JPH07108974B2 - Phosphor for X-ray intensifying screen and X-ray intensifying screen using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray intensifying screen phosphor which absorbs X-rays and emits light, and an X-ray intensifying screen using the phosphor. In particular the present invention exhibit effective emission spectrum with respect to the spectral sensitivity of the X-ray film, X-ray absorption is high emission efficiency much further, phosphor and for afterglow component is weak X-ray intensifying screen The present invention relates to an X-ray intensifying screen.

[0002]

2. Description of the Related Art X-ray intensifying screens are manufactured by applying a phosphor for X-ray intensifying screens . The X-ray intensifying screen is generally used by being laminated on a photographic film, and improves the sensitivity of an imaging system in medical radiography. This is because the X-ray intensifying screen absorbs X-rays and emits light, and the emitted light exposes the X-ray film.

For the phosphor of the X-ray intensifying screen used in this state, the following characteristics are important. High absorption of X-rays High emission efficiency Low afterglow component Emission spectrum for X-ray film spectral sensitivity

An X-ray intensifying screen coated with a phosphor having a large amount of X-ray absorption has good graininess of X-ray images and improves diagnostic efficiency in medical radiography. Phosphors with high luminous efficiency can be used with a small amount of X-ray irradiation, and the exposure dose of the subject can be reduced. The fluorescent substance having a small afterglow component can prevent a misdiagnosis due to an afterimage.

Further, it is important that the phosphor for the X-ray intensifying screen shows an emission spectrum effective for the spectral sensitivity of the X-ray film. This is because the emission of the X-ray intensifying screen phosphor exposes the X-ray film. Fluorescence for X-ray intensifying screen
Even if the luminous efficiency of the body is high, if the light with the low spectral sensitivity of the X-ray film, that is, the light with the low exposure sensitivity of the X-ray film is emitted , the phosphor of the X-ray intensifying screen efficiently emits light through the X-ray film. Can not be exposed. Therefore, the phosphor for X-ray intensifying screen has a high emission efficiency and a high emission spectrum.
It is extremely important to set the area of the X-ray film with high exposure sensitivity. Firefly for X-ray intensifying screens with high emission efficiency and emission spectrum for exposing X-ray film efficiently.
The photoconductor has an excellent feature that it can reduce the X-ray exposure dose, improve the image quality, and improve the diagnostic efficiency.

[0006] In particular, in recent years, came to be is a request to reduce the exposure dose of the subject. For this reason, Gd ₂ O ₂ S: Tb, BaFCl: Eu, LaOB is used instead of the CaWO ₄ phosphor that has been conventionally used for X-ray intensifying screens.
An X-ray intensifying screen using a phosphor such as r: Tm, YTaO ₄ : Tm has been put into practical use.

However, BaFCl: Eu phosphor and LaO
Since the Br: Tm phosphor has a small X-ray absorption amount, it has a drawback that the granularity of X-ray photography is poor. Also, these X-ray intensifying screens
Since the phosphor for use has a tabular particle shape, a lot of light generated by X-rays is scattered and the sharpness of the X-ray image is lowered.

Since Gd ₂ O ₂ S: Tb is used in combination with an ortho film which emits in the blue to green region and has sensitivity in the blue to green region, the film is easily exposed to light in a dark room and a dark room lamp is used. Workability is poor because it needs to be dark.

The rare earth tantalate phosphor represented by YTaO ₄ : Tm has a high luminous efficiency, but has a strong afterglow component, and noise is generated due to the afterglow during continuous shooting, which limits its use. The present inventors have conducted various studies on rare earth tantalate phosphors and rare earth niobate phosphors, and as a result, by incorporating a divalent metal in these phosphors in a specific range, the luminous efficiency and residual Succeeded in significantly improving the light characteristics (Japanese Patent Publication No. 4-2753).
4 publication). This phosphor for X-ray intensifying screen is LnMD
This is represented by the general formula of O ₄ : Tm. However, in this general formula, Ln is at least one element of Y, Gd, La, and Lu, and M is Be, Mg, Ca, Sr,
It is at least one divalent metal selected from the group consisting of Ba, Zn, and Cd. Further, D is either or both of Ta and Nb.

