JPH06289143A - Radioactive ray detector - Google Patents

Abstract

PURPOSE:To provide a radioactive ray detector which is small-sized and lightweight and can be made portable. CONSTITUTION:A radioactive ray detector is constituted of a scintillator 1 which radiates fluorescent light from an irradiation surface for the inputted radiactive ray, and three photoelectron multiplier tubes 2a, 2b and 2c which are arranged on the radiation surface of the scintillator 1 and output electric current in correspondence with the inputted fluorescent light. The scintillator 1 is constituted of NaI (Tl) and has and incidence surface and an outgoing surface each of which has a diameter of about 40mm and forms to a thin cylinder having an axis height of about 10mm. Further, each of the photoelectron multiplier tubes 2a, 2b, and 2c has an radiation surface having a diameter of 15.24mm, and forms a thin cylinder shape having an axis height of 10mm, and is arranged on the concentric circls for the center of the outgoing surface of the scintillator 1. Since the photoelectron multiplier tube is thin, the quantity of shielding member for the enviromental radioactive ray can be reduced. Accordingly, a radicactive ray detector can be made small-sized and lightweight, and can be made portable, and in particular, can be used in a fixed state on a physical body.

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 measuring radiation using scintillation counting.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view showing the structure of a conventional radiation detector. A conventional radiation detector is a scintillator 1 that emits fluorescence from an emission surface with respect to incident radiation.
And a photomultiplier tube (PM) which is installed on the emission surface of the scintillator 1 and outputs an electric current in response to the incident fluorescence.
T) 4.

FIG. 5 is a sectional side view showing the structure of a photomultiplier tube used in a conventional radiation detector. The photomultiplier tube 4 is provided with a photocathode (photocathode) 15 for converting incident light into electrons, not shown, on the inner upper surface of the bulb (vacuum container) 10 to accelerate photoelectrons emitted from the photocathode 15. An electrode 22, a focusing electrode 23 for focusing the photoelectrons, and an electron multiplying unit 18 including a box-type dynode for multiplying the photoelectrons are provided inside the bulb 10. The inner surface of each dynode of the electron multiplying section 18 is coated with a secondary electron emission surface.

Further, the bulb 10 has a side tube 11 which is entirely made of glass and which is exposed in a substantially cylindrical shape in plan view, and an upper portion of an opening of the side tube 11 which is integrally airtightly fused from the lower inside to a lower surface thereof. A light receiving face plate 13 which is transparent and has a substantially circular plate shape to which a photocathode 15 is adhered, and a substantially flat plane circle which is heat-melted by a gas burner (not shown) and airtightly fused to an airtight weld 12 at the lower end of the opening of the side tube 11. It is composed of a plate-shaped stem 14.

The stem 14 is formed of glass, and a plurality of pins 16 for supplying a voltage to each dynode forming the photocathode 15 and the electron multiplying portion 18 are vertically inserted and penetrated. Further, an exhaust pipe 17 made of hanging glass is continuously provided in the center of the stem 14 by thermal fusion, and connects the photomultiplier tube 4 and an exhaust system such as a vacuum pump (not shown).

After the exhaust pipe 17 is connected to the exhaust system, the inside of the bulb 10 is evacuated and an alkali metal vapor (not shown) is introduced into the interior of the bulb 10 to form the photocathode 15. Further, the exhaust pipe 17 is the photomultiplier tube 4
In the final stage of the manufacturing process of (1), it is melted and cut by a gas burner not shown.

Therefore, in the manufacturing process of the photomultiplier tube 4,
First, the stem 14 is heated and melted by the gas burner and hermetically welded to the airtight weld 12 of the side pipe 11. Next, the exhaust pipe 17 is connected to the exhaust system, the inside of the valve 10 is evacuated, and the alkali metal vapor is introduced into the inside, so that the photocathode 15 and the secondary electron emission surface of the electron multiplying unit 18 are introduced. Are deposited and activated. After that, the exhaust pipe 17 is heated and melted from the exhaust system by a gas burner to be cut, and the length is shortened as much as possible.

