JP3352491B2 - Radiation detector - Google Patents

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 includes a scintillator 1 that emits fluorescence from an emission surface with respect to incident radiation.
And a photomultiplier tube (PM) installed on the emission surface of the scintillator 1 and outputting a current corresponding to the incident fluorescence.
T) 4).

FIG. 5 is a cross-sectional side view showing the structure of a photomultiplier 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 vessel) 10 and accelerates photoelectrons emitted from the photocathode 15. An electrode 22, a focusing electrode 23 for focusing the photoelectrons, and an electron multiplier 18 composed of a box dynode for multiplying the photoelectrons are provided in the bulb 10. A secondary electron emission surface is provided on the inner surface of each dynode of the electron multiplier 18.

Further, the bulb 10 has a side tube 11 entirely formed of glass and exposing a substantially cylindrical shape in a plane, and is integrally hermetically sealed from the lower portion of the upper portion of the opening of the side tube 11 from the inside to the lower surface. A substantially disc-shaped transparent light-receiving face plate 13 having a photoelectric surface 15 attached thereto, and a substantially substantially flat circle which is heat-melted by a gas burner (not shown) and hermetically welded to the hermetically welded portion 12 at the lower end of the opening of the side tube 11. And a plate-shaped stem 14.

The stem 14 is made of glass, and has a plurality of pins 16 for supplying a voltage to each of the dynodes forming the photocathode 15 and the electron multiplying portion 18 which are vertically inserted through the stem. At the center of the stem 14, an exhaust pipe 17 made of hanging glass is connected by heat fusion, and connects the photomultiplier tube 4 to an exhaust system such as a vacuum pump (not shown).

After the exhaust pipe 17 is connected to the exhaust system, the interior of the valve 10 is evacuated and an alkali metal vapor (not shown) is introduced into the interior to form the photoelectric surface 15. The exhaust pipe 17 is a photomultiplier tube 4
In the final stage of the manufacturing process, the resin 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 a gas burner to the hermetically welded portion 12 of the side tube 11 and hermetically welded. Next, an exhaust pipe 17 is connected to the exhaust system, the interior of the valve 10 is evacuated, and alkali metal vapor is introduced into the interior of the exhaust pipe, and the secondary electron emission surface of the photocathode 15 and the electron multiplier 18. Is activated when activated. After that, the exhaust pipe 17 is heated and melted by the gas burner from the exhaust system and cut off, thereby shortening as much as possible.

[0008]

However, there is a problem that the above-mentioned conventional radiation detector has an excessively large size when it is used in a portable manner, especially when it is fixed to a body. For example, a photomultiplier tube that is optically coupled to a scintillator having an emission surface with an effective diameter of about 40 mm includes:
Similarly, if the incident surface has an effective diameter of about 40 mm, its axial height becomes about 100 mm. In addition, the incident surface having the minimum diameter as a conventional photomultiplier has an effective diameter of about 10 mm, and its axial height is about 45 mm.

In addition, when such a portable radiation detector has a large size, a large amount of lead used as a shielding material for environmental radiation is required, and there is a problem in that the radiation detector becomes excessively heavy.

Accordingly, the present invention has been made in view of the above problems, and has as its object to provide a small and lightweight radiation detector which is portable.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a scintillator for emitting fluorescence from an emission surface in response to incident radiation, and a scintillator installed on the emission surface and having an incident light. In a radiation detector including a photomultiplier tube that outputs a current in response to fluorescence, the photomultiplier tube includes a side tube formed of metal and exposing a substantially cylindrical shape to form a bulb; A substantially disc-shaped light-receiving surface plate which is air-tightly fused to the upper opening of the light-receiving plate, has a light-transmitting property, a photoelectric surface which is attached to the lower surface of the light-receiving surface plate, receives fluorescent light, and emits photoelectrons; An electron multiplying unit comprising a stacked dynode for multiplying photoelectrons, a flange-type hermetic weld around the lower periphery of the side tube, and a flange made of metal vacuum-sealed to the hermetic weld Disk with an airtight weld on the outer periphery And the stem is inserted through the respective glass to the stem, characterized in that it is composed of a voltage and a plurality of pins for supplying the photocathode and the electron multiplier section.