[0010]

SUMMARY OF THE INVENTION X-ray sensitization of this general formula
The phosphor for paper has high luminous efficiency and exhibits extremely excellent afterglow characteristics. Therefore, X using this phosphor
The line intensifying screen has a feature that noise due to afterglow can be minimized to reduce the X-ray exposure dose. However, the LnMDO ₄ : Tm X-ray intensifying screen phosphor developed by the present inventors is
If a fluorescent substance for X-ray intensifying screens that does not exhibit an ideal emission spectrum but has an even better emission spectrum can be put to practical use, the X-ray exposure dose should be reduced to create an X-ray intensifying screen with high diagnostic properties. It can be put to practical use.

Due to the high luminous efficiency, the efficiency of X-ray film
The fluorescent substance for X-ray intensifying screens with a light emission spectrum that can be exposed to light
Image sharpness, which is extremely important for X-ray diagnosis,
To improve the resolution of whether you can accurately shoot even the smallest parts
It How to improve the image resolution in X-ray photography
Ruka is inferior to reducing the amount of X-ray exposure.
Not an extremely important characteristic. Image resolution is medical
Because it determines the accuracy of diagnosis in radiography of
It In order to increase the image resolution, X-ray intensifying screen firefly
It is necessary to apply a thin layer of the optical layer. The thick phosphor layer is X
X-rays that emit light from a part away from the surface of the film
Exposure of the film reduces the sharpness of the image. X
The closer the phosphor for the intensifying screen to the X-ray film,
The sharpness of the image exposed to the phosphor for X-ray intensifying screen is high.
It Fluorescence for X-ray intensifying screens to increase image resolution
When the thickness of the body layer is reduced, the emission output of the phosphor layer is reduced, and X
The exposure of the line film is reduced. Therefore, the X-ray intensity
You need to be strong. To reduce the amount of X-ray exposure
And increasing the resolution of the image is the fluorescence for X-ray intensifying screens.
These are the most important properties for the body, but these properties are mutually exclusive.
The characteristics are contradictory, and both must be satisfied at the same time.
Is extremely difficult. Improve diagnostic accuracy by reducing X-ray exposure
Reduce or diagnose by increasing the amount of X-ray exposure
Higher precision is selected. Patients undergoing X-ray diagnosis
Everyone, without exception, reduces the amount of X-ray exposure,
Eager to improve diagnostic accuracy with high resolution images
It

The present invention was developed for the purpose of achieving this, and an important object of the present invention is to show an emission spectrum effective for the spectral sensitivity of an X-ray film,
Further , a phosphor for an X-ray intensifying screen and this phosphor are used, which have a large amount of X-ray absorption and a high luminous efficiency, and have a weak afterglow component, which can reduce the radiation dose to the subject and improve the diagnostic performance. To provide X-ray intensifying screens.

[0013]

DISCLOSURE OF THE INVENTION Firefly for X-ray intensifying screen of the present invention
The light body and the X-ray intensifying screen have the following configurations in order to achieve the above-mentioned object. X-ray sensitization of the present invention according to claim 1 .
The phosphor for paper is a further improvement of the phosphor for X-ray intensifying screen , which was previously developed by the present inventors and is represented by the following general formula (1).

The phosphor for an X-ray intensifying screen of the present invention is characterized in that in the general formula (1), R which represents an activator is used and Gd is used instead of conventional Tm. X-ray sensitization represented by the general formula of LnMDO ₄ : Tm previously developed by the present inventors .
The phosphors for paper also include those containing Gd in the matrix of the phosphor. However, the activator was Tm.
The phosphor for an X-ray intensifying screen of the present invention is characterized by using Gd instead of Tm as an activator. Therefore, the phosphor for an X-ray intensifying screen of the present invention has an emission spectrum of Gd regardless of the emission spectrum of Tm.

