JPH02290600A - Radiation image converting screen - Google Patents

Abstract

PURPOSE:To obtain images having good sharpness or the like by providing phosphors consisting of blue light emitting rare earth oxysulfide phosphors for specific radiations on a base and further, providing phosphor layers contg. La, Gd an Lu thereon. CONSTITUTION:The blue light emitting phosphor layer 12 consisting of the blue light emitting phosphors is provided on the base 11 and further, the green light emitting phosphor layer 13 consisting of the green light emitting rare earth phosphors is formed thereon. One kind among the La, Gd and Lu activated by terbium, for example, rare earth oxyhalogen compd. phosphors or the like are used as the green light emitting rare earth phosphors to be used for the radiation converting screen. The rare earth oxysulfide phosphors or the like which are expressed by, for example, compsn. formula (Ln1-a-b, Tba, Tmb, Rb)2O2S, (Ln is one among La, Gd and Lu, (a) and (b) are respectively the numbers satisfying the conditions 0.0005<=a<=0.09, and 0<=b<=0.01) and are activated by the terbium or coactivated by the terbium and thulium are preferable in terms of light emission efficiency are graininess.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation image conversion screen. More details《
is a radiation intensifying screen (hereinafter simply referred to as "intensifying screen") that has multiple phosphor layers consisting of a green-emitting rare earth phosphor layer and a blue-emitting phosphor layer, and exhibits high sensitivity and excellent image characteristics.
and radiation fluorescent screens (hereinafter simply referred to as "fluorescence"), that is, radiation image conversion screens (herein, intensifying screens and phosphors are collectively referred to as "radiation image conversion screens"). .

As is well known, radiation image conversion screens are used for purposes such as medical diagnosis and non-destructive inspection of industrial products, and they absorb the radiation that has passed through the subject and emit ultraviolet or visible light, converting the radiation image into an ultraviolet image or visible light. Convert to visual image. When using a radiation image conversion screen as an intensifying screen, when performing radiography, it is placed in close contact with a radiographic film (hereinafter simply referred to as "film") and the radiation image is transferred to the intensifying screen. The radiation image of the subject is converted into a visible image on the phosphor screen and converted into an ultraviolet image or a visible image on the phosphor screen, which is then exposed to a film and recorded.When used as a phosphor screen, the radiation image of the subject is converted into a visible image on the phosphor screen of the phosphor screen. It can be photographed with a photo camera, projected on a television set with a video tube, or observed directly with the naked eye. The structure of a radiation image conversion screen basically consists of a support such as paper or plastic sheet, and a phosphor layer formed on the support.

The phosphor layer consists of a binder and a phosphor that is dispersed in the binder and emits light efficiently when excited by radiation such as X-rays (radiation phosphor), and its surface is generally covered with a transparent protective film. protected.

In medical diagnosis using radiography, there is a need for a radiography system (combination of film and intensifying screen) with higher sensitivity in order to reduce the exposure dose of the patient, who is the subject.
At the same time, do you need a radiographic system that can obtain photographic image quality (sharpness, graininess, contrast) suitable for diagnosis using clinical photographs? Therefore, it is desired that intensifying screens have high sensitivity, as well as good sharpness, graininess, and contrast. Similarly, fluorescent screens with higher sensitivity and especially better contrast are desired in order to reduce the radiation dose to examinees and obtain good image quality. As a highly sensitive radiation image conversion screen, for example, a terbium-activated rare earth oxysulfide phosphor (Ln.Tb)*O■S (Ln.
(Y,Tb) *s} (
Radiation image converting screens made of rare earth oxysulfide phosphors such as U.S. Pat. Gd, Tb) *0*S), terbium-activated lanthanum oxysulfide fluorescence? {(La, Tb
) Intensifying screens using rare earth oxysulfide phosphors such as However, compared to other high-sensitivity intensifying screens, the graininess is relatively good, so the Orthomatic type (orthomatic type) has spectral sensitivity from the blue region to the green region.
It is used in a high-sensitivity radiographic system in combination with a film called "orthotybe" (hereinafter abbreviated as "orthotybe"). By the way, in recent high-sensitivity radiographic systems that combine a green-emitting rare earth intensifying screen and orthotibe film, fine-grain halogenation is used to reduce the amount of silver used in the film and to improve image quality, especially graininess, in the high-sensitivity region. The use of low-sensitivity type orthofilms using silver has become mainstream. Therefore, there is a demand for higher sensitivity of the intensifying screen in consideration of reducing the radiation dose of the subject, and there is also a strong desire to improve the sharpness of the intensifying screen, which decreases due to higher sensitivity.

