JP6957422B2 - Fluorescent plate and X-ray inspection equipment - Google Patents

Description

The present invention relates to a fluorescent plate and the X-ray examination apparatus.

When bringing luggage into an aircraft as a countermeasure against terrorism, the luggage is inspected in advance at the airport to ensure the safe operation of the aircraft. As such a baggage inspection device, several methods are known, a transmitted X-ray inspection device using X-ray transmission, a Compton scattered X-ray inspection device using X-ray Compton scattering, and an X-ray energy difference. The dual energy type X-ray inspection device used is generally widely used, and recently, an X-ray tomography device (CT) has also begun to be used.

Transmitted X-rays can relatively easily find metal articles that are difficult for X-rays to pass through, such as metal weapons such as firearms and cutlery. On the other hand, substances mainly composed of elements with small atomic numbers such as plastic bombs and drugs easily transmit X-rays, so inspection equipment using Compton scattering and high-energy X-ray images and low-energy X-ray images X obtained from image processing
It can be discovered with an inspection device that uses the difference in linear energy.

In general, an X-ray inspection device as described above guides X-rays transmitted through an object to be inspected to an X-ray detector, converts these detected X-rays into visible light with a phosphor, and then determines the intensity of the visible light. It is configured to perform inspection by detecting with a photoelectric conversion element or a photomultiplier tube and imaging the inside of the baggage according to its intensity.

In order to improve the accuracy of baggage inspection, it is necessary to obtain a clearer image, and for this purpose, it is required that visible light of sufficient intensity is input to a detector such as a photoelectric conversion element. To increase the intensity of visible light, it is possible to increase the intensity of X-rays to irradiate luggage, etc., but X-rays to be irradiated by an X-ray inspection device installed in a public place such as an airport baggage inspection device Increasing the strength of the line leads to an increase in the size of the device and also increases the risk of exposure to leaked X-rays.

Therefore, what is important is the conversion efficiency of the fluorescent plate from X-rays to visible light. When converting X-rays to visible light, if a phosphor with high conversion efficiency is used, high-intensity visible light can be obtained without increasing the intensity of X-rays, which is sufficient for a detector such as a photoelectric conversion element. Intense visible light will be input.

By the way, in the transmission X-ray detector as described above, usually, as shown in FIG. 1, 400 to 90
A photoelectric conversion element having a spectral sensitivity characteristic at 0 nm is used. Therefore, as a phosphor that converts X-rays into visible light, it is advantageous to use a phosphor having an emission wavelength peak at 400 to 900 nm. On top of that, using a fluorophore with high conversion efficiency is the most desirable choice.

Japanese Patent No. 2928677 Japanese Patent No. 5759374 Japanese Patent No. 5241979

J. Electrochem. Soc. , Vol. 136, No. 9, PP. 2713-2716

According to Patent Document 1, as the most suitable phosphor for such applications, A ₂ O ₂ S: D (A is Gd,
Indicates at least one element selected from La and Y, D indicates at least one element selected from Pr, Ce and Yb), BaFX: Eu, A (X is selected from Cl and Br). Indicates at least one element, and A indicates at least one element selected from Ce and Yb.) As a material for converting a phosphor such as transmitted X-rays or Compton-scattered X-rays into visible light. It is disclosed that it can be used effectively. Also, in such a system,
It is also disclosed that when used as a fluorescent plate, a high output can be obtained when the coating amount (weight of the phosphor) is ^{about 200 mg / cm 2.}

Patent Document 2 _{discloses a scintillator material in which 25% or more of Gd of a GOS (Gd 2} O ₂ S) material is replaced with a rare earth element such as La or Lu, and at least one of Ce and Pr is doped. The amount of these dopings is 100 mol pp with respect to the GOS material.
It is exemplified that it can be doped at a Pr3 + concentration of m to 1000 mol ppm and a Ce3 + concentration of 0 to 50 mol ppm.