Further, the phosphor for X-ray intensifying screen of the present invention comprises
Since Gd is contained as an activator rather than as a matrix of the phosphor, the content thereof is very small. In the general formula (1), the value of X is 1 × 10 ⁻⁵ ≦ x ≦ 3 × 10 ⁻¹ . It is characterized by setting to a small range. The value of X is set in such a small range because Gd is contained as an activator. If Gd contained as an activator is wider than this range, the luminous efficiency will decrease. Also, Gd
If the amount is less than this range, the luminous efficiency is lowered.
The content of Gd is set in the above range in consideration of luminous efficiency.

Ln _{1- xy My} DO _{4-1 / 2y} : XR (1) However, in this general formula, Ln is Y, La and Lu.
Is at least one element of M, and M is Be, Mg, C
It is at least one divalent metal selected from the group consisting of a, Sr, Ba, Zn, and Cd, D includes either or both of Ta and Nb, and y is in the range of 1 × 10 ⁻⁵ ≦ y ≦ 1. Is set to. When the content of the divalent metal contained in the phosphor is large, the afterglow property is improved, but when it is too large, the luminous efficiency is reduced. The y value of the general formula showing the content of the divalent metal M is determined in the range of 1 × 10 ₋₅ ≦ y ≦ 1 in consideration of the afterglow characteristics and the luminous efficiency.

Further, the X-ray intensifying screen of the present invention according to claim 2 is characterized in that the above-mentioned X-ray intensifying screen phosphor is used as a phosphor.

[0018]

The X-ray film uses AgBr as a negative emulsion. As shown in FIG. 1, the absorption coefficient of AgBr changes depending on the wavelength. The absorption coefficient of AgBr tends to decrease as the wavelength increases. Especially 300n
It exhibits excellent absorption efficiency in the wavelength range from m to 400 nm. Further, Table 1 shows changes in scattering, transmission, and absorptance with respect to the wavelength of AgBr. This table shows AgBr
Shows that the absorption rate is low, the scattering and the transmission rate are high with respect to the light emission having a long wavelength of 490 nm or more. On the contrary, 380n
Light having a short wavelength of m or less has an extremely high absorptance and scatters,
It shows that the transmittance is low. Further, FIG. 2 shows the spectral sensitivity of the X-ray film. As can be seen from this figure, the X-ray film has a property of high spectral sensitivity in a wavelength region shorter than about 400 nm.

[0019]

[Table 1]

The emission spectrum of the phosphor for X-ray intensifying screen of the present invention is shown in FIG. As shown in this figure, the X-ray of the present invention
The phosphor for the intensifying screen has a Gd emission spectrum of 315
There is an emission peak at nm. The band width of the emission peak is very narrow, the absorption rate of AgBr is high, and it is concentrated in the wavelength region where the scattering rate is small. Therefore, when the phosphor of the present invention is used in an X-ray intensifying screen, it is possible to reduce the exposure dose, obtain an X-ray image of high sharpness with less crossover light, and improve the radiation diagnostic efficiency. It

[0021]

Embodiments of the present invention will be described below with reference to the drawings. However, embodiments described below are intended to illustrate the X-ray intensifying screens phosphor for embodying the intensifying screen of the technical idea of the present invention, for X-ray intensifying screens of the present invention The phosphor and the intensifying screen do not specify the raw materials used, the composition of the X-ray intensifying screen and the like as described below. The phosphor for an X-ray intensifying screen and the intensifying screen of the present invention can be modified without departing from the scope of the claims.

Example 1 A phosphor for an X-ray intensifying screen is manufactured by the following steps. After sufficiently mixing the following raw materials, the alumina crucible is filled and baked at 1000 ° C. for 15 hours. Yttrium oxide: 64.02 g Gadolinium oxide: 0.54 g Strontium carbonate: 6.64 g Tantalum pentoxide: 132.57 g

100 g of lithium chloride is blended with this fired product, which is put into a ball mill and ground and mixed. Next, the obtained mixture was filled in an alumina crucible, and 1
Bake at 200 ° C. for 10 hours. Then, it is put in the ball mill again and pulverized, and by decantation, washing with pure water is repeated 5 times, and suction filtration is performed. Further, it is dried at 120 ° C. for 15 hours.

