JPH0149438B2 - - Google Patents

Description

[Detailed description of the invention]

A. Industrial Application Field The present invention relates to an X-ray intensifying screen that uses a phosphor that emits light when stimulated by X-rays, and is mainly used in medical radiography or industrial radiography. Regarding photosensitive paper. B. Prior Art and Problems X-ray intensifying screens are generally used in combination with photographic film to improve the sensitivity of imaging systems in medical radiography. The phosphor used in such an X-ray intensifying screen is required to have a large amount of X-ray absorption, high luminous efficiency, and weak afterglow component. An X-ray intensifying screen coated with a phosphor that absorbs a large amount of X-rays has good graininess in X-ray images and improves diagnostic efficiency in medical radiography. An intensifying screen with high luminous efficiency can be used with less X-ray irradiation, reducing the exposure dose of the examiner. Furthermore, an intensifying screen with less afterglow components can prevent misdiagnosis due to afterimages (afterglow noise). In recent years, due to the demand for reducing the exposure dose of subjects, _{Gd 2 O 2} S:Tb,
X-ray intensifying screens using phosphors such as BaFCl:Eu, LaOBr:Tm, and YTaO ₄ :Tm have been put into practical use. However, BaFCl:Eu and LaOBr:Tm have poor X-ray granularity due to their low X-ray absorption.
Furthermore, since the grains have a tabular shape, light generated by X-rays is often scattered, reducing the sharpness of the X-ray image. Gd ₂ O ₂ S: Tb emits light in the blue to green region and is used in combination with orthofilm, which is sensitive in the blue to green region, so the film is easily exposed to light in the dark room, making it necessary to dim the dark room lamp. It is hot and workability is poor. YTaO ₄ :Tm phosphor has a strong afterglow component and noise due to afterglow occurs during continuous shooting, which limits its uses. The afterglow component is weak, and
If a phosphor with the characteristics of YTaO ₄ :Tm phosphor can be developed, it will be possible to create a phosphor with ideal characteristics for X-rays. The present invention was developed to achieve this, and an important objective of the present invention is that the phosphor has a large amount of X-ray absorption, has high luminous efficiency, and has a weak afterglow component. Therefore, it is an object of the present invention to provide an X-ray intensifying screen that reduces the exposure dose to a subject and has high diagnostic performance. C Means for Solving Conventional Problems In order to achieve the above object, the present inventor conducted various studies on X-ray intensifying screens having rare earth tantalate phosphors and rare earth niobate phosphors. . As a result, Be, Mg, Ca,
By containing at least one divalent metal among Sr, Ba, Zn, and Cd in a specific range, we succeeded in significantly improving the afterglow characteristics. In addition, the phosphor obtained by containing a specific amount of divalent metal is
Not only does it have significantly improved afterglow properties,
It was also possible to significantly improve luminous efficiency. Therefore, in the X-ray intensifying screen of the present invention, the phosphor is attached to the surface of the support in a dispersed state with a binder,
This phosphor is represented by the following general formula (). M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ () However, M is Be, Mg, Ca, Sr, Ba, Zn, Cd
at least one divalent metal selected from the group, Ln is at least one element of Y, Gd, La, and Lu, D includes either or both of Ta and Nb, and a is 1×10 ^-5 ≦a≦1, x is 0≦x≦
It is in the range of 0.05. When the content of M, which is a divalent metal contained in the phosphor, is large, the afterglow characteristics are improved, but when the content is too large, the luminous efficiency is reduced. In the general formula representing the content of the divalent metal M, a is determined in the range of 1×10 ⁻⁵ to 1 in consideration of afterglow characteristics and luminous efficiency. In addition, Tm, which is an activator, is