Among green-emitting rare earth phosphors, gadolinium oxysulfide phosphor, which is particularly prized for use in high-sensitivity intensifying screens, has a 50. To convert the K absorption edge to 2Kev,
Due to the Xl1 absorption characteristics of the phosphor, the intensifying screen using this intensifying screen has an X-ray tube voltage range (60~
1 4 0 KVp. ) has poor contrast;
This method has the drawback that the sensitivity of the intensifying screen changes greatly with respect to changes in tube voltage, making it difficult to set conditions during imaging.

The present invention was made in view of the above-mentioned situation in a radiological diagnostic system using a radiation image conversion screen, and when used as an intensifying screen in combination with an orthotype film, it is possible to use a green-emitting rare earth phosphor. It has a sensitivity equal to or higher than that of conventional intensifying screens, which maintains image quality, especially graininess, and provides images with good sharpness and contrast. The object of the present invention is to provide a radiation image conversion screen with less sensitivity dependence.

Furthermore, when used as a fluorescent screen in combination with a photographic camera or an X-ray television digital camera, the present invention has a sensitivity equal to or higher than that of a conventional fluorescent screen using a green-emitting rare earth phosphor.
Rather than this, the purpose is to provide a radiation image conversion screen with particularly improved contrast. In order to achieve the above object, the present inventors conducted various studies on the phosphors used in the phosphor layer of the radiation image conversion screen and their combinations, and as a result, they discovered a specific rare earth phosphor that emits green light when irradiated with radiation. It is also used in combination with a rare earth oxysulfide phosphor of a specific composition that emits blue light when irradiated with radiation, and instead of simply mixing these phosphors, a phosphor layer made of the green emitting rare earth phosphor is placed on the surface layer side. We have discovered that the above objective can be achieved by providing a phosphor layer consisting of a blue-emitting rare earth oxysulfide phosphor with a specific composition on the support side (on the side from which light is extracted) and forming the phosphor layer into a multi-layer structure. , we have completed the present invention. The Q radiation image converting screen of the present invention has a composition formula (Yi-c-a-e+Gdc, Tba, Tm.) aOx on a support.
S (however, c, d and e each satisfy O≦c≦o. e
o, 0. 0005≦d≦0.02 and 0≦e≦0.
A phosphor layer made of a blue-emitting rare earth oxysulfide phosphor for radiation represented by 01) is provided, and furthermore, La, Gd, and Lu are added as matrix constituents of the phosphor.
The present invention is characterized in that it is provided with a phosphor counterfeit made of a green-emitting rare earth phosphor for radiation containing at least one of the following.

The radiation image conversion screen of the present invention has a blue-emitting rare earth oxysulfide phosphor of a specific composition (hereinafter, this phosphor is simply referred to as "radiation radiation" in this specification) between a phosphor counterfeit made of a green-emitting rare earth phosphor and a support. Since the screen is equipped with a phosphor layer made of a blue-emitting phosphor (referred to as "blue-emitting phosphor"), it emits blue and green light and has a sensitivity equal to or greater than that of a conventional radiation image conversion screen made only of a green-emitting rare earth phosphor. ．． Furthermore, images with better image quality, especially contrast, can be obtained compared to conventional radiation image conversion screens, and when used in combination with orthotype film as an intensifying screen, the sharpness is improved compared to conventional intensifying screens. However, the sensitivity dependence of X-rays on tube voltage is also improved.

