JPS60181675A - radiation detector - Google Patents

Abstract

PURPOSE:To make it possible to enhance position resolving capacity by reducing a scintillation width and to suppress the rising in cost, by discriminating the emission outputs of radiation incident scintillators from outputs of plural photomultiplier tubes PMT. CONSTITUTION:One or plural photomultiplier tubes 12 having a pluraity of scintillators 1-6 to which radioactive rays are incident and a plurality coupled with output surfaces of a plurality scintillators 1-6 and input surface of a plurality of optical detection systems. Further, the same number of mutually independent light guides 20a, 20b as the optical detection systems are provided and the output surfaces of the light guides are respectively coupled with only one optical detection system while the input surfaces thereof are coupled so as to be extended over output surfaces of the scintillators, the input surface of each light guide is coupled with each of split parts formed by splitting the output surface thereof in a predetermined ratio and the splitting ratio is made different with each scintillator output surface and the radiation incident scintillator is discriminated by utillizing the difference of this splitting ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a radiation detector used in a positron ECT device (emissigon computed tomography device), a single photon ECT device, and the like.

(b) Prior art Conventional positron ECT device and single photon ECT
In equipment, one scintillator l as shown in Figure 1 is used.
A large number of radiation detectors each having one photomultiplier tube (hereinafter abbreviated as PMT) 11 optically coupled to each other are arranged in a ring shape, but there is a limit to how small the PMTII can be. The detector width d could not be made very small, and the spatial resolution was limited.

Furthermore, even if small PMTs can be made, arranging them in a ring will increase the number of PMTs, increasing the manufacturing cost of the entire device.

(c) Purpose This invention has extremely high position detection resolution and
It is an object of the present invention to provide an inexpensive radiation detector that requires only a small number of T's and is suitable for application to an ECT device in which detectors are arranged in a ring shape.

(D) Configuration The radiation detector according to this invention 1) includes a plurality of scintillators through which radiation is applied, one or more photomultiplier tubes having a plurality of mutually independent photodetection systems, and the above-mentioned It has the same number of mutually independent light guides as the two photodetection systems, optically coupling the output surfaces of the plurality of scintillators and the input surfaces of the plurality of photodetection systems, and the output surface of each light guide. are coupled to only one photodetection system, and the input surface of each light guide is coupled across the output surface of each scintillator, and for each scintillator output surface, each of the output surfaces is divided at a predetermined ratio. division 8
At 11 minutes, the input surfaces of each light guide are combined, and the division ratios described in "2" are made different for each scintillator output surface, and the difference in division ratios is used to identify the scintillator.

(e) Example In FIG. 2, a large number of thin scintillators l, 2,...
・are arranged in one direction so that there is no optical crosstalk with each other. These scintillators l, 2,...
A light reflecting material is coated on each surface of the light guides 20a and 20b, except for the output surface connected to the light guides 20a and 20b, to improve light collection efficiency. In addition, each scintillator 1.2
, . . . may be configured to insert a thin lead plate or the like between them to reduce radiation crosstalk. Radiation enters from the front surface (lower surface in the figure) of these scintillators 1, 2, . is combined with This light guide 20a, 2
0b is made of glass, acrylic, or the like that has low absorption for the wavelength of light emitted by the scintillators 1, 2, . . . and has a unique shape. The input surface of the PMT 12 is optically coupled to the output surface on the back surface of the light guides 20a, 20b. In this embodiment, the PMT 12 incorporates two independent photodetection systems A and B.
It is a rectangular type with a built-in circuit, and the input surface of each of the photodetection systems A and H is connected to the output surface of the light guide 20a and the light guide 20.
They are optically coupled to the output surface of b.

As shown in FIG. 2, the light guides 20a and 20b are each shaped like a partially cut out triangular prism. That is, the output surfaces of scintillators 1 to 6 are quadrilaterals PQ
R3, the input surface of PMT12 is a quadrilateral TUVW, the input surface of photodetection system A is a quadrilateral TUZX, the input surface of photodetection system B is a quadrilateral xzvw, and the midpoint of xZ is Y, then a quadrilateral prism P
Divide QR5TUVW into two by its diagonal line PRVT to create two triangular prisms, then divide the YZRV part and YXPT.
If you cut out the parts from these triangular prisms, you will get the light guide 20.
a, 20b can be formed. In addition, these light guides 2
The surfaces of each of 0a and 20b other than the input surface coupled to the scintillators 1 to 6 and the output surface coupled to the PMT 12 are coated with reflective material and light shielding material to prevent light attenuation and crosstalk. has been done. The output surface of the light guide 20a has a trapezoidal TUZY shape and is optically coupled only to the input surface of the photodetection system A. The output surface of the light guide 20b is trapezoidal vwxy, and is optically coupled only to the input surface of the photodetection system B. Light guide 20a.