[0008]

However, the above-mentioned conventional radiation detector has a problem that it has an excessively large size for portable use, particularly when it is fixed to the body. For example, a photomultiplier tube that is optically coupled to a scintillator having an exit surface with an effective diameter of about 40 mm is
Similarly, when the incident surface has an effective diameter of about 40 mm, its axial height is about 100 mm. Further, the incident surface having the smallest diameter as a conventional photomultiplier tube has an effective diameter of about 10 mm, and its axial height is about 45 mm.

Further, if such a portable radiation detector has a large size, a large amount of lead used as a shielding material against environmental radiation is required, and there is a problem that it becomes heavy.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a portable and small-sized and lightweight radiation detector.

[0011]

In order to achieve the above object, the present invention provides a scintillator that emits fluorescence from an emission surface in response to incident radiation, and a scintillator installed on the emission surface and incident. In a radiation detector including a photomultiplier tube that outputs an electric current in response to fluorescence, the photomultiplier tube is a side tube that is made of metal and exposes a substantially cylindrical shape to form a valve, and this side tube. The light-receiving face plate of a substantially disc shape that is light-tightly fused to the upper opening of the light-transmitting plate, the photocathode that is attached to the lower face of the light-receiver face plate, emits photoelectrons when fluorescence is incident, and inside the bulb. An electron multiplying part that is installed and consists of a stacked dynode that multiplies photoelectrons, a flange-type airtight weld around the lower circumference of the side tube, and a flange made of metal that is vacuum-tightened to this airtight weld. Substantially circular plate with airtight welded part on outer periphery And the stem is inserted through the respective glass to the stem, is composed of a plurality of pins for supplying a voltage photocathode and the electron multiplier unit, characterized in that it is a thin.

Further, in order to achieve the above-mentioned object, the present invention provides a scintillator which emits fluorescence from the first emission surface in response to the incident radiation, and a scintillator which is installed on the first emission surface and is incident. Radiation including a light guide that collects the emitted fluorescence and emits it from the second emission surface, and a photomultiplier tube that is installed on the second emission surface and outputs a current corresponding to the incident fluorescence. In the detector, the photomultiplier tube is a side tube which is made of metal and exposes a substantially cylindrical shape to form a valve, and a substantially circular plate which is hermetically fused to the upper opening of the side tube and has a light transmitting property. -Shaped light-receiving surface plate, a photocathode that is attached to the lower surface of the light-receiving surface plate and emits photoelectrons when fluorescent light is incident, and an electron multiplying section that is provided inside the bulb and that is composed of a stacked dynode that multiplies photoelectrons. And a flange-type air-tight melter that is installed around the lower outer circumference of the side pipe. Section, a substantially disk-shaped stem having a flange-type airtight weld made of a metal that is vacuum-tightly sealed to the airtight weld, and a stem that is inserted into each of the stems via glass, and has a photocathode and an electron multiplier. It is characterized by being thin and composed of a plurality of pins for supplying a voltage to the double section.

Further, in the present invention, in order to achieve the above object, it is preferable that a plurality of the photomultiplier tubes are installed on the emission surface.

[0014]

According to the present invention, in the photomultiplier tube, the electron multiplying section is composed of the laminated dynode, so that the photoelectrons emitted from the photocathode are not accelerated or focused by the conventional electrodes, and the electrons are not focused. It can be incident on the multiplication section. Therefore, the electron multiplying part is formed thin, and the distance between the photocathode and the electron multiplying part is reduced.

Further, since the side tube which constitutes the valve, the airtight welded portion formed on the outer periphery of the lower portion of the side tube and the airtight welded portion formed on the outer periphery of the stem are all made of metal, both airtight portions are formed. The weld is hermetically welded by helium arc welding or resistance welding. Therefore, since the welding time is shortened and the heating amount is suppressed, even though the photocathode is arranged close to the thin electron multiplying part, the photocathode and the electron multiplying part are not adhered. Deterioration due to oxidation of highly reactive alkali metal is prevented.