Formula Patent Document _{3: (Gd 1-X,} RE 'X) 2 O 2 S: Pr
(In the formula, RE'represents at least one element selected from Y, La and Lu, and X
Is a number satisfying 0 <X ≦ 0.1), and is a ceramic composed of a gadolinium acid sulfide phosphor powder containing at least one selected from cerium, zirconium, and phosphorus as a scintillator. A method for producing a scintillator material is disclosed. Furthermore, the average particle size of the gadolinium acid sulfide phosphor powder is 6 to 10 μm, and the Pr content is 0.001 to 1.
The content of the co-active agent selected from Ce, Zr and P in the range of 10 mol% is 0.0001 to
It is disclosed to be in the range of 0.1 mol%.

Non-Patent Document 1 _{discloses an X-ray scintillator material having a composition of Gd 2} O ₂ S: Pr, Ce, F, in which the Pr content is 1 × 10 ^-3 atomic%, and Ce and F are after-emission of light emission. Glow (af)
It is disclosed to reduce tergrow).

In recent years, the range of use of inspection devices using photoelectric conversion elements that convert visible light into electrical signals has expanded, and a fluorescent plate capable of supporting such a system is required. In addition, due to the diversification of inspection packages, it has become necessary to more accurately discriminate complicated shapes, and it has become necessary to improve the inspection accuracy more than before. Therefore, in addition to high light output characteristics, fluorescent plates having characteristics with less afterglow have become more important.

Recently, the use of aircraft has become easier, and the amount of baggage and air cargo for travelers has increased.
Moreover, inspections are being conducted at high speeds, and improvements in afterglow characteristics are being sought after. From a different point of view, there are cases where the inspection speed is limited due to the afterglow characteristics of the phosphor, and from this aspect as well, a phosphor with a short afterglow is desired.

The afterglow characteristic is that when the phosphor is irradiated with X-rays, the X-rays absorbed by the phosphor are converted into visible light and the phosphor begins to emit light, but then the X-ray irradiation is blocked. , The light emission of the phosphor gradually decreases and eventually disappears. The light emission after the X-ray irradiation is stopped at this time is called afterglow. When such a phosphor that strongly exhibits afterglow is used for baggage inspection, the inspection accuracy is adversely affected. This is because, in the case of continuous baggage inspection, when the target image is observed, it overlaps with the afterimage of the previous image, so that a clear image cannot be obtained.

As a characteristic similar to afterglow, there is an afterglow characteristic. The afterglow characteristic is a determination of the time required for the emission intensity of the phosphor to decrease to one tenth after blocking the X-ray irradiation. For example, in Patent Document 1, afterimages are taken by controlling the afterimage characteristics of the phosphor to 1 ms or less. However, under recent inspection conditions, it has become clear that management of afterglow characteristics alone is not sufficient.

Even if the emission intensity of the phosphor is reduced to one tenth in a short time, the faint light may continue steadily after being reduced to about one-hundredth to one-thousandth. This is because such faint light affects as an afterimage and becomes a problem in baggage inspection. The afterglow characteristic is a characteristic obtained by observing the emission of the phosphor to a point as close to zero as possible, and it is important to control this afterglow characteristic.

More recently, in order to deal with the photoelectric conversion element system, there is a demand for a fluorescent plate having higher output while maintaining the afterglow characteristics, and it has become necessary to deal with the demand.
As a method of obtaining a higher light output, it has become possible to increase the intensity of the irradiated X-ray in the X-ray inspection apparatus from the conventional X-ray tube voltage of 80 to 120 kV. Therefore, it is necessary to provide a fluorescent plate which is compatible with the conventional X-ray inspection apparatus using irradiated X-rays having an X-ray tube voltage exceeding 120 kV and has less afterglow.

The present invention has been made to address such a problem, and an object of the present invention is to provide an X-ray inspection apparatus having high inspection accuracy that is optimal for the usage environment and conditions of the X-ray inspection apparatus in recent years. It is an object of the present invention to provide an X-ray inspection apparatus capable of obtaining a clear image without a problem of afterglow while obtaining a high detection sensitivity.

That is, the X-ray inspection device of the present invention is particularly suitable for an X-ray inspection device that uses an irradiation X-ray having an X-ray tube voltage exceeding 120 kV, and has a fluorescent plate that converts X-rays into visible light and visible light. In an X-ray detector having a photoelectric conversion element that converts The concentration of praseodymium (Pr) is 0.01 to 0.3% by weight, preferably 0.03 to 0.2% by weight, more preferably 0.0.
It contains 4 to 0.1% by weight and cerium (Ce) as a co-activator at 5 to 30 ppm, preferably 10 to 25 ppm, more preferably 12 to 22 ppm.

