JPH0593781A - Radiation detector - Google Patents

Abstract

PURPOSE:To enable an output of a photomultiplier tube to be improved by suppressing waste of an output light from a scintillator where an anode output tends to be reduced easily out of scintillators in a scintillator array of a radiation detector. CONSTITUTION:An output surface 16 of scintillators 12A-12L which are located at an outer-periphery position in a scintillator array 12 is used as an inclined surface which faces a direction of center of a photomultiplier tube 14, thus preventing an output light from the scintillator at an outer-periphery position from entering a direction of a side-tube glass and being wasted and then enabling an output of the photomultiplier tube 14 to be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector for gamma rays and the like.

[0002]

2. Description of the Related Art A conventional radiation detector, for example, a γ-ray position detector, has a plurality of scintillators 1 as shown in FIG.
And a photomultiplier tube 3 connected to the output surface of the scintillator array 2.

Further, as shown in FIG. 8, a γ-ray position having a scintillator array 2 similar to that shown in FIG. 7 and a photomultiplier tube 4 having a number of anodes 4 smaller than the number of scintillators 1 in this scintillator array 2. There is a detector.

[0004]

In the radiation detector of FIG. 7, as shown in FIG. 9, the scintillator 1A at the outer peripheral portion of the scintillator array 2 is continuous from the input face glass 3A of the photomultiplier tube 3 to the side face. Since the output surface is placed at the position of the side tube glass 3B, the output light from the scintillator 1A at the outer peripheral portion is less likely to reach the photocathode 3C of the photomultiplier tube 3, and therefore the photomultiplier tube. There is a problem that the output from 3 is reduced.

Further, in the γ-ray position detector comprising the scintillator array 2 and the photomultiplier tube 5 as shown in FIG. 8, when the number of the anodes 4 is smaller than the number of the scintillators 1, the anodes 4 of the anodes 4 are smaller. The scintillator having an output is discriminated by using the distribution of the output, for example, by calculating the center of gravity.

Here, what is important is the output distribution of the anode obtained by the output from each scintillator. This control is a problem because this distribution determines the quality of the scintillator discrimination.

On the other hand, the output distribution of the anode 4 is determined by the distribution of the light from the scintillator 1 on the photocathode 5C, and this distribution is the input surface glass 5 in the photomultiplier tube.
The thickness of A, the scintillator 1, the optical coupling agent, and the refractive index ratio of the input surface glass 5A determine the photoelectric surface 5C of light.
There is a problem that it is difficult to adjust the above distribution.

The present invention has been made in view of the above problems of the prior art. The output light from the scintillator at the outer peripheral position of the scintillator array efficiently reaches the photocathode and the output from the photomultiplier tube. An object of the present invention is to provide a radiation detector designed to prevent deterioration.

Further, there is provided a radiation detector capable of easily adjusting the distribution of light from the scintillator on the photocathode, which determines the distribution of anode output when the number of anodes is smaller than the number of scintillators. The purpose is to

[0010]

The present invention provides a radiation detector comprising a scintillator array consisting of a plurality of scintillators, and a photomultiplier tube connected to the output surface of the scintillator array. The above-mentioned object is achieved by a radiation detector characterized in that the output surface of the scintillator at the outer peripheral position in the array is an inclined surface whose normal line is directed toward the center of the photomultiplier tube.

The output surface of the scintillator located closer to the center of the scintillator array than the scintillator at the outer peripheral position is an inclined surface whose normal line is directed toward the center of the photomultiplier tube, and the output surface and The inclination angle of the output surface of the scintillator at the outer peripheral position may be set to be smaller toward the center of the scintillator array.

Further, the second invention of this application is a scintillator array comprising a plurality of scintillators, and a photomultiplier tube having a smaller number of anodes than the scintillators, which is connected to the output surface of the scintillator array. In the radiation detector including, the above object is achieved by individually changing the inclination of the surface of the plurality of scintillators according to the relative position with the anode.

Further, as described in claim 4, the space between the inclined surface and the input surface of the photomultiplier tube may be filled with an optical coupling agent.

Further, a reflecting surface for reflecting light emitted from the inclined surface is formed on an adjacent surface of the scintillator adjacent to the inside of the inclined surface in the scintillator array, facing the inclined surface and facing the space. You may do it.

Further, the inclination angle of the output surface is determined by the shape of the scintillator, the input surface of the photomultiplier tube, the thickness of the glass, and the optical binder filled in the space between the output surface and the input surface. Alternatively, it may be determined by the ratio of the refractive index between the scintillator and the input surface glass.

[0016]

According to the first aspect of the invention, the output light of the scintillator at the outer peripheral position in the scintillator array is directed toward the center of the photomultiplier tube because the output surface is inclined, and the output light loss is reduced. The output of the photomultiplier tube is thus improved.