Therefore, since the photomultiplier tube is made thin, the radiation detector can be downsized. Therefore, the amount of the shielding material against environmental radiation is small, so that the weight of the radiation detector can be reduced.

Further, by interposing a light guide between the exit surface of the scintillator and the entrance surface of the photomultiplier tube, the fluorescence emitted from the scintillator is condensed by the light guide and enters the photomultiplier tube. It Therefore, the energy resolution with respect to the detected radiation can be improved.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of an embodiment according to the present invention will be described below with reference to FIGS. In addition,
In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings do not always match those described.

FIG. 1 shows a first embodiment of the radiation detector of the present invention.
The structure of an Example is shown, (a) is a top view, (b) is a side view. The first embodiment of the radiation detector of the present invention corresponds to the scintillator 1 which emits fluorescence from the emission surface with respect to the incident radiation and the fluorescence which is installed on the emission surface of the scintillator 1 and is incident. It is composed of three photomultiplier tubes (PMT) 2a, 2b, and 2c that output a current. The scintillator 1 is made of NaI (Tl), has a diameter of about 40 mm for an incident surface and an exit surface, and has a cylindrical height of about 10 mm. In addition, the photomultiplier tube 2
Reference characters a, 2b, and 2c each have a light entrance surface with a diameter of about 15.24 mm, are thin columnar shapes with an axial height of about 10 mm, and are arranged concentrically with respect to the center of the exit surface of the scintillator 1.

On the emission surface of the scintillator 1,
The portions not covered with the photomultiplier tubes 2a, 2b, 2c are covered with a reflective material such as Teflon or an aluminum thin film having a good light reflectance, a reflective agent coated with barium sulfate or the like. The contact surface between the scintillator 1 and the photomultiplier tubes 2a, 2b, 2c is coated with epoxy resin, silicone oil or the like, and both are optically coupled.

2A and 2B show the construction of a photomultiplier tube used in the radiation detector of the present invention. FIG. 2A is a plan view, FIG. 2B is a sectional side view, and FIG. 2C is a bottom view. Photomultiplier tube 2a,
2b and 2c are laminated types in which a photocathode (photocathode) 15 for converting incident light into electrons (not shown) is attached to the inner upper surface of the bulb (vacuum container) 10 to multiply photoelectrons emitted from the photocathode 15. An electron multiplying unit 18 composed of a dynode is provided inside the valve 10. The electron multiplying units 18 are arranged in a two-dimensional matrix or a one-dimensional array,
The inner surface of each dynode is coated with a secondary electron emission surface.

Further, the valve 10 is integrally and airtightly fused to a ring-shaped upper portion having an opening of the side tube 11 and a side tube 11 which is formed of a metal and has a substantially cylindrical shape in plan view from below inside. And a transparent substantially light-receiving face plate 13 having a photocathode 15 attached to the lower surface thereof, and a flange-type hermetically welded portion 12 that is provided around the lower end outer peripheral surface of the side tube 11 and projects in the outer axial radial direction. And a stem 14 having a substantially disk-like plane that is airtightly fused to the airtight weld 12 by helium arc welding or resistance welding.

A plurality of pins 16 for supplying a voltage to the dynodes forming the photocathode 15 and the electron multiplying part 18 are vertically inserted through the stem 14 through the tapered hermetic glass 19. , And the bottom surfaces are arranged in a substantially rectangular shape. An anode electrode 20 is horizontally connected and placed on the uppermost part of the plurality of pins 16. Further, in the center of the stem 14, an exhaust pipe 17 made of metal with a hanging flare is fusion-bonded by resistance welding and continuously provided,
The photomultiplier tube 2 and an exhaust system including a vacuum pump (not shown) are connected. Furthermore, on the outer peripheral surface of the stem 14,
A flange-type airtight weld portion 21 is provided so as to project in the radial direction of the outer shaft, and is positioned in the airtight weld portion 12 of the side pipe 11 and then airtightly welded by helium arc welding or resistance welding.

