JP7055342B2 - Light multiplier - Google Patents

Description

The present invention relates to a light multiplying device for converting weak light such as a scintillation signal or fluorescence into an electric current and multiplying it to display an image based on the weak light.

Conventionally, there was a device called an image intensifier with a built-in microchannel plate as a device for converting weak light such as a scintillation signal or fluorescence into an electric current and multiplying it to display an image based on the weak light.

This conventional image intensifier has a scintillator that emits weak light when excited by radiation, a photocathode that converts the weak light from the scintillator into electrons, and a microchannel that multiplies the electrons converted by the photocathode. It comprises a plate and a scintillator that converts the electrons multiplied by the microchannel plate into an optical signal.

The spatial resolution of this image intensifier was about 20 μm. The conventional image intensifier is a precision instrument using a vacuum tube, is very expensive, and the price is about several million yen to 10 million yen, and it is not an easy-to-use device.

In addition, the maximum diameter of the image intensifier is about 2 inches. In the conventional image intensifier, the quantum efficiency from the photo cathode to the microchannel plate is typically limited to about 10%, and the image quality is significantly deteriorated for an image having a small number of photons.

Although there is an image intensifier capable of a time gate of about 3 nanoseconds (only one-frame shooting), it is basically impossible to continuously multiply an image signal that changes at high speed.

Further, due to the structure of the image intensifier, the light receiving surface of the photocathode is covered with a fixed frame made of metal or the like, which is a dead area. Therefore, even if a large number of these photocathodes are arranged, it is not possible to assemble them into a large panel without image defects, and it is not possible to realize a light receiving surface having a diameter larger than 10 cm.

Further, since the microchannel plate is used by applying a high voltage of about -5000V, a special power supply device is required. In addition, the microchannel plate is easily damaged when excessive light is input to the photocathode, and it is necessary to prepare a darkroom device and a darkbox device and operate them carefully.

In recent years, the development of semiconductor devices instead of vacuum tube devices such as microchannel plates has been remarkable. The quantum efficiency of silicon photodiodes has reached 60%. Avalanche photodide can multiply weak light by ¹⁰⁶ times while having a quantum efficiency of about 60%.

A single output current of an avalanche photodiode can only be a binary value of on or off, but a large number of microelements of an avalanche photodiode are arranged in a circuit and connected to one to realize linear amplification. A multipixel photodiode counter (MPPC) is known (Patent Document 1). The device achieves linear amplification performance with a quantum efficiency of 60%, a Magnification of ¹⁰⁶ , and a dynamic range of 1000 or more. An MPPC array in which a large number of MPPCs are arranged in a pixel size of about 1 mm can perform the same function as a microchannel plate.

Japanese Unexamined Patent Publication No. 2011-211070 (published on October 20, 2011)

In recent years, using X-rays and neutrons generated by nuclear reactors, accelerators, lasers, etc., it has become possible to detect internal defects of metric-sized objects such as highways and concrete bridges in a non-destructive manner using radiographs. It is becoming. In particular, neutrons are difficult to generate and detect, but since they can be seen through even metric-sized concrete, technological development of the generation method and detection method is underway.

As a neutron detection method, a method of taking an image of scintillation light emitted from a scintillator excited by neutrons with a CCD camera is generally used. A photomultiplier is essential to capture images of faint scintillation light.

As the scintillator for neutron imaging, a scintillator array in which a large number of fibrous plastic scintillators having a diameter of about 1 mm are bundled is used. Also, instead of such a plastic scintillator fiber bundle (scintillator array), a liquid scintillator is filled in an aluminum honeycomb panel and sealed with a glass window to make a metric-sized scintillator array panel with similar performance at low cost. Can be done.

In order to capture a metric-sized scintillation emission image with a conventional small-diameter image intensifier camera (CCD camera), it is necessary to reduce the image. Typically, it is necessary to install the lens of a low noise cooling type CCD camera with a diameter of 3 cm and a focal length of about 3 cm at a position 1 meter from the scintillator array panel, but in this case, only a small part from the scintillator array panel. Only light can be collected in the lens. Since there is no device in the world that can generate neutrons that can cover this poor efficiency, except for super-large accelerators (J-PARC, etc.), it has been difficult to generalize neutron imaging devices with conventional techniques.

One aspect of the present invention is to realize a general-purpose light multiplying device capable of displaying an image based on weak light corresponding to radiation from a metric-sized object.

In order to solve the above problems, the optical multiplier according to one aspect of the present invention includes an avalanche panel in which a plurality of avalanche photodiodes in which weak light is converted into an electric current and multiplied in a grid pattern are arranged. It is characterized by including a light emitting panel in which a plurality of light emitting elements for converting a current from the avalanche photodiode into visible light in order to display an image based on the weak light are arranged in a grid pattern.