If it is too large, the luminous efficiency will decrease. However, since the phosphor of the present invention emits light from its matrix, it can also be used in a self-activated manner without containing any activator. D Usage, Effects The phosphor represented by the above general formula () used in the X-ray intensifying screen of the present invention has excellent X-ray absorption characteristics and luminous efficiency, and has also been significantly improved. It exhibits afterglow characteristics. Furthermore, by adjusting the content of each element within a specific range, it is possible to achieve higher luminance than conventional phosphors. The X-ray intensifying screen using the phosphor represented by the above general formula () can constantly obtain images of excellent image quality with little noise due to afterglow, and
It is also possible to improve the sensitivity of X-ray images,
The amount of radiation exposure of the subject can be reduced. The features of the present invention will be explained in detail with reference to FIGS. 1 to 11. In Fig. 2, curve B is expressed by the general formula, M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ , where M is Sr,
When Ln is Y, D is Ta, a=0.075, x=0, that is, Sr _0.075 Y _0.950 TaO ₄ The afterglow characteristic of the phosphor is shown. For comparison, the conventional case where a=0, that is,
Curve A shows the afterglow characteristics of YTaO ₄ phosphor. In Figure 2, the vertical axis is the relative afterglow amount (log [light emission amount after a certain period of time/light emission amount during X-ray stimulation]), and the horizontal axis is
It shows the afterglow decay time (time elapsed after X-ray irradiation was stopped). According to FIG. 2, X of the present invention where a=0.075
It can be seen that the phosphor used in the line intensifying screen has significantly better afterglow characteristics than the conventional phosphor in which a=0. Furthermore, in FIG. 2, in the above general formula () M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ , M is Sr,
Ln is Y, D is Ta, x=0, a=0.375, a=
In the case of 0.600, that is, the afterglow characteristics of the phosphors Sr _0.375 Y _0.750 TaO ₄ and Sr _0.600 Y _0.600 TaO ₄ are shown in order by curves C and D. According to this figure, a=0.075, a=0.375, a=
The phosphor of the X-ray intensifying screen of the present invention of 0.600 is a=0
It is clear that the afterglow property is especially excellent compared to the phosphors of conventional X-ray intensifying screens. Next, the emission characteristics of the phosphor Sr _a Y _1-x-(2/3)a TaO ₄ :xTm ³⁺ of the X-ray intensifying screen of the present invention are
This will be explained based on the drawings and FIG. 11. 7 and 11 show the emission spectra of the phosphors, with the horizontal axis showing the emission wavelength (in nm) and the vertical axis showing the amount of light emission (in arbitrary units). In Figure 7, curves A, B, and C are each a
=0.075, 0.375, 0.600, X of the present invention where x=0
Curve D shows the emission spectra of the phosphors of the line intensifying screen, namely, Sr _0.075 Y _0.950 TaO ₄ (Curve A), Sr _0.375 Y _0.750 TaO ₄ (Curve B), and Sr _0.600 Y _0.600 TaO ₄ (Curve C). , conventional X-ray intensifying screen phosphor
The _YTaO4 emission spectrum is shown. According to this figure, the phosphors of the present invention with a = 0.075, 0.375, and 0.600 have a broader emission spectrum in the vicinity of 370 nm, compared to the phosphor of the conventional X-ray intensifying screen with a = 0. It can be seen that there is a second emission peak at . In particular, a=
The 0.075 phosphor emits significantly more light than the phosphor of conventional X-ray intensifying screens that do not contain Sr. Moreover, in FIG. 11, curves A and B are
Conventional X-ray intensifying screen phosphor Y _0.995 TaO ₄ :
0.005Tm ³⁺ and the phosphor of the X-ray intensifying screen of the present invention
The emission spectrum of Sr _0.075 Y _0.945 TaO ₄ :0.005Tm ³⁺ is shown. According to this figure, the phosphor of the X-ray intensifying screen of the present invention (curve B) has a higher concentration of Tm ³⁺ as an activator than the phosphor of the conventional X-ray intensifying screen (curve A). It can be seen that in addition to the increase in the emission peak near 350 nm, the amount of emission in the parent emission ranges of 300 nm to 340 nm and 370 nm to 440 nm has increased significantly. Next, the phosphor Cd _a of the X-ray intensifying screen of the present invention
