JPH0442082A - Scintillation detector - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a scintillation detector used in a radiation monitoring device used, for example, in a nuclear facility, and particularly as a large-area radiation detector. The present invention relates to a scintillation detector used as a surface contamination monitor of a large area measurement object such as a gate monitor (body surface monitor), an article discharge monitor, a lumen monitor, or a human body.

(Prior Art) In recent years, for example, in nuclear facilities, devices have been used to monitor surface contamination of objects to be measured or human bodies that have a large area, such as gate monitor devices (body surface monitor devices), article discharge monitor devices, and lantern monitor devices. Scintillation detectors, which are large-area radiation detectors, are often used.

FIG. 8 is a diagram showing an example of the configuration of this type of conventional scintillation detector.
) respectively show sectional views taken along line A-A in FIG.

That is, in a conventional scintillation detector, the detection surface side is covered with a light-shielding film 1 to let in only radiation without letting in external light, and a flat scintillator 2 that emits light when radiation is incident is fixed to a transparent plate 3. and scintillator 2
It is configured to be housed in a case 5 along with photomultiples 4a and 4b that receive light from the outside, convert it into an electrical signal corresponding to the amount of light, and extract it.

Here, the conventional scintillator 2, as shown in its plan view and AA sectional view in FIGS. 9CB) and 9(b),
It consists of a scintillator plate that is uniform over the entire surface.

However, such conventional scintillation detectors have a characteristic that the detection efficiency is high at the center of the detection surface and decreases toward the edges of the detection surface, as shown in FIG. 10(a). are doing. Then, using a scintillation detector with such detection efficiency characteristics,
When measuring contamination on the surface of a human body or the surface of an article, even if two locations have the same surface contamination, the outputs of the detectors will differ. As a result, measurement unevenness occurs, making it impossible to perform uniform measurements.

(Problems to be Solved by the Invention) As described above, in conventional scintillation detectors, only the center of the detection surface has a high detection efficiency characteristic, causing measurement unevenness and making it impossible to perform uniform measurements. There was a problem.

The purpose of the present invention is to provide extremely reliable scintillation detection that can prevent high detection efficiency characteristics from occurring only in the center of the detection surface, and can perform uniform measurements without measurement unevenness. It is about providing the equipment.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention includes a flat scintillator that emits light when radiation is incident, and a scintillator that receives light from the scintillator and adjusts the amount of light. In a scintillation detector, the amount of light emitted per unit area on the photomultiple's light receiving surface and its vicinity is greater than the amount of light emitted per unit area on the photomultiple's light receiving surface and its vicinity. A light emitting amount correcting means is provided for correcting the light emitting amount so as to increase the light emitting amount per unit area in a portion/minute other than the portion.

Specifically, (a) a flat scintillator is divided into a plurality of parts, and each divided unit scintillator is made of a different material depending on the detection location, or (b) a flat scintillator is divided into a plurality of parts, Either the divided unit scintillators are constructed with different thicknesses depending on the detection location, or (C) the flat scintillator is divided into a plurality of parts, gaps are provided between the divided unit scintillators, and the gap dimensions are adjusted accordingly. (d) Provide multiple holes in a flat scintillator and set the aperture ratio per unit area to a different value depending on the location; (e) Flat scintillator An optical mask is installed between the scintillator and the photomultilayer, and the optical aperture ratio per unit area is set to a different value depending on the location.

(Function) Therefore, in the scintillation detector of the present invention,
By correcting the amount of light emitted so that the amount of light emitted per unit area in areas other than the light receiving surface and its vicinity is larger than the amount of light emitted per unit area in the light receiving surface and its vicinity, By using a scintillator whose entire plate has negative light emission characteristics, it is possible to compensate for the "characteristic of high sensitivity at the center of the detection surface" of detectors that convert photomultipliers into electrical signals. Therefore, it is possible to obtain flat detection efficiency characteristics over the entire detection surface. Thereby, uniform measurement can be performed without measurement unevenness.