The average particle size (D) of the phosphor is in the range of 10 to 20 μm, preferably 13 to 18 μm.
The particle shape is preferably spherical, and the sphericity (Ψ) of Wadell is 0.8 or more, preferably 0.85 or more. And the phosphor weight (CW) of the fluorescent screen is 270 to 38.
0 mg / cm ^2, preferably characterized in that the 300~350mg / cm ^2.

As a result, it is possible to provide a fluorescent plate having an optical output 1.4 times or more that of the conventional one and an afterglow of 0.06% or less after 20 ms of X-ray stop. Such an X-ray fluorescent plate is particularly suitable for a transmitted light detection X-ray inspection apparatus using an irradiation X-ray having an X-ray tube voltage exceeding 80 to 120 kV.

In the X-ray detector of the present invention, it is possible to simultaneously obtain the characteristics that the relative light output is at least 110% (against the standard phosphor) and the afterglow after 20 ms is 0.06% or less. If an X-ray inspection device is configured using a line detector, sufficient detection sensitivity can be obtained with relatively low-intensity X-rays, and a clear inspection image without afterimages can be obtained. Reduced afterglow It enables highly accurate inspection even if the inspection is continuously performed at high speed. The X-ray inspection device of the present invention can be applied not only to the airport baggage inspection device but also to various security systems.

It is an image figure which shows the spectral sensitivity characteristic of a photodiode (PD) used for an X-ray detector. It is a figure which showed the light output of the fluorescent screen at the X-ray tube voltage 160kV with respect to the average particle diameter (D) and the weight of a phosphor (CW). It is a figure which showed the light output and the afterglow characteristic of this invention with respect to the added Ce concentration. It is a figure which shows the emission wavelength characteristic of Gd ₂ O _{2 S: Pr phosphor.} It is a figure which shows typically the structure of one Example of the X-ray inspection apparatus of this invention. It is sectional drawing which shows one Example of the X-ray detector of this invention, and the structural example of the fluorescent screen used for this invention.

As the phosphor used in the X-ray detector and the X-ray inspection apparatus of the present invention, gadolinium sulfide gadolinium sulfide with praseodymium Gd ₂ O ₂ S: Pr is used.
First, since there is a strong demand for improving the light output by X-rays, it is necessary to increase the luminous efficiency of the fluorescent plate that converts X-rays into visible light. One way to do this is to increase the average particle size of the phosphor. By increasing the average particle size, the phosphor layer becomes transparent, and the emitted light reaches the photodiode (PD) without being attenuated, so that the light output is improved. However, increasing the average particle size has the demerit that the obtained image quality becomes coarse and the sharpness decreases. Therefore, conventionally, a phosphor having an average particle size of 5 to 10 μm has been mainly used.

Another example is to thicken the phosphor layer of the fluorescent screen, and the light output is improved by increasing the amount of the phosphor emitted by X-rays. However, when the phosphor layer becomes extremely thick, it becomes difficult for X-rays to pass through, and it becomes difficult for the emitted light to reach the photodiode (PD), so that the light output begins to decrease. Therefore, conventionally, a fluorescent plate having a weight of a phosphor layer of about 200 mg / cm ² has been a general-purpose product.

However, the average particle size of the phosphor and the thickness of the phosphor layer are conditions that have been used in an X-ray inspection apparatus in which the X-ray tube voltage is in the range of 80 to 120 kV, and the X-ray tube voltage is currently 120 kV.
By making it larger, the light output is being earned. FIG. 2 shows the light output at an X-ray tube voltage of 160 kV, which is currently being tried, with respect to the average particle size (D) and the weight of the phosphor (CW). Using a phosphor containing no Ce, these The effect is investigated. As for the light output, the light output of the fluorescent screen under the conventional conditions (average particle size (D) 8 μm, phosphor weight (CW) 200 mg / cm ² ) was shown as 100.

