METHOD FOR RECORDING AND REPRODUCING A RADIATION IMAGE BY USING A STIMULABLE PHOSPHOR

Abstract: A radiation image is recorded on a stimulable phosphor panel and the recorded image is reproduced by stimulating the phosphor panel with visible rays. As the phosphor, a Samarium and/or Praseodymium activated rare earth oxyhalide phospor is used, preferably a phosphor represented by the formula: LaOBr : aA, bB, wherein A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce and a and b are numbers satisfying the conditions 10<-8> <= a <= 10<-4> and 0 <= b <= 10<-4>.

Description: Method For Recording And Reproducing a Radiation Image . By Using a Stimulable Phosphor. FIELD OF THE INVENTION This invention relates to a method for recording a radiation image on a radiation image storage panel and reproducing the recorded radiation image by stimulating the radiation image storage panel. The invention further relates to a stimulable rare earth activated rare earth oxyhalide phosphor and to a radiation storage panel utilizing the same. BACKGROUND OF THE ART US Patent no. 3,859,527 discloses a method for recording and reproducing a radiation image using a radiation image storage panel comprising a stimulable phosphor which emits light when stimulated by visible or infrared light after exposure to that radiation (the radiation meaning an electromagnetic wave or a corpuscular radiation such as X-ray, Of-rays, p-rays, ^-rays, neutron rays, cathodic rays, ultraviolet rays, or similar). However, as stimulable phosphors which can be employed in this method, only several phosphors, such as SrS:Ce,Smj SrS:Eu,Smj La 0 S:Eu,Sm and [(Zn,Cd)S] :Mn,X wherein X is halogen, are known. Further, the sensitivity in the method in which these phosphors are used is very low because the stimulability of these phosphors is very low. US Patents nos. 4,236,0783 4,239, 68 } 4,261,854 5 4,368,390, the French Patent Application S.N. 2,430,970 and the European Patent Application S.N. 29,963 all disclose other stimulable phosphors. All these phosphors exhibit a stimulable emission in the wavelength region of the visible spectrum shorter than 500 nm, and they must be stimulated with light of wavelength higher than 500 nm (such as a He-Ne laser beam of 633 nm), where they exhibit the maximum stimulability. Accordingly, from the viewpoint of a larger practical use of the method, stimulable phosphors which emit light of higher luminance upon stimulation, which have a wider latitude of wavelengths of the emitted light and are stimulated more efficiently by radiations having higher energy (that is rays of shorter wavelength) are desired. SUMMARY OF THE INVENTION It has been found that Samarium and Praseodymium activated rare earth oxyhalide phosphors exhibit high stimulability under stimulation of visible rays, have a wide latitude of wavelengths of the emitted light (they are blue, green and/or red-emitting phosphors) and their stimulability increases by decreasing the wavelength of the stimulating radiations (in particular is higher with stimulating radiations lower than 500 nm). Hence, the present invention relates to a method for recording and reproducing a radiation image comprising the steps of (i) causing a visible radiation-stimulable phosphor to absorb a radiation passing through an object, (ii) stimulating said phosphor with visible radiations to release the energy stored therein as fluorescent light, and (iii) detecting said fluorescent light with a photodetector, said method being characterized in that said phosphor is selected from the group of Samarium and/or Praseodymium activated rare earth oxyhalide phosphors. Preferably the present invention relates to a method as described above wherein said phosphor is represented by the formula LaOBr : aA,bB in which A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce and a and b are numbers satisfying the —8 —A conditions: 10 _! a 10 and - J - In particular the present invention relates to a method as described above wherein the wavelength of said stimulating radiations is within the range of 540 to 400 nm, the wavelength of said light detected by the photodetector is within the range of 560 to 650 nm and said phosphor is a Samarium