JP2012220348A - X-ray detector and x-ray inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray inspection device which has high detection sensitivity and reduced afterglow.SOLUTION: In the X-ray detector including an intensifying screen, at least one kind of GdOS:, Pr, Ce or GdOS:Pr is used in either a transmission type intensifying screen 10 or a reflection type intensifying screen 11 as a fluorescent material for the intensifying screen. In the X-ray detector, since optical output of the afterglow after 3 msec is 0.2% or less, a clear image without problems such as an afterimage is obtained.

Description

  The present invention relates to an X-ray detector and an X-ray inspection apparatus using the same.

Generally, when bringing a baggage into an aircraft, the baggage is inspected in advance in an airport in order to ensure safe operation of the aircraft. As such a baggage inspection apparatus, a transmission X-ray inspection apparatus using X-ray transmission and a Compton scattering X-ray inspection apparatus using X-ray Compton scattering are generally widely used. The former can relatively easily find metal articles that are difficult to transmit X-rays, such as metal weapons such as firearms and blades. On the other hand, substances mainly composed of elements having a small atomic number such as plastic bombs and narcotics can easily be detected by using the latter inspection apparatus using Compton scattering because X-rays are easily transmitted.

An X-ray inspection apparatus using transmitted X-rays or Compton scattered X-rays as described above generally guides transmitted X-rays or Compton scattered X-rays to an X-ray detector, and these detected X-rays are visualized by a phosphor. After being converted to, the intensity of this visible light is detected by a photomultiplier tube, so-called photomultiplier (hereinafter abbreviated as “photomal”), and the inside of the baggage is imaged according to the intensity so that the inspection is carried out. It is configured.

In order to increase the accuracy of the package inspection, it is necessary to obtain a clearer image. For this purpose, it is required that a visible light with sufficient intensity is input to the photo. Increasing the intensity of visible light can be achieved by increasing the intensity of X-rays applied to luggage, etc. X-ray inspection equipment installed in public places like airport luggage inspection equipment Increasing the strength of the wire increases the size of the apparatus and increases the danger.

Therefore, the brightness of the phosphor is important. When converting X-rays into 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. Will be entered.

By the way, in the X-ray detector as described above, a photomultiplier having a spectral sensitivity characteristic peak in the vicinity of 400 nm is usually used as shown in FIG. Therefore, as a phosphor that converts X-rays into visible light, it is advantageous to use a phosphor having an emission wavelength peak near 400 nm in combination with a photomultiplier. The most desirable choice is to use a phosphor with high conversion efficiency.

Japanese Patent No. 2,928,677

According to Patent Document 1, A ₂ O ₂ S: D (A represents at least one element selected from Gd, La and Y, and D represents Pr and Ce as phosphors suitable for such applications. And BaFX: Eu, A (X represents at least one element selected from Cl and Br, and A represents at least one element selected from Ce and Yb) It is disclosed that phosphors such as can be effectively used as a material for converting transmission X-rays and Compton scattered X-rays into visible light.

  However, recently, due to diversification of inspection packages, it has been required to more accurately determine more complicated shapes, and it has become necessary to improve inspection accuracy more than before. For this reason, as a matter of course, a phosphor with higher luminance is demanded, and recently, in addition to luminance characteristics, improvement of afterglow characteristics has been required.

In recent years, the use of aircraft has become easier, and the baggage and air cargo of travelers has increased, and it has come to be inspected continuously and at a high speed, and there is a strict demand for improved afterglow characteristics. It is like. In other words, there are cases where the inspection speed is limited due to the afterglow characteristics of the phosphor. From this aspect, a phosphor having a short afterglow is desired.

What is afterglow characteristics? When X-rays are irradiated to the phosphor, the X-rays absorbed by the phosphor are converted into visible light, and the phosphor starts to emit light, but then the X-ray irradiation is blocked The light emission of the phosphor gradually decreases and eventually disappears. At this time, the light emission after X-ray irradiation is stopped is called afterglow. When such a phosphor that exhibits strong afterglow is used for baggage inspection, the inspection accuracy is adversely affected. This is because, when carrying out a package inspection continuously, if a target image is observed, a clear image cannot be obtained because it overlaps an afterimage of the previous image.

