the application. Sufiicient dielectric material may be incorporated with the phosphor to cause the phosphordielectric layer to be about 0.3mm. thick. This thickness is given only by way of example and not by way of limitation and may be varied according to the application.
In Fig. 5 is illustrated a graph of arbitrary brightness units vs. time in minutes of X-ray irradiation for a fluoroscopic screen incorporating a known uoroscopic phosphor .and adapted to have an electric field applied thereacross. The prior art phosphor material utilized in the screen is ZnCdS:Ag of 0.2 mm. thickness, which is a well-known X-ray-sensitive phosphor. In this experiment this phosphor is placed between two electrodes, as illustrated in Fig. 3. When the liuoroscopic screen embodying this phosphor is irradiated with X-rays, the brightness increases following the curve OABC. When a field is applied between the two electrodes, simultaneously with the X-ray irradiation, the brightness may be represented by the curve OA'BC. If the electric field is applied only between the time t1 and t2 there is a sudden drop AD in brightness upon application of the field at t1, after which the brightness slowly increases from its minimum at D to point B', which is the brightness normally expected with both X-ray irradiation and applied field. When the field is removed at time t2, there is experienced a small drop B'E, after which the brightness increases to that normally expected with only X-ray irradiation.
If a ZnCdS:Mn phosphor is incorporated in the pre- CII ferred embodiment of the screen, as illustrated in Fig. 3, the effect of decreased brightness, as illustrated in Fig. 6, is completely reversed and an increased brightness is obtained. There is illustrated in Fig. 6 a graph of arbitrary brightness units vs. periods of X-ray irradiation for the preferred ZnCdS:Mn phosphor incorporated into a fluoroscopic screen, as illustrated in Fig. 3, All brightness measurements referred to were made under the same test conditions and thus represent relative values.
One embodiment of this phosphor consists of 2 moles CdS, 7 moles ZnS and activated by 5 10-2 mole Mn. Such a phosphor may be prepared by ball-milling the aforementioned ingredients and firing in an oxygen-free atmosphere for about one hour at l200 C.
Where this aforementioned ZnCdszMn phosphor is incorporated into the tiuoroscopic screen, an exactly opposite result is obtained than was obtained with the prior art X-ray phosphors. With reference to Fig. 6, if no field is applied and the screen is irradiated with X- rays, the brightness follows the curve PFGH. If an electric field is applied simultaneously with X-ray irradiation, the brightness follows the curve PF'G'H, which curve PF G'H is above the curve PF GH, contrary to the results obtained with prior art phosphors. If the screen is irradiated only with X-rays up to the time t1 and then the field is suddenly applied, there is a sudden increase in brightness from F to K. The brightness then slowly decreases to the brightness which is to be expected when both electric field excitation and X-ray irradiation are simultaneously applied. lf the field is removed at t3 there is a small increase in brightness which follows the curve GL and the brightness then decreases to that which would be normally expected were only X-ray irradiation applied to the screen. It is to be observed that just the opposite results are obtained where the phosphor of this invention is used, as has been experienced where the X-ray sensitive luminescent materials of the prior art have been used in identical experiments.
As heretofore noted, a specific example of the phosphor which may be used in the fluoroscopic screen consists of 2 moles Cds, 7 moles ZnS and activated by 5x10-2 mole Mn. It has been found that this luminescent material activated by from about 0.01 X10*2 to 6 102 mole Mn per mole of zinc plus cadmium Will be satisfactory and apparently the main constituents of the phosphor which affect its properties regarding increased brightness when irradiated by X-rays and placed within an electric field are CdS and Mn. lt has been found that the ratio of Cd to Zn in the luminescent material should be from between 1 mole CdS; 9 moles ZnS to 7 moles CdS; 3 moles ZnS, if a satisfactory output is to be obtained. Any molar ratio of Cd to Zn within these aforementioned limitations will produce a luminescent material which is generally satisfactory for the disclosed uoroscopic screens. The moles of Mn activator per mole of Cd and Zn are preferably from about '0.3 10-2 to about 1.l l02, although this range may vary from 0.01 to 10-2 to 6 102 mole Mn activator per mole of luminescent material, as heretofore mentioned.
In order to increase the X-ray sensitivity of the luminescent material, there may be added to the aforementioned phosphor from traces, e. g. 0.001X l0-2 mole Ag up to about 1.0)(10-2 mole of Ag activator per mole of Mn activator. This Ag activator addition will not measurably decrease the increase in brightness which is realized thru the screen excitation by both X-ray irradiation and an electric field, but the silver activator addition increases somewhat the X-ray sensitivity of the phosphor.
Luminescent material compositions according to this invention are given in the following examples:
Example 1 2 moles CdS 7 moles ZnS 5 X 10-2 mole Mn Example 2 1.5 moles CdS moles ZnS 2 1O2 mole Mn Example 3 2 moles CdS 7 moles ZnS 5 X10"2 mole Mn 0.01 2 mole Ag In the usual type of electroluminescent cell, which is normally co-nstructed as a phosphor-embedded dielectric sandwiched between two electrodes, the cell brightness is directly proportional to the eld intensity. In contrast, in the iiuoroscopic screen used with this invention, the iield intensity is at an optimum at about -25 kv. per cm. There is illustrated in Fig. 7 a graph of relative intensity vs. applied electric iield for the phosphor as given in Example 1. As sho-wn, the maximum phosphor relative brightness occurs at about 15 kv. per cm. and is about 2.3 P1. P1 is a sensitizing ratio and represents the brightness (b1) of the fluoroscopic screen when the screen is irradiated by X-rays and has 'simultaneously applied thereto an electric iield, dividedrby the brightness (bo) of the same screen when irradiated by X-rays only. Thus P1=b1/ 170.