Each input surface of 20b is a triangle PQR1 and a triangle R5.
P, and these triangular input surfaces are scintillators 1 to 6
The light guide 20a is optically coupled across all output surfaces of one scintillator.
, 20b are optically coupled, but the ratio of the area coupled to the input surface of the light guide 20a and the area coupled to the input surface of the light guide 20b is different for each scintillator. In other words, the output surfaces of the scintillators 1 to 6 are divided into the light guide 20a side and the light guide 20b side by the diagonal line PR, and the area of each divided portion is different for each of the scintillators 1 to 6. The area increases as the scintillator number increases, and conversely, the area decreases on the light guide 20b side.

When radiation is incident on one of the scintillators 1, 2, . This light enters the light guides 20a and 20b, travels through these light guides 20a and 20b, respectively, and enters the photodetection systems A and H of the PMT 12. The ratio of the amount of light incident on each of the photodetection systems A and B corresponds to the division ratio of the output surface of the scintillator 4 divided into the light kites 20a and 20b, and this division ratio is predetermined. It can be seen from the output ratio of the photodetection systems A and H that the scintillator 4 emitted light. In other words, the ratio of the respective outputs of the photodetection systems A and B differs depending on the scintillator that emitted light, and from this ratio it can be determined which scintillator the radiation has entered.

Therefore, as shown in FIG.
1. Input to the adder circuit 22 to obtain a subtraction signal and an addition signal. The added signal corresponds to the energy of the incident radiation and is used as an energy signal. Scattered rays can be removed by dividing this energy signal into wave heights 5r by the wave height discrimination circuit 25. When applied to a positron ECT device, a timing signal is obtained from this pulse height discrimination circuit 25.

On the other hand, the subtracted signal includes positional information, and is normalized by dividing this subtracted signal by the energy signal in the division circuit 23 to obtain a signal having more accurate positional information. is converted into a digital signal and a position signal is obtained. This position signal takes the largest negative value when radiation is incident on scintillator 1, and gradually approaches the positive side for scintillators 2, 3, ...
The scintillator 6 takes the largest positive value.

By arranging a large number of radiation detectors constructed in this manner in a ring shape as shown in FIG. 4, a ring-type ECT device can be constructed, and the number of PMTs and the number of built-in circuits can be reduced in spite of the high positional resolution.

Note that the shape of the light guide is not limited to the shape of the above embodiment. In addition, in the above embodiment, the PMT 12 is of a type with two built-in circuits, but a plurality of cylindrical PMTs each having one circuit built-in may be used.In this case, the shape of the output surface of the light guide is simply All you have to do is change the . Sa°
Furthermore, the circuit for determining which scintillator the radiation is incident on is not limited to the configuration shown in FIG. 3, but can have various configurations.

(f) Effects According to the present invention, since it is determined from the outputs of a plurality of PMTs which scintillator the radiation has entered, the scintillator is not restricted by the geometric size of the PMT. The scintillator width can be reduced to improve positional resolution, and since the number of PMTs does not increase, manufacturing costs can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the appearance of a conventional example, Fig. 2 is a perspective view showing the appearance of an embodiment of the present invention, Fig. 3 is a block diagram showing the circuit of the same embodiment, and FS4 is an example of the arrangement. FIG. 1 to 6...Scintillator 11.12...Photomultiplier tubes 20a, 20b...Light guide 21...Subtraction circuit 22...Addition circuit 23...Divide circuit 24...A/ D converter 25... Wave height discrimination circuit Applicant: Shimadzu Corporation

Claims (1)

[Claims] (1) A plurality of scintillators into which radiation enters, one or more photomultiplier tubes having a plurality of mutually independent photodetection systems, and an output surface of the plurality of scintillators and a plurality of photodetectors. It has the same number of mutually independent light guides as the light detection systems, which are optically coupled to the input surface of the system, and the output surface of each light guide is respectively coupled to only one light detection system, and the input surface of each light guide is coupled across each scintillator output surface, and for each scintillator output surface, the input surface of each light guide is coupled to each divided portion obtained by dividing this output surface at a predetermined ratio, A radiation detector characterized in that the above-mentioned division ratio is made different for each scintillator output surface, and the scintillator on which radiation is incident is discriminated based on each division ratio of the writing by each output of the above-mentioned plurality of photodetection systems.