JP2928677B2 - X-ray detector and X-ray inspection device - 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 detector and an X-ray inspection apparatus using the same.

[0002]

2. Description of the Related Art Generally, when carrying luggage into an aircraft, the luggage is inspected in advance at an airport in order to ensure safe operation of the aircraft. As such a baggage inspection apparatus, a transmission X-ray inspection apparatus utilizing transmission of X-rays is frequently used. According to this transmission X-ray inspection apparatus,
It is possible to relatively easily find a metal article hard to transmit X-rays, for example, a metal weapon such as a firearm or a knife.

However, substances mainly composed of elements having a small atomic number, such as plastic bombs and narcotics, easily transmit X-rays.
It was difficult to detect with a line inspection device. Therefore,
An inspection device using Compton scattered X-rays is being developed. Compton scattered X-rays, that is, X-rays reflected from an object when irradiated with X-rays, can be obtained more with an element having a smaller atomic number. This makes it possible to discover plastic bombs, drugs, and the like.

An X-ray inspection apparatus using the above-described transmitted X-rays or Compton scattered X-rays generally guides the transmitted X-rays or Compton scattered X-rays to an X-ray detector, and converts the detected X-rays into a phosphor. After converting to visible light, the intensity of this visible light is detected by a photomultiplier tube, a so-called photomultiplier (hereinafter abbreviated as photomultiplier), and inspection is performed by imaging the inside of the baggage according to the intensity. It is configured to be.

By the way, in the above-mentioned X-ray detector, usually, as shown in FIG. 11, a photomar having a spectral sensitivity characteristic peak near 400 nm is used. Therefore, phosphors that convert X-rays into visible light include those that have an emission wavelength peak near 400 nm, such as LaOBr: Tb.
LaOBr: Tm and the like have been used. FIG. 12 shows the emission wavelength characteristics of the LaOBr: Tm phosphor.

[0006]

However, an X-ray detector using a phosphor such as LaOBr: Tb or LaOBr: Tm as described above cannot detect Compton scattered X-rays with sufficient sensitivity. There was a problem. For this reason, in the conventional Compton scattered X-ray inspection apparatus, the intensity of the irradiated X-ray is increased to such an extent that sufficient inspection accuracy is obtained, that is, a clear inspection image is obtained. However, in an X-ray inspection apparatus installed in a public place, such as an airport luggage inspection apparatus, increasing the intensity of the irradiated X-rays increases the size of the apparatus and increases the risk. .

Therefore, there has been a strong demand for an X-ray detector capable of obtaining a sufficient detection sensitivity even when relatively low-intensity irradiated X-rays are used. In addition, the use of such an X-ray detector has strongly demanded the appearance of an X-ray inspection apparatus which is small, has little risk, and can obtain a clear inspection image.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and has as its object to provide an X-ray detector capable of obtaining sufficient detection sensitivity with relatively low-intensity X-rays. It is another object of the present invention to provide an X-ray inspection apparatus which is small, has little risk, and can obtain a clear inspection image.

That is, the X-ray detector of the present invention comprises a housing-like detector main body having an X-ray incident portion, a transmission type fluorescence generating means disposed at the incident portion, and the above-mentioned excluding the incident portion. In an X-ray detector comprising a reflection type fluorescence generating means arranged along the inner wall surface of the detector main body and a photoelectric conversion means installed in the detector main body, the transmission type fluorescence generating means is a transmission type fluorescence generating means. An intensifying screen, and the reflection-type fluorescence generating means
Has a reflective intensifying screen , the transmission intensifying screen and the reflective intensifying screen.
At least one intensifying _{screen, A 2 O 2 S: D} (A represents at least one element selected Gd, from La and Y, D is
At least one element selected from Tb and Pr or a mixture thereof with at least one element selected from Ce and Yb), and BaFX: E (X is at least one selected from Cl and Br) Represents one element, E is Eu or
And a mixture of Eu and at least one element selected from Ce and Yb). Further, in the X-ray detector, both the transmission intensifying screen and the reflective intensifying screen are provided with the A ₂ O
_{2 The} same or different phosphors selected from S: D and BaFX: E are used.