Note that there is an afterglow characteristic as a characteristic similar to afterglow. The afterglow characteristic is obtained by determining the time until the emission intensity of the phosphor is reduced to a tenth after blocking X-ray irradiation. For example, in Patent Document 1,
By managing the afterglow characteristics of the phosphor to 1 msec or less, measures against afterimages are taken. However, in recent inspection conditions, it has become clear that management of afterglow characteristics is insufficient. This is because even if the emission intensity of the phosphor is reduced to one-tenth in a short period of time, weak light may continue to be dull after it has decreased from one hundredth to one thousandth. This is because such a weak light has an effect as an afterimage in the baggage inspection. The afterglow characteristic is a characteristic obtained by observing the light emission of the phosphor as close to zero as possible, and it is particularly important to manage the afterglow characteristic.

The present invention has been made to cope with such problems, and has an object to provide an X-ray inspection apparatus with high inspection accuracy. Sufficient detection sensitivity can be obtained by relatively low-intensity X-rays. At the same time, 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.

That is, the X-ray inspection apparatus of the present invention includes a housing-like detector body having an X-ray incident portion, transmissive fluorescence generating means disposed in the incident portion, and the detector body excluding the incident portion. An X-ray detector comprising a reflection type fluorescence generating means disposed along an inner wall surface and a photoelectric conversion means disposed in the detector body, wherein the transmission type fluorescence generating means is a transmission type intensifying screen And the reflection type fluorescence generating means has a reflection type intensifying screen, and at least one of the transmission type intensifying screen and the reflection type intensifying screen, Gd ₂ O ₂ S: Pr, Ce (In the formula, the concentration of Pr and Ce, when Gd ₂ O ₂ S is 100% by weight, Pr is 0.03% to 0.3% by weight, and Ce is 0.005% by weight or less. ) It is characterized by using a phosphor. The phosphor used is characterized in that the afterglow output after 3 msec is 0.2% or less.

Further, the X-ray inspection apparatus of the present invention includes an X-ray irradiation means for irradiating an inspection object with X-rays, an X-ray detection means for detecting Compton scattered X-rays or transmitted X-rays from the inspection object, In the X-ray inspection apparatus comprising a means for imaging the inside of the inspection object based on the X-ray intensity measured by the X-ray detection means, the X-ray detection means has Compton scattered X-rays or transmitted X-rays. It has a means for generating fluorescence when irradiated, and this fluorescence generating means includes at least Gd ₂ O ₂ S: Pr, Ce (wherein the concentrations of Pr and Ce are 100 weights of Gd ₂ O ₂ S). %, Pr is contained in an amount of 0.03% by weight or more and 0.3% by weight or less, and Ce is contained in an amount of 0.005% by weight or less.) It is characterized by having an intensifying screen using a phosphor.

According to the X-ray inspection apparatus of the present invention, sufficient detection sensitivity is exhibited by relatively low-intensity X-rays, and afterglow output after 3 msec is improved to 0.2% or less, so that there is no afterimage or the like. This makes it possible to obtain a high-precision inspection image even when an inspection is carried out continuously at a high speed in baggage inspection at an airport or the like.

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 the structure of one Example of the X-ray detector of this invention. It is sectional drawing which shows the structural example of the intensifying screen used for this invention. Gd ₂ O ₂ S :: Pr, it shows emission wavelength characteristics of Ce phosphor. Gd ₂ O 2 _S: In _Pr intensifying screen phosphor used is a view showing when varying the Pr concentration in the phosphor, the change of the relative light output. Gd ₂ O 2 _S: In _Pr intensifying screen phosphor was used, when changing the Pr concentration in the phosphor, after glow - is a graph showing changes in characteristics Gd ₂ O 2 _{S: Pr,} the intensifying screen using a Ce phosphor is a diagram illustrating the case of changing the Ce concentration in the phosphor, the change of the relative light output. Gd ₂ O 2 _{S: Pr,} the intensifying screen using a Ce phosphor, when changing the Ce concentration in the phosphor, after glow - is a graph showing changes in characteristics. It is a figure which shows the spectral sensitivity characteristic of the photomar used for an X-ray detector.