According to this feature, a current converted and multiplied from weak light by an avalanche photodiode arranged in a grid pattern is converted into visible light by a light emitting element arranged in a grid pattern. Since the avalanche photodiodes are arranged in a grid pattern, a dead region is not generated unlike an image intensifier, and the avalanche photodiode can be assembled into a large panel. As a result, it is possible to realize a general-purpose light multiplying device capable of displaying an image based on weak light of a metric-sized object.

In the photomultiplier device according to one aspect of the present invention, the plurality of light emitting elements may be arranged so as to have a one-to-one correspondence with the plurality of avalanche photodiodes.

According to the above configuration, an image having an avalanche photodiode as a pixel can be displayed.

The photomultiplying device according to one aspect of the present invention has a plurality of wirings for connecting the plurality of light emitting elements to the plurality of avalanche photodiodes on a one-to-one basis, and is coupled to each avalanche photodiode in parallel. A photodiode voltage source and a light emitting device voltage source coupled in parallel with each light emitting device may be further provided.

According to the above configuration, each avalanche photodiode and each light emitting element can be operated with a simple configuration.

In the photomultiplying device according to one aspect of the present invention, the photodiode voltage source has a first positive electrode that supplies a positive voltage to each avalanche photodiode, and a first negative electrode grounded to the ground. The element voltage source may have a second negative electrode that supplies a negative voltage to each light emitting element and a second positive electrode that is grounded to the ground.

According to the above configuration, each avalanche photodiode and each light emitting element can be operated with a simple configuration.

The photomultiplier device according to one aspect of the present invention further includes a scintillator that emits the weak light when excited by radiation, and the avalanche photodiode converts the light emitted by the scintillator into the current to increase the light. You may double it.

According to the above configuration, it is possible to display an image based on weak light excited by radiation.

The light multiplying device according to one aspect of the present invention may further include a camera that captures the image displayed on the light emitting panel.

According to the above configuration, an image based on weak light can be captured.

In the light multiplying device according to one aspect of the present invention, the light emitting element may be a light emitting diode.

According to the above configuration, the current from the avalanche photodiode can be efficiently converted into visible light.

According to one aspect of the present invention, it is possible to realize a general-purpose light multiplying device capable of displaying an image based on weak light corresponding to radiation from a metric-sized object.

It is a schematic diagram of the light multiplying apparatus which concerns on embodiment. It is a block diagram which shows the structure of the light multiplying panel provided in the said light multiplying apparatus. (A) is a perspective image of the light multiplying panel viewed from the avalanche panel side, and (b) is a perspective image of the light multiplying panel viewed from the light emitting panel side. (A) is a perspective image of the main part of the light multiplying panel seen from the avalanche panel side, and (b) is a perspective image seen from the light emitting panel side. It is an image of a scintillation signal from a scintillator provided in the photomultiplier device. It is a waveform diagram which shows the time response of the optical signal which is output when the pulsed light is input to the said optical magnification panel. It is a schematic diagram which shows the setup of the neutron image measurement experiment by the said light multiplier. It is an image which shows the setup of the said neutron image measurement experiment. It is an image which shows the result of the said neutron image measurement experiment.

Hereinafter, one embodiment of the present invention will be described in detail.

(Configuration of optical multiplier 1)
FIG. 1 is a schematic diagram of a light multiplying device 1 according to an embodiment. FIG. 2 is a block diagram showing a configuration of a light multiplying panel 16 provided in the light multiplying device 1.

The light multiplying device 1 includes a light multiplying panel 16. The photomultiplier panel 16 is an avalanche panel 2 provided for converting weak light 17 into a current 18 and multiplying the light, and a light emission provided for converting a current 18 from the avalanche panel 2 into visible light 19. It has a panel 3.

FIG. 3A is a perspective image of the magnification panel 16 viewed from the avalanche panel 2 side, and FIG. 3B is a perspective image of the light magnification panel 16 viewed from the light emitting panel 3 side. FIG. 3A is a perspective image of the main part of the light multiplying panel 16 seen from the avalanche panel 2 side, and FIG. 3B is a perspective image seen from the light emitting panel 3 side.

On the avalanche panel 2, a plurality of avalanche photodiodes 4 that convert weak light 17 into a current 18 and multiply it are arranged in a grid pattern. The light emitting panel 3 has a plurality of light emitting diodes (LEDs, Light Emitting Diodes) 5 (light emitting elements) that convert the current 18 from the avalanche photodiode 4 into visible light 19 in order to display an image based on the weak light 17. They are arranged in a grid pattern. The plurality of light emitting diodes 5 are arranged so as to have a one-to-one correspondence with the plurality of avalanche photodiodes 4.