The present invention will be explained in more detail below.

The radiation image conversion screen of the present invention is manufactured by the method described below.

First, mix an appropriate amount of a blue-emitting phosphor for radiation use and a binder resin such as nitrified cotton, then add an appropriate amount of a solvent to this to create a phosphor coating liquid with an optimal viscosity. It is coated onto a support made of paper, plastic, etc. using a blade, roll coater, knife coater, etc. Some intensifying screens have a structure in which a light-reflecting layer such as a white pigment layer, a light-absorbing layer such as a black pigment layer, or a metal foil layer is provided between the phosphor layer and the support. When using the screen as an intensifying screen, if necessary, a light reflecting layer, a light absorbing layer or a metal foil layer is provided on the support in advance, and then the above method is applied. A blue phosphor layer may be formed using the following methods. Next, a phosphor coating liquid consisting of a green-emitting rare earth phosphor for radiation use and a binder resin such as nitrified cotton is prepared in the same manner as above, and this is coated on the blue-emitting phosphor layer to form a green-emitting rare earth phosphor. A phosphor layer is formed from the phosphor layer. After the two phosphors emitting different colors are coated on the support in this manner, they are dried to obtain the radiation image converting screen of the present invention. Generally, many radiation image conversion screens have a transparent protective film on the phosphor layer to protect it, but the radiation image conversion screen of the present invention also has a transparent protective film on the green-emitting rare earth phosphor layer. It is better to provide a protective film.

FIG. 1 shows a schematic cross-sectional view of the radiation image conversion screen of the present invention manufactured in this manner, in which a blue-emitting phosphor layer 12 made of a blue-emitting phosphor is provided on a support 11. Further, a green light emitting phosphor layer 13 made of a green light emitting rare earth phosphor is formed thereon. 14 is a transparent protective film provided on the surface of the green light emitting phosphor layer 13.

Furthermore, when producing the blue-emitting phosphor layer in the radiation image conversion screen of the present invention, the blue-emitting phosphor to be coated is previously separated into two or more types in terms of average particle diameter using a phosphor separation means such as a water droplet. After dispersing each phosphor in a suitable binder resin, the particles of the phosphor constituting the blue-emitting phosphor layer are coated onto the support in order of decreasing average particle size and repeatedly dried. Gradually from the green-emitting rare earth phosphor layer side to the support side. They can be arranged with a gradient in particle size so that the particle size becomes small.

FIG. 2 is a schematic cross-sectional view of the radiation image converting screen of the present invention manufactured in this way, in which a blue-emitting phosphor M22 made of a blue-emitting phosphor and a green color made of a green-emitting rare earth phosphor are placed on a support 21. The light-emitting phosphor M23 and the transparent protective film 24 are laminated in this order, but the blue-emitting phosphor particles constituting the blue-emitting phosphor layer 22 are gradually arranged as particles from the green-emitting phosphor layer 23 side toward the support 21 side. The phosphor particles with small diameters are arranged in a row. Such a radiation image conversion screen has a significantly better sharpness than the screen of FIG.