activated rare earth oxyhalide phosphor, preferably a phosphor represented by the formula: LaOBr : cSm,dB wherein B is at least one element selected from the group of Pr, Tb, Eu -8 and Ce and c and d are numbers satisfying the conditions: c^d, 10 ^ c^lO -4 and 0 d$10~ 4 . Still particularly, the present invention relates to a method as described above wherein the wavelength of stimulating radiations is within the range of 490 to 400 nm or 550 to 650, the wavelength of said light detected by the photodetector is within the range of 500 to 540 nm and said phosphor is a Praseodymium activated rare earth oxyhalide phosphor, preferably a phosphor represented by the formula: LaOBr : ePr,fC wherein C is at least one element selected from the group of Tb, Ce and —8 Sm and e and f are numbers satisfying the conditions e^f 10 e 10~ 4 and 0^ f £ 10 . Still more particularly, the present invention relates to a method described above wherein the wavelength of stimulating radiations is within the range of 520 to 460 nm, the wavelength of said light * detected by the photodetector is within the range of 350 to 450 nm and said phosphor is a phosphor represented by the formula: LaOBr : gSm,hTb or a phosphor represented by the formula: LaOBr : gPr,hCe —8 wherein g and h are numbers satisfying the conditions: g^h, 10~ ^ g^lθ " and 10~ h410~ 4 . In another aspect the present invention relates to a stimulable rare earth activated rare earth oxyhalide phosphor repre- " sented by the formula: LaOBr : aA,bB wherein A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce and a and b are numbers satisfying the -8 -4 -4 conditions: 10 ^a^lO and O4.b4.lO . In a further aspect the present invention relates to a radiation image storage panel having a fluorescent layer comprising a binder and a stimulable phosphor dispersed therein wherein said stimulable phosphor is at least one phosphor selected from the group of rare earth activated rare earth oxyhalide phosphors represented by the formula: LaOBr : aA,bB wherein A is Samarium and/or Praseodymium, B is at least one element selected from the group of Tb, Eu and Ce, and a and b are numbers -8 -4 -4 satisfying the conditions 10 4 a < 10 and 0£b . JIO . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the stimulated emission spectrum of a stimulable phosphor of the present invention. Fig. 2 is a graph showing the stimulation spectrum of a stimulable phosphor of the present invention. DETAILED DESCRIPTION OF THE INVENTION The method and the apparatus for recording and reproducing a radiation image using the radiation image storage panel of the present invention schematically comprises a radiation source, an object, a radiation image storage panel, a light source emitting stimulating radiations which stimulate the fluorescent layer of the panel to release the radiation energy stored therein as fluorescent light (comprising for example a quarze-iodine lamp, a grating monochromator, a shutter and a focusing optic), a focusing optic for collecting photostimulated and stimulating light respectively emitted and re¬ flected by the panel, a filter for cutting off the stimulating radiations emitted by the light source and reflected by the panel and for transmitting only the fluorescent light emitted by the panel. In the method, a photosensor is used as a detector for detecting the light emitted by the panel, the electrical signals are amplified and recorded or displayed by a reproduction device. More in particular, the object is positioned between the radiation source (such as an X-ray tube) and the radiation image storage panel of the present invention. When the object is exposed to X-rays, the radiation passes through the object. The intensity of the radiation which has passed through the object represents the transmit- tance of the object. Therefore, an image which represents the pattern of transmittance of the object is obtained by means of the radiation impinging upon the panel. The radiation is absorbed by the fluorescent layer of the panel and electrons or holes are generated in the fluorescent layer in proportion to the amount of the absorbed radiation. The electrons or holes are stored in the traps of the Samarium and Praseodymium