In the X-ray detector and the X-ray inspection apparatus of the present invention, the fluorescence generation means includes at least one intensifying screen phosphor, Gd ₂ O ₂ S: Pr, Ce (wherein the concentrations of Pr and Ce are Gd _{(When 2} O ₂ S is 100% by weight, Pr is contained in an amount of 0.03% to 0.3% by weight and Ce is contained in an amount of 0.005% by weight.) A phosphor is used. FIG. 4 shows the emission spectrum of the Gd ₂ O ₂ S: Pr, Ce phosphor of the present invention and the afterglow characteristics when used in an X-ray detector and inspection apparatus.

The emission spectrum of the Gd ₂ O ₂ S: Pr, Ce phosphor has a very high emission efficiency (efficiency for converting X-rays into visible light) although the emission wavelength peak deviates from around 400 nm (comparative standard fluorescence). To body LaOBr: Tm). Therefore, even when a photomultiplier having a light receiving sensitivity peak in the vicinity of 400 nm is used in the X-ray detector, Compton scattered X-rays and transmitted X-rays can be sufficiently detected. Further, the Ce co-activator added to Gd ₂ O ₂ S: Pr does not affect the emission wavelength, and even if Ce is added, the emission peak wavelength does not change.

As for the afterglow characteristics of one of the phosphors, the light output after 3 msec is desirably 0.2% or less. If it is 0.2% or less, a clear image with no residual image can be obtained even if X-rays are continuously detected under normal conditions. However, when inspection is performed under high-speed conditions, 0.2% or less may be insufficient. A more desirable characteristic is that the light output after 3 msec is 0.1% or less. With this characteristic, a clear image with no afterimage can be obtained at any speed using the current inspection apparatus. The phosphor of the present invention shown in FIG. 4 has a very low light output of about 0.2% after 3 msec after stopping the X-ray irradiation, and exhibits excellent afterglow characteristics. For this reason, when detecting X-rays continuously using an intensifying screen having such a phosphor, it is possible to obtain a clear image with no afterimage.

Such afterglow characteristics of the present invention can be obtained by optimizing the Pr concentration and co-activating Ce in the Gd ₂ O ₂ S: Pr phosphor. In Patent Document 1, examples of usable phosphors include phosphors such as Gd ₂ O ₂ S: Tb and BaFCl: Eu. In the case of a Tb-activated phosphor, the afterglow characteristics after 3 msec. It is difficult to obtain characteristics of 0.2% or less, which is not suitable for the purpose of the present invention. In addition, the BaFCl: Eu phosphor can satisfy only afterglow characteristics, but when compared in terms of overall characteristics including luminance, Gd ₂ O ₂ S: Pr or Gd ₂ O ₂ S: Pr, Ce Since it is inferior, this phosphor cannot be used alone.

Table 1, FIG. 5 and FIG. 6 show the relative light output of the detector and the afterglow characteristics when the Pr concentration is changed in the Gd ₂ O ₂ S: Pr phosphor. From Table 1 and FIG. 6, it can be seen that as the Pr concentration is increased, the afterglow characteristics decrease, but at 0.2 wt% or more, it hardly decreases, and thereafter it is saturated. On the other hand, as shown in FIG. 5, the relative light output increases as the Pr concentration increases and reaches the maximum output at 0.07 wt%, but starts to decrease when it exceeds 0.07 wt%. Naturally, the higher the relative light output is, the better. However, at least 150% or more of the relative standard phosphor (LaOBr: Tm) is required. Below this value, if the X-ray intensity is increased beyond the limit or the X-ray intensity is not changed, it is not possible to obtain a light output sufficient to analyze the image accurately. Therefore, considering the light output, the upper limit of the Pr concentration is 0.3% by weight. At this time, the afterglow after 3 msec is 0.1%, which shows sufficient characteristics from the afterimage surface. On the other hand, the lower limit of the Pr concentration may be 0.005% by weight when only the light output is considered. However, looking at the afterglow characteristics after 3 msec, even 0.1% by weight already exceeds 0.2%, and there is a lower limit within the range of 0.1% to 0.2% by weight. Become.