As the green-emitting rare earth phosphor that can be used in the radiation image conversion screen of the present invention, La. A rare earth oxysulfide phosphor that is at least one of Gd and Lu, and a rare earth oxyhalide phosphor (limited to phosphors in which the terbium concentration is more than o. oi moles per mole of the phosphor) ), the rare earth borate phosphor, the rare earth phosphate phosphor, the rare earth tantalate phosphor, etc., Tゎ and thulium (T,) . Dysbrosium (Dy), Braseodymium (Pr), Ytterbium (Yb) and Neodymium (Nd)
), a rare earth oxysulfide phosphor coactivated with at least one rare earth element such as T. , Tsukatsu or T,, and Tffl. Dy, Pr. Oxysulfide phosphors of Y and Gd co-activated with at least one of rare earth elements such as Yb and Nd (limited to cases where the content of gadolinium oxysulfide is 65 to 95 mol%), etc. La. as a parent constituent element. A rare earth phosphor containing at least one of Gd and Lu and exhibiting highly efficient green light emission upon X-ray excitation can be used;
Among these phosphors, aots with the composition formula (Ln+-a-b, Tba, Tmb) are particularly preferred from the viewpoint of luminous efficiency and granularity.
(However, Ln is at least one of La, Gd and Lu, and a and b are each 0.000
This number satisfies the conditions of 5≦a≦0.09 and 0≦b≦0.01. A rare earth oxysulfide phosphor activated with terbium or co-activated with terbium and thulium, represented by the composition formula (Ln+-a-t++Tba.Rb)zOzs
(However, Ln is at least one of La, Gd and Lu, R is at least one of Dy.Pr.Yb
species, a and b are each 0. 0005≦a≦
Terbium-activated or terbium and thulium co-activated rare earth oxysulfide phosphors are preferred.

The blue-emitting phosphor used in the radiation image conversion screen of the present invention is not particularly limited as long as it emits blue light with high efficiency upon excitation of radiation such as X-rays, but the radiation image conversion screen obtained In terms of sensitivity and sharpness, composition formula (Yi-c-6
-s+Gdc, Tba, Tnle) wows (However,
c, d and e each satisfy O≦c≦0. 90.0.
It is preferable to use an oxysulfide phosphor of yttrium or yttrium-gadolinium, which is a number satisfying the following conditions: 0005≦d≦0.02 and 0≦e≦0.01.

The radiation image conversion screen of the present invention has advantages. In terms of the sensitivity and sharpness of the radiation image conversion screen used, the average particle diameter and standard deviation value expressed in quarter deviation values of the phosphor used in the blue-emitting phosphor layer are 2 to 1OL, respectively.
Lm is preferably 0.20 to 0.50, and more preferably average particle diameter and standard deviation are 3 to 0.50, respectively.
6 μm and 0.30 to 0.45 μm, while the average particle diameter and standard deviation value expressed in quarterly deviation values of the phosphor used in the green-emitting phosphor layer are 5 to 20 μm and 0.15 to 0.45 μm, respectively. The average particle size and standard deviation value are preferably 6 to 12 μm, respectively.
and 0.20 to 0.35. In addition, from the viewpoint of the sensitivity and sharpness of the similarly obtained radiation image conversion screen, the coating weight of the phosphor in the blue-emitting phosphor layer and the phosphor coating weight in the green-emitting phosphor layer are 2 to 1, respectively.
00 mg/cm2 and 5 to 100 mg
/cm'', and more preferably, the coating weight of the phosphor in the blue-emitting phosphor layer and the phosphor coating weight in the green-emitting phosphor layer are each 5 to 60 m
g/cm" and 10 to 60 fflg/CffI!. At this time, it is better to make the average particle diameter of the phosphor in the blue-emitting phosphor layer smaller than the average particle diameter of the phosphor in the green-emitting rare earth phosphor layer. More preferable in terms of sharpness.

Figure 3 shows one of the green-emitting rare earth phosphors (Gdo.
oes, Tbo. aos) aO2S phosphor, and FIG. 4 shows the emission spectrum of the radiation image conversion screen of the present invention. The illustrated radiation image conversion screen has a blue-emitting phosphor layer (phosphor coating weight 20 mg/cm2) of (Y...., T
b. ．． ．． ．． ．． ). O. Made of S phosphor? The color-emitting phosphor layer (phosphor coating weight 30 mg/cm2) was (Gd
o. sss, Tt) a. . . 6), consisting of O■S phosphor.