activated rare earth oxyhalide phosphors of the present invention. The radiation image stored in the panel is visualized by stimulation with the stimulating radiation beam emitted by the light source. For example, the stimulating radiation beam may be given by a Philips 12 V-100 W quartz-iodine lamp and a Hilger-Watts grating monochromator to select any wavelength from near UV to near IR or by a laser beam emitting light of a single wavelength such as an Ar ion laser beam (488 nm and 514-5 nm) or a He-Ne laser beam (633 nm). The fluorescent layer of the panel is scanned with the stimulating radiations emitted by the light source and focused on the panel in a 2 small (such as 0.7 mm ) spot, where the electrons or holes stored in the trap level of the storage phosphor are expelled therefrom, and the radiation image stored in the panel is released as fluorescent light. ύ '-* Λ - " υ ~ \ The luminance of the fluorescent light emitted by the panel is in proportion to the number of the electrons or holes stored in the fluorescent layer of the panel, that is, the amount of the radiation absorbed thereby. A suitable optic is used to collect photostimulated and stimulating light respectively emitted and reflected by the panel. The unwanted stimulating light is filtered-out by an interference filter whose transmission peak is tuned to the wavelength of the signal emitted by the sample. The fluorescent light.is detected and converted into an electrical signal by the photosensor which is for example an EMI 9558 QB photomultiplier, then amplified by a picoammeter, for example a Kithley 417 high speed picoammeter. The electrical signal obtained is converted into an image signal corresponding to a radiation image, by a reproduction device, such as a fast Gould brush 2200 chart recorder or a storage oscilloscope. The radiation image storage panel of the method above has a fluorescent layer comprising as a stimulable phosphor at least one phopshor selected from the group of Samarium and/or Praseodymium activated rare earth oxyhalide stimulable phosphor represented by the formula: LaOBr : aA,bB wherein A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce, and a and b are numbers satisfying the -8 -4 -4 conditions 10 ^ a ..10 and 04b 10 . It has been found that by varying the presence and the amounts of the various rare earth activators above, LaOBr stimulable phosphors which emit in the blue, green and/or red region of the visible spectrum can be obtained, so that from the practical point of view, phosphors with wider latitude of use have been found. Moreover, it has been found that the efficiency of the above phosphors is higher than that of the other known storage phosphors and that the luminance of the stimulated light emitted by the storage phosphors of the present invention increases when stimulating the phosphor with vi shorter wavelength, preferably stimulating the phosphors with light not higher than 500 nm, where the phosphors exhibit their maximum efficiency. In particular, it has been found that Samarium activated rare earth oxyhalide phosphors emit in the red region of the visible light with two main emission peaks at 613 and 568 nm, so that these phosphors can be stimulated with light in the range of 540 to 400 nm. Preferably, said phosphors are represented by the formula: LaOBr : cSm,dB wherein B is at least one element selected from the group of Tb, Eu and -8 Ce and c and d are numbers satisfying the conditions c^d, 10 -4 -4 4 C4rlO and 04dj 10 . Fig. 1 is a graph showing the relative intensity (I) of the stimulated light emitted by the storage phosphor LaOBr:1.56.10 Sm of the present invention. Fig. 2 is a graph showing the relationship between the wavelength of the stimulation radiations and the luminance (L) of the stimulated light, that is the stimulation spectrum of the storage phosphor LaOBr: 1.56.10 Sm above: the light emitted by the storage phosphor above is red with the main peaks at 613 and 568 nm and the stimulated emission increases sharply by decreasing the wavelength of the stimulating radiations under 500 nm. A useful light source emitting stimulating radiations which stimulate the Samarium activated storage phosphor above is a light source