JP2732701B2 - Scintillation detector - Google Patents

Description

The present invention relates to a scintillation detector used for a radiation monitoring device used in a nuclear facility, for example, and particularly to a large area radiation detector. The present invention relates to a scintillation detector used as a surface contamination monitoring device for a measurement object having a large area or a human body, such as a gate monitoring device (body surface monitoring device), an article unloading monitoring device, and a landry monitoring device.

(Prior Art) In recent years, for example, in a nuclear facility, as a monitoring device having a large area such as a gate monitor device (body surface monitoring device), an article unloading monitoring device, a land re-monitoring device, or a surface contamination monitoring device of a human body, a large monitoring device is widely used. Scintillation detectors, which are area radiation detectors, are widely used.

FIG. 8 is a diagram showing a configuration example of a conventional scintillation detector of this type, wherein FIG. 8 (a) is a plan view, and FIG. 8 (b) is a cross-sectional view taken along the line AA in FIG. Each is shown.

That is, in the conventional scintillation detector, the detection surface side is covered with a light shielding film 1 so as to take in only radiation without external light, and a flat scintillator 2 which emits light when radiation is incident is fixed to the transparent plate 3. The light from the scintillator 2 is received, converted into an electrical signal corresponding to the amount of light, and taken out together with the photomultipliers 4a and 4b in a case 5.

Here, the conventional scintillator 2 is composed of a uniform scintillator plate as shown in the plan view and the AA sectional view in FIGS. 9 (a) and 9 (b).

However, such a conventional scintillation detector has such a characteristic that the detection efficiency characteristic is high at the center of the detection surface and decreases toward the end of the detection surface, as shown in FIG. 10 (a). ing. Then, using a scintillation detector having such detection efficiency characteristics, when measuring the contamination of the human body surface, or the surface of the article,
Even if there are two places having the same surface contamination, there is a difference between the outputs of the detectors. As a result, measurement unevenness occurs and uniform measurement cannot be performed.

(Problems to be Solved by the Invention) As described above, in the conventional scintillation detector, only the central part of the detection surface has high detection efficiency characteristics, and measurement unevenness occurs, and uniform measurement cannot be performed. There was a problem.

An object of the present invention is to provide a highly reliable scintillation detector capable of preventing only a central portion of a detection surface from having high detection efficiency characteristics and performing uniform measurement without causing measurement unevenness. To provide equipment.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, according to the present invention, a flat scintillator that emits light when radiation is incident thereon, light from the scintillator is received, and the light amount (A) dividing a plate-shaped scintillator into a plurality of parts, and dividing the divided unit scintillators in accordance with a detection location. (B) dividing the plate-shaped scintillator into a plurality of parts, and dividing the unit scintillators into different thicknesses according to the detection locations, or (c) dividing the plate-shaped scintillator into a plurality. Dividing the unit scintillator and providing a gap between the divided unit scintillators and setting the dimension of the gap to a different value depending on the detection location; A plurality of holes are provided in the oscillator, and the aperture ratio per unit area is set to a different value depending on the location; or (e) an optical mask is provided between the flat scintillator and the photomultiplier, and The light aperture ratio per unit area is set to a different value depending on the location.

(Operation) Therefore, in the scintillation detector of the present invention, the plate-shaped scintillator is divided into a plurality of parts, and the divided unit scintillators are formed of different materials depending on the detection place, or the plate-shaped scintillator is divided into a plurality of pieces. Split,
And, the divided unit scintillators may be configured with different thicknesses according to the detection location, or the flat scintillator may be divided into a plurality of sections, and a gap may be provided between the divided unit scintillators, and the dimension of the gap may be determined at the detection location. Depending on the location, the aperture ratio per unit area is different depending on the location, or between the flat scintillator and the photomultiplier. By setting a light mask on the light-receiving surface and setting the light aperture ratio per unit area to a different value depending on the location, the light-receiving surface can be more than the light-emitting amount per unit area on the light-receiving surface of the photomultiplier and its vicinity. In addition, since the light emission amount can be corrected so as to increase the light emission amount per unit area in a portion other than the vicinity portion thereof, the entire plate has a uniform light emission characteristic. It is possible to compensate for the "characteristic of high sensitivity on the center side of the detection surface" of the detector of the type that converts the signal into an electrical signal by using a photomultiplier by using a chilator, and the detection efficiency is flat over the entire detection surface. Properties can be obtained. Thus, uniform measurement can be performed without causing measurement unevenness.

(Example) First, the concept of the present invention will be described.