Become. The curves shown by dotted lines and chain lines in FIGS. 3 and 4 show the spectral sensitivity curve of the orthotype film and the spectral sensitivity curve of the image pickup tube, respectively.
As is clear from the comparison between the figure and FIG. 4, the radiation image conversion screen of the present invention has an emission spectrum distribution ranging from green to blue to the near ultraviolet region, so that it can be used as Compared to other radiation image conversion screens, this method better matches the spectral sensitivity of the orthotype film and the photocathode of the image pickup tube, and is particularly advantageous in terms of sensitivity.

Figure 6 shows the ratio (expressed as a percentage) of the phosphor coating weight of the blue-emitting phosphor layer to the total phosphor coating weight of the phosphor layer in the radiation image conversion screen of the present invention, and the sensitivity of the resulting radiation image conversion screen. The relative sensitivity on the vertical axis is the photographic sensitivity when combined with an orthotype film, and the relative sensitivity when the blue-emitting phosphor layer is not included. It is shown as a relative value when the photographic sensitivity in the case (consisting only of a green-emitting rare earth phosphor layer) is set to 100. Note that the curves a and b indicate that the blue-emitting phosphor layer is (Yo.+
+*a, Tba. oot) aOas phosphor and (Gdo
．． s. Yo-4*ajbo. oos+Tma. oz)t
In both cases, the total coating weight of the phosphor layer is 50 mg/cm'', and the green-emitting rare earth phosphor layer is (Gdo.sss, Tbo.

as) Made of JtS phosphor. ' As is clear from FIG.
,Tb). 0. By providing a blue-emitting phosphor layer under a green-emitting phosphor layer made of S phosphor,
Tb). A screen having a photographic sensitivity equal to or higher than that of a conventional radiation image converting screen consisting of a single phosphor layer made of O■S phosphor (consisting only of a green-emitting phosphor layer) can be obtained.

Figure 6 shows the ratio (expressed as a percentage) of the phosphor coating weight of the blue-emitting phosphor layer to the total phosphor coating weight of the phosphor layer in the radiation image conversion screen of the present invention, and the sharpness of the resulting radiation image conversion screen. This shows the relationship between In FIG. 6, curves a and b indicate that the blue-emitting phosphor layer is (Yo.sa, Tbo-...z) al
as phosphor and (Gdo.s+Yo.+ss+Tbo.
oos+Tmo. ooz) i0ss phosphor, and in each case, the total coating weight of the phosphor layer is 50 m
g/cm', and the green-emitting rare earth phosphor eyebrows are (Gda
．． sss, Tbo-oos) aoas phosphor. In addition, the sharpness of each radiation image conversion screen was determined by calculating the MTF value at a photographic density of 1.5 and a spatial frequency of 2 lines/mm, and determined the MTF value for each radiation image conversion screen without a blue-emitting phosphor layer (consisting only of a green-emitting rare earth phosphor layer). It is shown as a relative value when the MTF value of the image conversion screen is set to 100.

As is clear from FIG. 6, the radiation image conversion screen of the present invention, which has a blue-emitting phosphor layer under the green-emitting phosphor layer, has improved sharpness compared to the conventional screen that does not have a blue-emitting phosphor layer. do.