emitting light of a single wavelength such as an Ar ion laser beam (emitting light at 514 * 5 and 488.0 nm) and a useful filter for recovering the signal is a combination of two filters having one its maximum transmittance from about 590 nm foreward and 50% of transmit- tance at about 550 nm and the other its maximum transmittance at about 380 nm and 50% of transmittance at about 300 and 450 nm. It has been further found that Praseodymium activated rare earth oxyhalide phosphors emit in the green region of the visible light having the main peak at about 505 nm, so that they can be stimulated with light in the range of 490 to 400 nm or in the rang nm. Preferably, said phosphors are represented by the formula: LaOBr : ePr,fC in which C is at least one element selected from the group of Tb, Ce -8 and Sm and e and f are numbers satisfying the conditions ^ , 10 e 4»10 and O^ ^10 . A useful stimulating light source is a 488 nm Ar ion laser beam or a 633 nm He-Ne laser beam and useful filters for recovering the signal of said phosphor are respectively a filter having the maximum transmittance at about 380 nm and at least 50% of transmittance at about 300 and 450 nm, when stimulating with Ar ion laser beam and a filter having the maximum transmittance from about 400 to about 580 nm and at least 50 of transmittance at about 390 and 590 nm, when stimulating with a He-Ne laser beam. It has also been found that the Samarium and Praseodymium activated rare earth oxyhalide phosphors can transfer part of the storage energy to other rare earths, such as Tb, Ce and Eu when the amount of said rare earths is higher or equal to that of Sm or Pr. The result is a change in color of the storage signal with an improvement in the efficiency with respect to the other rare earths when used alone as activators in rare earth oxyhalide phosphors. In particular it has been found that Samarium preferably transfers part of its storage energy to Tb and Praseodymium preferably transfers part of its storage energy to Ce giving rise to blue-emitting rare earth oxyhalide phosphors having high storage efficiency. Such » phosphors surprisingly allow to use high concentrations of the second activator, Tb or Ce, higher or equal to 0.1% by weight, without quenching the storage ability of the first activator, Sm or Pr. More in particular, it has been found that the signal of the phosphors: LaOBr : gSm,hTb and LaOBr : gPr,hCe —8 in which g and h are numbers satisfying the conditions ^h, 10 . .g410 and 10 «£h410 , is substantially blue, having three main emission peaks at 440, 419 and 384 nm (peaks of Tb) and two secondary emission peaks at 613 and 568 nm (peaks of Sm) for LaOBr:gSm,hTb phosphors and a broad band (350-480 nm) and a peak at 505 nm (peak of Sm) for LaOBr:gPr,hCe phosphors. Such phosphors can be usefully stimulated with light in the range of 520 to 46θ nm, where they exhibit the maximum efficiency under stimulation. A useful stimulating light source is a 488 nm and 514 * 5 nm Ar ion laser and a useful filter for recovering the signal is a filter having the maximum transmittance at about 38O nm and at least 50% of transmittance at about 300 and 450 nm. The Samarium and/or Praseodymium activated Lanthanum oxy- halides stimulable phosphors of the present invention can be prepared by the following process. La 0 is first throughly mixed with the activators (Sm and/or 3 Pr alone or in selected admixtures with Tb, Ce and Eu coactivators). This may be done in several ways well known in the art such as co-precipitation or slurring. The resulting product is mixed with Li C0„ and NH.Br to provide a slight excess of NH Br when all the 2 3 4 4 Li Λ C0 Λ has been converted to LiBr and all the La 0„ to LaOBr. This 2 3 2 3 mixture is then fired to produce a phosphor of the desired particle size in one or more firing stages. Preferred furnace temperatures are in the range of 600 to 1200°C, the higher temperature giving rise to coarser phosphor grains. The fired product is dispersed in a suitable solvent (e.g. alcohol as ethanol or ethanol) which will dissolve out the LiBr and also any small amounts of LaBr , leaving behind LaOBr 9 phosphor. The above mentioned use of LiBr as the flux has the advantage