The afterglow characteristics and luminescence characteristics of A _1-x-(2/3)a TaO ₄ :xTm ³⁺ will be explained with reference to FIG. 4, FIG. 10, and FIG. 11. Figure 4 shows the influence of Cd _a Y _1-(2/3)a TaO ₄ , the cadmium content (a value) of the phosphor, on the afterglow characteristics. A, B, C,
In the above general formula, D is, in order, a=0, a=
0.030, a=0.075, and a=0.150. As is clear from this figure, a=0.030, a=
0.075, a=0.150 in the X-ray intensifying screen of the present invention, the afterglow property was significantly improved compared to the phosphor in the conventional X-ray intensifying screen in which a=0. Also, as is clear from Figure 10, Cd _a
Y _1-(2/3)a TaO ₄ phosphor (curves A, B, C) has a broader emission spectrum compared to YT _a O ₄ (curve D), a phosphor used in conventional X-ray intensifying screens. However, especially in the case of a phosphor with a=0.030 shown by curve A, the amount of light emission increases significantly. Furthermore, as shown in Figure 11,
Compared to the phosphor of the conventional X-ray intensifying screen (curve A), the phosphor of the X-ray intensifying screen of the present invention (curve C) exhibits both luminescence from Tm ³⁺ , which is an activator, and luminescence from the matrix. , was confirmed to increase significantly. Such trends shown in FIGS. 2, 4, 7, 10, and 11 can be seen in the general formula (),
M appears in the same way for Be, Mg, Ca, Ba, and Zn, and the afterglow characteristics and luminescence amount can be improved. In Figures 1 and 3, M in the general formula () is
The afterglow characteristics of a phosphor with Ca and Ba and x=0 are shown. As is clear from these figures, the X of the present invention
As shown by curves B, C, and D, the phosphor of the X-ray intensifying screen exhibited superior afterglow characteristics compared to the phosphor of the conventional X-ray intensifying screen (curve A). Furthermore, in FIG. 5, FIG. 6, FIG. 8, and FIG. 9, in the general formula (), M is Mg, Ca, Ba, Zn,
2 shows the emission characteristics of the phosphor of the X-ray intensifying screen of the present invention where x=0. As is clear from these figures, the phosphor of the X-ray intensifying screen of the present invention, as shown by curves A, B, and C, has a broader spectrum than the conventional phosphor of a=0 (curve D). It had a unique emission spectrum, and the amount of light emission was significantly increased. Furthermore, as shown in Table 1, the X-ray intensifying screen using the above- _mentioned phosphor has a luminance of 60 to It exhibited excellent luminance of 140%. X
The luminance of the line intensifying screen was similar to that of phosphor powder, and a phosphor with high luminance was used in powder form.

[Table] The X-ray intensifying screen showed high luminance. The afterglow properties did not change between the state of the phosphor powder and the state of the X-ray intensifying screen, and an X-ray intensifying screen with excellent afterglow properties was realized. However, in the measurements shown in Table 1, the brightness of the phosphor is measured by irradiating the phosphor with X-rays, transmitting the emitted light from the phosphor through a filter with the characteristics shown in FIG.
I irradiated the photo multiplier, and even with this,
The luminescence intensity was converted to current, and the magnitude of the output current was compared. FIG. 13 shows the sensitivity characteristics of the photomultiplier. Also, in the general formula (), M is Be, Mg,
In the case of two or more types of Ca, Sr, Ba, Zn, and Cd, the excellent trends shown in FIGS. 1 to 11 also appeared. E Preferred Embodiment An X-ray intensifying screen basically consists of a support and a phosphor layer provided thereon, and the phosphor layer is made of a phosphor represented by the above general formula (). It consists of a binder containing and supporting the following in a dispersed state.