FIG. 7 shows the radiation image conversion screen of the present invention. It is a graph illustrating the X-ray tube voltage dependence of the sensitivity of a conventional radiation image conversion screen. In FIG. 7, curves a and b indicate that the green light-emitting phosphor layer (Gdo.*es, Tbo.oos
) J*S phosphor, and the blue-emitting phosphor layer is (Ya.
sss, Tbo. . . t) This is the case of the radiation image conversion screen of the present invention made of 20zS phosphor (the green-emitting phosphor coating weight is 30 mg/cm", the blue-emitting phosphor coating weight is 20 mg/cm"), and curve b is the case of the fluorescent This is the case of a conventional radiation image converting screen (phosphor coating weight: 50 mg/cm2) whose body layer is (Gd..@.., Tb..,) and composed only of O■S phosphors. 7th
The vertical axis of the figure shows the photographic sensitivity when each radiation image conversion screen is combined with an orthotype film for each X-ray tube voltage. (when combined with regular type film). As is clear from FIG. 7, the radiation image conversion screen of the present invention is used for taking X-ray photographs during medical diagnosis! X-ray tube voltage 60 KVp. ~140 KVp. In the region (Gd, Tb). O. Compared to conventional radiation image conversion screens consisting of a single phosphor layer made of only S phosphor, the change in sensitivity due to differences in X-ray tube voltage is small.

Note that when a green-emitting rare earth phosphor for radiation use other than the (Gdo-ess.Tbo.oos) tchs phosphor is used in the green-emitting phosphor layer, and when (Y..., Tb. ..*)
Even when a blue-emitting phosphor for radiation use other than the JmS phosphor is used, the ratio of the coating amount of the phosphor in the blue-emitting phosphor layer to the total coating amount of the phosphor is similar to the radiation image conversion screen illustrated in FIG. When the sensitivity of the radiation image conversion screen is within a specific range, the sensitivity of the radiation image conversion screen obtained is equal to or higher than that of a conventional screen consisting of only a green-emitting rare earth phosphor layer, and
Similar to the case of the radiation image conversion screen illustrated in Fig. 7 and Fig. 7, the sharpness is improved compared to the conventional radiation image conversion screen consisting only of a green-emitting rare earth phosphor layer, and the sensitivity is less dependent on the X-ray tube voltage. It was confirmed that

Furthermore, the radiation image conversion screen of the present invention has improved photographic contrast compared to the conventional radiation image conversion screen consisting only of a green-emitting rare earth phosphor layer, and can be used as a fluorescent screen for X-ray television screens compared to the conventional radiation image conversion screen. It exhibited superior characteristics, especially in terms of sensitivity and contrast, compared to a fluorescent screen with only a green-emitting rare earth phosphor layer. In addition, from the viewpoint of graininess and sharpness of the resulting radiation image conversion screen, it is preferable to mix each phosphor as in the radiation image conversion screen of the present invention rather than simply mixing the green-emitting rare earth phosphor and the blue-emitting phosphor. Separate phosphor layers and multiple phosphor layers showed superior properties. As described above, the radiation image conversion screen of the present invention has a sensitivity equal to or higher than that of the conventional radiation image conversion screen consisting only of a green-emitting phosphor layer, and does not deteriorate image quality, especially graininess. In addition to improving sharpness and contrast, the sensitivity is less dependent on the X-ray tube voltage, making it easier to set the imaging conditions during X-ray photography. It has great industrial value as a radiation image conversion screen that provides images. Next, the present invention will be explained by examples.

Example The following method was carried out in exactly the same manner except that one of the 10 combinations listed in (1) to (lO) in the table below was used as the green-emitting rare earth phosphor and the blue-emitting phosphor. Radiation image conversion screen (1) to (lO)
was manufactured.

A phosphor coating solution was prepared by mixing 8 parts by weight of a blue-emitting phosphor, 1 part by weight of nitrified cotton, and a solvent. This phosphor coating liquid was coated with a carbon black light absorbing layer on the surface.
The phosphor was coated uniformly onto a thick polyethylene terephthalate support using a knife coater so that the coating weight of the phosphor was as shown in the table below to form a blue-emitting phosphor.