After the exhaust pipe 17 is connected to the exhaust system, the bulb 10 is internally evacuated and an alkali metal vapor (not shown) is introduced into the interior thereof to form the photocathode 15. Further, the hermetic glass 19 has a withstand voltage,
The creepage surface is tapered in consideration of leakage current.
Further, the exhaust pipe 17 is cut by cold pressure welding at the final stage in the manufacturing process of the photomultiplier tube 2.

Therefore, in the manufacturing process of the photomultiplier tube 2,
First, the airtight welded portion 21 of the stem 14 is positioned at the airtight welded portion 12 of the side pipe 11, and these airtight welded portions 12, 21
Is airtightly welded by helium arc welding or resistance welding. Next, the exhaust pipe 17 is connected to the exhaust system, and the valve 10
The inside of the vacuum chamber is evacuated, and the alkali metal vapor is introduced into the inside of the vacuum chamber, and the photocathode 15 and the electron multiplier 18
The secondary electron emission surface of is deposited and activated. afterwards,
The exhaust pipe 17 is cut from the exhaust system with a pinch-off seal,
It is shortened as much as possible.

Next, the operation of the first embodiment will be described.
When the radiation particles are incident on the incident surface of the scintillator 1, fluorescence is generated with an emission amount proportional to the energy of the radiation particles and emitted from the emission surface. This fluorescence passes through the light-receiving face plate 13 which is the incident surface of the photomultiplier tubes 2a, 2b, 2c and enters the photocathode 15. Therefore, each time, photoelectrons are emitted from the photocathode 15 with energy proportional to the intensity of fluorescence, and are accelerated by the electric field generated between the photocathode 15 which is the cathode and the anode electrode 20, and the electron multiplying unit 1
It is incident on 8. In the electron multiplying section 18, photoelectrons enter the first dynode, and a large number of secondary electrons are emitted. Subsequently, these secondary electrons enter the second dynode, and a large number of new secondary electrons are emitted. 2 like this
The process of producing the secondary electron emission effect is repeated one after another, and these electrons are multiplied and emitted from the electron multiplying unit 18.
As a result, the electrons are collected in the anode electrode 20 and taken out as an output signal proportional to the photoelectron flow from the photocathode 15. Therefore, this output signal is obtained as a pulse whose magnitude is proportional to the energy of the incident radiation particle.

Since the electron multiplying section 18 is formed of a laminated dynode, the photoelectrons emitted from the photocathode 15 can enter the electron multiplying section 18 without being accelerated and focused by the conventional electrodes. You can for that reason,
The electron multiplying part 18 is formed thin, and the photocathode 15 is formed.
The distance between the electron multiplying unit 18 and the electron multiplying unit 18 is reduced.

Further, the side tube 11 constituting the valve 10, the airtight welded portion 12 provided on the outer periphery of the lower portion of the side tube 11 and the airtight welded portion 21 formed on the outer periphery of the stem 14 are all made of metal. Both airtight welds 1
2, 21 are hermetically welded by helium arc welding or resistance welding. Therefore, since the welding time is shortened and the heating amount is also suppressed, the photocathode 15 and the electron multiplying part 18 are arranged close to each other even though the photocathode 15 is arranged close to the thin electron multiplying part 18. Deterioration of the deposited highly reactive alkali metal due to oxidation is prevented.

Therefore, since the photomultiplier tube 2 is made thin, the radiation detector can be downsized. Therefore, the amount of the shielding material such as lead against the environmental radiation becomes small, and the weight of the radiation detector can be reduced.

FIG. 3 shows a second embodiment of the radiation detector of the present invention.
The structure of an Example is shown, (a) is a top view, (b) is a side view. The second embodiment of the radiation detector of the present invention is a scintillator 1 that emits fluorescence from an emission surface with respect to incident radiation, and is installed on the emission surface of this scintillator 1 to collect incident fluorescence. And a light guide 3 which is emitted from the emission surface, and three photomultiplier tubes (PMT) 2a, 2b which are installed on the emission surface of the light guide 3 and which output an electric current in response to the incident fluorescence. 2c.