Further, in order to achieve the above object, the present invention provides a scintillator for emitting fluorescence from a first emission surface in response to incident radiation, and a scintillator installed on the first emission surface, A light guide that emits the emitted fluorescence from the second emission surface, and a photodetector that is provided on the second emission surface and that outputs a current corresponding to the incident fluorescence, and a radiation detector including: The photomultiplier tube is made of metal, has a substantially cylindrical shape, and constitutes a bulb, and a substantially disc-shaped light-receiving surface plate which is air-tightly fused to the upper opening of the side tube and has light transmittance. A photocathode that is attached to the lower surface of the light-receiving surface plate, emits photoelectrons when fluorescent light is incident thereon, an electron multiplying unit that is provided inside the bulb and includes a stacked dynode that multiplies photoelectrons, and a side tube. A flange-type airtight weld around the lower periphery of the A substantially disk-shaped stem having a flange-shaped hermetic weld made of a metal that is vacuum-sealed to the hermetic weld at the outer periphery thereof, and the stem is inserted through the respective glass via glass, and is used for a photocathode and an electron multiplier. And a plurality of pins for supplying a voltage. Also,
In order to achieve the above object, the present invention provides a scintillator that emits fluorescence from a first emission surface in response to incident radiation, and a scintillator that is installed on the first emission surface and collects the incident fluorescence. A light guide that emits light and exits from the second exit surface;
A photomultiplier tube installed on the second emission surface and outputting a current in response to incident fluorescence, wherein the photomultiplier tube is formed of metal and has a substantially cylindrical shape. A side tube forming a bulb, a substantially disc-shaped light-receiving surface plate which is air-tightly fused to the upper opening of the side tube and has light transmittance, and is attached to a lower surface of the light-receiving surface plate, and fluorescent light is incident thereon. A photocathode that emits photoelectrons, and inside the bulb,
An electron multiplier consisting of a stacked dynode that multiplies photoelectrons, a flange-type hermetic weld around the lower periphery of the side tube, and a flange-type hermetic seal made of metal that is vacuum-sealed to this hermetic weld It is characterized by comprising a substantially disk-shaped stem having a welded portion on the outer periphery, and a plurality of pins that are inserted into the stem via glass, respectively, and that supply a voltage to the photocathode and the electron multiplier. I do.

In order to achieve the above object, it is preferable that a plurality of the photomultiplier tubes are provided on the emission surface.

[0014]

According to the present invention, in the photomultiplier tube, the electron multiplier is composed of a stacked dynode, so that the photoelectrons emitted from the photocathode are not accelerated and focused by the conventional electrodes. The light can enter the multiplier. Therefore, the electron multiplying unit is formed thin, and the distance between the photocathode and the electron multiplying unit is reduced.

Further, since the side pipe constituting the valve, the hermetically welded portion provided on the outer periphery of the lower portion of the side tube and the hermetically welded portion formed on the outer periphery of the stem are all formed of metal, both hermetic seals are provided. The weld is hermetically welded by helium arc welding or resistance welding. Therefore, since the welding time is shortened and the amount of heating is suppressed, the photocathode is attached to the photocathode and the electron multiplier even though the photocathode is arranged close to the thin electron multiplier. Deterioration due to oxidation of highly reactive alkali metal is prevented.

Accordingly, since the photomultiplier tube is thinned, the size of the radiation detector can be reduced. Therefore, the amount of shielding material for environmental radiation is reduced, 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, the fluorescent light emitted from the scintillator is condensed by the light guide and made incident on the photomultiplier. You. Therefore, the energy resolution with respect to the detected radiation can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction 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. Also, 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.
3A and 3B show a configuration of an example, in which FIG. 3A is a plan view and FIG. The first embodiment according to the radiation detector of the present invention has a scintillator 1 that emits fluorescence from an emission surface with respect to incident radiation, and is provided on the emission surface of the scintillator 1 and corresponds to the incident fluorescence. And three photomultiplier tubes (PMTs) 2a, 2b, and 2c that output current. This scintillator 1 is made of NaI (Tl), has an entrance surface and an exit surface with a diameter of about 40 mm, and has a cylindrical shape with an axial height of about 10 mm. The photomultiplier tube 2
Each of a, 2b, and 2c has a light incident surface with a diameter of about 15.24 mm, is a thin cylindrical shape with an axial height of about 10 mm, and is disposed on a concentric circle with respect to the center of the light emitting surface of the scintillator 1.

