JPH07119414B2 - Phosphor for X-ray intensifying screen and X-ray intensifying screen - 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 and a phosphor for an X-ray intensifying screen used for medical radiography or industrial radiography.

[0002]

2. Description of the Related Art Generally, a phosphor for an X-ray intensifying screen is used in combination with an X-ray photographic film to improve the sensitivity of an imaging system in medical radiography. Generally, this X-ray intensifying screen has an intensifying screen base, a phosphor layer containing an organic binder and a phosphor coated thereon, and a transparent protective film of about 10 μm covering the phosphor layer. .
The X-ray film is used by being sandwiched between a pair of X-ray intensifying screens so that the emulsion layer formed with a thickness of about 20 to 30 μm on both sides and the protective film of the X-ray intensifying screen are in contact with each other. To be done. In order to improve the sharpness of the X-ray image, it is important that the X-ray film and the intensifying screen are in close contact with each other.

Phosphors used in such X-ray intensifying screens have characteristics such as high luminous efficiency, large absorption of X-rays, and emission spectrum matching the spectral sensitivity of the X-ray film. Required.

Generally, an X-ray intensifying screen coated with a phosphor having a large amount of X-ray absorption has good graininess of an X-ray image and improves diagnostic ability in medical radiography. Further, since the fluorescent material having high luminous efficiency has high sensitivity in the imaging system, it is possible to perform imaging even when the X-ray irradiation amount is small, so that the exposure dose of the subject can be reduced.

If the emission spectrum does not match the spectral sensitivity of the X-ray film, a part of the emission of the X-ray phosphor is not absorbed by the emulsion coated on the incident side of the film, but is scattered and transmitted. To do. The light thus scattered and transmitted causes light that is absorbed by the emulsion layer on the opposite side, so-called crossover light, and reduces the sharpness of X-rays.

As described above, in order to obtain an excellent image,
The three major factors of sharpness, graininess and sensitivity are essential. However, if you try to increase the sensitivity,
It is extremely difficult to keep all three of these high levels, such as reduced sharpness and granularity.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention was made in view of the above circumstances, and it is a fluorescent material for X-ray intensifying screens which can obtain an X-ray image having a high level of sensitivity, sharpness and graininess. To provide the body. Further, another object of the present invention is to
An object of the present invention is to provide an X-ray intensifying screen capable of obtaining an X-ray image having a high level of sensitivity, sharpness and graininess.

[0008]

The phosphor for X-ray intensifying screen of the present invention comprises: a phosphor represented by the following composition formula (1): BaFBr: aEu ²⁺ (5 × 10 ^-4 ≦ a ≦ 5 × 10 ⁻² ) ... (1) Represented by the following composition formula (2), Y _{1-2 / 3x} M _x TaO ₄ : bNb (10 ⁻⁵ ≦ x ≦ 1, 0 ≦ b ≦ 0.05) ... (2) The M includes at least one kind of phosphor selected from the group consisting of Ca, Sr, and Cd.

If the value of a is less than 5 × 10 ⁻⁴ , the amount of afterglow increases, so that an image remains on the X-ray intensifying screen that is continuously used, and a new image is taken by the remaining image. Fog occurs on the statue. When it exceeds 5 × 10 ^-2 , the amount of afterglow is small, but concentration quenching occurs due to excess activator. Further, if expensive Eu is excessively used, the cost becomes high. Further, it is preferable that 3 × 10 ⁻³ ≦ a ≦ 3 × 10 ⁻² .

If the value of x is less than 10 ^-5 , the amount of afterglow increases and the luminous efficiency decreases. When it exceeds 1, the luminous efficiency is lowered. Further, it is preferable that 1 × 10 ⁻³ ≦ x ≦ 1 × 10 ⁻² . When the value of b exceeds 0.05, the luminous efficiency is reduced. Further, preferably 0 ≦ b ≦ 0.0
It is 2.

[0011]

The phosphor according to the present invention has particularly good X-ray absorption characteristics and good emission efficiency, and its emission spectrum shows a wavelength at which silver bromide used as a negative emulsion for X-ray films has a high absorptivity. Concentrated in the region (ultraviolet to 490 nm), there is little long-wavelength emission above 490 nm and 380 n
There are many short-wavelength light emission of m or less. Scattering / transmission of this silver bromide
Table 1 shows the wavelength dependency of the absorptance.

As can be seen from this table, for silver bromide,
Light emission with a long wavelength of 490 nm or more has low absorptance and high scattering / transmittance. On the other hand, light emission with a short wavelength of 380 nm or less has extremely high absorptance and low scattering / transmittance.
Therefore, when the phosphor of the present invention is used for an X-ray intensifying screen, an X-ray image with high cross sharpness and high sharpness can be obtained. As a result, the radiation diagnostic ability is improved.

