JPS63188788A - radiation 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] [Industrial application field]

The present invention relates to a radiation detector used in a nuclear medicine diagnostic apparatus such as an ECT apparatus (emission computer tomography apparatus).

[Conventional technology]

In conventional ECT devices, a radiation detector that combines one scintillator and one photomultiplier tube is often used. That is, a large number of radiation detectors made of a combination of such a scintillator and a photomultiplier tube are arranged in a ring shape. Therefore, in such an ECT device, the spatial resolution depends on the arrangement density of the radiation detectors as described above.

[Problems to be solved by the invention]

Therefore, in order to increase the spatial resolution of an ECT device, it is sufficient to make the radiation detectors as small as possible and arrange them at high density. However, this is extremely difficult in reality. First of all, there is a limit to the size of photomultiplier tubes, and they cannot be made smaller beyond a certain point.Secondly, even if they could be made smaller, it would be difficult to arrange a large number of photomultiplier tubes. This is because the cost would be extremely high, making it impractical. An object of the present invention is to provide a radiation detector that can easily improve spatial resolution while avoiding an increase in price.

[Means to solve the problem]

A radiation detector according to the present invention includes a plurality of scintillators that emit different amounts of light due to differences in impurity concentration, a photomultiplier tube optically coupled to the plurality of scintillators, and a photomultiplier tube that determines the amount of light emitted from the output of the photomultiplier tube. and a circuit that discriminates the emitted scintillator based on the difference in the scintillator.

[For production]

In the case of a scintillator made of pure cesium iodide (CsI), the spectrum of scintillation light becomes like the dotted line in FIG. 5, but when bromine (Br) is added as an impurity, it becomes like the solid line in the figure. That is, when bromine is added, the decay time of the fast component decreases by 10
n5ec, peak wavelength 300 nm), the slower component (attenuation time 10 μsec, peak wavelength 450 nm) becomes larger. And the greater the concentration of bromine, the greater the intensity of the slow component. Therefore, when multiple scintillators with different impurity concentrations are lined up and connected to a single photomultiplier tube, by determining the magnitude of the slow component in the output of the photomultiplier tube, it is possible to It is possible to determine in which of them scintillation occurred.

【Example】

In FIG. 1, nine scintillators 1 to 9 are optically coupled to the input surface of one photomultiplier tube 11 via a light guide 10. These scintillators 1 to 9 are mainly made of cesium iodide, scintillator 1 is made of pure cesium iodide without any additives, and scintillators 2 to 9 are made by adding bromine to cesium iodide. The impurity concentration increases as the number increases. The photomultiplier tube 11 is preferably of the rectangular type as shown in the figure. The output of the photomultiplier tube 11 is sent to an integrator 22 via an amplifier 21, and its integrated output is discriminated by a pulse height discriminator 23. When γ-rays enter any of the scintillators 1 to 9 and scintillation light emission occurs, the light is transmitted to the light guide 10.
is guided to the photomultiplier tube 11, where an electrical output signal is generated. This output signal consists of a fast component A and a slow component B, as shown in FIG. 2, and since this slow component B becomes larger as the impurity concentration increases, the scintillator with a higher number becomes larger. Therefore, when this output signal is integrated over an integration time that is sufficiently long with respect to the decay time of the fast component, the integrated value becomes larger for scintillators with higher numbers as shown in FIG. Therefore, by discriminating the peak value of the output of the integrator 22 using the peak discriminator 23, it is possible to determine which scintillator has emitted light, that is, which scintillator has the γ-ray incident. In the above, nine scintillators 1 to 9 with different impurity concentrations are two-dimensionally arranged, and the two-dimensional γ-ray incident position is determined from the output of the photomultiplier tube 11. If a plurality of scintillators with different values are arranged one-dimensionally, it is possible to one-dimensionally determine the γ-ray incident position. In the second embodiment shown in FIG. 4, one-dimensional discrimination is performed depending on the discrimination of the difference in output due to the difference in impurity concentration. In this figure 4, 5 different impurity concentrations are shown.
Thin scintillators 1 to 5 are arranged in the X direction, and optically coupled by a light guide 10 to a plurality of (three in this case) photomultiplier tubes 11 to 13 arranged in the Y direction. It is possible to determine which of the scintillators 1 to 5 the gamma rays are incident on, that is, to determine the incident position in the X direction, based on the difference in the slow output components of the photomultiplier tubes 11 to 13. In this embodiment, the determination of the γ-ray incident position in the Y direction can be performed in the same manner as in a normal Angular one-type scintillation camera. In other words, by taking advantage of the fact that when light emission occurs at a certain position, photomultiplier tubes near that position produce a large output, the outputs of the three photomultiplier tubes 11 to 13 are compared to determine the Y direction of the γ-ray. Determine the incident position. With these combinations, the γ-ray incident position can be determined two-dimensionally. It should be noted that the number of scintillators is of course not limited to that in the above embodiment, but the impurity concentration may not only be changed stepwise as described above, but may be changed continuously. Furthermore, although the above description has been made assuming that the present invention is used in an ECT apparatus, it is also possible to apply the present invention to radiation measurement apparatuses such as scintillation cameras that obtain planar images in addition to ECT apparatuses.

【Effect of the invention】

According to the radiation detector of the present invention, a single photomultiplier tube can discriminate which of the plurality of scintillators coupled to the photomultiplier tube has been hit by radiation, so that the spatial resolution can be very high. Moreover, this does not require an increase in the number of photomultiplier tubes, and the structure is simple, so the price can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an embodiment of the present invention, FIG. 2 is a graph showing temporal changes in photomultiplier tube output, and FIG. 3 is a temporal change in integral value of photomultiplier tube output. FIG. 4 is a schematic perspective view of another example, and FIG. 5 is a graph showing a scintillation spectrum. 1 to 9...scintillator, 10...light guide,
11-13...Photomultiplier tube, 21...Amplifier, 2
2... Integrator, 23... Wave height discriminator.

Claims (1)

[Claims] (1) A plurality of scintillators that emit different amounts of light due to differences in impurity concentration, a photomultiplier tube that is optically coupled to the plurality of scintillators, and a photomultiplier tube that emits light based on the difference in the amount of light emitted from the output of the photomultiplier tube. A radiation detector comprising a circuit for discriminating scintillators.