In Fig. 8 is represented the sensitizing ratio (P1) vs. eld in applied kv. per cm. for the phosphor given in Example 2. As illustrated, the maximum sensltizing ratio occurs at about 18 kv. per cm. and is about 1.6, after which the sensitizing ratio decreases. This phenomenon of decreasing sensitizing ratio after an optimum has been cached has been generally observed with the luminescent materials of this invention and in all experiments conducted so -far the optimum iield occurs between 15 and 25 kv./cm. ln order to operate at the field of 20 kv./ cm. for the specific example of the embodiment as illustrated in Fig. 3, wherein the combined thickness of phosphor and dielectric is 0.25 mm., the applied voltage to the electrodes should be about 500. In order to operate at about the optimum for the specilic example of the alternate embodiment as given in Fig. 4 where the phosphor-dielectric is 0.3 mm. thick, the applied Voltage to the electrodes sho-uld be about 600.
It will be observed that when operating a fluoroscopic apparatus, as shown in Fig. l, when examining an iron casting, etc. the X-ray irradiation and electric field excitation may be simultaneously applied to the liuoroscopic screen which will result in a brightness far superior to that realized in prior art practices.
As an alternative method of operation, the X-ray in tensity may be decreased from the X-ray intensity required to operate the fluoroscopes of the prior art, and a picture of equivalent brightness may still be obtained. This of course has the advantage of decreasing the hazards encountered in operating X-ray equipment.
It will be recognized that the objects of the invention have been achieved by providing an X-ray device which operates with increased brightness, or which device may be operated with decreased X-ray intensity and still have a brightness which is equivalent to that of the X-ray devices of the prior art. Phosphor materials for use in combination with such X-ray devices have also been provided. t
While in accordance with the patent statutes one best known embodiment of the invention has been illustrated and described in detail, it is to be generally understood that the invention is not limited thereto or thereby.
1. An X-ray sensitive device comprising, a screen comprising luminescent material sandwiched between two electrodes, means for applying an alternating current pomeans, and means tential between said electrodes, means for irradiating said luminescent material with X-rays, and Said luminescent material consisting of ZnS and CdSwherein the molar ratio of Zn to Cd is from 9 Znzl Cd to 3 Zn:7 Cd and activated by from 0.01 102 to 60x102 mole Mn per mole of luminescent material.
2. An X-ray sensitive device comprising, a screen comprising luminescent material sandwiched between two electrodes, means for applying an alternating current potential between said electrodes, means for irradiating said luminescent material with X-rays, and said luminescent material consisting of ZnS and CdS wherein the molar ratio of Zn to Cd is from 9 Zn:1 Cd to 3 Zn:7 Cd and activated by from 03x10-2 to 1.1)(102 mole Mn per mole of luminescent material.
3. A iiuoroscopic device comprising, a luminescent material and a dielectric sandwiched between two electrodes, means for applying an alternating current potential between said electrodes, means for irradiating said luminescent material with X-rays, said luminescent material consisting of ZnS and CdS wherein the molar ratio Zn to Cd is from 9 Zn:1 Cd to 3 Zn:7 -Cd and activated by one of the group consisting of Mn, and Mn and Ag, said Mn activator being present in amounts of from 0.3 102 to 1.1 102 mole per mole of luminescent material, and said Ag activator being present in amounts of from traces to 1.0 102 mole per mole of Mn activator.
4. An X-ray sensitive device comprising, a screen including luminescent means which exhibits the property of sustained luminescence under excitation by X-rays and sustained enhanced luminescence under the simultaneous inuence of an alternating electric iield, means for applying an alternating electric field across said luminescent for simultaneously irradiating said luminescent means with X-rays.
5. An X-ray sensitive device comprising, a screen of dielectric and luminescent means, said luminescent means exhibiting the property of sustained luminescence under excitation by X-rays and sustained enhanced luminescence under the simultaneous iniiuence of an alternating electric field, means for applying an alternating electric ield across said screen, and means for simultaneously irradiating said screen with X-rays.
6. An X-ray sensitive device comprising, a screen including linely-divided luminescent means which exhibits the property of sustained luminescence under excitation by X-rays and sustained enhanced luminescence under the simultaneous influence of an alternating electric lield, means for applying an alternating electric eld across said luminescent means, and means for simultaneously irradiating said luminescent means with X-rays.
7. An X-ray sensitive device comprising, a screen of dielectric and finely-divided luminescent means, said luminescent means exhibiting the property of sustained luminescence under excitation by X-rays and sustained enhanced luminescence under the simultaneous influence of an alternating electric field, means for applying an alternating electric iield across said'screen, and means for simultaneously irradiating said screen with X-rays.
References Cited in the lile of this patent UNITED STATES PATENTS Mager Sept. 4, 1951 White Aug. 25, 1953 OTHER REFERENCES