FIG. 2 shows the spectral sensitivity of the X-ray film. As can be seen from this figure, the X-ray film has a high spectral sensitivity of 490 nm or less. Therefore, 490
The phosphor of the present invention in which the emission energy is concentrated in a short wavelength of nm or less has extremely high sensitivity as compared with the conventional CaWO ₄ phosphor. FIG. 3 shows the BaFB used in the present invention.
r: aEu ²⁺ phosphor and Y _{1-2 / 3x} M _x TaO ₄ : bNb
And a phosphor, which is a graph comparing the X-ray absorption coefficient of the conventional CaWO ₄ phosphor. From this graph, the energy range of X-rays used for normal radiography (50 to 1
At 30 keV), the X-ray absorption amounts of the BaFBr: aEu phosphor and the Y _{1-2 / 3x} M _x TaO ₄ : bNb phosphor are
It turns out that it is more than CaWO ₄ .

As described above, the phosphor of the present invention has good X-ray absorption characteristics and luminous efficiency, so that the sensitivity of the photographing system becomes good. When an X-ray intensifying screen using such a phosphor is used, it is possible to reduce the X-ray dose to be irradiated, so that it is possible to reduce the exposure dose of a subject in radiography, which has been impossible in the past. In addition, it is possible to harmonize the three elements that are contradictory to each other, that is, sensitivity, graininess, and sharpness at a high level.

As described above, by performing radiography using the intensifying screen using the phosphor of the present invention, an image with less crossover light and good graininess and sharpness can be obtained.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples. Examples 1-3

Barium carbonate (7.6 kg), europium oxide (48.4 g) and hydrobromic acid (47% by weight) (8.52 kg) were added to pure water (2.3 l) to prepare a suspension containing a mixture of barium bromide and barium carbonate. A suspension was obtained. The suspension is then warmed to 80 ° C. and hydrofluoric acid (50% by weight) 1.1.
After adding Kg, the mixture was reacted for 2 hours with sufficient stirring. After completion of the reaction, unreacted barium bromide was separated and removed, and then dried to obtain 6.55 Kg of a mixture of barium fluorobromide and europium fluoride.

To 2 kg of the raw material mixture thus obtained, 6 g of ammonium bromide and 50 mg of sodium bromide were added and mixed well, then filled in a quartz tray and placed at 880 in a carbon dioxide atmosphere containing carbon monoxide. It was baked at a temperature of ° C for 2 hours and 30 minutes. The obtained fired product was pulverized with a ball mill, 20 g of silicon dioxide was added to 2 kg of the pulverized product, and the mixture was thoroughly mixed, filled in a quartz tray, and re-fired in an electric furnace. The re-baking was performed in a carbon dioxide atmosphere containing carbon monoxide at a temperature of 740 ° C. for 4 hours. The obtained fired product was washed in methanol and then dried to obtain a divalent europium-activated barium fluorobromide phosphor (BaFBr: 0.01E).
u ²⁺ ) was obtained.

Next, 111.78 g of yttrium oxide,
Strontium carbonate 2.21g, tantalum pentoxide 21
8.74 g and 1.33 g of niobium pentoxide were used as raw materials, 25 g of lithium chloride was blended as a flux, and the mixture was crushed and mixed by a ball mill. Next, the obtained raw material mixture was filled in an alumina crucible, baked in air at 1200 ° C. for 10 hours, pulverized with a ball mill, and purely washed 5 times by decantation, and suction filtered. Furthermore, this is 120 ℃
After drying for 15 hours, Sr _0.015 Y _0.99 TaO ₄ : 0.0
A 1Nb phosphor was obtained.

BaFBr: 0.01 thus obtained
Eu ²⁺ phosphor and Sr _0.015 Y _0.99 TaO ₄ : 0.01
Using the Nb phosphor, the phosphor mixtures of the following Examples 1 to 3 were prepared.

A mixture of these phosphors and B as a comparative example
aFBr: 0.01Eu ²⁺ phosphor (Comparative Example 1), Sr
_The relative energy intensity of the _0.015 Y _0.99 TaO ₄ : 0.01Nb phosphor (Comparative Example 2) and the CaWO ₄ phosphor (Comparative Example 3) with respect to the wavelength of the emission spectrum was measured. The energy distribution of this emission spectrum is shown in FIG. The relative energy intensity was measured at a voltage of 50 V using an X-ray tube using a Cu target and an Al filter (3 mm) as an X-ray source. Next, using these phosphors, as shown in FIG.
An X-ray intensifying screen 14 having the phosphor layer 12 formed thereon was manufactured.