Thus, the general formula is Y _0.993 Sr
_A phosphor for X-ray intensifying screen which was wet with _0.002 TaO _3.999 : 0.005 Gd ³⁺ was obtained.

The emission spectrum of the obtained phosphor for X-ray intensifying screen is shown by curve A in FIG . In this figure, curve B is
The above composition formula except that the value of X representing the content of Gd is set to 0
The emission spectrum of a phosphor having the same composition as
Is the above except that the content of Gd is increased (X = 0.05)
The emission spectrum of the phosphor with the same composition formula is shown.
You The phosphor for the X-ray intensifying screen prototyped in the example is shown in FIG.
As shown, the value of X, which indicates the amount of Gd added, falls within a specific range.
By many Oite, you to 315nm peak wave length
The luminous brightness can be dramatically increased. As shown in this figure, the phosphor for X-ray intensifying screen manufactured in Example 1 was 315
The relative energy intensity of nm is remarkably high, and further, excellent characteristics are shown in which the emission is concentrated in a narrow band width effective for the spectral sensitivity of the X-ray film. However, the relative energy intensity was measured by irradiating the phosphor with X-rays, irradiating the photomultiplier with the emission of the phosphor, converting the emission intensity into current with the photomultiplier, and comparing with the magnitude of the output current.
It was The photomultiplier used had the sensitivity characteristics shown in FIG. Furthermore, the obtained X-ray intensifying screen
FIG. 6 shows the afterglow characteristics of the phosphor for use . As shown in this figure, the phosphor for X-ray intensifying screen produced in Example 1 exhibited extremely low afterglow characteristics. In this figure, the vertical axis represents the amount of afterglow (logarithmic value of [amount of light emission after a lapse of a certain time / light-emission scene upon X-ray stimulation]), and the horizontal axis represents decay time of afterglow (stopping X-ray irradiation). (Elapsed time since the start).

Further, in the manufacturing method of Example 1, the addition amounts of gadolinium oxide and yttrium oxide were changed without changing the addition amounts of strontium oxide and tantalum pentoxide.
A phosphor for an X-ray intensifying screen was manufactured by changing the above, and the relative emission intensity of the phosphor for an X-ray intensifying screen with respect to the content of gadolinium was measured. Figure 7: X-ray intensifying screen for gadolinium content
3 shows the relative emission luminance of the phosphor for use at 315 nm. As shown in this graph, in the general formula (1), by setting the value of x indicating the added amount of gadolinium in the range of 5 × 10 ⁻³ to 10 ⁻¹ , the emission luminance can be about 30% or more. Can be higher

Further, in the manufacturing method of Example 1, the addition amounts of strontium oxide and yttrium oxide were changed without changing the addition amounts of gadolinium oxide and tantalum pentoxide.
A phosphor for X-ray intensifying screen was manufactured by changing the above, and the relative emission intensity of the phosphor for X-ray intensifying screen with respect to the strontium content was measured. Figure 8 shows X-ray sensitization for strontium content.
The relative emission brightness of the phosphor for paper is shown. As shown in this graph, in the general formula (1), by setting the value of y indicating the added amount of strontium in the range of 5 × 10 ^{−4 to} 2.5 × 10 ⁻³ , the emission luminance is about Can be 20% higher.