The afterglow characteristics of Gd ₂ O ₂ S: Pr can be improved by co-activating Ce in addition to Pr. Table 2 and FIGS. 7 and 8 show the relative light when Ce is co-activated in a phosphor having a Pr concentration of 0.07% by weight that maximizes the light output in the Gd ₂ O ₂ S: Pr phosphor. It shows the output and afterglow characteristics. It can be seen that as the Ce concentration of the coactivator is increased, the light output gradually decreases, but the afterglow characteristics are also improved at the same time. If the Ce concentration exceeds 0.002% by weight, the afterglow characteristic after 3 msec becomes sufficiently small at 0.1%. Therefore, even if the Ce concentration is increased further, the afterglow characteristic is no longer improved. On the other hand, since the light output decreases with the Ce concentration, when Pr is 0.07% by weight, the upper limit is 0.005% by weight which is the Ce concentration when the relative light output is 152%. In the case of a Gd2O2S phosphor, the light output is maximum at a Pr concentration of 0.07% by weight. Therefore, when the Ce concentration exceeds 0.005% by weight, only a phosphor whose light output is below the lower limit can be obtained. Therefore, the maximum Ce concentration is 0.005% by weight. On the other hand, the lower limit value of Ce concentration may be zero. This is because, for example, a phosphor having a Pr concentration of 0.2% by weight has a relative light output of 167%, an afterglow after 3 msec is 0.1%, and the afterglow characteristics can be obtained without adding Ce. This is to sufficiently satisfy the object of the present invention.

Thus, Ce, which is a coactivator, can improve the afterglow characteristics of the phosphor. Therefore, the Pr and Ce coactivator phosphors have a lower limit of Pr concentration than the Pr alone activator phosphor. The value can be expanded to a lower range. Specifically, in the case of a phosphor activated solely with 0.03% by weight of Pr, afterglow characteristics after 3 msec are 0.5%, and an afterimage becomes a problem. When 0008% by weight is added, the afterglow characteristics after 3 msec are improved to 0.2%, and the improvement effect of the present invention is obtained. At this time, the relative light output of the co-activated phosphor is 151%, and Ce cannot be co-activated in the phosphor with less than 0.03% by weight of Pr.

As described above, in the Gd ₂ O ₂ S: Pr, Ce phosphor of the present invention, the desirable concentration range of the activator is such that Pr is 0.03% by weight or more, 0.3% by weight or less, and Ce is 0 or more. 0.005% by weight or less. From the viewpoint of afterimages, if Pr is 0.1 wt% or more and 0.3 wt% or less, a more desirable range is obtained. In this case, the Ce concentration is 0.005% or less and does not change.

In the present invention, afterglow characteristics were improved by co-activating Ce with Gd ₂ O ₂ S: Pr, but it is desirable to add as little Ce as possible. This is because Ce improves the afterglow characteristics of the phosphor, but has a problem that the light output decreases. By adding Ce, the body color of the phosphor becomes yellowish white, and the body color of the phosphor absorbs the light emission of the phosphor itself, and the amount of light extracted from the phosphor is reduced. Because.

Therefore, in the phosphor of the present invention, the phosphor manufacturing method has been improved so that the amount of Ce added can be reduced as much as possible. A co-precipitation raw material powder of Ce and Pr is prepared, and the amount of Ce is reduced by using an activator powder that is uniformly mixed in advance as a raw material at the time of phosphor synthesis. This brings the atomic distance of Pr and Ce introduced into the phosphor powder crystal as close as possible, increases the proportion of Ce that affects the emission of Pr, affects only the body color of the phosphor, and reduces brightness. It aims at low afterglow and high light output by reducing Ce that causes turbulence as much as possible.

Table 3 summarizes the comparison characteristics of the afterglow characteristics and the light output characteristics of the intensifying screens of the phosphors of the present invention and the phosphors according to the conventional method. The phosphor used is a Gd ₂ O ₂ S: Pr, Ce phosphor, and the characteristics produced by the conventional method and the method of the present invention are compared. Comparing the characteristics of the three types of intensifying screens in the table, in the phosphor of the present invention, when trying to obtain afterglow characteristics at the same level as the conventional method, the amount of Ce added is about 10% (0 It was found that an intensifying screen having a higher light output can be obtained with the same afterglow characteristics. On the other hand, when the same concentration of Ce as in the conventional method is added to the phosphor of the present invention, it is simultaneously confirmed that the afterglow characteristics are improved while suppressing a decrease in luminance.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration of an embodiment in which the X-ray inspection apparatus of the present invention is applied to an airport luggage inspection apparatus. In the figure, reference numeral 1 denotes an X-ray irradiation means, for example, an X-ray tube. The X-ray A emitted from the X-ray tube 1 is first collimated by a linear collimator 2 into a slit shape having a predetermined width. The collimated X-ray B is further converted into a pencil beam C which is repeatedly linearly moved by a rotating collimator 3 provided with a plurality of slits in the radial direction. Scanning irradiation is performed. Note that the luggage 5 as the inspection object moves at a speed corresponding to the detection sensitivity of the X-rays.