92 parts by weight of phosphor particles and 8 parts by weight of linear polyester resin were mixed, and methyl ethyl ketone was added thereto. Furthermore, nitrocellulose having a nitrification degree of 11.5% was added to obtain a phosphor dispersion liquid. Diethyl phthalate, phthalic acid and methyl ethyl ketone were added to this phosphor dispersion liquid, and then thoroughly mixed with stirring using a homogenizer. Thus, a phosphor coating solution having a mixing ratio of the binder and the phosphor of 1:10 and a viscosity of 30 Pas (25 ° C.) was prepared. A titanium dioxide-kneaded polyester sheet (support thickness 200 μm) was used as the support 11, was placed horizontally on a glass plate, and this coating solution was uniformly applied onto the support 11 using a doctor blade, Dried. Furthermore, it is dried in a dryer at 60 ° C. for 8 hours,
A phosphor layer 12 having a thickness of 70 to 100 μm was formed on the support. A polyethylene transparent film was adhered onto the obtained phosphor layer 12 using a polyester adhesive to form a transparent protective film (thickness 10 μm) 13 and an intensifying screen 14 was obtained.

The relative intensities, graininess and sharpness (MTF) of the obtained intensifying screens were measured using a DuPont Kronex 10 X-ray film. The results are shown in Table 2. This sharpness is an MTF value that can be placed at a spatial frequency of 3 LP / mm. Examples 4-6

Yttrium oxide 112.76 g, strontium carbonate 0.30 g, tantalum pentoxide 220.95
Sr was prepared in the same manner as in Example 1 except that g was used as the raw material.
333.9 g of _0.002 Y _0.9987 TaO ₄ phosphor was obtained. The obtained phosphor and BaF obtained in the same manner as in Example 1.
Br: 0.01Eu ²⁺ phosphor was mixed in the following ratio.

A mixture of these phosphors and Sr _0.002 Y
_{For the 0.9987} TaO ₄ phosphor (Comparative Example 4), the relative energy intensity of the emission spectrum with respect to the wavelength was measured in the same manner as in Example 1. FIG. 5 shows the energy distributions of these emission spectra and the emission spectra of Comparative Examples 1 and 3 for comparison. Next, using these phosphors, an X-ray intensifying screen was produced in the same manner as in Example 1.

The relative intensities, graininess and sharpness (MTF) of the obtained intensifying screens were measured using a DuPont Kronex 10 X-ray film. The results are shown in Table 3.

As can be seen from FIGS. 4 and 5, the phosphor of the present invention (Examples 1, 2, 3, 4, 5, 6) and the BaFBr: 0.01Eu ²⁺ phosphor of Comparative Example 1 are Comparative Example 3
CaWO ₄ phosphor and Sr _0.015 Y _0.99 T of Comparative Example 2
aO ₄ : 0.01Nb phosphor or Sr of Comparative Example 4
Compared with the _0.002 Y _0.9987 TaO ₄ phosphor, it emits less long-wavelength light over 490 nm. X-ray film is usually second
It has a spectral sensitivity curve as shown in the figure, and energy is concentrated at short wavelengths of 490 nm or less. Therefore,
The phosphor of the present invention and the phosphor of Comparative Example 1 have a large absorption of X-rays and have an emission spectrum suitable for the spectral sensitivity of the X-ray film. However, the BaFBr of Comparative Example 1:
As shown in Table 2, the 0.01 Eu ²⁺ phosphor has good sensitivity and sharpness, but is not practically sufficient because of poor image graininess. On the other hand, as shown in Tables 2 and 3, the phosphor according to the present invention, namely BaFB
r: 0.01 Eu ²⁺ phosphor and Sr _0.015 Y _0.99 Ta
O _4: phosphor mixture of 0.01Nb phosphor and BaF
Br: 0.01Eu ²⁺ phosphor and Sr _0.002 Y _0.9987 Ta
The mixture with the O ₄ phosphor has good image characteristics such as relative sensitivity, graininess and sharpness. Examples 7-9