An X-ray inspection apparatus according to the present invention comprises: an X-ray irradiating means for irradiating an X-ray to an inspection object; and an X-ray detection apparatus for detecting Compton scattered X-rays or transmitted X-rays from the inspection object. and means, within said object to be inspected based on the X-ray intensity measured by the X-ray detecting means Te X-ray examination apparatus odor and means for imaging, the X-ray detecting means, Compton scattered X-ray or It has a means for generating fluorescence when irradiated with transmitted X-rays, and the means for generating fluorescence includes A ₂ O ₂
S: D (A represents at least one element selected from Gd, La and Y, and D represents at least one element selected from Tb and Pr
Species, or a mixture of these with at least one element selected from Ce and Yb), and BaFX: E
(X represents at least one element selected from Cl and Br, and E represents Eu or a mixture of Eu and at least one element selected from Ce and Yb). It is characterized by having an intensifying screen .

[0011]

The fluorescence generating means in the X-ray detector and X-ray inspection apparatus of the present invention uses at least one kind of phosphor selected from A ₂ O ₂ S: D and BaFX: E. Here, among the above-mentioned phosphors, representative Gd ₂ O ₂ S: Tb (including Gd ₂ O
₂ S: Tb, Ce), Gd ₂ O ₂ S: Pr, BaFCl: Eu and BaFBr: Eu show the emission wavelength characteristics of FIGS. 7, 8, 9 and 10, respectively.
Shown in Each of the above phosphors has an emission wavelength peak of 400
Although deviated from the vicinity of nm, the luminous efficiency (the efficiency of converting X-rays into visible light) is very high. Therefore, even in the case of using a photomar having a light receiving sensitivity peak near 400 nm in the X-ray detector, the detection sensitivity of Compton scattered X-rays and transmitted X-rays can be greatly improved.

As shown in FIGS. 7 to 10,
Since the afterglow (time required for the intensity of the emitted light to reach a value of 1/10) is as small as 1.0 msec or less for each of the above-described phosphors, the detection speed is high when detecting X-rays continuously. Can be hastened.

[0013] By constructing an X-ray inspection apparatus using the X-ray detector as described above, the image quality of the inspection image can be greatly improved, and the inspection accuracy can be improved. At the same time, the processing capacity can be improved.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram schematically showing the configuration of an embodiment in which the X-ray inspection apparatus of the present invention is applied to an airport luggage inspection apparatus. In FIG. 1, reference numeral 1 denotes an X-ray irradiating means, for example, an X-ray tube. X-rays A emitted from the X-ray tube 1 are first collimated by a linear collimator 2 into a slit having a predetermined width. The collimated X-rays B are further turned into a pencil beam C that repeats a linear motion by a rotary collimator 3 provided with a plurality of slits in the radial direction. Scanning irradiation is performed on the light. Note that the baggage 5, which is the inspection object, moves at a speed corresponding to the X-ray detection sensitivity.

The X-rays reflected by the load 5, that is, Compton scattered X-rays D, are detected by a scattered X-ray detector 6. The X-rays E transmitted through the package 5 are detected by the transmitted X-ray detector 7. The Compton scattered X-rays D and transmitted X-rays E detected by the scattered X-ray detector 6 and the transmitted X-ray detector 7 are measured as continuous intensity values, and are not shown according to the X-ray intensity. The state inside the package 5 is imaged on a display device such as a CRT. Then, the inside of the package 5 is inspected based on this image.

The above-mentioned scattered X-ray detector 6 and transmitted X-ray detector 7 have the following configuration. For example, taking the scattered X-ray detector 6 as an example, as shown in FIG. 2, the two scattered X-ray detectors 6 are formed so that a gap for passing the pencil-shaped X-ray C is formed. Are arranged and configured.

Each scattered X-ray detector 6 has a detector body 8 in the form of a housing with one side surface inclined. The surface of the detector body 8 facing the object 5 to be inspected is an X-ray incident surface 8a, and the X-ray incident surface 8a is formed of a material that transmits X-rays, such as a resin. ing. Other parts of the detector main body 8 except for the X-ray incident surface 8a are as follows.
In order to maintain the strength of the detector main body 8, the main body is made of, for example, aluminum or the like. The outer surface of the other part of the detector body 8 except 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.

On the inside of the X-ray incidence surface 8a of the detector main body 8, a transmission intensifying screen 10 whose emission direction is directed toward the inside of the detector main body 8 is provided as transmission type fluorescence generating means. In addition, on the inner wall surface of the detector main body 8 except for the X-ray incident surface 8a, a reflection type intensifying screen 11 is provided as reflection type fluorescence generating means. On a side surface 8b of the detector main body 8 which is perpendicular to the X-ray incident surface 8a, a photomultiplier 12 is provided as a photoelectric conversion unit.
Is installed. 400 nm for this photomultiplier 12
The one having a peak of the light receiving sensitivity in the vicinity is used, for example, R-1307 (trade name, manufactured by Hamamatsu Photonics KK) is used.