The phosphor layer can be formed on the support by the following method. First, the phosphor represented by the above general formula () and a binder are added to a solvent and mixed to prepare a coating solution in which the phosphor particles are uniformly dispersed in the binder solution. As examples of binders for the phosphor layer, mention may be made of nitrocellulose, polyalkyl (meth)acrylates, linear polyesters and mixtures thereof. Examples of solvents for preparing coating solutions include esters of lower fatty acids and lower alcohols such as ethyl acetate and butyl acetate, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and ethylene glycol monoethyl ether, and mixtures thereof. be able to. The mixing ratio of the binder and the phosphor in the coating solution varies depending on the characteristics of the intended intensifying screen, the particle size of the phosphor, etc., but in general, the mixing ratio of the binder and the phosphor is 1. :8 to 1:40 (weight ratio) is preferable. The coating solution also contains a dispersant to improve the dispersibility of the phosphor particles in the coating solution, and a dispersant to improve the bonding force between the binder and the phosphor particles in the phosphor layer after formation. Additives such as plasticizers may be mixed. The coating solution prepared as described above is coated uniformly on the surface of the support using a conventional coating means such as a doctor blade, roll coater, knife coater, etc. to form a film of the coating solution. Form. After the coating film is formed, the coating film is dried to complete the formation of the phosphor layer on the support. The thickness of the phosphor layer varies depending on the intended characteristics of the intensifying screen, the particle size of the phosphor, the mixing ratio of the binder and the phosphor, etc., but it is usually preferably selected from the range of 70 μm to 700 μm. Note that the phosphor layer may have only one layer, but may have two or more layers. When laminated, at least one of the layers contains a phosphor represented by the above general formula (). The support can be arbitrarily selected from various materials known as supports for intensifying screens. Examples of such materials include films of plastic materials such as cellulose acetate, polyester, polyamide, polycarbonate, metal sheets such as aluminum foil, aluminum alloy foil, pigmented paper containing titanium dioxide, etc. . In addition, when using plastic film,
A light-absorbing substance such as carbon black may be incorporated, or a light-reflecting substance such as titanium dioxide may be incorporated. The former is a support suitable for a high sharpness type intensifying screen, and the latter is a support suitable for a high sensitivity type intensifying screen. In a typical X-ray intensifying screen, a transparent protective film for physically and chemically protecting the phosphor layer is provided on the surface of the phosphor layer on the opposite side that is in contact with the support. It is preferable that such a transparent protective film be provided also for an intensifying screen in which the phosphor of the present invention is used. The transparent protective film is made of, for example, a cellulose derivative such as cellulose acetate or nitrocellulose, or
polymethyl methacrylate, polycarbonate,
It can be formed by coating the surface of the phosphor layer with a solution prepared by dissolving a transparent polymeric substance such as polyvinyl acetate in an appropriate solvent. Alternatively, it can also be formed by a method in which a transparent thin film separately formed from polyethylene, polyethylene terephthalate, polyamide, etc. is adhered to the surface of the phosphor layer using a suitable adhesive. Next, examples of the phosphor and the X-ray intensifying screen used in the X-ray intensifying screen of the present invention will be described. However, these examples do not limit the present invention. Example 1 Weighed 107.26 g of yttrium oxide, 11.07 g of strontium carbonate, and 220.95 g of tantalum pentoxide.
Add 25 g of lithium chloride as a flux and mix by pulverizing with a ball mill. Next, the obtained raw material mixture is filled into an alumina crucible, calcined at 1200°C for 10 hours, pulverized in a ball mill, washed 5 times with pure water by decantation, and suction filtered. Furthermore, this is dried at 120°C for 15 hours. The general formula of the phosphor thus obtained is Sr _0.075 Y _0.950 TaO ₄
It was confirmed that it can be expressed as As shown in Table 1, this phosphor exhibits significantly lower afterglow property than conventional product 1 (YTaO ₄ ), which does not contain strontium, and has a relative luminance that is lower than that of conventional product 1.
Improved by 44%. Next, using this phosphor, an X-ray intensifying screen was made in the following manner. Methyl ethyl ketone was added to a mixture of phosphor particles and linear polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was further added to prepare a phosphor dispersion. After adding diethyl phthalate, phthalic acid, and methyl ethyl ketone to this dispersion, they were thoroughly stirred and mixed using a homogenizer, so that the mixing ratio of binder and phosphor was 1:20 (weight ratio), and the viscosity was 30PS (at 25°C). ) was prepared. This coating liquid was kneaded into titanium dioxide placed horizontally on a glass plate, and uniformly applied onto a polyester sheet (support, thickness 200 μm) using a doctor blade. After coating, the support on which the coating film has been formed is dried in a dryer.