Example 2 A phosphor for an X-ray intensifying screen was manufactured in the same manner as in Example 1 except that the following materials were used as the phosphor raw material. Yttrium oxide: 64.02 g Gadolinium oxide: 0.54 g Strontium carbonate: 6.64 g Tantalum pentoxide: 132.37 g Niobium pentoxide: 0.12 g Lithium chloride: ...... 100g

The general formula of the produced phosphor for X-ray intensifying screen was as shown below. Y _0.993 Sr _0.002 T
a _0.9985 Nb _0.0015 O _3.999 : 0.0
05Gd ³⁺ The emission spectrum of the obtained X-ray intensifying screen phosphor is shown by the curve A in FIG. 9 . In this figure, curve B is
The above composition formula except that the value of X representing the content of Gd is set to 0
The emission spectrum of a phosphor having the same composition as
Is the above except that the content of Gd is increased (X = 0.05)
The emission spectrum of the phosphor with the same composition formula is shown.
You The phosphor for the X-ray intensifying screen produced as a prototype in the example is added with Gd.
To increase the value of X, which indicates the amount of addition, within a specific range
More dramatically the emission brightness at 315 nm peak wavelength
Can be very expensive. As shown in this figure, the phosphor for X-ray intensifying screen manufactured in Example 1 has a remarkably high relative energy intensity of 315 nm and emits light in a narrow band width effective for the spectral sensitivity of the X-ray film. It has excellent characteristics of focusing.

Further, in the manufacturing method of Example 2, the addition amounts of gadolinium oxide and yttrium oxide were changed without changing the addition amounts of strontium oxide and tantalum pentoxide.
A phosphor for an X-ray intensifying screen was manufactured by changing the above, and the relative emission intensity of the phosphor for an X-ray intensifying screen with respect to the content of gadolinium was measured. Figure 10: X-ray sensitization for gadolinium content
3 shows the relative emission brightness of a phosphor for paper at 315 nm. As shown in this graph, in the general formula (1), the emission brightness at the 315 nm peak wavelength can be dramatically increased by setting the value of x indicating the addition amount of gadolinium in a specific range.

Further, in the manufacturing method of Example 2, the addition amounts of strontium oxide and yttrium oxide were changed without changing the addition amounts of gadolinium oxide and tantalum pentoxide.
A phosphor for X-ray intensifying screen was manufactured by changing the above, and the relative emission intensity of the phosphor for X-ray intensifying screen with respect to the strontium content was measured. Fig. 11 shows the X-ray increase with respect to the strontium content.
The relative emission brightness of the phosphor for a sensitive paper is shown. As shown in this graph, in the general formula (1), the emission brightness can be considerably increased by setting the value of y indicating the added amount of strontium within a specific range.

Further, the afterglow characteristics of the obtained phosphor for X-ray intensifying screen are shown in FIG. As shown in FIG.
The phosphor for X-ray intensifying screen manufactured in 1) showed extremely low afterglow characteristics.

Example 3 Using the phosphors for X-ray intensifying screens produced in the following Examples 1 and 2, X-ray intensifying screens were prepared as follows. In a mixture of phosphor particles and linear polyester resin,
Methyl ethyl ketone was added, and the nitrification degree was further increased to 11.5.
% Nitrocellulose was added to prepare a phosphor dispersion liquid. Diethyl phthalate, phthalic acid and methyl ethyl ketone were added to this dispersion, and the mixture was thoroughly stirred and mixed using a homogenizer, and the binder and phosphor were mixed at a mixing ratio of 1 :.
A coating solution of 20 (weight ratio) and a viscosity of 30 PS (25 ° C.) was prepared. This coating solution was kneaded into titanium dioxide horizontally placed on a glass plate to form a polyester sheet (support, thickness 2).
(00 μm) was uniformly applied using a doctor blade. After coating, the support having the coating film formed was dried in a dryer to form a phosphor layer having a thickness of 180 μm on the support. Then, a polyethylene transparent film was adhered onto the phosphor layer using a polyester adhesive to form a transparent protective film (thickness 10 μm), and an intensifying screen was produced.

This intensifying screen has a remarkably high sensitivity of AgBr as compared with the X-ray intensifying screen using the phosphor for X-ray intensifying screen previously developed by the present inventor having Tm as the activator. Improved.
In addition, the film was excellent in sensitization due to afterglow.