X-rays reflected by the load 5, that is, Compton scattered X-rays D, are detected by a scattered X-ray detector 6. Further, the X-ray E transmitted through the load 5 is detected by the transmitted X-ray detector 7. The Compton scattered X-ray D and the transmitted X-ray E detected by the scattered X-ray detector 6 and the transmitted X-ray detector 7 are measured as continuous intensity values, and the illustration is omitted according to the X-ray intensity. The state inside the luggage 5 is imaged on a display device such as a liquid crystal display. Then, the inside of the luggage 5 is inspected by this image.

The scattered X-ray detector 6 and the transmitted X-ray detector 7 have the following configurations. For example, the scattered X-ray detector 6 will be described as an example. As shown in FIG. 2, the two scattered X-ray detectors 6 are formed so that a gap for passing the X-ray C made into a pencil beam is formed. Is arranged and configured.
Each scattered X-ray detector 6 has a housing-like detector body 8 whose one side surface is inclined. The surface of the detector body 8 that faces the object 5 to be inspected is an X-ray incident surface 8a. The X-ray incident surface 8a is formed of a material that transmits X-rays, such as a resin. ing. Further, other portions of the detector main body 8 excluding the X-ray incident surface 8a are made of, for example, aluminum in order to maintain the strength of the detector main body 8. The outer surface of the other part of the detector main body 8 excluding the X-ray incident surface 8a is covered with an X-ray shielding member 9 such as lead. This is to eliminate the influence of external X-rays.

Inside the X-ray incident surface 8a of the detector main body 8, a transmission type intensifying screen 10 is installed as a transmission type fluorescence generating means with the light emitting direction facing the inside of the detector main body 8. A reflection type intensifying screen 11 is installed on the inner wall surface of the detector body 8 excluding the X-ray incident surface 8a as reflection type fluorescence generating means. A photomultiplier 12 is installed as a photoelectric conversion means on the side surface 8b of the detector main body 8 which is perpendicular to the X-ray incident surface 8a. As this photomaru 12, what has a peak of light reception sensitivity near 400 nm is used, for example, R-1307 (trade name, manufactured by Hamamatsu Photonics Co., Ltd.) is used.

First, the Compton scattered X-ray D1 is irradiated to the transmission type intensifying screen 10 arranged inside the X-ray incident surface 8a, and the visible light a corresponding to the phosphor selected from the transmission type intensifying screen 10 is detected. Light is emitted toward the inside of the vessel body 8. Further, the reflective intensifying screen 11 is irradiated with Compton scattered X-rays D2 transmitted through the X-ray incident surface 8a, and similarly, visible light b is emitted toward the inside of the detector body 8. Then, these visible lights a and b are detected by the photomultiplier 12, and the intensity of the incident Compton scattered X-rays D is obtained by measuring the total intensity of the visible lights a and b.