Next, 8 parts by weight of the green-emitting rare earth phosphor and 1 part by weight of nitrified cotton were mixed using a solvent to prepare a phosphor coating solution. This phosphor coating liquid was uniformly coated on the blue-emitting phosphor layer using a knife coater so that the phosphor coating weight was as shown in the table below. A rare earth phosphor fake was formed. Furthermore, nitrified cotton was uniformly applied on the green-emitting rare earth phosphor layer to form a transparent protective film with a thickness of approximately 10 μm. On the other hand, the average particle diameter is 5 μm, the deviation value (quarter deviation value) is 0.35 (
Y0. . . -,Tbo,. . , ), O■S phosphor is preliminarily sized to 3 μm or less, 3 to 5 μm. 5~7μ
8 parts by weight of the phosphor and 1 part by weight of nitrified cotton were mixed using a solvent,
Various types of phosphor coating solutions were prepared. The above phosphor coating solution was coated on a 250 lLm thick polyethylene terephthalate support having a carbon black light absorption layer on the surface, in order from the smallest phosphor particle size to the phosphor coating weight of 5 mg each.
/cm'' + 5 mg/c becomes + 5 mg/cm2 and 5 mg/c, and the phosphor particles are coated uniformly with a knife coater and dried repeatedly for a long time to obtain different phosphor particle sizes (Yo.

ms, Tbo. . . 8) Multiple phosphor layers consisting of 20 Mushroom S phosphors were created. Next, (Gdo,.*s, T with an average particle diameter of 8 μm and a deviation value (quarter deviation value 0.30)
bo-. . s) 8 parts by weight of *0*S phosphor and 1 part by weight of nitrified cotton are mixed using a solvent to make a light carrier coating liquid, and this is used as the above (Yo-e-.Tbo...t) JAS fluorescence The phosphor was applied uniformly onto the body layer using a knife coater so that the coating weight of the phosphor was 30 mg/am'' (Gd...).

. s, Tbo. . . s)*0*S phosphor counterfeit was formed.

Furthermore, (Gd...es.Tt)o. . . s) ala
s Nitrogen cotton was uniformly applied onto the phosphor layer and dried to obtain a radiation image conversion screen (1 liter) as a transparent protective film with a film thickness of approximately 10 μm. Apart from these, as a comparative example, a (Gdo, sea, Tba...) 20S phosphor with an average particle diameter of 8 μm and a deviation value (quarter deviation value) of 0.30 was used, and the phosphor coating weight was 50 mg. A radiation image conversion screen (R) was produced in the same manner as the radiation image conversion screens (1) to (10) above, except that a single phosphor layer of /cm2 was provided on the support. The 11 types of radiation image conversion screens (1) to (11) of the present invention obtained as described above and the radiation image conversion screen (R) manufactured as a comparative example were combined with an orthotibe film to determine their photographic sensitivity, Adjust sharpness, graininess and contrast? However, the results shown in the table below were obtained, and the photographic sensitivity, sharpness and contrast were all better than the conventional radiation image conversion screen (R), and almost no decrease in graininess was observed.

In the table below, the photographic performance of each radiation image conversion screen is determined using ortho G Film (manufactured by Kodak) and an X-ray tube voltage of 80 KVp through an 80 cm thick water phantom. This shows the photographic sensitivity, sharpness, graininess, and contrast when photographed with X-rays, and each display value is displayed as the following value.

Photographic sensitivity: Displays the relative value when the photographic sensitivity of a radiation image conversion screen (KYOKKO FS, manufactured by Kasei Obtonics) having a phosphor layer made of CaWO4 phosphor is set to 100.

Sharpness... The MTF value at a spatial frequency of 2 lines/mm is determined, and (Gd0..m s 1 Tb 6-) at the spatial frequency.

. , ) 20■S Expressed as a relative value when the MTF value of a radiation image conversion screen consisting of a single phosphor layer is set to 100. Graininess... Photographic density l. 0, expressed as RMS value at spatial frequency of 0.5 to 5.0 lines/mm. Contrast... When photographing 1 mm thick Al and 2 mm thick Al, the respective contrasts are determined from the density difference (light intensity) of the photographic film. Displayed as a relative value when the contrast of FS (manufactured by Kasei Obtonics Co., Ltd.) is set to 100.