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

The present invention is characterized by changing the amount of light emitted from the scintillator or the transmission of light from the scintillator to the photomultiple.
This method takes advantage of the fact that detection efficiency characteristics change. In other words, it uses a conventional scintillator whose entire plate has a -like luminescence characteristic, and compensates for the detection efficiency characteristic of a scintillation detector that converts into an electrical signal using a photomultiplier, in which the center side is highly sensitive. This is intended to ensure flat detection efficiency characteristics over the entire detection surface.

Generally, there are two possible reasons why the detection efficiency characteristic at the center of the detection surface of a radiation detector becomes high. One of them is the solid angle at which the radiation source views the detection surface. The radiation emitted from the source is emitted in the 4π direction,
The amount reaching the detector depends on its solid angle. and,
This solid angle is necessarily at its maximum when the radiation source is directly above the center of the detection surface, and therefore the detection efficiency is also at its maximum accordingly.

The other factor is the amount of light that enters the photosensitive surface (photocathode) of the photomultiplier from the scintillator.

The 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 is generally larger at the center. This contributes to the fact that the detection efficiency is maximized at the center of the detection surface.

Therefore, in the present invention, for example, the material and thickness of the scintillator can be changed depending on the detection location, that is, the position of the scintillator, and the amount of light transmitted from the scintillator to the photomultiple can be changed by providing an optical mask to improve the detection efficiency. This is an attempt to flatten the curve.

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

FIG. 1 is a diagram showing an example of the configuration of a scintillation detector according to the present invention, and FIG. 1(a) shows a plan view, and FIG.
3A and 3B respectively show cross-sectional views taken along line A-A in FIG. In the figure, the same elements as in FIGS. 8 and 9 are designated by the same reference numerals.

As shown in FIG. 1, the scintillation detector according to this embodiment has a flat plate-like structure whose detection surface side is covered with a light-shielding film 1 to let in only radiation without letting in external light, and which emits light when radiation is incident. A scintillator 21 is fixed to a transparent plate 3, and photomultiples 4a, 4 receive light from the scintillator 2, convert it into an electrical signal according to the amount of light, and take it out.
It is constructed by being housed in the case 5 together with the case 5.

Here, the scintillator 21 according to the first embodiment of the present invention
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 according to the detection location. The scintillator material is composed of materials with different amounts of light emission, that is, a scintillator material with a small amount of light emission at the edge of the detection surface is selected, and scintillator materials with a larger amount of light emission are selected gradually toward the center along the longitudinal direction of the photomultiples 4a and 4b. I try to choose.

In this case, the amount of light emitted can be changed by selecting an inorganic scintillator (various types available) or an organic crystal scintillator (various types available), or by changing the type or amount of solute in a plastic scintillator. I can do it.

For example, as a specific example in the case of a plastic scintillator, it is possible to make the following selections.

That is, toluene, phenylcyclohexane, polystyrene, polyvinyltoluene, etc. are selected as the solute, and terphenyl (TP) is selected as the first solute.
Tetraphenylbutadiene (TPB), defhenyloxazole (PPO), phenyloxacyl (P
BD), diphenylstilbene (DPS), and as the second solute, a wavelength shifting material (POPOP) and naphthyl phenyl oxazole (N P O) are selected, and the scintillator's luminescence amount is changed by changing their concentration. can be created.

Note that the above-mentioned materials are examples of scintillators, and even materials other than those mentioned above are within the scope of the present invention as long as they are made of materials that emit light that differs depending on the location. It is.

In this example, the amount of light emitted per unit area after the radiation interacts with the scintillator changes depending on the material of the scintillator.

Therefore, the material of the scintillator 21 is photomul 4a,
By gradually varying the length of 4b,
Since the detection efficiency characteristics of the scintillation detector are flat, when using this scintillation detector to measure contamination on the surface of a human body or the surface of an article, even if there are two locations with the same surface contamination, the detector There is no difference in the outputs of each, and as a result, uniform measurements without unevenness can be performed.

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

Figure (b) shows an example in which the part of the radiation source close to the detector is made flat (the effect of the present invention is less), and Figure (c) shows an example in which the part of the radiation source near the detector is made flat. An example is shown in which the portion is made flat (the effect of the present invention is increased).