As is clear from FIG. 2, at the X-ray intensity of the X-ray tube voltage of 160 kV, the light output is high under conditions different from the conventional ones. High output is obtained in the region where the average particle size exceeds 10 μm. However, in an actual image test, when the average particle size exceeds 20 μm, the sharpness is significantly reduced. Therefore, it was found that the preferable range is 10 to 20 μm, and more preferably the range is 13 to 18 μm.

Further, regarding the thickness of the phosphor layer, although a high output can be obtained in a region thicker than the conventional one, a decreasing tendency is observed when the weight of the phosphor is about 400 mg / cm2. Therefore, the preferred region is 270-380 mg / cm ^{2 in} fluorophore weight (CW), more preferably 300-350 mg / cm / cm.
High light output can be obtained in the range of cm ^2. This tendency is that the X-ray tube voltage is 140 to 180 kV.
It was almost the same in the range of.

Table 1 shows the shape of the phosphor particles, with the average particle size (D) of the phosphor being about 15 μm.
It shows the fluorescence output by X-ray of the fluorescence plate using the phosphor which changed the sphericity (Ψ) of ell. The weight of the phosphor was 300 mg / cm ² , and the X-ray tube voltage was measured at an X-ray intensity of 160 kV. The light output clearly tends to increase with the value of Wadell's sphericity (Ψ). The preferred sphericity (Ψ) is 0.8 or more, more preferably 0.85 or more.

Inside the fluorescent screen, the light radiated from the phosphor is reflected on the surface of the other phosphor, and multiple reflections are repeated to take out the light to the outside. When light reflection occurs, the energy efficiency of light decreases. Sphericity (Ψ) of the particle shape of the phosphor to suppress the decrease in light energy efficiency
It seems that the increase in output was influenced by the improvement of the particle size and the reduction of the surface area of the particles.

Wadell's sphericity (Ψ) (hereinafter, also referred to as "sphericity") is an index for determining whether or not the particle shape of a phosphor is spherical, and is a three-dimensional scale. As such an index, an aspect ratio, a circularity (perimeter of a circle having the same projected area / perimeter of a particle) based on an SEM image of a particle, a projected image, or the like is used. All of these are two-dimensional scales, not strictly spherical scales. For example, in the case of coin-shaped particles, even if a high value of 0.9 or more is obtained in the circularity, the value is less than 0.6 in the sphericity of Wadell.

The sphericity can be increased by producing a phosphor by using the production method described later. In the production of phosphors, several types of raw materials containing the constituent elements of the phosphor and fluxes that promote synthetic reactions (
Flux) is used. Alkali metal phosphate is generally used as the flux for rare earth acid sulfides, and the shape of the particles can be changed by changing the type and amount. Sphericity 1 means a true sphere, but in reality, it is difficult to obtain a phosphor having a sphericity of 0.96 or more, and the cost is high. Therefore, the preferable sphericity of the phosphor of the present invention is 0. It is 8 or more and 0.96 or less, more preferably 0.85 or more and 0.96 or less.

The sphericity (Ψ) of Wadell is defined by the following equation (A1) as the ratio of the surface area of an actual particle to the surface area of a sphere having the same volume as the particle.
Ψ = (surface area of a sphere having the same volume as a particle) / (actual surface area of a particle) (A1)

Usually, among particles having an arbitrary volume, the particles having the smallest surface area are spherical particles. Therefore, the sphericity (Ψ) of Wadell is 1 or less for ordinary particles, and when the particle shape is not spherical, the closer it is to a sphere, the closer it is to 1.

The sphericity (Ψ) of Wadell is obtained by the following method. First, the particle size distribution of the powder phosphor is measured by the Coulter counter method. The Coulter counter method is a method of defining the particle size from the voltage change according to the volume of the particles. In the particle size distribution obtained by the Coulter counter method, the number frequency at a certain particle size Di is Ni. The particle size Di is the diameter of spherical particles having the same volume as the actual particles whose particle size is defined by the Coulter counter method.

