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Radiation image converting panelRadiation image converting panel description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090261272, Radiation image converting panel. Brief Patent Description - Full Patent Description - Patent Application Claims
1. Field of the Invention The present invention relates to a radiation image converting panel comprising a radiation converting film having a columnar crystal structure, which converts an incident radiation ray to a visible light. 2. Related Background Art Radiation images typified by X-ray images have conventionally been widely used for purposes such as disease diagnosis. As a technique for obtaining such a radiation image, for example, a radiation image recording and reproducing technique using a radiation converting film that accumulates and records irradiated radiation energy, and also emits a visible light according to radiation energy accumulated and recorded as a result of irradiating an excitation light has been widely put into practical use. A radiation image converting panel to be applied to such a radiation image recording and reproducing technique as this includes a support body and a radiation converting film provided on the support body. As the radiation converting film, a photostimulable phosphor layer having a columnar crystal structure formed by vapor-phase growth (deposition) has been known. When the photostimulable phosphor layer has a columnar crystal structure, since a photostimulable excitation light or photostimulable emission is effectively suppressed from diffusing in the horizontal direction (reaches the support body surface while repeating reflection at crack (columnar crystal) interfaces), this allows remarkably increasing the sharpness of an image by photostimulable emission. For example, Japanese Patent Application Laid-Open No. H02-58000 has proposed a radiation image converting panel having a photostimulable phosphor layer for which formed by a vapor-phase deposition method on a support body are slender columnar crystals with a constant tilt with respect to a normal direction of the support body. Furthermore, Japanese Patent Application Laid-Open No. 2005-315786 has proposed a technique for preventing, by sealing a photostimulable phosphor layer formed on a support body with a moisture-proof protective film made of a base material having a surface roughness Ra of 20 nm or less and a multilayered moisture-proof layer, deterioration of the photostimulable phosphor layer due to moisture and the like. The present inventors have examined the conventional radiation image converting panels in detail, and as a result, have discovered the following problems. That is, as a result of a fluorescence lifetime evaluation performed for a radiation converting film of the conventional radiation image converting panel at a constant temperature and high humidity by the inventors, it has been discovered that there is a considerable difference in drops in luminance between the vicinity of center and periphery of the radiation converting film. Here, the fluorescence lifetime evaluation is a test for quantifying drops in luminance value by showing luminance values of samples used for one month (720 hours) under an environment with a temperature of 25° C. and a humidity of 50% as ratios to initial luminance values. In the technique described in the above Japanese Patent Application Laid-Open No. 2005-315786, the characteristics of a radiation converting film as described above have not been taken into consideration at all. Therefore, in accordance with the technique of Japanese Patent Application Laid-Open No. 2005-315786 for uniformly sealing a radiation converting film as a whole by a moisture-proof protective film with a special structure, there has been a problem that the structure of a radiation image converting panel as a whole is complicated (complication of the manufacturing process). The present invention has been developed to eliminate the problems described above. It is an object of the present invention to provide a radiation image converting panel that effectively prevents deterioration in fluorescence lifetime of the entire panel by a simpler structure. A radiation image converting panel according to the present invention has been completed by the inventors\' discovery that a drop in luminance of the panel can be effectively suppressed by controlling the concentration of Eu to be doped in a radiation converting film. In concrete terms, a radiation image converting panel according to the present invention comprises a support body, and a radiation converting film formed on the support body. The support body includes a parallel plate having a first main surface on which the radiation converting film is formed and a second main surface opposing the first main surface. The radiation converting film is formed on a film forming region which exists within the first main surface of the support body and is located so as to include at least a gravity center position of the first main surface. The radiation converting film is an Eu-doped photostimulable phosphor layer, and is comprised of columnar crystals which are coincident or tilted at a predetermined angle with respect to a normal direction of the first main surface. Particularly, in the radiation image converting panel according to the present invention, for an Eu concentration distribution of the radiation converting film, a concentration gradient is provided so as to become higher in a peripheral area than in the radiation converting film located on the gravity center position (a central area). In concrete terms, in the film forming region of the first main surface, an Eu concentration of the radiation converting film, located on a peripheral area sandwiched by an edge of the film forming region and a circumference of a reference circle around the gravity center position, is set higher than an Eu concentration of the radiation converting film located on the gravity center position. Here, the reference circle has a radius of 40% or more but 80% or less of a minimum distance from the gravity center position to the edge of the film forming region. Also, in the radiation image converting panel according to the present invention, the Eu concentration of the radiation converting film preferably monotonically increases from the gravity center position toward the circumference of the reference circle. Moreover, since an optimal value of the Eu concentration corresponding to the gravity center position changes depending on the laser wavelength and laser beam characteristics of an optical scanning device, sensitivity of an image pickup device, and the like, the Eu concentration of the radiation converting film located on the gravity center position is preferably 0.001 wt % or more but 0.3 wt % or less. In the radiation image converting panel according to the present invention, for more effectively suppressing a drop in luminance of the radiation converting film, the Eu concentration of the radiation converting film located on the peripheral area is preferably 0.06 wt % or more. However, for maintaining the luminance of the entire radiation image converting panel in a uniform state, the Eu concentration of the radiation converting film on the peripheral area is preferably two times or less higher than the Eu concentration of the radiation converting film located on the gravity center position. Furthermore, the radiation image converting panel according to the present invention may comprise a moisture-resistant protective film (transparent organic film) that covers an exposed surface of the radiation converting film without a surface of the radiation converting film covered by the first main surface of the support body (the surface attached to the first main surface). The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will be apparent to those skilled in the art from this detailed description. Continue reading about Radiation image converting panel... Full patent description for Radiation image converting panel Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Radiation image converting panel patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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