The larger the difference in the amount of light emitted between the center and the edges of the detection surface, the more
The effect of the present invention is enhanced, but as shown in the figure, the effect varies depending on the distance between the radiation source and the detection surface, and the effect of the present invention can be adjusted according to the distance at the time of measurement.

Next, other embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a diagram showing an example of the configuration of a scintillator according to a second embodiment of the present invention, and FIG.
b) shows a sectional view taken along line A-A in FIG.

That is, in the scintillator 22 of this embodiment, the scintillator 22 is divided into a plurality of parts vertically and horizontally, and each divided unit scintillator is configured to have a different thickness depending on the detection location.

In this example, as the thickness of the scintillator increases, the probability per unit area that radiation interacts with the scintillator increases, and the amount of light emitted after the interaction increases as the thickness increases. (The trajectory of radiation becomes longer).

Therefore, the thickness of the scintillator 22 is made thinner at the center,
By gradually increasing the thickness at the ends of the photomultiples 4a and 4b along the longitudinal direction, the same effects as in the above embodiment can be obtained.

FIG. 4 is a diagram showing an example of the configuration of a scintillator according to a third embodiment of the present invention, and FIG.
b) shows a sectional view taken along line A-A in FIG.

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

In this embodiment, by setting the size of the gap between unit scintillators, the probability per unit area that radiation will interact with the scintillator 23 can be changed.

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

FIG. 5 is a diagram showing an example of the configuration of a scintillator according to a fourth embodiment of the present invention, and FIG.
b) shows a sectional view taken along line A-A in FIG.

That is, in the scintillator 24 of this embodiment, a plurality of holes are provided in the scintillator 24, and the aperture ratio per unit area is set to a different value depending on the detection location.

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

Therefore, 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 photomultiples 4a and 4b, the same effects as in the above embodiment can be obtained.

Next, FIG. 6 is a diagram showing another example of the configuration of the scintillation detector according to the present invention, and FIG.
The figure (b) shows a sectional view taken along the line AA in the figure (a). In the figure, the same elements as in FIGS. 8 and 9 are designated by the same reference numerals.

As shown in FIG. 6, the scintillation detector according to this embodiment has a flat plate-like structure whose detection surface side is covered with a light-shielding film 1 to take in only radiation without letting in external light, and which emits light when radiation is incident. A scintillator 21 is fixed to a transparent plate 3, and photomultiples 4a, 4 receive light from the scintillator 2, convert it into an electrical signal according to the amount of light, and take it out.
It is housed in case 5 together with b. Furthermore, an optical mask 6 is installed between the scintillator 2 and the photomultiples 4a and 4b (in the figure, between the transparent plate 3 and the photomultiples 4a and 4b).

Here, the optical mask 6 according to this embodiment is shown in FIG.
As shown in the plan view and A-A cross-sectional view in a) and (b), the optical aperture ratio per unit area of the optical mask 6 is configured to have a different value depending on the detection location.

In the scintillation detector equipped with the optical mask 6 of this embodiment, by setting the optical aperture ratio per unit area of the optical mask 6, the degree of light transmission can be changed depending on the location.

Therefore, by decreasing the optical aperture ratio per unit area of the optical mask 6 at the center and gradually increasing it at the ends along the longitudinal direction of the photomultiples 4a and 4b, the above embodiment can be improved. The same effects can be obtained as in the case of

In each of the above embodiments, the case where the amount of light emitted and the amount of light transmitted is reduced at the center of the detection location and increased at the edges has been explained.
Depending on the orientation of the light-receiving surfaces (photocathode) of a and 4b, the highest sensitivity may not necessarily be at the center, and the highest sensitivity may be at a position offset from the center 7. Even in such a case, the present invention is an extremely effective means for ensuring that the entire detection surface has a flat detection efficiency characteristic.

That is, flattening of the detection efficiency characteristics can be realized by adjusting the amount of light emitted and the amount of light transmission per unit area so as to compensate for the distribution of the detection efficiency characteristics caused by the arrangement of the photomultiples 4g and 4b. I can do it.