[Brief explanation of the drawing]

1 and 2 are schematic cross-sectional views of the radiation image conversion screen of the present invention, FIG. 3 is a graph of the emission spectrum of the conventional radiation image conversion screen, and FIG. 4 is a graph of the radiation image conversion screen of the present invention. FIG. 5 and FIG. 6 are graphs of the relative sensitivity and relative sharpness depending on the blue-emitting phosphor proportion of the radiation image conversion screen of the present invention, respectively, and FIG. 7 is a graph of the relative sensitivity and relative sharpness of the radiation image conversion screen of the present invention and 2 is a graph of the relative sensitivity of a conventional radiation image conversion screen depending on the X-ray tube voltage. Fig. 6. (Kakuzu Raiga) x 100 ('/.) Tube electric t (kVp)

Claims (5)

[Claims] (1) On the support (i) compositional formula (Y_1_-_c_-_d_-_e, Gd_c, Tb_
a, Tm_e)_2O_2S (where c, d and e are respectively 0≦c≦0.60, 0.0005≦d≦0.0
2 and 0≦e≦0.01) A phosphor layer made of a blue-emitting rare earth oxysulfide phosphor for radiation is provided, and furthermore, La is provided as a matrix component of the phosphor on top of the phosphor layer. A radiation image conversion screen characterized in that a phosphor layer is provided with a phosphor layer made of a green-emitting rare earth phosphor for radiation containing at least one of , Gd, and Lu. (2) The green light-emitting rare earth phosphor for radiation has a compositional formula (Ln_1_-_a_-_b, Tb_a, Tm_b)_
2O_2S (However, Ln is at least one of La, Gd, and Lu, and a and b are each 0.00
05≦a≦0.09 and 0≦b≦0.01)
___1_-_a_-_b, Ln_1, Tb_a, Tm
_b)_2O_2S (However, Ln is La, Gd and L
u, and i, a and b are 0.65≦i≦0.95, 0.0005≦a≦0.
09 and 0≦b≦0.01) The radiation image conversion screen according to claim 1, wherein the radiation image conversion screen is a rare earth oxysulfide phosphor represented by: (3) The average particle diameter of the phosphor in the blue-emitting rare earth oxysulfide phosphor layer for radiation, its standard deviation value (quarterly deviation value), and the coating weight of the phosphor are each 2 to 10 μm1.
0.20~0.50mg/cm^2 and 2~10.0
mg/cm^2, and the phosphor average particle diameter, its standard deviation value (quarterly deviation value), and phosphor coating weight of the green-emitting rare earth phosphor layer for radiation are 5 to 20 μm and 0, respectively.
．． 15-0.40mg/cm^2 and 5-100mg
3. The radiation image conversion screen according to claim 1 or 2, wherein the radiation image conversion screen has a diameter of /cm^2. (4) The average particle diameter of the phosphor in the blue-emitting rare earth oxysulfide phosphor layer for radiation, its standard deviation value (quarterly deviation value), and the coating weight of the phosphor are 3 to 6 μm and 0, respectively.
．． 30-0.45mg/cm^2 and 5-60mg/
cm^2, and the average particle size, standard deviation value (quarter deviation value), and phosphor coating weight of the green light-emitting rare earth phosphor layer for radiation are 6 to 12 μm and 0.20 to 0.2 μm, respectively.
4. The radiation image conversion screen according to claim 3, characterized in that it is 35 mg/cm^2 and 10 to 60 mg/cm^2. (5) Regarding the particle size of the phosphor particles constituting the blue-emitting rare earth oxysulfide phosphor layer for radiation, the particle size is gradually reduced from the side of the green-emitting rare earth oxysulfide phosphor layer for radiation toward the support side. Claims 1 to 4 characterized in that the arrangement is inclined.
The radiation image conversion screen according to any one of.