According to the second aspect, the scintillator further inside the scintillator at the outer peripheral position in the scintillator array has a smaller inclination angle of its output surface toward the center side.
The output of each scintillator can be leveled.

According to the second invention of claim 3, by individually adjusting the inclination angle of the output surface of the scintillator,
The distribution of the input light on the photocathode of the photomultiplier can be easily adjusted.

According to the fourth aspect, the space between the inclined surface which is the output surface of the scintillator and the input surface of the photomultiplier tube is filled with the optical coupling agent, so that the output light from the scintillator is surely provided. It can be input to the photomultiplier tube.

According to the fifth aspect of the present invention, the adjacent surface of the scintillator adjacent to the inside of the scintillator whose output surface is inclined,
Since the reflecting surface that reflects the light emitted from the inclined surface is formed, the emitted light from the inclined surface can be reliably guided to the photomultiplier tube direction.

According to the sixth aspect, the inclination angle of the output surface of the scintillator is appropriately changed according to the conditions such as the shape of the scintillator and the thickness of the input surface glass of the photomultiplier tube. The distribution on the surface can be adjusted optimally. Therefore, the discrimination characteristics of the scintillator can be optimized.

[0022]

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

As shown in FIGS. 1 and 2, the radiation detector 10 according to the first embodiment of the first invention is a scintillator array 12 including a plurality of scintillators 12A to 12P.
And a position detection type photomultiplier tube 14 connected to the output surface of the scintillator array 12, and among the scintillators 12A to 12P, the output surface 16 of the scintillators 12A to 12L at the outer peripheral position is formed by the method. The line is an inclined surface facing the center of the photomultiplier tube.

Therefore, the four central scintillators 12M
The output surfaces 16 to 12P are orthogonal to the central axis in the vertical direction in the drawing.

As shown in FIG. 2, the space between the output surface 16 of the scintillators 12A to 12L at the outer peripheral position and the input surface glass 14A of the photomultiplier tube 14 is filled with an optical binder 18. There is.

In this embodiment, the scintillators 12A to 12A at the outer peripheral position of the scintillator array 12 are arranged.
Since the 2 L output surface 16 is inclined toward the center of the photomultiplier tube 14, as shown in FIG. 2, the output light that enters the side of the photomultiplier tube 14B toward the side tube glass 14B and is wasted. Decrease and pass through the input surface glass 14A
Since the output light reaching 4C is increased, the output of the photomultiplier tube 14 is improved.

As shown by the two-dot chain line in FIG. 2, the optical coupling is made so as to face the inclined output surface 16 of the scintillators 12M to 12P adjacent to the inside of the scintillators 12A to 12L at the outer peripheral position. A reflective surface 20 made of a reflective agent that reflects the light emitted from the inclined output surface 16 may be formed on the adjacent surface facing the space filled with the agent 18.

By the reflecting surface 20, of the light output from the inclined output surface 16, the output light reaching the wall of the adjacent scintillator is reflected in the direction of the photomultiplier tube 14, and therefore the scintillator at the peripheral position. It is possible to further suppress the output reduction of the photomultiplier tube 14 corresponding to 12A to 12L.

In the above embodiment, the scintillator 12A at the outer peripheral position of the scintillator array 12 is used.
With respect to the output of ~ 12L, an output increase of about 20% has been observed as compared with the case where the output surface 16 is not tilted.

Next, a second embodiment of the first invention shown in FIG. 3 will be described.

In the second embodiment, the number of scintillators forming the scintillator array is larger, and in one cross section of the scintillator array 22, the scintillator 22B arranged from the outer peripheral side scintillator 22A to the center side. , 22C and 22D each output surface 16
The inclination angle of is larger at the outer peripheral position.

In this way, the distribution of the input light from the scintillator on the photocathode 14C of the photomultiplier tube 14 is determined by the output plane 1 as shown by the chain double-dashed line in FIG.
As compared with the case where 6 is not tilted, the distribution of its output can be more leveled as shown by the solid line.

Here, the inclination angle of the output surface 16 is
The discrimination characteristics of the scintillator based on the anode and output of the photomultiplier tube 14 are set so as to be optimized.

That is, the inclination of the output surface 16 depends on the shape of the scintillator, the thickness of the input surface glass of the photomultiplier tube, and the ratio of the refractive index between the scintillator, the optical binder, and the input surface glass of the photomultiplier tube. Determine the optimum value for the angle.

Next, an embodiment of the second invention shown in FIG. 4 will be described.