ａＩ₀は、原子番号によらない一定値なので、コンプトン散乱Ｘ線は物質によって変化する、σC ／（μ＋ｂμ′）の値によって、その強度が変化する。このσC／（μ＋ｂμ′）の値は原子番号が小さい物質ほど大きくなる。よって、コンプトン散乱Ｘ線を検出することにより、プラスチック製品のような原子番号が小さい元素によって主として構成される物質を見分けることができる。 The detection principle using Compton scattered X-rays is as follows. That is, the intensity I after the X-ray having the energy E ₀ and the intensity I ₀ is transmitted through the absorber having the thickness t is obtained by the following equation.
I = I ₀ e-μt (1)
Μ in the above formula is a coefficient specific to the substance (unit: cm ⁻¹ ), which is called a linear attenuation coefficient, and indicates a ratio of attenuation while the X-ray of energy E ₀ travels 1 cm. μ has a property that a substance having a larger atomic number is larger, and can be decomposed as follows.
μ = τ + σT + σC + κ (2)
(Where τ is the absorption coefficient due to photoelectric effect, σT is the scattering coefficient due to Thomson scattering, σC is the scattering coefficient due to Compton scattering, and κ is the absorption coefficient due to electron pair creation) and the energy is E ₁ When the X-ray having the intensity I ₀ is incident from the absorber surface to the position of the depth x, the X-ray intensity I _{1 at} the position of x is obtained by the following equation.
I ₁ = I ₀ e-μx (3)
(Wherein μ represents the X-ray attenuation coefficient of the X-ray whose energy is E ₁ ) and the Compton scattered X-ray generated at the position x and scattered in the direction of the angle θ with respect to the incident direction of the X-ray. intensity I ₂ is given by the following equation.
I ₂ = aσCI ₁ ......... (4)
(Where a is a proportionality constant) The intensity I ₃ at which the generated Compton scattered X-rays emerge from the surface is bx (b = 1 / cos θ) from the point of occurrence to the surface.
I ₃ = I ₂ e-μ'bx (5)
(Wherein μ ′ represents the linear attenuation coefficient of scattered X-rays). Therefore, the intensity I ₃ of Compton scattered X-rays can be calculated from Equations (3), (4) and (5):
I ₃ = aσC I ₀ e-(μ + bμ ′) x (6)
It becomes. Therefore, the total amount of Compton scattered X-rays when passing through an absorber having a thickness t can be obtained from the following equation.

Since aI ₀ is a constant value that does not depend on the atomic number, the intensity of Compton scattered X-rays changes depending on the value of σC / (μ + bμ ′). The value of σC / (μ + bμ ′) increases as the substance has a smaller atomic number. Therefore, by detecting Compton scattered X-rays, a substance mainly composed of an element having a small atomic number, such as a plastic product, can be distinguished.

In this embodiment, the transmission-type intensifying screen 10 on the incident side and the other intensifying screens 11 have Gd ₂ O ₂ S: Pr, Ce (Gd ₂ O ₂ S is 100 wt%, and Pr is 0. 0.07% by weight and Ce is contained by 0.002% by weight.) A phosphor is used.

This phosphor is manufactured through the following steps. First, praseodymium oxide and cerium oxide are dissolved in nitric acid at a ratio of 97.3 parts by weight to 2.7 parts by weight of Pr and Ce to prepare a mixed solution of both. Next, this solution is reacted with, for example, a predetermined amount of dimethyl oxalate solution to obtain a coprecipitated oxalate salt of Pr and Ce. This coprecipitated oxalate is fired in the atmosphere at a temperature of 1000 ° C. or lower for several hours to obtain a mixed oxide of Pr and Ce. Thus, a mixed powder in which Pr and Ce are uniformly dispersed to a minute unit is obtained. Next, as a step of synthesizing the phosphor, the raw material gadolinium oxide is added at a ratio that the Pr addition amount to the Gd ₂ O ₂ S matrix is 0.07 wt% (at the same time the Ce addition amount is 0.002 wt%). The active agent mixed oxide (Pr, Ce), sulfur, and a flux material are sufficiently mixed in a powder state, placed in a container, and fired at a temperature of 1000 to 1400 ° C. for several hours. The phosphor fired product thus obtained is subjected to processes such as washing, dispersion, and sieving to obtain a phosphor finished product.

Next, as a comparative example, a phosphor produced by a conventional manufacturing method was synthesized at the same time. The amount of Pr and Ce added was the same as that of the present invention to produce a Gd ₂ O ₂ S phosphor. In the manufacturing method of the comparative example, a mixed oxide containing only an activator is not prepared. As a starting material, gadolinium oxide, praseodymium oxide, cerium oxide, sulfur, and a predetermined amount of each fluxing agent are mixed and sufficiently in a powder state. The raw material mixed powder was obtained by mixing. Next, after the firing step, a finished phosphor was obtained in exactly the same manner as in the present invention.

Subsequently, a transmission type intensifying screen 10 on the incident side and other reflection type intensifying screens 11 were prepared. As shown in FIG. 3, these intensifying screens are obtained by applying a slurry obtained by mixing the phosphor of the present invention or the comparative example together with a binder and an organic solvent onto a support 13 made of plastic film or nonwoven fabric. 14 is formed.
At this time, the amount of the phosphor applied was 90 mg / cm ² for any intensifying screen.