The inner surface and the emission surface of the light guide 3 which are not covered with the photomultiplier tubes 2a, 2b and 2c are made of Teflon or aluminum thin film having a good light reflectance, or barium sulfate. Etc. are coated with a reflecting agent or the like. The contact surfaces of the scintillator 1, the light guide 3, and the photomultiplier tubes 2a, 2b, 2c are coated with epoxy resin, silicone oil, etc., and both are optically coupled. Further, the scintillator 1 and the photomultiplier tubes 2a, 2b, 2c are configured similarly to the first embodiment.

Next, the operation of the second embodiment will be described.
The emission surface of the scintillator 1 and the photomultiplier tubes 2a, 2b, 2
By interposing the light guide 3 between it and the incident surface of c, the fluorescence emitted from the scintillator 1 is condensed by the light guide 3 and is incident on the photomultiplier tubes 2a, 2b, 2c. Therefore, the energy resolution with respect to the detected radiation can be improved. In other respects, this embodiment can also obtain substantially the same operational effects as the first embodiment.

Here, the energy resolution corresponding to the number of photomultiplier tubes (PMT) obtained by irradiating the scintillator having a diameter of about 40 mm with gamma rays of 122 keV in the first and second embodiments is shown below. .

[0034]

[Table 1]

The present invention is not limited to the above embodiment, but various modifications can be made.

For example, although NaI (Tl) is used as the scintillator in the above-mentioned embodiments, it is suitable for measuring γ-rays, but one that emits fluorescence in response to the radiation to be measured is used. According to the above, the same effect can be obtained.

Further, in the above-mentioned embodiments, the laminated dynode is used as the electron multiplying part, but the same operational effect can be obtained by using an MCP (micro channel plate), a semiconductor element or the like.

Further, in the above-mentioned embodiments, the hermetic glass of the photomultiplier tube is tapered, but when the operating voltage is low, the flat surface can be used and the diameter of the glass can be increased. it can.

Further, in the above-mentioned embodiments, the inside of the valve 10 is evacuated by the exhaust system connected to the exhaust pipe 17, but after the photocathode 15 and the secondary electron emission surface of the electron multiplier 18 are formed. , Indium seal or resistance welding is performed in a vacuum using a transforer device to form an airtight welded portion 12,
By welding 21 the exhaust pipe 17 can be eliminated.

Further, the anode electrodes used in the above-mentioned embodiments are replaced with a multi-anode fitted in a substantially rectangular mounting hole penetrating the stem and arranged vertically and horizontally. The position can be detected by extracting output signals from a large number of vertically mounted anode pins.

Further, in the above-mentioned embodiments, the light-receiving face plate is airtightly fused from below the inside of the side tube, but the effective area of the photocathode can be enlarged by airtightly fused from above. Furthermore, since the atmospheric pressure acts to press the light receiving face plate onto the upper opening of the side tube, it is possible to improve the reliability of the valve while reducing the pressure contact area.

Further, in the above-mentioned embodiments, the light-receiving surface plate is formed into a substantially disc shape, but a substantially hemispherical projecting portion which is bulged by being exposed to the outside through the opening of the annular upper portion of the side tube is formed. By using the light-receiving face plate that is provided, light in an oblique direction can be easily incident without being reflected.

Further, in the above-mentioned embodiments, a plurality of pins are vertically inserted through the stem through the tapered hermetic glass, and are arranged in a substantially rectangular bottom face. By fitting a large disk-shaped tapered hermetic glass into the substantially disk-shaped mounting hole that was drilled through, and inserting multiple pins directly through the bottom edge of the disk, the number of parts can be increased. Can be reduced to reduce the cost.

[0044]

As described in detail above, according to the present invention, since the photomultiplier tube is thin, the amount of shielding material against environmental radiation is small. Therefore, the radiation detector can be reduced in size and weight. Therefore, there is a remarkable effect that it is possible to provide a radiation detector that is portable and can be fixed to the body and used.