The photomultiplying device 1 includes a plurality of wirings 6 in which a plurality of light emitting diodes 5 are coupled to a plurality of avalanche photodiodes 4 on a one-to-one basis, and a photodiode voltage coupled in parallel to each avalanche photodiode 4. A source 7 and a light emitting element voltage source 8 coupled in parallel with each light emitting diode 5 are provided. The photodiode voltage source 7 has a positive electrode 9 (first positive electrode) that supplies a positive voltage of about + 55 V to each avalanche photodiode 4, and a negative electrode 10 (first negative electrode) that is grounded to the ground G. The light emitting element voltage source 8 has a negative electrode 12 (second negative electrode) that supplies a negative voltage of about −2 V to each light emitting diode 5, and a positive electrode 11 (second positive electrode) that is grounded to the ground G. The light emitting element voltage source 8 can drive the light emitting diode 5 in a high speed pulse.

The light multiplying device 1 further includes a scintillator 13 that emits weak light 17 when excited by radiation 15. The avalanche photodiode 4 converts the weak light 17 emitted by the scintillator 13 into a current 18 and multiplies it.

The light multiplying device 1 is provided with a CCD camera 14 (camera) that captures an image displayed on the light emitting panel 3.

The photomultiplier tube 1 according to the present embodiment solves the drawbacks of the conventional microchannel plate type image intensifier. This optical multiplier 1 converts weak light 17 into a current 18 (electrons) using an avalanche panel 2 composed of MPPC arrays in which avalanche photodiodes 4 are arranged in a grid pattern, and then multiplies the light 17 to a plurality of currents 18 (electrons). The light emitting diodes 5 of the above are converted into an image signal by visible light 19 by a light emitting panel 3 composed of light emitting LED arrays arranged in a grid pattern.

The quantum efficiency of the MPPC array is typically 60%, the image magnification of the electrons is ¹⁰⁶ , and the photon efficiency of the electrons to the LED (light emitting diode 5) is about 10%. The magnification is about ¹⁰⁵ times.

When the light multiplying panel 16 is combined with the scintillator 13, the scintillation signal due to the weak light 17 can be observed with the naked eye, so that the radioactive substance emitting the radiation 15 can be observed with the naked eye.

(Operation of optical multiplier 1)
FIG. 5 is an image of a scintillation signal from a scintillator 13 provided in the photomultiplier tube 1.

This is done by adhering a sealed radiation source to a scintillator 13 made of a NaI: Tl scintillator, multiplying the scintillation signal (weak light 17) generated from the scintillator 13 with a light multiplying panel 16, and using a CCD camera 14 made of a digital camera. This is an image taken. According to the optical multiplier 1, it is shown that a weak optical signal such as a scintillation signal can be multiplied with high sensitivity so that it can be photographed by a normal digital camera.

FIG. 6 is a waveform diagram showing the time response of the output optical signal when the pulsed light is input to the optical magnification panel 16.

The response speed can be increased to a minimum of about 3 ns by appropriately selecting the type of the avalanche photodiode 4 and the type of the light emitting diode 5.

In FIG. 6, an impulse light (weak light 17) is input to the input surface of the avalanche panel 2 of the actually manufactured light multiplying panel 16, and the light emission of the light emitting diode 5 of the light emitting panel 3 is measured by a high-speed photodetector. The response is shown. The response speed of this optical magnification panel 16 is about 100 ns, but it can be increased to about 10 ns depending on the selection of the MPPC type and the circuit design. By combining with a high-speed shooting camera, it is possible to continuously shoot while multiplying the signal of the weak light 17 that changes with time at high speed. In addition, the LED circuit for driving the light emitting diode 5 is equipped with a gate circuit, and only a momentary image signal can be cut out and multiplied, and a high-speed gate can be obtained by shooting with a normal CCD camera or digital camera. It can also function as a camera.

An MPPC whose pixel size of the avalanche photodiode 4 is currently 2 mm is used for the avalanche panel 2, but even when an off-the-shelf product of the avalanche photodiode 4 is used, it is possible to manufacture an MPPC having a pixel size of 1 mm, which is a principle. It is also possible to reduce the pixel size to about 0.1 mm.

Since the avalanche photodiode 4 is composed entirely of semiconductor elements, it can be driven by a voltage as low as about 55 V and driven by a battery via boosting by a DC-DC converter. Therefore, the avalanche panel 2 of the photomultiplier 1 does not require a high voltage power supply and is much more compact than the conventional image intensifier with a built-in microchannel plate.

The avalanche photodiode 4, which is a photodiode element, is unlikely to be damaged because the output is only saturated even if an excessive light is incident on the avalanche photodiode 4. Therefore, the avalanche photodiode 4 is overwhelmingly more resistant to excessive light than the conventional microchannel plate, and can be used without a special dark room or dark box device.

