JPS63183982A - Radiation image conversion screen - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a radiation image conversion screen (hereinafter abbreviated as 7-image conversion screen). More specifically, the present invention relates to a highly sensitive image conversion screen that emits green light and uses a terbium-activated rare earth orthophosphate phosphor as a phosphor layer.

[Technical Background of the Invention and its Problems 2] Conventionally, image conversion screens have been used, for example, as intensifying screens, fluorescent screens, etc., to convert an X-ray image of a subject into a visible image, for the purpose of medical diagnosis or non-destructive testing of materials. is used as. This filtration image conversion screen basically consists of a support such as paper, plastic, or thin aluminum plate, and a phosphor layer provided on one side of the support. It is composed of a phosphor that emits light dispersed in a binder resin. Furthermore, when using it as an intensifying screen, fluorescent screen, etc., the surface of this phosphor layer (the side opposite to the support side) may be protected with a transparent protective film such as cellulose acetate, cellulose acetate butyrate, or polyethylene terephthalate. has been done.

Therefore, the image conversion screen used as an intensifying screen, which is the main application of the present invention, will be described in more detail below.

In order to improve the sensitivity of the imaging system in radiography, the image conversion screen is used by bringing the emulsion surface of an X-ray photographic film (hereinafter referred to as 7 film) into close contact with the phosphor layer surface of the image conversion screen. The phosphor layer of the image conversion screen emits light when exposed to X-rays that have passed through the subject, and the film is exposed to this light. Therefore, in order to reduce the exposure dose to the subject as much as possible, it is natural that the image conversion screen used for radiography should be as bright as possible and emit light at a spectral wavelength that matches the spectral sensitivity of the film used. requested.

By the way, conventionally, a regular type film having spectral sensitivity in the blue to near ultraviolet region and Ca'/10s,
Ba5al, :6u'-, BaFC(i :Eu'-
Radiography has not yet been carried out in combination with an image converting screen that emits mainly blue to near-ultraviolet light. After that, orthochromatic type films (hereinafter referred to as "orthofilms"), which have increased spectral sensitivity in the green region in addition to the blue region, rapidly became popular, and in recent years, orthochromatic films with increased spectral sensitivity in the green region in particular A film is being developed.

With this trend, it is desired to develop a highly sensitive green light image conversion screen that is compatible with these orthofilms.

Accordingly, an object of the present invention is to provide a highly sensitive green luminescent image conversion sphinium that is particularly suited to the spectral sensitivity of orthofilms.

The present inventors have discovered that terbium-activated yttrium phosphate phosphor (YPO, Tb) and lutetium phosphate phosphor (LuPO+'Tb) exhibit high-intensity green light emission under X-ray excitation (U.S. Patent No. 3.431.8
H), Y, -,, Gd-PO4 (X = 0.3~0
．． 1) in extremely small amounts (0.00 per mole of rare earth element phosphate)
A phosphor activated with Tb (8 to 0.01 mol) emits blue light upon X-ray excitation and is compatible with the X-ray image response characteristics of a blue-sensitive X-ray film (Japanese Patent Publication No. 57-35227)
Based on these findings, the present invention was achieved as a result of intensive research, particularly on phosphate-based phosphors. That is, gadolinium phosphate (GdPO) activated with a relatively high concentration of terbium.
< : Tb ) by dissolving YPO4:Tb as a solid solution, especially within a specific solid solution range under X-ray excitation;
It was discovered that YOGdPIJl:Tb or YPO::Tb exhibits green light emission with higher brightness, and by further using this as a phosphor layer5), it was possible to create a more sensitive image conversion screen. This heading led to the present invention.

[Means for solving problems]

That is, the image conversion screen of the present invention has a phosphor layer formed of a terbium-activated gadolinium-yttrium orthophosphate phosphor represented by the composition formula %), which satisfies the following conditions, on a support. It's something you wear.

The present invention will be explained in more detail below.

The image conversion screen of the present invention has a compositional formula of (Gd, -, -y+ YX, Tb, )+1104 as a phosphor layer.
(However, X and y are numbers that satisfy the conditions of 0.1≦x≦0.65 and 0.O1≦y≦0,2, respectively.

It is manufactured using the same materials and by the same method as conventional image conversion screens, except that it uses a terbium-activated gadolinium yttrium orthophosphate phosphor represented by ().