The present invention utilizes the property that the detection efficiency characteristic changes due to a change in the amount of light emitted from the scintillator or the transmission of light from the scintillator to the photomultiplier. That is, a conventional scintillator having a uniform light emission characteristic over the entire plate is used to compensate for the "detection efficiency characteristic at which the center side has high sensitivity" of a scintillation detector of a type that converts the signal into an electric signal by a photomultiplier. By doing
It is intended to ensure flat detection efficiency characteristics over the entire detection surface.

In general, there are two possible causes that the detection efficiency characteristic of the central part of the detection surface in the radiation detector becomes high. One of the causes is a solid angle at which the radiation source views the detection surface. Radiation emitted from the source is emitted in the 4π direction, and the amount reaching the detector depends on its solid angle. Since this solid angle is inevitably maximized when the radiation source is directly above the center of the detection surface, the detection efficiency also increases accordingly.

The other is due to the amount of light incident on the light receiving surface (photoelectric surface) of the photomultiplier from the scintillator. Radiation incident on the detector interacts with the scintillator, and emitted light is emitted in the 4π direction. In this case, the amount of light transmitted to the light receiving surface of the photomultiplier is affected by the arrangement of the photomultiplier, but generally increases at the center.
Therefore, the detection efficiency also contributes to the maximum at the center of the detection surface.

Therefore, in the present invention, for example, the material and thickness of the scintillator are changed in accordance with the detection location, that is, the position of the scintillator, or the amount of light transmitted from the scintillator to the photomultiplier is changed by providing a light mask, so that the detection efficiency characteristics are improved. Is intended to be flattened.

Hereinafter, an embodiment of the present invention based on the above-described concept will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a scintillation detector according to the present invention. FIG. 1 (a) is a plan view, and FIG. 1 (b) is a cross-sectional view taken along the line AA in FIG. 1 (a). ing. In the drawings, the same elements as those in FIGS. 8 and 9 are denoted by the same reference numerals.

As shown in FIG. 1, the scintillation detector according to this embodiment has a detection surface side covered with a light-shielding film 1 for taking in only radiation without entering external light, and has a flat plate shape which emits light when radiation is incident. The scintillator 21 is fixed to the transparent plate 3, and is housed in the case 5 together with the photomultipliers 4 a and 4 b which receive light from the scintillator 2, convert the light into an electric signal corresponding to the amount of light, and take out the electric signal. .

Here, the scintillator 21 according to the first embodiment of the present invention is used.
As shown in FIGS. 2 (a) and 2 (b), the scintillator 21 is divided into a plurality of parts vertically and horizontally, and the divided unit scintillators are divided in accordance with the detection location, as shown in the plan view and the AA sectional view. A scintillator material composed of materials with different light emission amounts, that is, a scintillator material with a small light emission amount at the end of the detection surface is selected, and a scintillator material with a large light emission amount gradually toward the center along the longitudinal direction of the photomultipliers 4a and 4b. I am trying to select it.

In this case, as a method of changing the amount of light emission, a method of selecting a scintillator of an inorganic scintillator (various types) or an organic crystal (various types), or a method of changing the type and the amount of a solute of a plastic scintillator can be realized. Can be.

For example, as a specific example in the case of a plastic scintillator, the following selections can be made.

That is, toluene, phenylcyclohexane, polystyrene, polyvinyltoluene and the like are selected as solutes, and terphenyl (TP), tetraphenylbutadiene (TPB), dephenyloxazole (PPO), phenyl Oxazol (PBD), diphenyl stilbene (DPS), and as the second solute, the wavelength transition material (POPOP) and naphthyl phenyl oxazole (NPO) were selected, and the amount of light emitted from the scintillator was changed by selecting the concentration of the material. A scintillator can be created.

In addition, the above-mentioned material is an example of a scintillator, and even if it is a material other than the above, if a material having a different light emission amount is used depending on the place, it is included in the scope of the present invention. It is.

In this embodiment, since the scintillator is made of a different material, the amount of light emitted per unit area after radiation interacts with the scintillator changes.

Therefore, the material of the scintillator 21 is changed to the photomultipliers 4a and 4b.
By gradually changing along the longitudinal direction of the, the detection efficiency characteristics of the scintillation detector become flat,
Using this scintillation detector, when measuring the contamination of the human body surface or the surface of the article, even if there are two places with the same surface contamination, there is no difference in the output of the detector, As a result, uniform measurement without measurement unevenness can be performed.

FIG. 10 shows an example of the detection efficiency characteristics of the detection surface in the scintillation detector having the scintillator 21 configured as described above.

FIG. 2B shows an example in which the portion where the radiation source is close to the detector is flattened (the effect of the present invention is slightly reduced), and FIG. 3C shows that the radiation source is separated from the detector. An example in which the portion is flattened (the effect of the present invention is increased) is shown.