In this embodiment, the photomultiplier tube 2 has a small number of anodes 26A to 26C with respect to the number of scintillators 24A to 24J in the scintillator array 24.
In the case of using No. 6, the citrinator 24A ~
Of 24J, scintillators 24A, 24B, 24D, 24E, 2 which are not on the central axis of the anodes 26A to 26C.
The output surface 16 of 4G, 24H, and 24J is an inclined surface directed toward the closest anode.

That is, the scintillators 24B, 24 on both sides of the scintillator 24C on the central axis of the anode 24A.
In D, their output surfaces 16 are inclined toward the anode 26A. Similarly, the output surfaces 16 of the scintillators 24E and 24G are tilted toward the anode 26B, and the output surfaces 16 of the scintillators 24H and 24J are the anode 26C.
Is tilted towards.

In this embodiment, for example, when an output is given to the scintillator 24G, the scintillator 24 on the photocathode of the input face glass 14A of the photomultiplier tube 14 is provided.
The distribution of the output light from G is as shown by reference numeral 28 in FIG. 4, and the center thereof is located at a position deviated to the scintillator 24F side from directly below in the figure of the scintillator 24G.

Further, when the output surface 16 of the scintillator 24G is not inclined, the distribution of the output light is located directly below in the figure of the scintillator 24G.

Thus, the output light distribution on the photocathode changes due to the inclination of the output surface of the scintillator, and the output distribution at the anode also changes accordingly. Therefore, the anode output distribution can be optimized by individually changing the inclination of the scintillator output surface.

As shown in FIG. 5, the inclination angle θ of the output surface
The BGO scintillator 32 of 50 °, 60 °, 70 °, 80 °, 90 ° is placed at the end of the input surface of the photomultiplier tube 34, and only the BGO scintillator 32 is irradiated with γ-rays to output. It was measured.

The results are shown in FIG. 6 with the horizontal axis representing the tilt angle θ and the vertical axis representing the relative output. From this figure, under this measurement condition,
It can be seen that the inclination angle θ = 60 ° is optimal.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a first embodiment of the first invention.

FIG. 2 is an enlarged sectional view showing an essential part of the first embodiment.

FIG. 3 is a sectional view showing a second embodiment of the first invention.

FIG. 4 is a sectional view showing an embodiment of the second invention.

FIG. 5 is a schematic cross-sectional view showing a state of an experiment in which a BGO scintillator is placed at an end of an input surface of a photomultiplier tube and an inclination angle of an output surface is changed.

FIG. 6 is a diagram showing the experimental results of FIG.

FIG. 7 is a perspective view showing a conventional radiation detector.

8 is an enlarged sectional view showing a main part of the radiation detector of FIG.

FIG. 9 is a cross-sectional view showing a main part of a conventional position detection type radiation detector.

[Explanation of symbols]

12, 22, 24 ... Scintillator array, 12A-12P, 22A-22D, 24A-24J ... Scintillator, 14, 26, 34 ... Photomultiplier tube, 14A ... Input surface glass, 14B ... Side tube glass, 14C ... Photoelectric surface , 16 ... Output surface, 18 ... Optical coupling agent, 20 ... Reflecting surface, 26A to 26C ... Anode, 32 ... BGO scintillator.

Claims (6)

[Claims] 1. A radiation detector comprising a scintillator array comprising a plurality of scintillators and a photomultiplier tube connected to the output surface of the scintillator array, wherein the scintillator output at the outer peripheral position of the scintillator array. A radiation detector, wherein the surface is an inclined surface whose normal line is directed toward the center of the photomultiplier tube. 2. The output surface of the scintillator at a position closer to the center of the scintillator array than the scintillator at the outer peripheral position is an inclined surface whose normal line is directed toward the center of the photomultiplier tube, and The radiation detector, wherein the inclination angles of the output surface and the output surface of the scintillator at the outer peripheral position are set to be smaller toward the center of the scintillator array. 3. A radiation detector comprising a scintillator array comprising a plurality of scintillators, and a photomultiplier tube connected to the output surface of the scintillator array and having a smaller number of anodes than the scintillators. In the radiation detector, the inclination of the output surface of each of the plurality of scintillators is individually changed according to the relative position of the photomultiplier tube to the anode. 4. The radiation detector according to claim 1, wherein the space between the inclined surface and the input surface of the photomultiplier tube is filled with an optical coupling agent. 5. The scintillator according to any one of claims 1 to 4, wherein the scintillator adjacent to the inner side of the inclined surface in the scintillator array emits light from the inclined surface to an adjacent surface facing the inclined surface and facing the space. A radiation detector having a reflecting surface for reflecting the generated light. 6. The tilt angle of the output surface according to claim 1, wherein the inclination angle of the output surface is the shape of the scintillator, the input surface of the photomultiplier tube, the thickness of the glass, and the output surface and the input surface. A radiation detector characterized by being determined by an optical coupling agent filled in a space between the scintillator and the input surface glass.