that it is soluble in alcohol, whereas NaBr and KBr, which are commonly used or quoted as a flux, are sparingly soluble in alcohol, even methanol. The resulting phosphor product of the synthesis is filtered, washed copiously with alcohol and dried at about 90°C by the usual techniques well-known in the art. The radiation image storage panel of the present invention has a fluorescent layer comprising a binder and at least one phosphor selected from the group of the above mentioned Samarium and/or ,-" • ;_ _,- ' - - ~- C- ■ . ' *?! Praseodimiu activated rare earth oxyhalide phosphors of the present invention dispersed therein. The fluorescent layer is formed by dispersing the phosphor in the binder to prepare a coating dispersion, and then applying the coating dispersion by a conventional coating method to form a uniform layer. Although the fluorescent layer itself can be a radiation image storage panel when the fluorescent layer is self-supporting, the fluorescent layer is generally provided on a substrate to form a radiation image storage panel. Further, a protective layer for physically and chemically protecting the fluore- scent layer is usually provided on the surface of the fluorescent layer. Furthermore, a primer layer is sometimes provided between the fluorescent layer and the substrate to closely bond the fluorescent layer to the substrate. As the binder employed in the fluorescent layer of the radiation image storage panel of the present invention, there can, for example, be used such binders commonly used in forming layers such as gum arabic, protein such as gelatin, polysaccharides such as dextrane, organic polymeric binders such as polyvinylbutyral, polyvin lacetate, nitrocellulose, ethylcellulose, vinylidenechloride-vinylchloride co- polymer, polymethylmethacrylate, polybutylmethacrylate, vinylchloride- vinylacetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, and the like. Generally, the binder is used in an amount of 0.01 to 1 part by weight per one part by weight of the rare earth element oxyhalide phosphor. However, from the viewpoint of the sensitivity and the sharpness of the panel obtained, the amount of the binder should preferably be small. Accordingly, in consideration of both the sensitivity and the sharpness of the panel and the easiness of application of the coating dispersion, the binder is preferably used in an amount of 0.03 to 0.2 parts by weight per one part by weight of the rare earth oxyhalide phosphor. The thickness of the fluorescent layer is generally within the range of 10 ,u to 1 mm. In the radiation image storage panel of the present invention, the fluorescent layer is generally coated on a substrate. As the substrate, various materials such as polymer material, glass, wool, cotton, paper, metal, or the like can be used. From the viewpoint of handling the panel as an information recording medium, the substrate should preferably be processed into a sheet or a roll having flexibility. In this connection, as the substrate is preferable an organic polymeric film such as a cellulose acetate film, polyester film, polyethylene terephthalate film, polyamide film, triacetate film, polycarbonate film, or the like3 ordinary paper3 or processed paper such as photographic paper, baryta paper, resin-coated paper, pigment- containing paper which contains a pigment such as titanium dioxide, or the like. The substrate may have a primer layer on one surface thereof (the surface on which the fluorescent layer is provided) for the purpose of holding the fluorescent layer tightly. As the material of the primer layer, an ordinary adhesive can be used. In providing a fluorescent layer on the substrate or on the primer layer, a coating dispersion comprising the rare earth oxyhalide phosphor dispersed in a binder may be directly applied to the substrate or to the primer layer to form a fluorescent layer. Alternatively, a fluorescent layer formed beforehand may be bonded to the substrate or to the primer layer. Where the substrate used is permeable to the stimulating radiations of the rare earth element activated complex halide phosphor, the radiation image storage panel can be exposed to the stimulating radiations from the substrate