The effect of the present invention increases as the difference between the light emission amounts at the center and the end of the detection surface increases. However, when the distance between the radiation source and the detection surface is different, there is a difference in the effect as shown in FIG. The effect of the present invention can be adjusted according to.

Next, another embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a view showing a configuration example of a scintillator according to a second embodiment of the present invention. FIG. 3 (a) is a plan view, and FIG. 3 (b) is a cross section taken along line AA in FIG. Each figure is shown.

That is, as the scintillator 22 of the present embodiment, the scintillator 22 is divided into a plurality of parts vertically and horizontally, and the divided unit scintillators are configured to have different thicknesses according to the detection locations.

In the present embodiment, the probability of radiation interacting with the scintillator per unit area increases due to the increase in the thickness of the scintillator, and the amount of light emitted after the interaction increases as the thickness increases. (Radiation tracks become longer).

Therefore, the thickness of the scintillator 22 is reduced at the center,
By gradually increasing the thickness at the ends along the longitudinal direction of the photomultipliers 4a and 4b, the same operation and effect as in the above embodiment can be obtained.

That is, when a flat scintillator is used, the radiation efficiency is different depending on the detection location because there is a radiation incident from an oblique direction, but in the present embodiment, by compensating this with the thickness of the scintillator, Measurement unevenness can be eliminated.

FIG. 4 is a diagram showing a configuration example of a scintillator according to a third embodiment of the present invention. FIG. 4 (a) is a plan view, and FIG. 4 (b) is a cross-sectional view taken along line AA in FIG. Each figure is shown.

That is, as the scintillator 23 of the present embodiment, the scintillator 22 is divided into a plurality of parts vertically and horizontally, and the gaps between the divided unit scintillators are configured to have different dimensions depending on the detection location.

In the present embodiment, by setting the size of the gap between the unit scintillators, the probability of radiation interacting with the scintillator 23 per unit area can be changed.

Therefore, by increasing the gap size of the scintillator 23 at the center and gradually decreasing the size at the ends along the longitudinal direction of the photomultipliers 4a and 4b, the same operation and effect as in the above embodiment can be obtained. be able to.

FIG. 5 is a diagram showing a configuration example of a scintillator according to a fourth embodiment of the present invention. FIG. 5 (a) is a plan view, and FIG. 5 (b) is a cross-sectional view taken along line AA in FIG. Each figure is shown.

That is, as the scintillator 24 of the present embodiment, a plurality of holes are provided in the scintillator 24, and the aperture ratio per unit area is configured to be different depending on the detection location.

In the present embodiment, by setting the aperture ratio per unit area of the scintillator 24, the probability that the radiation interacts with the scintillator 24 can be changed.

Accordingly, the aperture ratio per unit area of the scintillator 24 is
By increasing the aperture ratio at the center and gradually decreasing it at the ends along the longitudinal direction of the photomultipliers 4a and 4b, the same operation and effect as in the above embodiment can be obtained.

Next, FIG. 6 is a diagram showing another configuration example of the scintillation detector according to the present invention, wherein FIG. 6 (a) is a plan view and FIG. 6 (b) is AA in FIG. The sectional views are respectively shown. In the drawings, the same elements as those in FIGS. 8 and 9 are denoted by the same reference numerals.

As shown in FIG. 6, the scintillation detector according to the present embodiment has a detection surface side covered with a light shielding film 1 in order to take in only radiation without entering external light, and has a flat plate shape which emits light when radiation is incident. The scintillator 21 is fixed to the transparent plate 3 and housed in the case 5 together with the photomultipliers 4a and 4b which receive light from the scintillator 2 and convert it into an electric signal corresponding to the amount of light. Further, an optical mask 6 is provided between the scintillator 2 and the photomultipliers 4a and 4b (in the figure, between the transparent plate 3 and the photomultipliers 4a and 4b).

Here, as shown in FIGS. 7A and 7B, the optical aperture ratio per unit area of the optical mask 6 as shown in FIGS. 7 (a) and 7 (b) is shown. ,
It is configured as a different value depending on the detection location.

In the scintillation detector provided with the optical mask 6 according to the present embodiment, the degree of light transmission can be changed according to the location by providing the optical aperture ratio per unit area of the optical mask 6.

Therefore, the optical aperture ratio per unit area of the optical mask 6 is reduced at the central portion and gradually increased at the ends along the longitudinal direction of the photomultipliers 4a and 4b. The same operation and effect as in the case can be obtained.