First, the Compton scattered X-ray D ₁ is applied to the transmission intensifying screen 10 arranged inside the X-ray incident surface 8a.
And the visible light a corresponding to the phosphor selected from the transmission intensifying screen 10 is emitted toward the inside of the detector main body 8. When the reflection type intensifying screen 11 is irradiated with the Compton scattered X-rays D ₂ transmitted through the X-ray incident surface 8 a, the visible light b is similarly emitted toward the inside of the detector main body 8. . The visible light a and b are detected by the photomultiplier 12, and the total intensity of the visible light a and b is measured, whereby the intensity of the incident Compton scattered X-ray D is obtained.

The principle of detection using Compton scattered X-rays is as follows. That is, the intensity I _{0 after} the X-ray having energy E ₀ and intensity I ₀ has passed through the absorber having the thickness t.
Is obtained by the following equation.

[0022] ^{_{I = I 0 e -μt ......... (}} 1) specific coefficient μ is the material in the above formula (Unit: cm ^-1) in are those called linear attenuation coefficient, the energy E ₀ X Shows the rate at which the line attenuates while traveling 1 cm. μ has a property that a substance having a larger atomic number has a larger property, and can be decomposed as follows.

Μ = τ + σ _T + σ _C + κ (2) (where τ is the absorption coefficient due to the photoelectric effect, σ _T is the scattering coefficient due to Thomson scattering, σ _C is the scattering coefficient due to Compton scattering, κ also shows the absorption coefficient by the electron pair creation), if the energy is incident to a position of a depth x from the surface of the absorber X-ray intensity I ₀ at E _1, X-ray intensity I ₁ at the position of x Is obtained by the following equation. I ₁ = I ₀ e ^-μx (3) (in the formula, μ represents the X-ray attenuation coefficient of the energy of E ₁ ) Further, it is generated at the position of x and in the X-ray incident direction. On the other hand, the intensity I ₂ of the Compton scattered X-ray scattered in the direction of the angle θ is obtained by the following equation.

I ₂ = aσ _C I 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 from the point of occurrence to the surface. Is bx (b = 1 / cos θ), so that I ₃ = I ₂ e ^-μ′bx (5) (in the equation, μ ′ indicates the linear attenuation coefficient of scattered X-rays). .
Therefore, the intensity I ₃ of the Compton scattered X-ray is given by (3)
From the equations, (4) and (5), I ₃ = aσ _C I ₀ e- ^{(μ + bμ ′) x} (6) Therefore, the total amount of Compton scattered X-rays when passing through an absorber having a thickness of t can be obtained from the following equation.

[0025]

(Equation 1) Since aI ₀ is a constant value that does not depend on the atomic number, Compton scattered X-rays vary depending on the material, σ _C / (μ + b
μ ′) changes its intensity. This σ _C /
The value of (μ + bμ ′) increases as the atomic number of the substance decreases. Therefore, by detecting Compton scattered X-rays, it is possible to identify substances mainly composed of elements having small atomic numbers, such as plastic products.

The transmission type intensifying screen 10 and the other reflection type intensifying screen 11 on the incident side in this embodiment are made of A ₂ O ₂ S: D.
(A represents at least one element selected from Gd, La and Y, D represents at least one element selected from Tb and Pr, or at least one element selected from Ce and Yb And BaFX: E (where X is
At least one element selected from Cl and Br,
E is at least 1 selected from Eu or Eu and Ce and Yb
At least one selected from the group below)
It uses a kind of phosphor.

Here, Ce and Yb as activators have the effect of shortening the afterglow. In a Tb-activated phosphor having a large afterglow as compared with a Pr-activated phosphor, such an activator may be used. Use is effective. These Ce and Yb are relative to the total amount of activator.
It is preferably used in the range of about 0.001% by weight to 10% by weight. Specific phosphors include Gd ₂ O ₂ S: Tb, Gd ₂
O ₂ S: Tb, Ce, Gd ₂ O ₂ S: Tb, Yb, Gd ₂ O ₂ S: Pr, La ₂ O
₂ S: Tb, La ₂ O ₂ S: Tb, Ce, La ₂ O ₂ S: Tb, Yb, La ₂ O
₂ S: Pr, Y ₂ O ₂ S: Tb, Y ₂ O ₂ S: Tb, Ce, Y ₂ O ₂ S:
_{Tb, Yb, Y 2 O 2} S: Pr, BaFCl: Eu, BaFBr: Eu , and the like.