The specific surface area (S) of the powder phosphor is calculated using the number frequency Ni and the particle size Di. The specific surface area is the surface area of the powder divided by its weight and is defined as the surface area per unit weight. The weight of the particles having a particle size Di is (4π / 3) × (Di / 2) ³ × Ni × ρ (ρ is the density of the powder). The weight of the powder is the sum of the weights of the particles for each particle size, and is represented by the following formula (A2).
Powder weight = Σ {(4π / 3) x (Di / 2) ³ x Ni x ρ} (A2)

The surface area of the particles having a particle size Di is 4π × (Di / 2) ² × Ni. When the actual particle shape is not spherical, the specific surface area of the actual particle is the value obtained by dividing the surface area of the particle by the Wadell spherical degree (Ψ) ({4π × (Di / 2) ² × Ni} / Ψ). The specific surface area (S) of the powder is the sum of the specific surface areas of the particles for each particle size, and is represented by the following formula (A3). Actually, it is possible that the Wadel sphericity (Ψ) is a value different for each particle size, but it can be interpreted as an average value as the deviation from the sphere of the powder as a whole.
S = [Σ {4π × (Di / 2) ² × Ni} / Ψ] / [Σ {(4π / 3) × (Di / 2)
³ x Ni x ρ}]
= (6 / ρ / Ψ) × {Σ (Di ² × Ni)} / {Σ (Di ³ × Ni)} (A3)

As a method for measuring the particle size of powder, a ventilation method (Brain method, Fisher method, etc.) is known. In the ventilation method, powder is packed in a metal tube having both ends open, air is passed through the powder layer, and the particle size is defined from the air passing ratio. The particle size defined by the ventilation method is also referred to as the specific surface area diameter (d). The specific surface area diameter (d) and the specific surface area (S) have a relationship of the following formula (A4).
S = 6 / ρ / d (A4)

Therefore, the sphericity (Ψ) of Wadell is expressed by the following formula (A5) and can be calculated by comparing the specific surface area calculated from the particle size distribution with the specific surface area calculated from the particle size of the aeration method. can. The particle size of the particle size distribution is usually expressed as a particle size range, but in the present embodiment, the particle size Di is set as an intermediate value of the particle size range, and the particle size range is set to every 0.2 μm in order to improve accuracy. If the particle size distribution is plotted on lognormal probability paper, it can be approximated by two straight lines. Therefore, the number frequency data for every 0.2 μm can be easily obtained from the two normal probability distributions.
Ψ = d × {Σ (Di ² × Ni)} / {Σ (Di ³ × Ni)} (A5)

The afterglow of the phosphor can be controlled by adding, for example, Ce. FIG. 3 shows the light output and afterglow characteristics when the fluorescent plate using the Gd2O2S: Pr phosphor of the present invention is used in an X-ray detector and an X-ray inspection apparatus. The average particle size of the phosphor is about 15
It was measured at μm, the weight of the phosphor was 300 mg / cm ² , and the X-ray tube voltage was 160 kV.

_{The emission spectrum of the Gd 2} O ₂ S: Pr phosphor shown in FIG. 4 has a peak emission wavelength of 51.
It is around 2 nm, 670 nm, and 770 nm, and its luminous efficiency (efficiency of converting X-rays into visible light) is very high. Therefore, when a silicon photodiode (Si-PD) having a light receiving sensitivity peak at 400 to 900 nm is used in the X-ray detector, it is compatible with the fluorescent screen and can be detected with high output. Further, the _{Ce co-couple activator added to Gd 2} O 2 S: Pr does not affect the emission wavelength, and the emission peak wavelength does not change even if Ce is added.

As for the afterglow characteristics of one of the phosphors, it is desirable that the light output after 20 ms is 0.06% or less. If it is 0.06% or less, a clear image without an afterimage can be obtained even if X-rays are continuously detected under normal conditions. With this characteristic, it is possible to obtain a clear image without an afterimage at any speed using the current inspection equipment. In the phosphor of the present invention shown in FIG. 4, the light output 20 msec after the X-ray irradiation was stopped showed a very low value of 0.06%, showing excellent afterglow characteristics. Therefore, when a fluorescent plate having such a phosphor is used to continuously detect X-rays, a clear image without an afterimage can be obtained.