side. Further, in the radiation image storage panel of the present invention, a protective layer for physically and chemically protecting the fluorescent layer is generally provided on the surface of the fluorescent layer intended for exposure (on the side opposite the substrate). When, as mentioned above, the fluorescent layer is self-supporting, the protective layer may be provided on both surfaces of the fluorescent layer. The protective layer may be provided on the - - fluorescent layer by directly applying thereto a coating dispersion to form the protective layer thereon, or may be provided thereon by bonding thereto the protective layer formed beforehand. As the material of the protective layer, a conventional material for a protective layer such as nitrocellulose, ethylcellulose, cellulose acetate, polyester, polyethylene terephthalate, and the like can be used. The radiation image storage panel of the present invention may be colored with a colorant. Further, the fluorescent layer of the radiation image storage panel of the present invention may contain a white powder dispersed therein. By using a colorant or a white powder, a radiation image storage panel which provides an image of high sharpness can be obtained. The present invention will be hereinbelow described referring to the following examples. EXAMPLE 1 Preparation of phosphor LaOBr: 1.56.10 Sm,1.48.10 Tb (Phosphor 1) a) Preparation of La and Tb mixed oxide. The following solutions were prepared: Solution I: 1,000 g of La 0 were dissolved in 4 liters of HN0 (1 part) and H O (2 parts). Solution II: 10.2 g of Tb 0 were dissolved in 100 ml of HN0 Λ (l 47 3 part) and H O (l part). it Solution III: 2,500 g of oxalic acid were dissolved in 10 liters of demineralized water. Solution III was pumped into a reaction vessel fitted with a stir- rer, reflux condenser, vent and inlet tube and the solution heated to boiling. In the meanwhile, Solution II was added to Solution I and heated to boiling. The close to boiling mixed solution of I and II was then pumped slowly into the boiling oxalic acid solution under continuous stirring. Stirring and boiling under reflux were continued for 30 minutes after all the rare earth solution was added. When cool, the precipitate of rare earth oxalate was filtered off, dried and converted to the mixed oxide by firing at 1,000°C for 4 hours. b) Preparation of La and Sm mixed oxide. La and Sm mixed oxide was prepared as above, but Solution II was 10.7 g of Sm 0 dissolved in 100 ml of HN0 (l part) and H O (1 3 3 part) and then diluted to 500 ml with water. c) Conversion to oxybromide. A 1 liter porcelain ball-mill jar containing 500 g of 20 mm diameter porcelain balls was filled with: 78.4 g of La 2 0 3 3 0.8 g of La 0 /Tb mixed oxide as prepared in a); 2 3 0.8 g of La 0 /Sm mixed oxide as prepared in b)j 2 3 * 104 g of NH Br } and 4 18 g of LiC0„. 3 The mixture was milled (at 60 r.p.m.) for one hour, the powder was packed into a silica crucible and fired at about 500°C for 1 hour. The fired cake was re-milled as above for 1 hour and fired again in a silica crucible at 1,050°C for 1 hour. The resulting hard lump was dispersed in 500 ml of methanol to give a suspension of phopshor crystals. This phosphor was washed with alcohol until free of soluble bromide and finally filtered and dried at 90°C. The finished product is a friable phosphor powder comprising 0.01 grams respectively of Sm and Tb per 100 grams of the phosphor and corresponding to the stechiometric formula LaOBr:1.56.10 Sm, 1.48.10 -4Tb, wherein the amounts of the activators are expressed as gram-atoms per 1 mole of LaOBr. EXAMPLE 2 Following procedures similar to those described in Example 1, ^TOTϊ. v:. I the following phosphors were prepared: Phosphor no. 2: LaOBr:1.56.10 "3 Sm,1.48.10 Tb } Phosphor no. 3: LaOBr:7-81.10 Sm,7-39-10~ 4 Tbj Phosphor no. 4 LaOBr:1.56.10 S1113 Phosphor no. 5: LaOBr:1.56.10 Sm 5 Phosphor no. 6: LaOBr:1.56.10 Sm,1.55.10 Eu 5 - . - Phosphor no. 7: LaOBr:1.56.10 Sm,l.54-10 ' Eu 5 Phosphor no. 8: LaOBr:1.56.10 Sm,l.67.10 Pr } Phosphor no. 9: LaOBr:1.56.10 Sm,l.67-10 Pr • * - . -3 Phosphor no. 10: LaOBr:1.67.10 Pr,1.68.10 Ce 5 _ _3 Phosphor no. 11: LaOBr:1.67.10 Pr,1.68.10 Ce 