The transmission type intensifying screen 10 and the reflection type intensifying screen 11 may use the same phosphor or different phosphors. The combination of these phosphors is not particularly limited, and is appropriately set according to the required light output and the like. These intensifying screens 10, 11
As shown in FIG. 3, by applying a slurry in which the selected phosphor is mixed with a binder and an organic solvent on a support 13 such as a plastic film or a nonwoven fabric,
The phosphor layer 14 is formed.

The coating amount of the phosphor on the transmission type intensifying screen 10 and the reflection type intensifying screen 11 is set according to each. That is, the transmission type intensifying screen 10 on the incident side
In, if you set too much phosphor coating amount,
Due to the light absorption inside the phosphor layer 14, the light emission output of the fluorescence is reduced. In addition, since the absorption of Compton scattered X-rays also occurs, the amount of incidence on the reflective intensifying screen 11 decreases, and the total amount of visible light decreases. In the reflection type intensifying screen 11, the light output increases as the coating amount is increased. However, even if the coating amount is excessively increased, no further effect is obtained. FIG. 4 shows the respective optical outputs when BaFCl: Eu is used for both the transmission intensifying screen 10 and the reflection intensifying screen 11. The light output was measured using an X-ray tube voltage of 120 kVP using a Photomar R-980 (trade name, manufactured by Hamamatsu Photonics Co., Ltd.) having a bialkali photocathode, and the conventional phosphor (LaOBr:
It is shown as relative light output when the light output of Tb) is 100.

Further, as described above, the total amount of visible light varies depending on the amount of application of the transmissive intensifying screen 10 and the reflective intensifying screen 11, as described above. It is preferable to set the total application amount of the phosphor in consideration of the individual application amounts of the intensifying screen 11. FIG. 5 shows the relationship between the total application amount of the transmissive intensifying screen 10 and the reflective intensifying screen 11 and the relative light output based on a combination of typical phosphors. Although different depending on the combination of phosphors, by a range of coating total amount of ^{80mg / cm 2 ~300mg / cm 2} , it is seen that good optical output is obtained.

The relative light output when using the transmission intensifying screen 10 and the reflection intensifying screen 11 prepared by variously combining the respective phosphors according to the present invention are shown in Tables 1, 2, 3, 4 and 5. As shown in FIG.

[0032]

[Table 1]

[Table 2]

[Table 3]

[Table 4] As is clear from Table 1, Table 2, Table 3, Table 4, and FIG. 6, it is understood that the use of the phosphor according to the present invention can significantly improve the light output as compared with the conventional phosphor. That is, the light output is greatly improved,
The detection sensitivity of Compton scattered X-rays is improved, so that it is possible to more clearly image the inside of the baggage 5, which is the inspection object. This is the same for the detection sensitivity of transmitted X-rays. Therefore, more accurate inspection can be performed. Further, by improving the light output, the capacity of the X-ray tube 1 can be reduced, and the size of the apparatus can be reduced. Further, as shown in FIGS. 7 to 10, all of the phosphors according to the present invention have a low afterglow of 1.0 msec or less, so that the moving speed of the load 5 can be increased. Thereby, the processing capacity can be significantly improved.

In the above embodiment, both the transmission type intensifying screen 10 as the transmission type fluorescence generating means and the reflection type intensifying screen 11 as the reflection type fluorescence generating means are provided with the phosphor according to the present invention, that is, A An X-ray detector using a phosphor selected from ₂ O ₂ S: D and BaFX: E has been described.
As is apparent from the measurement results shown in Table 4, since the phosphor according to the present invention alone can improve the light output more than the conventional phosphor, the above-mentioned phosphor is used as the transmission type intensifying screen 10 and the reflection type. It is also effective to use only one of the intensifying screens 11.

In the above embodiment, an example in which the X-ray detector of the present invention is applied to a scattered X-ray detector has been described. Effects can be obtained. Further, the X-ray inspection apparatus according to the present invention is not limited to an airport baggage inspection apparatus but can be used as various security systems.

[0035]

As described above, according to the present invention, X-rays with which sufficient detection sensitivity can be obtained with relatively low-intensity X-rays can be obtained.
It is possible to provide a line detector. By configuring an X-ray inspection apparatus using such an X-ray detector, a clear inspection image can be obtained, and the apparatus can be downsized.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an embodiment of an X-ray inspection apparatus of the present invention.