Incidentally, on the exit surface of the scintillator 1,
Portions not covered by the photomultiplier tubes 2a, 2b, 2c are covered with a reflective material such as Teflon or aluminum thin film having a good light reflectivity, or 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 an epoxy resin, a silicone oil or the like, and both are optically coupled.

FIGS. 2A and 2B show the configuration of a photomultiplier used in the radiation detector of the present invention, wherein FIG. 2A is a plan view, FIG. 2B is a sectional side view, and FIG. Photomultiplier tube 2a,
Reference numerals 2b and 2c denote a stacked type 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 vessel) 10, and photoelectrons emitted from the photocathode 15 are multiplied. An electron multiplier 18 composed of a dynode is provided in the bulb 10. The electron multipliers 18 are arranged in a two-dimensional matrix or a one-dimensional array.
A secondary electron emission surface is attached to the inner surface of each dynode.

Further, the bulb 10 is integrally hermetically sealed from below into a ring-shaped upper portion having an opening of the side tube 11 having an opening of the side tube 11 formed entirely of metal and exposing a substantially cylindrical shape. A transparent light-receiving surface plate 13 having a substantially disc shape and having a photocathode 15 attached to a lower surface thereof, and a flange-type hermetically welded portion 12 which is provided on the outer peripheral surface of the lower end of the side tube 11 and protrudes in the outer axial direction. And a substantially disk-shaped stem 14 hermetically sealed to the hermetic weld 12 by helium arc welding or resistance welding.

A plurality of pins 16 for supplying a voltage to each dynode forming the photocathode 15 and the electron multiplier 18 are vertically inserted through the stem 14 through a tapered hermetic glass 19. And are arranged in a substantially rectangular bottom surface. An anode electrode 20 is mounted on the top of the plurality of pins 16 so as to be connected horizontally. At the center of the stem 14, an exhaust pipe 17 made of metal with a hanging flare is welded by resistance welding and connected to each other.
The photomultiplier tube 2 is connected to an exhaust system including a vacuum pump and the like (not shown). Furthermore, on the outer peripheral surface of the stem 14,
A flange-type hermetic welding portion 21 is provided so as to protrude in the radial direction of the outer shaft, is positioned at the hermetic welding portion 12 of the side tube 11, and is hermetically welded by helium arc welding or resistance welding.

After the exhaust pipe 17 is connected to the exhaust system, the interior of the valve 10 is evacuated, and an alkali metal vapor (not shown) is introduced into the interior of the valve 10 to form the photoelectric surface 15. The hermetic glass 19 has a withstand voltage,
The creeping surface is tapered in consideration of the leak 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 hermetic welding portion 21 of the stem 14 is positioned at the hermetic welding portion 12 of the side tube 11, and these hermetic welding portions 12, 21
Are hermetically welded by helium arc welding or resistance welding. Next, the exhaust pipe 17 is connected to the exhaust system, and the valve 10 is connected.
Is evacuated, alkali metal vapor is introduced into the interior, and the photocathode 15 and the electron multiplier 18
Are deposited and activated. afterwards,
The exhaust pipe 17 is cut from the exhaust system by a pinch-off seal,
It is shortened as much as possible.

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

Here, since the electron multiplier 18 is composed of a stacked dynode, the photoelectrons emitted from the photocathode 15 enter the electron multiplier 18 without being accelerated and focused by the conventional electrodes. Can be. for that reason,
The electron multiplier 18 is formed to be thin and the photocathode 15
The distance between the electron multiplier 18 and the electron multiplier 18 is reduced.

Further, the side tube 11 constituting the valve 10, the hermetic weld portion 12 provided around the outer periphery of the lower portion of the side tube 11, and the hermetic weld portion 21 formed around the outer periphery of the stem 14 are all formed of metal. The two airtight welds 1
2, 21 are hermetically welded by helium arc welding or resistance welding. Therefore, the welding time is shortened and the amount of heating is also suppressed, so that the photocathode 15 and the electron multiplying section 18 are provided despite the photocathode 15 being arranged close to the thin electron multiplying section 18. Deterioration due to oxidation or the like of the deposited reactive alkali metal is prevented.