[0035]

The phosphor for X-ray intensifying screen and the X-ray intensifying screen of the present invention do not show an emission spectrum spread over a wide wavelength region, unlike the conventional product using Tm as an activator. 315 nm
It emits light with a very narrow bandwidth. 315n
The emission of m is an emission spectrum effective for the spectral sensitivity of the X-ray film. Therefore, for the X-ray intensifying screen of the present invention
The phosphor and the X-ray intensifying screen can remarkably improve the substantial sensitivity as compared with the conventional product in which the activator is Tm. That is X
This is because the line film concentrates in a region having high spectral sensitivity and emits light with high brightness. Also, AgBr used for negative emulsion
By concentrating the light emission in the wavelength region where the scattering rate is low, it is possible to obtain a clear image with less noise.
The fact that the substantial sensitivity of the X-ray film can be increased has an advantage that the exposure dose can be reduced and the diagnostic performance can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the absorption coefficient of a negative emulsion AgBr with respect to wavelength.

FIG. 2 is a graph showing the specific sensitivity of X-ray film to wavelength.

FIG. 3 Fluorescence for X-ray intensifying screen of the present invention obtained in Example 1
Graph showing the emission spectrum of the body

FIG. 4 is a graph showing an emission spectrum of a conventional phosphor for an X-ray intensifying screen having Tm as an activator.

FIG. 5 is a graph showing the relative sensitivity of the photomultiplier used to measure the sensitivity.

FIG. 6 is a graph showing afterglow characteristics of the phosphor for X-ray intensifying screen obtained in Example 1.

7 is a graph showing the 315 nm emission intensity with respect to the Gd content of the phosphor for X-ray intensifying screen manufactured in Example 1. FIG.

FIG. 8 is a graph showing the relative emission intensity with respect to the Sr content of the phosphor for X-ray intensifying screen manufactured in Example 1.

FIG. 9 is a graph showing an emission spectrum of the phosphor for X-ray intensifying screen obtained in Example 2.

10 is a graph showing the 315 nm emission intensity with respect to the Gd content, which is the phosphor for an X-ray intensifying screen manufactured in Example 2. FIG.

FIG. 11 is a graph showing the relative emission intensity with respect to the Sr content of the phosphor for X-ray intensifying screen manufactured in Example 2;

FIG. 12 is a graph showing afterglow characteristics of the phosphor for X-ray intensifying screen obtained in Example 1.

Claims (2)

[Claims] 1. X-ray sensitization represented by the following general formula (1):
In the phosphor for paper, in the general formula (1), R representing the activator is Gd, and the value of X representing the content of Gd is 1 × 1.
A phosphor for an X-ray intensifying screen, which is set in a range of 0 ⁻⁵ ≦ x ≦ 3 × 10 ⁻¹ . _{Ln 1-x-y M y} DO 4-1 / 2y: XR ......... (1) However, in the general formula, Ln is Y, at least one element of La and Lu, M is, Be, Mg , Ca, Sr, Ba, Zn, Cd is at least one divalent metal selected from the group, D includes Ta or Nb, or both, and y is 1 × 10 ⁻⁵ ≦ y ≦ 1. Set to range. Wherein a support, an X-ray intensifying screen and a phosphor layer provided on the support, X of the phosphor layer is represented by the following general formula (1) in X-ray intensifying screen comprising a phosphor <br/> for ray intensifying screens, fluorescent X-ray intensifying screen phosphor layer
In the general formula (1), the luminous body is R, which represents an activator, is G
and the value of X, which represents the content of Gd, is 1 × 10 ⁻⁵ ≦ x ≦
An X-ray intensifying screen characterized by being set in a range of 3 × 10 ⁻¹ . _{Ln 1-x-y M y} DO 4-1 / 2y: XR ......... (1) However, in the general formula, Ln is Y, at least one element of La and Lu, M is, Be, Mg , Ca, Sr, Ba, Zn, Cd is at least one divalent metal selected from the group, D includes Ta or Nb, or both, and y is 1 × 10 ⁻⁵ ≦ y ≦ 1. Set to range.