Further, since the avalanche photodiode 4 does not have a dead space around the light receiving surface unlike the conventional image intensifier, it is easy to increase the size by arranging a large number of avalanche photodiodes 4 (FIG. 3). As shown in a), an avalanche panel 2 having a size of about 20 cm is also realized. Since the avalanche photodiode 4 is inexpensive, it is possible to realize an avalanche panel 2 having a size of 1 meter.

The optical multiplier 1 according to the present embodiment has a resolution of about 2 mm. The panel size of the avalanche panel 2 can be increased from a few centimeters to a metric. The light multiplying panel 16 can multiply the weak light 17 representing the optical image signal at a light-light magnification factor of 105, and continuously multiply the weak light 17 with a time response of 100 ^nssec or less. The light multiplying panel 16 is driven by a small power source and is less likely to be damaged by an excessive light input. The light multiplying panel 16 has a quantum efficiency of about 60% and has a very high efficiency sensitivity.

FIG. 7 is a schematic diagram showing the setup of a neutron image measurement experiment using the photomagnifying device 1. FIG. 8 is an image showing the setup of the neutron image measurement experiment. FIG. 9 is an image showing the result of the neutron image measurement experiment.

The photomultiplier panel 16 of the present embodiment is attached to the light emitting surface of a scintillator array plate (scintillator 13) in which an aluminum honeycomb is filled with a liquid scintillator and sealed in a container with a glass window, and the light emitting panel of the photomultiplier panel 16 is attached. The LED light emitting surface formed in 3 is imaged by the CCD camera 14. This light multiplying device 1 can be used as an X-ray camera or a neutron camera.

With the setup shown in Fig. 7, a radiation 15 consisting of 2.45 MeV neutrons was generated by a deuterium-deuterium fusion reaction using the intense light No. 12 laser of the Institute of Laser Engineering Osaka University, and this was used as a neutron source. FIG. 9 shows an image obtained by performing a shadow graph of the lead block 21 and the paraffin block 22. The shadow of lead and the shadow of paraffin are reflected. Neutrons are hardly attenuated by lead, but are attenuated by paraffin, so a dark shadow appears in the place of paraffin.

This image is an image taken by discriminating X-rays and neutrons by the flight time discrimination method and applying a time gate to the neutron time. Since the attenuation of the neutron signal is larger in paraffin than in lead, it can be seen that this image is based on the neutron signal.

The light multiplying device 1 according to the present embodiment is a handy type radiation image for use in a non-destructive inspection for visualizing internal defects of concrete placed in a tunnel, for example, by combining with a portable radiation source. It can be applied to a detector. Further, the light multiplying device 1 can be applied to a medical device using tomography (tomography) by combining with a radiation source.

As described above, in the optical multiplier 1 according to the present embodiment, it is also possible to manufacture a metric-sized optical multiplier panel. By installing a photomultiplier panel of the same size on the surface of a metric-sized scintillator panel and photographing the multiplied light with a CCD camera, large-scale neutron image measurement has become possible.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

1 Photomultiplier 2 Avalanche panel 3 Light emitting panel 4 Avalanche photodiode 5 Light emitting diode (light emitting element)
6 Wiring 7 Photodiode voltage source 8 Light emitting element voltage source 9 Positive electrode (first positive electrode)
10 Negative electrode (first negative electrode)
11 Positive electrode (second positive electrode)
12 Negative electrode (second negative electrode)
13 Scintillator 14 CCD camera (camera)
15 Radiation 16 Light multiplying panel 17 Weak light 18 Current 19 Visible light

Claims (4)

A portable neutron source that generates neutrons and
A scintillator that emits weak light when excited by neutrons generated by the portable neutron source.
An avalanche panel in which a plurality of avalanche photodiodes, which convert weak light generated by the scintillator into an electric current and multiply it, are arranged in a grid pattern.
A light emitting panel in which a plurality of light emitting diodes that convert the current from the avalanche photodiode into visible light in order to display a neutron image based on the neutrons are arranged in a grid pattern .
A light multiplying device including a camera that captures the neutron image displayed on the light emitting panel . The optical multiplier according to claim 1, wherein the plurality of light emitting diodes are arranged so as to have a one-to-one correspondence with the plurality of avalanche photodiodes. A plurality of wires for connecting the plurality of light emitting diodes to the plurality of avalanche photodiodes on a one-to-one basis.
A photodiode voltage source coupled in parallel with each avalanche photodiode,
The light multiplying device according to claim 1, further comprising each light emitting diode and a light emitting element voltage source coupled in parallel. The photodiode voltage source has a first positive electrode that supplies a positive voltage to each avalanche photodiode.
It has a first negative electrode grounded to the ground,
The light emitting element voltage source has a second negative electrode that supplies a negative voltage to each light emitting diode , and
The photomultiplying device according to claim 3, further comprising a second positive electrode grounded to the ground.

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