For example, (ea, −, −,,yi, rb, )PI
3. A phosphor coating solution with an optimal viscosity is prepared by mixing the phosphor and a binder resin, and then adding an appropriate amount of a solvent to the mixture.The phosphor coating solution is then coated onto a support made of paper, plastic, etc., and dried. Consists of scales. At that time, the coating weight of the phosphor coating liquid is preferably 20 to 180 mg/cnf. Then, if necessary, a protective layer such as a transparent plastic thin film made of polyethylene terephthalate, acetyl cellulose, nitrocellulose or the like is formed on the phosphor layer to obtain a desired image conversion screen.

Alternatively, a protective layer is formed in advance on a smooth substrate, a phosphor layer is formed on top of this, and then this is peeled off together with the protective layer, and a support is adhered to the side opposite to the protective layer side. Accordingly, one image conversion screen of the present invention can be provided.

Used in the phosphor layer of the one-image conversion screen of the present invention (
Gd=, y, Y, , Tby) PO, the phosphor is manufactured, for example, as follows.

First, Gd, 03. Compounds of gadolinium such as GdCL, compounds of yttrium such as Y2L, Y2(C21], )1, (~It4)2HPO,, ('JR,)
82P04 and other phosphorus compounds and Tb, O,, Tb(N
Compounds of terbium such as O3)3 are approximately stoichiometrically (Gd1-X-x-y, YN, Tb,
=, y, Y,, Tby)"/PO,'-ratio is approximately 1
．． The mixture is weighed and mixed so that it has a composition formula of 0 or slightly smaller than this, and then in step 51, this phosphor thickness mixture is packed into a heat-resistant container such as an aluminum crucible and placed in a firing furnace for about 1,000 -
Bake at a temperature of 1200°C for about 1 to 10 hours. next,
The fired product is taken out of the furnace and pulverized, washed with dilute acid, warm water, etc., dried, and sieved to make the particle size uniform and obtain the desired phosphor. Note that the above phosphor raw material mixture was prepared in advance at a concentration of about 500 ml.
It may be produced by pre-firing at a temperature of ~700°C for about 1~4 hours, pulverizing the fired product with a ball mill, etc., and then main firing at a temperature of about 1000~1200°C.

The attached FIG. 1 shows that the activation amount (X value) of Tll produced as described above is 0.05 (Gdo, 95-
+1 + Y This is an example of the relationship between the photographic sensitivity and the image conversion screen of each image conversion screen.In this figure, the vertical axis is (Gdo, ss, Tbo, os) PO1
fluorescence! (that is, when x=Q) is used as a phosphor layer, and is expressed as a relative value to the photographic sensitivity of the image conversion screen.

As shown in Figure 1, it is used as a phosphor layer of an image conversion screen (Gdo, ss, TbO, 03
) By dissolving Y in the PO1 phosphor (that is, increasing the X value), the photographic sensitivity of the resulting image conversion screen is further improved within a specific solid solution range.

In addition, when the activation amount (X value) of Tb as an activator is other than 0.05 (Gd, ~11-y+ y,, rby) in the phosphor in the image conversion screen using PO, the phosphor. The relationship between Y content (X value) and photographic sensitivity when using orthofilm is approximately the same as the relationship illustrated in Figure 1 if the Tb activation amount (X value) is greater than approximately 0.01. A similar relationship was confirmed in another study.

Therefore, (Gd
l-x-y, L, Tby) PO, the Y content of the phosphor (X (direct) is approximately O, I≦x≦0.65 from the viewpoint of the sensitivity of the image conversion screen, which is It is preferable that x be within the range of 0.15≦x≦0.50.

Next, FIG. 2 shows one of the image conversion screens of the present invention (Gdo, ss, Yo, 4o, TE]o, a
s) This figure illustrates the emission spectrum (solid line) and the spectral sensitivity curve (dotted line) of an orthofilm when an image conversion screen using a POa phosphor as a phosphor layer is irradiated with X-rays. As shown in Figure 2 (Gdo, 55.
Yo, 4G.

Tbo, 05) Image conversion screens using PO4 phosphors exhibit green emission with the main peak of the emission spectrum at about 550 nm and are therefore particularly sensitive when used in combination with orthofilms.