Further, according to the present invention, since the light guide is interposed between the emission surface of the scintillator and the incidence surface of the photomultiplier tube, the fluorescence emitted from the scintillator is condensed by the light guide. It is incident on the photomultiplier tube. Therefore, there is a remarkable effect that the energy resolution with respect to the detected radiation can be improved.

[Brief description of drawings]

FIG. 1 shows a configuration of a first embodiment of a radiation detector of the present invention, (a) is a plan view and (b) is a side view.

2A and 2B show the structure of a photomultiplier tube used in the radiation detector of the present invention, FIG. 2A is a plan view, FIG. 2B is a sectional side view,
(C) is a bottom view.

FIG. 3 shows a configuration of a second embodiment of the radiation detector of the present invention, (a) is a plan view and (b) is a side view.

FIG. 4 is a perspective view showing a configuration of a conventional radiation detector.

FIG. 5 is a sectional side view showing a configuration of a photomultiplier tube used in a conventional radiation detector.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Scintillator 2, 4 ... Photomultiplier tube, 3 ... Light guide, 10 ... Bulb, 11 ... Side tube, 12, 21 ... Airtight welding part, 13 ... Light receiving face plate, 14 ... Stem, 15 ... Photoelectric surface, 16 ... pin, 17 ... exhaust pipe, 18 ... electron multiplier, 1
9 ... Hermetic glass, 20 ... Anode electrode, 21 ...
Accelerating electrode, 22 ... Focusing electrode.

Front page continuation (72) Inventor Hiroyuki Hisashima 1126-1 Nono, Hamamatsu, Shizuoka Prefecture 1 Hamamatsu Photonics Co., Ltd.

Claims (3)

[Claims] 1. A scintillator that emits fluorescence from an emission surface in response to incident radiation, and a photomultiplier tube that is installed on the emission surface and outputs a current corresponding to the incident fluorescence. In the radiation detector, the photomultiplier tube has a side tube formed of a metal and exposing a substantially cylindrical shape to form a valve, and a light transmissive material that is hermetically fused to an upper opening of the side tube. A substantially disc-shaped light-receiving surface plate, a photocathode that is attached to the lower surface of the light-receiving surface plate and that emits photoelectrons upon receiving the fluorescence, and a stacked dynode that is provided inside the bulb and that multiplies the photoelectrons. An electron multiplying part consisting of, a flange type airtight weld around the outer periphery of the lower part of the side tube, and a flange type airtight weld made of metal vacuum-sealed to the airtight weld on the outer periphery. Disc-shaped stem and this stem Is inserted through each of the glass, consists voltages and a plurality of pins for supplying to said photocathode and said electron multiplier section, radiation detector, which is a thin. 2. A scintillator which emits fluorescence from a first emission surface in response to incident radiation, and a scintillator which is installed on the first emission surface and collects the incident fluorescence to generate a second emission light. A radiation detector comprising a light guide which is emitted from an emission surface and a photomultiplier tube which is installed on the second emission surface and which outputs an electric current in response to the incident fluorescence, wherein the photomultiplier tube is provided. Is a side tube that is made of a metal and exposes a substantially cylindrical shape to form a valve, a light receiving surface plate that is airtightly fused to the upper opening of the side tube and has a light transmitting property, and this light receiving surface. A photocathode that is attached to the lower surface of the face plate and that emits photoelectrons upon receiving the fluorescence, an electron multiplying unit that is provided inside the bulb and that includes a stacked dynode that multiplies the photoelectrons, and the side tube. With a flange type airtight weld around the lower part of the A substantially disk-shaped stem having a flange-type airtight weld made of metal that is vacuum-tightly sealed to the airtight weld, and a stem inserted into each of the stems via glass, and the photocathode and the electron multiplier are attached. A radiation detector characterized by comprising a plurality of pins for supplying a voltage to the section and being thin. 3. The radiation detector according to claim 1, wherein a plurality of the photomultiplier tubes are installed on the emission surface.