Accordingly, since the photomultiplier tube 2 is thinned, the radiation detector can be downsized. Therefore, the amount of shielding material such as lead against environmental radiation is reduced, so that the radiation detector can be reduced in weight.

FIG. 3 shows a second embodiment of the radiation detector according to the present invention.
3A and 3B show a configuration of an example, in which FIG. 3A is a plan view and FIG. The second embodiment of the radiation detector according to the present invention includes a scintillator 1 that emits fluorescence from an emission surface with respect to an incident radiation, and is provided on the emission surface of the scintillator 1 to collect the incident fluorescence. A light guide 3 that emits light from the light exit surface, and three photomultiplier tubes (PMT) 2a, 2b that are provided on the light exit surface of the light guide 3 and output a current corresponding to the incident fluorescence. 2c.

The portions of the inner surface and the exit surface of the light guide 3 which are not covered with the photomultiplier tubes 2a, 2b and 2c are made of a reflection material such as Teflon or aluminum thin film having a good light reflectivity or barium sulfate. And the like. The contact surfaces of the scintillator 1, the light guide 3, and the photomultiplier tubes 2a, 2b, and 2c are coated with an epoxy resin, a silicone oil, or the like, and are optically coupled to each other. The scintillator 1 and the photomultiplier tubes 2a, 2b, 2c are configured in the same manner as in the first embodiment.

Next, the operation of the second embodiment will be described.
Outgoing surface of scintillator 1 and photomultiplier tubes 2a, 2b, 2
By interposing the light guide 3 between the light guide 3 and the light incident surface c, the fluorescent light 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, the present embodiment also provides substantially the same operation and effects as those of the first embodiment.

Here, the energy resolution corresponding to the number of photomultiplier tubes (PMTs) obtained by irradiating a scintillator having a diameter of about 40 mm with a gamma ray 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, and various modifications are possible.

For example, in the above embodiments, NaI (Tl) is used as the scintillator, so that it is suitable for measuring γ-rays. However, it is necessary to use one that generates fluorescence corresponding to the radiation to be measured. Thereby, a similar effect can be obtained.

In each of the above embodiments, a stacked dynode is used as the electron multiplier. However, the same operation and effect can be obtained by using an MCP (micro channel plate), a semiconductor element, or the like.

In the above embodiments, the hermetic glass of the photomultiplier tube is tapered. However, when the operating voltage is low, the hermetic glass can have a flat surface, and the diameter of the glass can be increased. it can.

In the above embodiments, the interior of the valve 10 is evacuated by the exhaust system connected to the exhaust pipe 17, but after the formation of the photoelectric surface 15 and the secondary electron emission surface of the electron multiplying unit 18, Performing an indium seal or resistance welding in a vacuum using a transfer device to form an airtight weld 12,
By welding 21, the exhaust pipe 17 can be made unnecessary.

Further, the anode electrode used in each of the above embodiments is replaced with a multi-anode fitted in a substantially rectangular mounting hole penetrating through the stem, and is arranged vertically and horizontally on the multi-anode. By extracting output signals from a large number of vertically mounted anode pins, position detection becomes possible.

In the above embodiments, the light-receiving surface plate is hermetically sealed from below the inside of the side tube. However, the effective area of the photocathode can be enlarged by hermetically sealing it from above. Further, since the atmospheric pressure acts to press the light receiving face plate on the upper portion of the opening of the side tube, the reliability of the valve can be improved while reducing the pressure contact area.

In the above embodiments, the light-receiving surface plate is substantially disk-shaped. By using the light receiving surface plate having the light, the light in the oblique direction can be easily incident without being reflected.

In the above embodiments, a plurality of pins are vertically inserted through the stem through the tapered hermetic glass and are arranged in a substantially rectangular bottom surface. A large disk-shaped tapered hermetic glass is fitted into the substantially disk-shaped mounting hole that has been drilled, and a plurality of pins are directly inserted through the periphery of the bottom surface to penetrate it. And cost can be reduced.

[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 used by being fixed to the body.

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, the fluorescence emitted from the scintillator is collected by the light guide. The light 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 the drawings]

FIGS. 1A and 1B show the configuration of a first embodiment according to the radiation detector of the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a side view.

FIGS. 2A and 2B show a configuration of a photomultiplier used in the radiation detector of the present invention, wherein FIG. 2A is a plan view, FIG.
(C) is a bottom view.