Such light output and afterglow characteristics of the present invention can be obtained by optimizing the concentration of Pr and co-activating Ce in _{the Gd 2} O _{2 S: Pr phosphor.} The light output peaks in the range of 0.05 to 0.1% by weight with respect to the Pr concentration, and then gradually decreases. Practically, 0.01 to 0.3% by weight is preferable, 0.03 to 0.2% by weight is more preferable, and 0.0
A more preferred concentration range is 4 to 0.1% by weight. Further, in Ce, the addition is effective in reducing the afterglow, but causes a decrease in the light output, so an excessive addition is not preferable. Practically, the Ce concentration is 5 to 30 ppm, preferably 10 to 25 ppm, and more preferably 12 to 22 ppm.

In Patent Document 1, examples of usable phosphors include Gd ₂ O ₂ S: Tb and BaFCl: E.
Fluorescent materials such as u are also mentioned, but in the case of an active fluorescent material with Tb, it is difficult to obtain a characteristic of afterglow characteristics of 0.06% or less after 20 msec, which is not suitable for the object of the present invention. Further, although the BaFCl: Eu phosphor can satisfy only the afterglow characteristics,
Comparing the overall characteristics including brightness, Gd ₂ O ₂ S: Pr or Gd ₂ O ₂ S: Pr, C
Since it is inferior to e, this fluorophore cannot be used alone.

Hereinafter, examples of the present invention will be described with reference to the drawings.
FIG. 5 is a diagram schematically showing a configuration of an embodiment in which the X-ray inspection device of the present invention is applied to an airport cargo inspection device. In the figure, reference numeral 1 denotes an X-ray irradiation means, for example, an X-ray tube, and X-ray A emitted from the X-ray tube 1 is scanned and irradiated to an object 2 to be inspected, for example, a luggage moving on a conveyor or the like. .. The baggage to be inspected moves at a speed according to the detection sensitivity of X-rays.
The X-ray B that has passed through the luggage is detected by the X-ray detector 3. The transmitted X-rays detected by these X-ray detectors are measured as continuous intensity values, and the state inside the luggage is imaged on a display device 4 such as a liquid crystal display according to the X-ray intensity. Then, the inside of the cargo is inspected by this image.

The above-mentioned X-ray detector has a configuration as shown in FIG.
Inside the X-ray incident surface of the detector main body, a fluorescent plate whose emission direction is directed to the inside of the detector main body 5 is installed as a fluorescence generating means. A photodiode (PD) is installed as a photoelectric conversion means on the opposite side of the X-ray incident surface. As this PD, one having a light receiving sensitivity at 400 to 900 nm is used. First, the fluorescent plate arranged inside the X-ray incident surface is irradiated with X-rays and emitted toward the PD. Then, these visible lights are detected by PD, and the intensity of X-rays is obtained.

The fluorescent plate in Example 1 uses a Gd ₂ O ₂ S: Pr, Ce phosphor.
This phosphor is produced through the following steps. First, praseodymium oxide and cerium oxide,
Pr and Ce are dissolved in nitric acid at a desired ratio (99.3: 0.7) by weight to prepare a mixed solution of both. This solution is then reacted with, for example, a predetermined amount of dimethyl oxalate solution to give a co-precipitated oxalate of Pr and Ce. This co-precipitated oxalate is calcined in the air at a temperature of 1000 ° C. or lower for several hours to obtain a mixed oxide of Pr and Ce. In this way, a mixed powder in which Pr and Ce are uniformly dispersed to minute units is obtained.

Next, as a step of synthesizing the phosphor _{, the raw material gadolinium oxide was added at a ratio of the amount of Pr added to the Gd 2} O ₂ S matrix being 0.07% by weight (at the same time, the amount of Ce added was 0.0005% by weight). Active agent mixed oxide (Pr, Ce), sulfur, and flux material (alkali metal carbonate, alkali metal phosphate, alkali metal halide, etc.) are thoroughly mixed in a powder state and placed in a container at 1000 to 1400 ° C. Bake at the temperature of for several hours. Amount of sulfur and flux material,
By changing the type, the average particle size and particle shape of the phosphor can be controlled. The fired fluorescent material thus obtained is subjected to steps such as washing, dispersion, and sieving to obtain a finished fluorescent material.