5 Phosphor no. 12: LaOBr:1.67.10~ 3 Pr,1.48.10 Tb 3 Phosphor no. 13: LaOBr-.1.67.10 Pr. EXAMPLE 3 Samples of the phosphors of Examples 1 and 2 containing Sm activator were exposed to X-ray radiations of 40 KV/30 mA for 1 second and after 25 seconds stimulated with light of 488 and 514 nm which was obtained by causing the light to be emitted by a quartz-iodine lamp and passing through a grating monochromator. Photostimulated and stimulat¬ ing light, respectively emitted and reflected by the phosphor, was collected and the unwanted stimulating light was filtered out by an interference filter A (SCH0TT O87) and B * (SCH0TT BGl) having a transmission peak of 570 to 700 nm and of 380 to 450 nm, respectively. The stimulated light emitted by the phosphor was then detected by a photomultiplier. The following Table 1 reports the intensity of the stimulated light emitted by the phosphors in comparison with that of a conventional LaOBr:1.48.10 Tb,8.38.10 Ce phosphor (Phosphor A) of US patent 4,236,078, measured under the same conditions and the emission peaks under continuous X-ray irradiation. T A B L E Phosphor Gram-atoms of acti¬ Stimulated light finission Peaks no. vators per mole of Intensity Peaks (nm) Relative intensity LaOBr (arbitrary units) (Estimated values) 1.56.10 ~4 Sm,1.48.10 ~4 Tb 21.2 613,568 10 444,419,384 5 1.56.10 3 Sm,1.48.10 Tb 21.1 613,568 10 444,419,384 0.5 7.81.10 Sm,7-39-10 Tb 18.5 613,568 3 444,419,384 10 4 1.56.10 ~4 Sm 24.2 613,568 10 5 1.56.10 " Sm 22.5 613,568 10 6 1.56.10 ~5 Sm,1.55.10 ~5 Eu 22.4 613,568 10 Table 1 (follows) 1 Phosphor Gram-atoms of acti¬ Stimulated light | Emission peaks | no. vators per mole of intensity | Peaks (nm) |Relative intensity LaOBr (Arbitrary units) | |(Estimated values) 1 7 1.56.10 ~3 Sm,1.54.10 ~ Eu 16.0 |613,568 | 10 1 1.56.1θ " Sm,1.67.10~ Pr 39-9 |6l3,568 | 10 |505 1 0.5 1 9 1.56.10 -5 Sm,1.67.10 ~ Pr 34-3 |6l3,568 | 10 1 A 1.48.10~ 4 Tb,8.38.10~ 4 Ce 8.1 1444,419,384 1 10 |350-480 1 1(broad band) | 5 N.B.: While arbitrary units ape such that the intensity values can be compared with each other to understand the relative values of different phosphors, the estimated values are such that the relative intensities of the emission peaks are evaluated within each phosphor sample and cannot be compared with the intensities of EXAMPLE 4 Samples of the phosphors of Example 2 containing Pr as activator were exposed as described in Example 3, stimulated with light of 632 nm. The stimulating light, which was reflected, was then filtered out by an interference filter C (TMVI.5) having a transmission peak at 505 nm. The intensity of the stimulated light detected by a photomultiplier and the emission peaks under continuous X-ray irradia¬ tion are reported in the following Table 2. (follows Table 2) T B L E 2 Phosphor Gram-atoms of acti¬ Stimulated Light | Emission Peaks no. vators per mole of Intensity | Peaks (nm) Relative intensity LaOBr (Arbitrary units) (Estimated values) 10 1.67.10 ~3 Pr,1.68.10~ Ce 600 1505 10 |(broad band) 11 1.67.10 ~5 Pr,l.68.lO~ 3 Ce 730 1505 2 1 (broad band) 12 1.67.10- Pr,1.48.lO~ Tb 315 1505 10 1444,419,384 3 13 1.67.10 _4 Pr 210 1505 10 A l.48.10~ Tb,8.38.10~ 4 Ce 468 1444,419,384 10 EXAMPLE 5 A radiation image storage panel was manufactured in accord¬ ance with the following manufacturing process. A coating dispersion was prepared according to the following composition: Phosphor 1 500 g Gafac RE 410 (an oil-soluble anionic wetting agent sold by GAF) 2. 5 g Elvacite 2044 (a poly-n-butylmethacrylate sold by DuPont) 30 g Elvacite 2045 (a polyisobutylmethacrylate sold by DuPont) 40 g Tributoxyethylphosphate 1. 4 g Methylenechloride 44 g Toluene 36 g n-hexane 21 g n-heptane 21 g The coating dispersion was unformly applied to a polyethylene terephthalate film support provided in the order with: 1) a primer layer of 1 ,u comprising a mixture of 50% cellulose triacetate and 50% of a high molecular weight polyester of ethylene glycol and isophthalic and terephthalic acid5 and 2) a reflective layer of 20-30 comprising titanium dioxide di- spersed in a polyurethane resin obtained by blending 45% of Desmophen 650 and 55% of Desmodur L, sold by Bayer, to obtain a fluorescent layer of 150 ,u.