FIG. 2 is a sectional view showing a configuration of an embodiment of the X-ray detector of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration example of an intensifying screen used in the present invention.

FIG. 4 is a diagram showing a relationship between a coating amount of a phosphor on an intensifying screen and a relative light output in one embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the total applied amount of phosphors of the incident-side intensifying screen and the reflective-side intensifying screen and the relative light output in one embodiment of the present invention.

FIG. 6 is a diagram showing a relative light output of a phosphor used in the present invention.

FIG. 7 is a graph showing emission wavelength characteristics of Gd ₂ O ₂ S: Tb.

FIG. 8 is a graph showing emission wavelength characteristics of Gd ₂ O ₂ S: Pr.

FIG. 9 is a graph showing emission wavelength characteristics of BaFCl: Eu.

FIG. 10 is a graph showing emission wavelength characteristics of BaFBr: Eu.

FIG. 11 is a diagram showing spectral sensitivity characteristics of a photomal used in an X-ray detector.

FIG. 12 is a diagram showing emission wavelength characteristics of a conventional phosphor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 5 ... Luggage which is an object to be inspected 6 ... Scattered X-ray detector 7 ... Transmitted X-ray detector 8 ... Casing detector main body 8a ... X-ray incident surface 10 ... Transmission type Intensifying screen 11: Reflective intensifying screen 12: Photomaru

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-158383 (JP, A) JP-A-63-25537 (JP, A) JP-A-4-364454 (JP, A) 7240 (JP, B2) “Phosphor Handbook,” edited by the Society of Phosphors, 1st edition, 2nd printing, June 20, 1991, Ohm Co., Ltd., pp. 285-288 (58) Fields surveyed (Int .Cl. ⁶ , DB name) G01T 1/00-7/12 G01N 23/00-23/227

Claims (7)

(57) [Claims] 1. A housing-shaped detector main body having an X-ray incident part, a transmission type fluorescence generating means arranged at the incident part,
An X-ray detector comprising: reflection-type fluorescence generating means arranged along the inner wall surface of the detector main body excluding the incident portion; and photoelectric conversion means installed in the detector main body; The fluorescent light generating means has a transmission intensifying screen , and the reflective fluorescent light generating means has a reflective intensifying screen,
At least one type intensifying screen and reflective intensifying screen, A ₂
O ₂ S: D (A is at least one selected from Gd, La and Y
D represents at least one element selected from Tb and Pr, or a mixture thereof with at least one element selected from Ce and Yb), and Ba
FX: fluorescence selected from E (X represents at least one element selected from Cl and Br, E represents Eu or a mixture of Eu and at least one element selected from Ce and Yb) An X-ray detector comprising a body. 2. The X-ray detector according to claim 1, wherein the transmission type intensifying screen and the reflection type intensifying screen are the same selected from the group consisting of A ₂ O ₂ S: D and BaFX: E. An X-ray detector characterized by using different phosphors. 3. The X-ray detector according to claim 1 , wherein a total amount of an application amount of the phosphor on the transmission intensifying screen and an application amount of the phosphor on the reflection intensifying screen is: X-ray detector which lies in the range of ^{80mg / cm 2 ~300mg / cm 2} . 4. The X-ray detector according to claim 1, wherein the phosphor has an afterglow of 1.0 msec or less. 5. The X-ray detector according to claim 1, wherein Compton scattered X-rays are detected. 6. X-ray irradiating means for irradiating X-rays to an object to be inspected, X-ray detecting means for detecting Compton scattered X-rays or transmitted X-rays from the object to be inspected, and the X-ray detecting means wherein based on the measured X-ray intensity Te X-ray examination apparatus odor and means for imaging an interior inspection object, the X-ray detecting means, Compton scattered X-ray or transmitted X
A means for generating fluorescence when the line is irradiated,
This fluorescence generating means is A ₂ O ₂ S: D (A is Gd, La and Y
And D represents at least one element selected from Tb and Pr or a mixture thereof with at least one element selected from Ce and Yb), and BaFX: E (X represents at least one element selected from Cl and Br, and E represents Eu or Eu and Ce
And a mixture with at least one element selected from Yb).) An X-ray inspection apparatus characterized by having an intensifying screen using a phosphor selected from the group consisting of: 7. An X-ray inspection apparatus according to claim 6 , wherein said X-ray inspection apparatus is an airport luggage inspection apparatus.