Next, as a comparative example, a phosphor produced by a conventional production method was also synthesized at the same time. _{A Gd 2} O ₂ S phosphor similar to that of the present invention was produced in the amount of Pr and Ce added. In the production method of the comparative example, a mixed oxide containing only an activator is not produced, but a predetermined amount of gadolinium oxide, praseodymium oxide, cerium oxide, sulfur, and a flux agent are mixed as starting materials, and the powder state is sufficient. Mix and
Raw material mixed powder was obtained. Next, after the firing step, a finished phosphor was obtained by the same method as in the present invention. Subsequently, a fluorescent plate on the incident side was prepared. As shown in FIG. 6, the fluorescent plate formed a phosphor layer by applying a slurry in which the phosphor of the present invention or the comparative example was mixed with a binder and an organic solvent on a support of a plastic film or a non-woven fabric. ..

Similarly, in Example 2 and below, the characteristics of the X-ray detector when the various phosphors of the present invention are applied to the fluorescent plate are shown in Table 2 in comparison with the case where the fluorescent plate made of the fluorescent material of the comparative example is used. show. In these examples, only the type of phosphor and the weight of the phosphor were changed, and the same method as in Example 1 was used, such as the method for manufacturing the fluorescent plate and the configuration of the X-ray detector.
The light output may exceed 110%, and the afterglow after 20 ms is 0.
It may be 06% or less.

Table 2 shows the relative light output of the detector and the afterglow characteristics when the average particle size, the weight of the phosphor, and the Ce concentration are changed in the _{Gd 2} O _{2 S: Pr phosphor.} From Table 2, it can be seen that the relative light output increases as the average particle size increases. On the other hand, it can be seen that when the Ce concentration is increased, the relative light output becomes lower and the afterglow characteristic becomes smaller. Naturally, the higher the relative light output, the better, but at least 110% or more of the comparative standard phosphor (Comparative Example 1) is required. If it is lower than this value, if the X-ray intensity is increased beyond the limit or the X-ray intensity is not changed, it becomes impossible to obtain an optical output sufficient for accurately analyzing the image. On the other hand, if the afterglow is low, an X-ray image without an afterimage can be obtained, but if the Ce density is high, the required light output cannot be obtained, so at least 0.06.
% Or less is sufficient.

By using the fluorescent plate of the present invention, in baggage inspection in the direction of higher speed processing,
A clear image can be provided. Further, the X-ray inspection device using the fluorescent plate can be applied not only to the airport baggage inspection device but also to various security systems.

1 X-ray tube A Irradiated X-ray
2 Inspected object B Transmitted X-ray 3 X-ray detector 4 Display device 5 Detector

Claims (7)

A fluorescent plate that converts X-rays into visible light.
With the support
A phosphor layer coated on the support and containing praseodymium and a gadolinium sulfide phosphor with cerium.
Equipped with
The fluorescent substance contains praseodymium having a concentration of 0.01 to 0.3% by weight based on the total amount of the fluorescent substance, and cerium having a concentration of 5 to 30 ppm based on the total amount of the fluorescent substance. ,
The praseodymium and the cerium are _{co-activated in the Gd 2} O ₂ S matrix crystal and are co-activated.
The average particle size of the phosphor is 10 to 20 μm.
The coating weight of the phosphor is 300 ~380mg / cm ^2, fluorescent plate. The concentration of the praseodymium is 0.03 to 0.2% by weight based on the total amount of the phosphor.
The concentration of the cerium, Ru 10~25ppm der relative to the total amount of the phosphor, fluorescent screen according to claim 1. The fluorescent plate according to claim 1 or 2, wherein the average particle size is 13 to 18 μm. The fluorescent plate according to any one of claims 1 to 3, wherein the sphericity of Wadell in the phosphor is 0.8 to 0.96. The coating weight is 349 to 380 mg / cm. ² The fluorescent plate according to any one of claims 1 to 4. X-ray irradiation means for irradiating the object to be inspected with X-rays,
And X-ray detector for detecting transmitted X-rays from the object to be inspected,
A means for imaging the inside of the object to be inspected based on the intensity of the transmitted X-ray measured by the X-ray detection means, and a means for imaging the inside of the object to be inspected.
Equipped with
The X-ray detection means is an X-ray inspection apparatus including the fluorescent screen according to any one of claims 1 to 4. The X-ray inspection apparatus according to claim 6, wherein the X-ray detection means further includes a photodiode that converts the visible light into an electric signal.

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