Note that (Gdl-N-y, YX, Tby) pH, which is used as the phosphor layer of the image conversion screen of the present invention,
Fluorescence 1. t ; As the activation amount (y@) of Tb decreases, the peak intensity near 550 nm in the emission spectrum decreases to 4
This decreases relative to that around 80 nm, and blue light emission becomes dominant, resulting in a decrease in photographic sensitivity when used with orthofilm.

On the other hand, when the ToO activation amount (X value) is greater than about 0.2, the emission intensity of the phosphor itself decreases.

Therefore, in either case, the object of the present invention (the two-dimensional phosphor cannot be obtained).

And this tendency is (Gd, -, , YX, Tby
) P.O.

It is hardly affected by the Y content (X value) in the phosphor. Therefore, it is used in the image conversion screen of the present invention (G
d=, y, YX, Tb,) The activation amount (y value) of Tb, which is an activator for PO4 phosphor, is approximately 0.01≦y≦0.
y is preferably in the range of 2, particularly approximately 0.02≦y
More preferably, the range is ≦0.1.

Incidentally, from the viewpoint of the sensitivity and image quality of the resulting image conversion screen, these (Gd1-, y, Y,, Tt+,) PO4 phosphors that can be used in the image conversion screen of the present invention: Well, the median particle size is It is desirable to use a phosphor having a particle size distribution of approximately 3-20 microns and a standard deviation current (Q, D,) of 0.20-0.35.

Absolute excuse] Next, the present invention will be explained with reference to examples.

(Example 1) Gd203 271.9g (0.75 mol) LL 45.2g (0.2 mol)
(N11.) 2HPO, 277.3 g (2.1 mol) TI], 0□ 18.7 g (0.02
5 mol) The above phosphor raw materials were weighed out, mixed in a ball mill, packed into an alumina crucible, placed in an electric furnace, and heated at 600°C.
The calcined product was calcined at a temperature of , taken out of the furnace, and the calcined product was ground in a ball mill. Next, the fired product after pulverization was packed into an aluminium crucible, put into the electric furnace again, and main fired at a temperature of 1100°C for 4 hours. After being taken out of the furnace and roughly pulverized, the product was crushed with hydrochloric acid (
After washing with IN), washing with water, drying, and sieving, the particle size was made uniform. Thus, the composition is (Gdo, ts, Yo,
20. A phosphor (Tbo, as) PO4 with a median particle diameter of 5 μ and a standard deviation value (Q, D,) of 0.25
I) was obtained.

Next, butyl acetate (solvent) was added to a mixture of 100 parts by weight of the phosphor HE obtained as described above and 7 parts by weight of nitrified cotton, and the mixture was thoroughly mixed in a ball mill while adjusting the viscosity, and the phosphor was coated. A liquid was prepared. Next, this phosphor coating liquid was placed horizontally on a support made of polyethylene terephthalate having a thickness of 250 μm and having a light absorption layer of carbon black, so that the phosphor coating weight after drying was approximately 50 mg/day.
A phosphor layer was prepared by applying Cl11 using a knife coater and drying it. Furthermore, a protective layer made of a transparent polyethylene terephthalate film with a thickness of 6 μm was adhered onto the phosphor layer (Gdo, 7S).
, Yo, 2. Tbo, 05) An image conversion screen [I] having a PO4 phosphor layer was produced.

(Example 2) Gd2L 199.4g (0.55 mol) Y2O290.3g (0.40 mol) (NH+
)) 12PO4241.5g (2.10 mol) Tb
*Ot l 8.7 g (0,025 mol) Example 1 except that the phosphor raw material having the above composition was used and the pre-fired product was main fired at 1150°C for 4 hours.
Similarly to the phosphor CIF, the composition is (Gdo, ss
, Yo, 40. Tbo, O5') PO4, particle diameter center (5.2μ, standard difference (Q, D,)
0.25] was obtained.

Next, fluorescence 1. In the phosphor layer (Gdo
, ss, Yo, 4G, Tbo, 05) PO4
An image conversion screen l) with phosphor was produced.

(Example 3) Gd203 134.1g (0.37 mol) Y2O) 135.5g (0.60
mole) (NH4) 3PO,・3L0 426.6g
(2,10 mol) Tb, Ov 11.
2g (0,015 mol) Except for pre-sintering at 500°C for 2 hours using the phosphor raw material with the above composition, and then main-sintering the pre-sintered product at 1150°C for 5 hours: Well, in Example 1. Similarly to the phosphor [■], the composition is (Gdo, 2
7. Yo, 60° TI), 03) PO4, particle diameter center I diameter 5.0 μ, standard deviation 1 diameter (QSD, >
Same as the image conversion screen [1) of Example 1, except that the phosphor [■] obtained as described above is used instead of the phosphor C■] having a molecular weight of 0.28 with the quaternary phosphor CI]. and then apply the phosphor layer ('Gdo, zt, Yo, 8G+
Tbo, os) An image conversion screen CI) with PO-phosphor was produced.