Furthermore, in each of the above embodiments, the cases were explained in which improved scintillators or optical masks were provided.
, 4b, or the reflectance and shape of the optical mask 6 to change the amount of light transmitted per unit area depending on the location.
This corresponds to providing a light mask, and both fall within the scope of the present invention.

[Effects of the Invention] As explained above, according to the present invention, a flat scintillator is divided into a plurality of parts, and the divided unit scintillators are made of different materials depending on the detection location, or the flat scintillator is Either divide the unit scintillator into multiple parts and configure the divided unit scintillators with different thicknesses depending on the detection location, or divide the flat scintillator into multiple units and provide gaps between the divided unit scintillators. Either the dimensions should be set to different values depending on the detection location, or the flat scintillator should have multiple holes and the aperture ratio per unit area should be set to different values depending on the location, or the flat scintillator should be set to different values depending on the location. By installing an optical mask between the photomultiplier and setting the optical aperture ratio per unit area to different values depending on the location, the amount of light emitted per unit area on the photoreceptive surface of the photomultiplier and its vicinity can be reduced. Rather, the amount of light emitted is corrected to increase the amount of light emitted per unit area in areas other than the light-receiving surface and its vicinity, so that only the center of the detection surface has high detection efficiency characteristics. It is possible to provide an extremely reliable scintillation detector that can prevent the occurrence of measurement irregularities and perform uniform measurements without occurrence of measurement unevenness.

[Brief explanation of 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 diagram showing a configuration example of a scintillator according to a first embodiment of the present invention. FIG. 4 is a diagram showing an example of the configuration of a scintillator according to the third embodiment of the present invention. FIG. 5 is a diagram showing an example of the configuration of the scintillator according to the fourth embodiment of the present invention. , FIG. 6 is a diagram showing another example of the configuration of the scintillation detector according to the present invention, FIG. 7 is a diagram showing an example of the configuration of the optical mask in FIG. 6, and FIG. 8 is a diagram showing an example of the configuration of the conventional scintillation detector. FIG. 9 is a diagram showing an example of the configuration of the scintillator in FIG. 8, and FIG. 10 is a diagram showing a comparison of an example of the detection efficiency characteristics of the conventional scintillation detector and the scintillation detector of the present invention. DESCRIPTION OF SYMBOLS 1... Light shielding film, 2... scintillator, 21... scintillator, 22... scintillator, 23... scintillator, 24... scintillator, 3... transparent plate,
4a, 4b...Photomaru, 5...Case, 6...
・Light mask. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 9 Figure 4 Figure 4 Detection efficiency Figure 10

Claims (6)

[Claims] (1) Scintillation detection comprised of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. In the device, the amount of light emitted is set so that the amount of light emitted per unit area of the photomultiplier is larger than the amount of light emitted per unit area of the photomultiplier at the light receiving surface and its neighboring portions. A scintillation detector characterized by comprising a light emission amount correction means for correction. (2) Scintillation detection consisting of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. A scintillation detector, characterized in that the flat scintillator is divided into a plurality of parts, and the divided unit scintillators are made of different materials depending on the detection location. (3) Scintillation detection consisting of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. A scintillation detector, characterized in that the flat scintillator is divided into a plurality of parts, and each divided unit scintillator is configured to have a different thickness depending on a detection location. (4) Scintillation detection consisting of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. A scintillation detection device characterized in that the flat scintillator is divided into a plurality of units, gaps are provided between the divided unit scintillators, and the gap dimension is set to a different value depending on the detection location. vessel. (5) Scintillation detection comprised of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. A scintillation detector, characterized in that the flat scintillator is provided with a plurality of holes, and the aperture ratio per unit area is set to a different value depending on the location. (6) Scintillation detection comprised of a flat scintillator that emits light when radiation is incident, and a photomultiplier that receives light from the scintillator, converts it into an electrical signal according to the amount of light, and extracts it. A scintillation device characterized in that an optical mask is installed between the flat scintillator and the photomultilayer, and the optical aperture ratio per unit area is set to a different value depending on the location. Detector.