3A and 3B show the configuration of a second embodiment of the radiation detector according to the present invention, wherein FIG. 3A is a plan view and FIG. 3B is a side view.

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

FIG. 5 is a cross-sectional side view showing a configuration of a photomultiplier 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 welded part, 13 ... Light receiving face plate, 14 ... Stem, 15 ... Photocathode, 16 ... Pin, 17 ... Exhaust pipe, 18 ... Electron multiplier
9 ... hermetic glass, 20 ... anode electrode, 21 ...
Accelerating electrode, 22 ... Focusing electrode.

Continuation of the front page (72) Inventor Hiroyuki Kushima 1126-1 Nono-cho, Hamamatsu City, Shizuoka Prefecture Inside Hamamatsu Photonics Co., Ltd. (56) References JP-A-5-72344 (JP, A) JP-A-5-290793 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01T 1/00-7/12 H01J 43/00-43/30

Claims (4)

(57) [Claims] 1. A scintillator which emits fluorescence from an emission surface in response to incident radiation, and a photomultiplier tube which is installed on the emission surface and outputs a current in response to the incident fluorescence. In the radiation detector provided, the photomultiplier tube is formed of metal and has a substantially cylindrical shape and exposes a side tube to form a bulb, and has a light transmitting property by being hermetically fused to an upper opening of the side tube. A substantially disk-shaped light-receiving surface plate, a photoelectric surface which is attached to a lower surface of the light-receiving surface plate, receives the fluorescent light and emits photoelectrons, and a stacked dynode which is provided inside the bulb and multiplies the photoelectrons. An electron multiplier comprising: a flange-type hermetically welded portion provided around the lower periphery of the side tube; and a flange-type hermetic weld made of a metal which is vacuum-sealed to the hermetic weld. Disc-shaped stem and this stem Is inserted through the glass, respectively, a radiation detector, characterized by being composed voltages and a plurality of pins for supplying to said photocathode and said electron multiplying unit. 2. A scintillator for emitting fluorescence from a first emission surface in response to incident radiation, and a scintillator installed on the first emission surface and emitting the incident fluorescence from a second emission surface. A light guide, and a photomultiplier tube installed on the second exit surface and outputting a current in response to the incident fluorescence, wherein the photomultiplier tube is made of metal. A side tube that is formed and exposes a substantially cylindrical shape to constitute a valve, a substantially disc-shaped light-receiving surface plate that is air-tightly fused to an upper opening of the side tube and has light transmittance, and a lower surface of the light-receiving surface plate. A photocathode that is attached, emits photoelectrons upon incidence of the fluorescent light, an electron multiplying unit that is provided inside the bulb and includes a stacked dynode that multiplies the photoelectrons, and a lower outer periphery of the side tube. A flanged hermetic weld around A substantially disk-shaped stem having a flange-type hermetic weld made of metal to be vacuum-hermetically sealed to the weld, and a stem inserted into each of the stems through glass, to the photoelectric surface and the electron multiplier. A radiation detector, comprising: a plurality of pins for supplying a voltage. 3. A scintillator that emits fluorescence from a first emission surface in response to incident radiation, and a scintillator that is provided on the first emission surface and condenses the incident fluorescence to form a second scintillator. A radiation detector comprising: a light guide that emits light from an emission surface; and a photomultiplier tube that is installed on the second emission surface and outputs a current in response to the incident fluorescence. A side tube formed of metal and exposing a substantially cylindrical shape to constitute a bulb; a substantially disc-shaped light-receiving surface plate which is air-tightly fused to an upper opening of the side tube and has light transmittance; A photocathode that is attached to the lower surface of the face plate and emits photoelectrons when the fluorescent light is incident thereon; an electron multiplying unit that is provided inside the bulb and includes a stacked dynode that multiplies the photoelectrons; Flange-type hermetic weld around the lower periphery of the A substantially disk-shaped stem having a flange-shaped hermetic weld made of a metal to be vacuum-hermetically sealed to the hermetic weld at its outer periphery, and each of the stems is inserted into the stem via glass, and the photocathode and the electron multiplier are inserted. And a plurality of pins for supplying a voltage to the unit. 4. The radiation detector according to claim 1, wherein a plurality of the photomultiplier tubes are provided on the emission surface.