A phosphor layer with a thickness of 180 μm was formed on the support. Then, a polyethylene transparent film was adhered onto this phosphor layer using a polyester adhesive to form a transparent protective film (thickness: 10 μm), thereby creating an intensifying screen. The sensitivity of this X-ray intensifying screen was improved by 29% compared to conventional products that do not contain strontium, and furthermore, the sensitivity of the film due to afterglow was eliminated. (Table 1) Example 2 Yttrium oxide 107.26g, calcium carbonate
7.51 g of tantalum pentoxide and 220.95 g of tantalum pentoxide were weighed, and the other methods were the same as in Example 1 to obtain a phosphor having the general formula Ca _0.075 Y _0.950 TaO ₄ . This phosphor has a significantly weaker afterglow component than conventional products that do not contain calcium. (Table 1) Furthermore, the relative brightness was improved by 23% compared to the conventional product that does not contain calcium. (Table 1) The X-ray intensifying screen using this phosphor has a 21% improvement in sensitivity compared to the X-ray intensifying screen using conventional product 1, which does not contain calcium. It was confirmed that the optical properties were also extremely excellent. Example 3 Yttrium oxide 110.65g, barium carbonate 5.92g
g, 220.95 g of tantalum pentoxide were weighed, and the other methods were manufactured in the same manner as in Example 1, and the general formula
A phosphor of Ba _0.03 Y _0.98 TaO ₄ was obtained. The relative brightness of this phosphor was 49% higher than conventional product 1, which does not contain barium, and the relative afterglow amount was approximately 1/8. (Table 1) In addition, the X-ray intensifying screen using this phosphor has a sensitivity of 40° compared to the conventional X-ray intensifying screen using phosphor 1.
% improved. (Table 1) Example 4 Yttrium oxide 110.65g, magnesium carbonate
2.53 g of tantalum pentoxide and 220.95 g of tantalum pentoxide were weighed, and the other methods were the same as in Example 1 to obtain a phosphor having the general formula Mg _0.03 Y _0.98 TaO ₄ . The relative brightness and relative afterglow of this phosphor are the first in comparison to conventional products that do not contain magnesium.
The photometric results shown in the table were obtained. Furthermore, the sensitivity of the X-ray intensifying screen using this phosphor was improved by 23% compared to conventional product 1. Example 5 Yttrium oxide 101.62g, cadmium carbonate
25.86 g of tantalum pentoxide and 220.95 g of tantalum pentoxide were weighed, and the other methods were the same as in Example 1 to obtain a phosphor having the general formula Cd _0.15 Y _0.90 TaO ₄ . The relative brightness of this phosphor was improved by 43% compared to conventional product 1, and the relative afterglow amount was reduced to about 1/360. Furthermore, the sensitivity of the X-ray intensifying screen using this phosphor was improved by 41% compared to conventional product 1. (Table 1) Example 6 Yttrium oxide 110.65g, zinc carbonate 3.76g,
Weighed 220.95 g of tantalum pentoxide, otherwise manufactured in the same manner as in Example 1, and obtained the general formula
A phosphor of Zn _0.03 Y _0.98 TaO ₄ was obtained. The relative brightness and relative afterglow amount of this phosphor showed the photometric results shown in Table 1 compared to Conventional Product 1 which does not contain zinc. Furthermore, the sensitivity of the X-ray intensifying screen using this phosphor was improved by 27% compared to conventional product 1. (Table 1) Example 7 Yttrium oxide 110.08g, Thulium oxide 0.96
Dissolve g in 340ml of 10N hydrochloric acid and add pure water.
After reducing the volume to 1000 ml, heat to 80°C while stirring. On the other hand, an oxalic acid aqueous solution prepared by dissolving 220 g of oxalic acid in 1000 ml of pure water is heated to 80°C, and added to the hydrochloric acid solution heated to 80°C while stirring.