Claims: CLAIMS: 1. A method for recording and reproducing a radiation image comprising the steps of (i) causing a visible radiation-stimulable 5 phosphor to absorb a radiation passing through an object, (ii) stimu¬ lating said phosphor with visible radiations to release the energy stored as fluorescent light, and (iii) detecting said fluorescent light with a photodetector, said method being characterized in that said phosphor is selected from the group of Samarium and/or Praseodymium 10 activated rare earth oxyhalide phosphors. 2. The method as defined in claim 1, wherein said phosphor is represented by the formula: LaOBr : aA,bB lζ in which A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce, and a and b are numbers satisfying the -8 -4 -4 conditions 10 a 10 and 04b. 10 . 3. A method for recording and reproducing a radiation image 20 comprising the steps of (i) causing a visible radiation-stimulable phosphor to absorb a radiation passing through an object, (ii) stimu¬ lating said phosphor with visible radiations to release the energy stored as fluorescent light, and (iii) detecting said fluorescent light * with a photodetector, said method being characterized in that the 25 wavelength of said stimulating radiations is within the range of 540 to 400 nm, the wavelength of said light detected by the photodetector is within the range of 56O to 650 nm and said phosphor is Samarium acti¬ vated rare earth oxyhalide phosphor. 30 4- The method as defined in claim 3, wherein said phosphor is represented by the formula: LaOBr : cSm,dB wherein B is at least one element selected from the group of Tb, Eu and —8 Ce and c and d are numbers satisfying the conditions C ,d, 10 4 c 410~ 4 and 0 d<?10 . 5. A method for recording and reproducing a radiation image comprising the steps of (i) causing a visible radiation-stimulable phosphor to absorb a radiation passing through an object, (ii) stimu¬ lating said phosphor with visible radiations to release the energy stored as fluorescent light, and (iii) detecting said fluorescent light with a photodetector, said method being characterized in that the wavelenth of the stimulating radiations is within the range of 490 to 400 nm or 550 to 650 nm, the wavelength of said light detected by the photodetector is within the range of 500 to 540 nm and said phosphor is a Praseodimium activated rare earth oxyhalide phosphor. 6. The method as defined in claim 5, wherein said phosphor is represented by the formula: LaOBr : ePr,fC in which C is at least one element selected from the group of Tb, Ce —8 and Sm and e and f are numbers satisfying the conditions e^f, 10 4 e 410~ 4 and 0 f410~ 4 . 7. A method for recording and reproducing a radiation image comprising the steps of (i) causing a visible radiation-stimulable phosphor to absorb a radiation passing through an object, (ii) stimu¬ lating said phosphor with visible rays to release the energy stored as fluorescent light, and (iii) detecting said fluorescent light with a photodetector, said method being characterized in that the wavelenth of the stimulating rays is within the range of 520 to 400 nm, the wavelength of said light detected by the photodetector is within the range of 350 to 450 nm and said phosphor is a Samarium and Terbium coactivated rare earth oxyhalide phosphor. 8. The method as defined in claim 7, wherein said phosphor is represented by the formula: LaOBr : gSm,hTb —8 wherein g and h are numbers satisfying the conditions g . Th, 10 9. A method for recording and reproducing a radiation image comprising the steps of (i) causing a visible radiation-stimulable phsphor to absorb a radiation passing through an object, (ii) stimulating said phosphor with visible rays to release the energy stored as fluorescent light, and (iii) detecting said fluorescent light with a photodetector, said method being characterized in that the wavelength of the stimulating rays is within the range of 520 to 460 nm, the wavelength of said light detected by the photodetector is within the range of 350 to 450 nm and said phosphor is a Praseodymium and Cerium coactivated rare earth oxyhalide phosphor. 10. The method as defined in claim 9, wherein said phosphor is represented by the formula: LaOBr : gPr,hCe —8 wherein g and h are numbers satisfying the conditions g _.h, 10 g iiIO " and 10 ~ h 10~ 4 » 11. A Samarium and/or Praseodymium activated rare earth oxyhalide stimulable phosphor. 12. The stimulable phosphor as defined in claim 9 represented by the formula: LaOBr : aA,bB wherein A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce, and a and b are numbers satisfying the —8 A Λ conditions 10 ^ a410 and 04b 410 . 13. A radiation image storage panel having a fluorescent layer • comprising a binder and a stimulable phosphor dispersed therein characterized in that said stimulable phosphor is at least one phosphor selected from the group of Samarium and/or Praseodymium activated rare earth oxyhalide stimulable phosphors. 14. The radiation image storage panel as defined in claim 11, wherein said stimulable phosphor is represented by the formula: LaOBr : aA,bB wherein A is Sm and/or Pr, B is at least one element selected from the group of Tb, Eu and Ce and a and b are numbers satisfying the -8 -4 -4 conditions 10 4 a 410 and 04b410 .

Inventors: MORRONE LUCIANO, MORRONE, LUCIANO
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1984
Main classification: C09K11
IPC codes: C09K11, G21K4