107.26 g of yttrium oxide, 7.51 g of calcium carbonate and 220.95 g of tantalum pentoxide.
332. in the same manner as in Example 1 except that 332.
41 g of Ca _0.075 Y _0.95 TaO ₄ phosphor was obtained. The obtained phosphor and BaF obtained in the same manner as in Example 1.
Br: 0.01Eu ²⁺ phosphors were mixed in the ratios shown below to obtain phosphor mixtures of Examples 7 to 9. BaFBr: 0.01Eu ²⁺ Phosphor Ca _0.075 Y _0.95 TaO ₄ Phosphor (wt%) (wt%) Example 7 70 30 Example 8 50 50 Example 9 30 70 70 Ca as the phosphor mixture and Comparative Example 5 _0.075
An X-ray intensifying screen was produced in the same manner as in Example 1 using the Y _0.95 TaO ₄ phosphor. About the obtained intensifying screen,
The relative sensitivity, graininess, and sharpness (MTF) were measured by the same methods as in Examples 1 to 3. The results are shown in Table 4. Examples 10-12

Yttrium oxide 101.62 g, cadmium carbonate 25.86 g and tantalum pentoxide 220.95
Cd was used in the same manner as in Example 1 except that g was used as the raw material.
341.82 g of _0.15 Y _0.90 TaO ₄ phosphor was obtained.

Next, europium oxide 14.5 g, barium carbonate 7.6 Kg, hydrobromic acid (47 wt%) 8.5
In the same manner as in Example 1 except that 2 kg and 1.1 kg of hydrofluoric acid (50 wt%) were used as raw materials, BaFBr: 0.
6.52 kg of 003Eu ²⁺ phosphor was obtained. The two types of phosphors thus obtained were mixed in the following ratios. BaFBr: 0.003Eu ²⁺ Phosphor Cd _0.15 Y _0.90 TaO ₄ Phosphor (wt%) (wt%) Example 10 70 30 Example 11 50 50 Example 12 30 70

Example 1 using these phosphor mixture and BaFBr: 0.003 Eu ²⁺ phosphor as Comparative Example 6 and Cd _0.15 Y _0.90 TaO ₄ phosphor as Comparative Example 7
An X-ray intensifying screen was produced in the same manner as in. With respect to the obtained intensifying screens, relative sensitivity, graininess and sharpness (MTF) were measured in the same manner as in Examples 1-3. The results are shown in Table 5.

As can be seen from Table 4, Examples 7-9
Has good relative sensitivity, graininess and sharpness, but in the case of the Ca _0.075 Y _0.95 TaO ₄ phosphor of Comparative Example 5,
Relative sensitivity and graininess are not practical compared to Examples 7-9. Further, as can be seen from Table 5, Examples 10 to 10
No. 12 has good relative sensitivity, graininess and sharpness.
On the other hand, in Comparative Example 6, the relative sensitivity and sharpness were good, but the graininess was not practically sufficient, and Comparative Example 7
Has good graininess and sharpness, but the relative sensitivity is not practically sufficient.

[0033]

According to the present invention, it is possible to provide a phosphor for an X-ray intensifying screen which can obtain an X-ray image having a high level of sensitivity, sharpness and graininess. Further, by using such a phosphor, it is possible to provide an X-ray intensifying screen capable of obtaining an X-ray image having a high level of sensitivity, sharpness and graininess.

According to the present invention, by using the phosphor for the X-ray intensifying screen having such a high level of sensitivity, it is possible to reduce the exposure dose of the subject in medical radiography.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an X-ray intensifying screen according to the present invention.

FIG. 2 is a diagram showing a spectral sensitivity curve of an X-ray film.

FIG. 3 shows the BaFBr: aEu phosphor and the Y _{1-2 / 3x} M _x TaO ₄ : bNb phosphor used in the present invention, and the conventional C.
graph showing the X-ray absorption coefficient of the AWO ₄ phosphor.

FIG. 4 is a diagram showing relative energy distributions of a conventional phosphor and a phosphor used in the present invention.

FIG. 5 is a diagram showing relative energy distributions of a conventional phosphor and a phosphor used in the present invention.

[Explanation of symbols]

 11 ... Support, 12 ... Phosphor layer, 14 ... Intensifying screen

Claims (3)

[Claims] 1. BaFBr: aEu ²⁺ (5 × 10 ⁻⁴ ≦ a
≦ 5 × 10 ⁻² ) and Y _{1-2 / 3x} M _x Ta
O ₄ : a phosphor represented by bNb (10 ⁻⁵ ≦ x ≦ 1, 0 ≦ b ≦ 0.05) (M is at least one selected from the group consisting of Ca, Sr, and Cd). A phosphor for an X-ray intensifying screen, comprising a phosphor mixture consisting of: 2. The mixing ratio of the BaFBr: aEu ²⁺ phosphor and the Y _{1-2 / 3x} M _x TaO ₄ : bNb phosphor is 5 /.
It is 95-90 / 10, The fluorescent substance for X-ray intensifying screens of Claim 1 characterized by the above-mentioned. 3. An X-ray intensifying screen comprising the phosphor according to claim 1.