(Comparative Example 1) The same phosphor raw materials as in Example 1 were used, except that Y2O2 was not used and 344.4 g (0.95 mol) of Gd2O was used, and the composition was prepared in the same manner as phosphor [I]. (Gdo
, 95. Tbo, as) PO4, and the particle size is at the center! A phosphor [:RI] having a standard deviation value (Q, D,) of 0.28 was obtained.

Next, the phosphor layer (Gdo, ss, Tb
o, os) PO, image conversion screen with phosphor (R
I) was produced.

(Comparative Example 2) Y2O. The same phosphor raw material as in Example 2 was used except that 344.4 g (0.95 mol) of Gd, 03 was not used, and the composition was changed to (G
Phosphor 1:RII] which is POs, has a median particle size of 5.7 μm, and a standard deviation value (Q, D,) of 0.29 is obtained.

Next, a phosphor layer (Gdo, ss
, Tbo, os) An image conversion screen CRIII with PO4 phosphor was fabricated.

(Comparative Example 3) The same phosphor raw material as in Example 3 was used except that Y2O3 was not used and 351.6 g (0.97 mol) of Gd, 03 was used, and the same procedure as for phosphor [II] was used. The composition is (Gdo, sw, Tbo, .3)PO4, the median particle size is 5.8 μ, and the standard deviation value (Q, D,) is 0.28.
A phosphor CRIII) was obtained.

Next, a phosphor layer (Gdo, 97
．． Tbo, 03) An image conversion screen (RII[) with PO4 phosphor was fabricated.

(Comparative Example 4) Instead of the phosphor [I], the median particle diameter was 5μ, the standard deviation value (
Q, D,) The phosphor layer (:
An image conversion screen (RrV) with aWO4 phosphor was fabricated.

(Photographic sensitivity test) Image conversion screens [■], [
■], [■], and the image conversion screen [R■], which was also produced as the above-mentioned comparative example.

For [RII], CRIII), and [:RIV), the photographic sensitivity of each image conversion screen was determined from the degree of blackening of the developed film when used in combination with an ortho film. The results shown in the table below were obtained.

In this table, the photographic sensitivity of each image conversion screen is [:
It is shown as a relative value when the degree of distortion of the image conversion screen CRrV) using aWO4 phosphor is set to 100.

Image conversion screen of the present invention [I:1. [II] and C■
) is Cai~0. The image conversion screen [RIB, [:R[[ ) and [R■], both had high sensitivity.

〔Effect of the invention〕

As detailed above, (Gd, -, x-y, YN, T
by) PO4 phosphor emits high-intensity green light under X-ray excitation, and the image conversion screen of the present invention using this as a phosphor layer can be used as a highly sensitive intensifying screen especially when used with orthofilm. It can be used to improve the sensitivity of photography systems. Furthermore, by appropriately selecting the method of forming the phosphor layer, the thickness of the phosphor layer, the material of the support, etc., it can be useful as a highly sensitive phosphor screen or a phosphor screen for an X-ray image intensifier.

[Brief explanation of the drawing]

FIG. 1 shows the image conversion screen used in the present invention (Gd
1YM, Tby) is a graph showing the relationship between the Y content (X value) in the PO4 phosphor and the photographic sensitivity of the image conversion screen. FIG. 2 is a graph illustrating the emission spectrum of the image conversion screen of the present invention.

Claims (1)

[Claims] 1) The compositional formula is (Gd_1_-_x_-_y, Y_N, T
b_y) PO_4 (where x and y are numbers satisfying the conditions of 0.1≦x≦0.65 and 0.01≦y≦0.2, respectively) Terbium-activated gadolinium yttrium orthophosphoric acid A radiation image conversion screen comprising a phosphor layer made of a salt phosphor deposited on a support. 2) The x value and the y value are numbers satisfying the conditions of 0.15≦x≦0.50 and 0.02≦y≦0.1, respectively, according to claim 1. Radiographic image conversion screen.