In each of the above embodiments, the case where the amount of light emission or light transmission at the center of the detection location is reduced and increased at the end has been described, but the arrangement of the photomultipliers 4a and 4b and the photomultipliers 4a and 4b are described.
Depending on the direction of the light receiving surface (photoelectric surface), the center portion may not always have the highest sensitivity, and a position shifted from the center portion may have the highest sensitivity. Also in such a case, the present invention is an extremely effective means for making the entire detection surface have flat detection efficiency characteristics. That is,
By adjusting the amount of light emission and light transmission per unit area so as to compensate for the distribution of the detection efficiency characteristics generated by the arrangement of the photomultipliers 4a and 4b, the detection efficiency characteristics can be flattened. .

Further, in each of the above embodiments, the case where the improved scintillator or the optical mask is provided has been described, but the transparent plate 3 existing between the scintillators 2, 21, 22, 23, and 24 and the photomultipliers 4a and 4b is described. Or processing the reflectivity or shape of the optical mask 6 to change the amount of light transmitted per unit area depending on the location is equivalent to providing an optical mask. It is within the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, a plate-shaped scintillator is divided into a plurality of parts, and the divided unit scintillators are formed of different materials depending on detection locations, or the plate-shaped scintillator is formed by It is divided into a plurality, and the divided unit scintillators are configured with different thicknesses according to the detection locations, or the flat scintillator is divided into a plurality, and a gap is provided between the divided unit scintillators, and the gap is provided. The dimensions may be different values depending on the detection location, or a plurality of holes may be provided in the flat scintillator, and the aperture ratio per unit area may be different depending on the location, or the flat scintillator and A photomask is installed between the photomultiplier and the light aperture ratio per unit area is set to a different value depending on the location. Since the light emission amount can be corrected so that the light emission amount per unit area in the portion other than the light receiving surface and the vicinity thereof is larger than the light emission amount per unit area in the vicinity thereof and the vicinity thereof, the center of the detection surface is It is possible to provide a highly reliable scintillation detector that can prevent only a portion from having high detection efficiency characteristics and can perform uniform measurement without causing measurement unevenness.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a scintillation detector according to the present invention, FIG. 2 is a diagram showing a configuration example of a scintillator according to a first embodiment of the present invention, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a diagram showing a configuration example of a scintillator according to a third embodiment of the present invention, and FIG. 5 is a diagram showing a configuration example of a scintillator according to a fourth embodiment of the present invention. 6 is a diagram showing another configuration example of the scintillation detector according to the present invention, FIG. 7 is a diagram showing a configuration example of the optical mask in FIG. 6, and FIG. 8 is a configuration example of a conventional scintillation detector. FIG. 9 is a diagram showing a configuration example of the scintillator in FIG. 8, and FIG. 10 is a diagram showing an example of detection efficiency characteristics of the scintillation detectors of the prior art and the present invention in comparison. DESCRIPTION OF SYMBOLS 1 ... Light shielding film, 2 ... Scintillator, 21 ... Scintillator, 22
... Scintillator, 23 ... Scintillator, 24 ... Scintillator, 3 ... Transparent plate, 4a, 4b ... Photomultiplier, 5 ... Case, 6
... light mask.

Claims (5)

(57) [Claims] 1. A flat scintillator that emits light when radiation is incident thereon, and a photomultiplier that receives light from the scintillator, converts the light into an electric signal corresponding to the amount of light, and extracts the electric signal. A scintillation detector, wherein the flat scintillator is divided into a plurality of parts, and the divided unit scintillators are made of different materials depending on a detection location. 2. A flat scintillator which emits light when radiation is incident thereon, and a photomultiplier which receives light from the scintillator, converts the light into an electric signal corresponding to the amount of light, and takes out the electric signal. In the scintillation detector, the flat scintillator is divided into a plurality of parts, and the divided unit scintillators are configured to have different thicknesses according to detection locations. 3. A scintillator having a flat plate shape that emits light when radiation is incident thereon, and a photomultiplier that receives light from the scintillator, converts the light into an electric signal corresponding to the amount of light, and extracts the signal. In the scintillation detector, the plate-shaped scintillator is divided into a plurality, and a gap is provided between the divided unit scintillators, and the gap dimension is set to a different value depending on a detection location. Scintillation detector. 4. A flat scintillator which emits light when radiation is incident thereon, and a photomultiplier which receives light from the scintillator, converts the light into an electric signal corresponding to the amount of light, and takes out the electric signal. In the scintillation detector, a plurality of holes are provided in the plate-shaped scintillator, and an aperture ratio per unit area is set to a different value depending on a location. 5. A flat scintillator that emits light when radiation is incident thereon, and a photomultiplier that receives light from the scintillator, converts the light into an electrical signal corresponding to the amount of light, and extracts the signal. In the scintillation detector, an optical mask is provided between the flat scintillator and the photomultiplier, and the light aperture ratio per unit area is set to a different value depending on the location. Scintillation detector.