In this way, yttrium and thulium oxalates are produced and co-precipitated in the mixed solution. Next, the solution containing the precipitate is left to cool, and then washed with pure water five times by decantation, and the precipitate is suction-filtered. This precipitate is thermally decomposed at 850° C. for 3 hours to convert oxalate into an oxide. 111.04 g of the thus obtained oxide, 0.75 g of beryllium oxide, 219.85 g of tantalum pentoxide, and 0.66 g of nibium pentoxide were weighed. _0.03 Y _0.975
A phosphor with Ta _0.995 Nb _0.005 O ₄ :0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow amount of this phosphor are
Compared to Conventional Product 2 which does not contain beryllium, the photometric results shown in Table 1 are shown, demonstrating that the X-ray intensifying screen using this screen exhibits excellent characteristics. Example 8 Yttrium oxide 110.08g, thulium oxide 0.96
g, strontium carbonate 4.43g, tantalum pentoxide
220.95g was weighed, and the other methods were the same as in Example 7, and the general formula Sr _0.030 Y _0.975 TaO ₄ :
A phosphor with 0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow amount of this phosphor showed the photometric results shown in Table 1 compared to conventional product 2 which does not contain strontium, and the X-ray intensifying screen using this phosphor showed superior characteristics. was demonstrated. Example 9 Yttrium oxide 50.53g, gadolinium oxide
81.11g, thulium oxide 0.96g, barium carbonate
Weighed 29.60g, tantalum pentoxide 220.95g,
Other methods were similar to those in Example 7,
A phosphor having the general formula Ba _0.1500 Y _0.4475 Gd _0.4475 TaO ₄ :0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow of this phosphor show the photometric results shown in Table 1 compared to conventional products that do not contain barium, and it is clear that the X-ray intensifying screen using this phosphor exhibits excellent characteristics. Proven. Example 10 Yttrium oxide 44.88g, lanthanum oxide 64.76
g, thulium oxide 0.96g, cadmium carbonate 51.72g
g, 220.95 g of tantalum pentoxide were weighed, and the other methods were the same as in Example 7, and the general formula
A phosphor with Cd _0.300 Y _0.3975 La _0.3975 TaO ₄ :0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow amount of this phosphor are the first compared to conventional product 4 that does not contain cadmium.
The photometric results shown in the table demonstrate that the X-ray intensifying screen using this screen exhibits excellent characteristics. In Table 1, the relative afterglow amount is Log[30
Afterglow amount after seconds/light emission amount]. As shown in Examples 1 to 6, the phosphor of the X-ray intensifying screen of the present invention emits light itself, so it can be used without containing any Tm as an activator. Furthermore, in the phosphor of the present invention whose matrix emits light, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Yb, etc. may be used as an activator in addition to or in place of Tm. .

[Brief explanation of drawings]

Figures 1 to 4 are graphs showing the afterglow characteristics of phosphors that emit light when stimulated by X-rays, and Figures 5 to 11 are graphs showing changes in the element M and the value of a in the general formula (). Figure 12 is a characteristic diagram of the filter used to measure the luminance of the phosphor, and Figure 13 is a sensitivity characteristic diagram of the photomultiplier used to measure the luminance of the phosphor. be.

Claims (1)

[Scope of Claims] 1. An X-ray intensifying screen comprising a support and a phosphor layer provided on the support and having a binder containing and supporting the phosphor in a dispersed state. The phosphor in the body layer is expressed by _{the general formula (), where} M is Be, Mg, ^Ca , Sr, Ba, Zn, or Cd. At least one divalent metal selected from the group Ln
is at least one element of Y, Gd, La, and Lu, D includes either or both of Ta and Nb, and a
is in the range of 1×10 ^-5 ≦a≦1, and x is in the range of 0≦x≦0.05. 2 In the general formula () showing the composition of the phosphor, M
The X-ray intensifying screen according to claim 1, wherein is Ca and a is 1×10 ⁻⁵ ≦a≦3×10 ⁻¹ . 3 In the general formula () showing the composition of the phosphor, M
The X-ray intensifying screen according to claim 1, wherein is Sr and a is 1×10 ⁻⁵ ≦a≦6×10 ⁻¹ . 4 In the general formula () showing the composition of the phosphor, M
The X-ray intensifying screen according to claim 1, wherein is Ba and a is 1×10 ⁻⁵ ≦a≦6×10 ⁻¹ . 5 In the general formula () showing the composition of the phosphor, M
The X-ray intensifying screen according to claim 1, wherein Cd is Cd and a is 1×10 ⁻⁵ ≦a≦6×10 ⁻¹ . 6 In the general formula () showing the composition of the phosphor, M
The X-ray intensifying screen according to claim 1, wherein is Zn and a is 1×10 ⁻⁵ ≦a≦6×10 ⁻¹ .