The thus obtained intensifying screen was incorporated into an X-ray detector, and the characteristics were evaluated. The relative output of the X-ray detector of the present invention was 174%, and the after glow after 3 msec was 0.14%. One X-ray detector of the comparative example has a relative light output of 175% and an afterglow of 0.21% after 3 msec. In the present invention, the light output is substantially the same as that of the comparative example, and the afterglow characteristic is high. A good detector could be obtained.

Similarly, the characteristics of the X-ray detector when various phosphors of the present invention are applied to the transmission-type intensifying screen 10 and the reflection-type intensifying screen 11 are shown below in Example 2 and below. Table 4 shows a comparison with the case of using the intensifying screen. In these examples, only the type of phosphor was changed, and the same method as in Example 1 was used for the intensifying screen manufacturing method, the configuration of the X-ray detector, and the like.

Note that the phosphor of the present invention may be used for at least one of the transmission type intensifying screen and the reflection type intensifying screen. However, with respect to afterglow characteristics, an afterimage remains if there is a problem with one of the phosphors, and a phosphor whose afterglow after 3 msec is 0.2% or less cannot be used. On the other hand, the light output may be over 150% as a whole, and various combinations other than the phosphor of the present invention are possible.

  According to the characteristics of Table 4, in the X-ray detector of the present invention, the relative light output is 150% (vs. standard phosphor) or more and the afterglow is 0.2% or less. If an X-ray inspection apparatus is configured using such an X-ray detector, sufficient detection sensitivity is obtained by relatively low-intensity X-rays, and afterglow is improved, so that a clear inspection image with no afterimage or the like is obtained. Therefore, even if the inspection is continuously performed at a high speed, the inspection can be performed with high accuracy. The X-ray inspection apparatus of the present invention is applicable not only to airport baggage inspection apparatuses but also to various security systems.

DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... Collimator, 3 ... Rotary collimator, 4 ... Conveyor, 5 ... Test object,
6 ... Scattered X-ray detector, 7 ... Transmitted X-ray detector, 8 ... Housing-like detector body, 8a ... X-ray incident surface, 10 ... Transmission type intensifying screen, 11 ... Reflective type intensifying screen, 12 ... Photomaru, 13 ... Support, 14 ... Fluorescent film

Claims (6)

A case-like detector main body having an X-ray incident portion, transmission-type fluorescence generating means disposed in the incident portion, and reflection-type fluorescence disposed along the inner wall surface of the detector main body excluding the incident portion. Generating means and photoelectric conversion means installed in the detector body, wherein the transmission type fluorescence generation means is a transmission type intensifying screen, and the reflection type fluorescence generation means is a reflection type intensifying screen. In the X-ray detector provided, at least one of the transmission type intensifying screen and the reflection type intensifying screen is either Gd ₂ O ₂ S: Pr or Gd ₂ O ₂ S: Pr, Ce phosphor. And the afterglow light output of the intensifying screen after 3 msec is 0.2% or less. 2. The X-ray detector according to claim 1, wherein the phosphor is Gd ₂ O ₂ S: Pr, Ce (wherein the concentration of Pr and Ce is such that Pr is 100 wt% when Gd ₂ O ₂ S is 100 wt%). The X-ray detector is characterized by being 0.03% by weight or more and 0.3% by weight or less and Ce is 0.005% by weight or less. 3. The X-ray detector according to claim 1, wherein the phosphor is a phosphor manufactured through a process in which Pr and Ce raw materials are mixed in advance by a coprecipitation method and fired together with a Gd oxide or the like. X-ray detector. 4. The X-ray detector according to claim 1, wherein the X-ray detector detects Compton scattered X-rays. X-ray irradiation means for irradiating the inspection object with X-rays, X-ray detection means for detecting Compton scattered X-rays or transmitted X-rays from the inspection object, and X-ray intensity measured by the X-ray detection means X-ray inspection comprising: means for imaging the inside of the object to be inspected based on the X-ray; and the X-ray detection means includes means for generating fluorescence when irradiated with Compton scattered X-rays or transmitted X-rays In the apparatus, the fluorescence generating means has an intensifying screen using a Gd ₂ O ₂ S: Pr or Gd ₂ O ₂ S: Pr, Ce phosphor, and the phosphor has an afterglow after 3 msec. An X-ray inspection apparatus having an optical output of 0.2% or less. 6. The X-ray inspection apparatus according to claim 5, wherein the X-ray inspection apparatus is an airport luggage inspection apparatus.

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