JP3168905B2 - Radiation shield, and beam transport tube, beam stopper, and collimator having the shield - 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 shield, a beam transport tube having the shield, a beam stopper,
In particular, radiation shields suitable for radiation shielding technology in accelerators, nuclear fusion, nuclear power, medical equipment, industrial applications, and basic research fields, and beam transport tubes having the shields, It relates to a beam stopper and a collimator.

[0002]

2. Description of the Related Art Conventional radiation shielding designs are implemented using a design theory describing the particle behavior of radiation, such as the Monte Carlo method, because the energy of the radiation to be handled is high and the beam transmission power is strong. In general, an existing shield has a simple configuration in which a radiation source is surrounded by a single-layer or multi-layer absorbent material.

[0003]

In recent years, with the increase in the size of accelerators, nuclear fusion devices, and synchrotron radiation devices, high-energy, high-intensity radiation exceeding conventional levels has been generated. For this reason, these shielding equipment for radiation protection has been increased in size, and higher performance and cost reduction of shielding technology have been required.

[0004] However, the radiation shielding analysis method using the conventional particle handling method has already been advanced,
It is believed that the approach to greatly improving the shielding performance over the extension of the particulate method is accompanied by considerable difficulties.

[0005] The object of the present invention is different from the conventional idea.
A radiation shield capable of improving the performance and economical efficiency of shielding equipment by introducing a new optical method (hereinafter, abbreviated as an optical shielding method) in consideration of the wave property of radiation, and this shielding. Beam transport tube with body,
A beam stopper and a collimator are provided.

[0006]

In order to make the shield function optically, the shield material layer has a multilayer structure, and the following three types of solutions are employed.

(1) A vacuum or gas void layer is provided between the shielding material layers. (2) As the shielding material layer material, a composite component combining a scattering material and an absorbing material is used.
(3) The surface of the multilayer shielding material layer is covered with an absorbent material.

Next, from the viewpoint of practical use of the optical shielding method, it is sufficient to segment the multilayer shield, and as a point to be noted in the production and construction of the shield structure, the potential fixation of the shield is also required. Considering.

Further, as for the main components of the beam application device, the principle of the optical shielding method was applied to the beam transport tube, the beam stopper, and the collimator.

First, the basic concept of a method for optically shielding radiation, which is the origin of the present invention, will be described by taking high-energy X-ray shielding as an example. The type of radiation is X-ray,
There are electron beams, heavy ion beams, neutron beams, and α-rays, β-rays, and γ-rays emitted from radioactive materials, but most of the following description will take X-rays as typical examples of radiation and will be described in detail.

When an X-ray beam passes through a shielding material layer, collision with the shielding material causes X-ray absorption, scattering and transmission phenomena. Focusing on the scattering phenomenon among these phenomena,
As shown below, it is possible to replace the particle image on the left side with the optical image on the right side.

Forward scattered X-ray energy flux ⇔ Refracted transmitted light Back scattered X-ray energy flux 反射 Reflected light It has been noticed for the first time that a change in the idea that shielding design is possible based on this optical analogy is realized by the present invention. It is the beginning.

Next, in order for the optical shielding method to function effectively, it is important to select a scattering substance which controls the reflection and refraction phenomena and an absorbing substance which controls the absorption phenomenon. The rate at which these phenomena occur varies depending on the type of substance and the X-ray energy. The X-ray energy range used in a CT device, a synchrotron radiation device, or the like to which the present invention is applied is several keV to several Me.
V. Since the main cause related to the passage of X-rays in this region is the Compton effect, the relationship between the ratio of the true scattering and absorption of the shielding material and the X-ray energy can be obtained by calculation. It is possible to select with an absorbent material.

For example, lead (Pb) or tungsten (W), which is a heavy element, can be handled as an absorbing substance at an X-ray energy of about 1 MeV or less. On the other hand, iron (Fe), which is a medium amount element, shows a function as a scattering substance at about 70 to 80 keV or more, but becomes remarkable as an absorbing substance in an energy region below that. Further, as the element becomes lighter, the transition point of the X-ray energy from the function as a scattering substance to the function as an absorbing substance is about 20 to 30 keV for aluminum (Al) and about ten and several keV for carbon (C). It can be seen that it gradually decreases. By understanding these properties, it becomes possible to select a scattering substance and an absorbing substance suitable for the equipment to be used. It should be noted that the classification of the scattering substance and the absorbing substance is not a property inherent to the element.

[0015] The optical shielding method is a method for improving the shielding performance by effectively making the multilayer shield have optical characteristics such as radiation reflection and absorption, and is described below. The operation of is described.

In the radiation shield having a multilayer structure according to claim 1, a part of the incident radiation energy is reflected by the material layer by a scattering phenomenon due to the provision of a vacuum layer or a gas gap layer between each shielding material layer. Released into the layer. Since the air gap is a medium capable of carrying radiation energy at the speed of light or the speed of particles, the role of the air gap layer is to very quickly disperse and average the scattered radiation energy throughout the shield. I can say.

[0017] Also, the function of each shielding material layer constituting material of the multilayer shield built according to Claim 1, firstly, by using a scattering material improves the reflective properties of the radiation beam, emitted into the air gap layer In addition to increasing the amount of radiation energy to be emitted, it serves to reduce radiation energy due to collisional scattering. Next, by selectively using the scattering / absorbing composite component, the reflection / absorption characteristics of radiation of the shielding material layer can be controlled to be moderate, so that optimization can be performed to meet the specification of the target product. In addition, a small amount of the absorbing substance contained in the composite component functions to efficiently capture low-energy scattered radiation.

[0018] constitutes an outermost layer of the multilayer shield of claim 2, for the work of the absorbent material surrounding the outer surface, confining the low-energy radiation inside shield, reducing the amount of radiation leaking out Have a role.

The shielding material segment according to the third aspect is an element part of a shielding structure in which the function of the above-mentioned optical shielding method is integrated, and the shielding equipment is constructed by combining these components. Repair, remodeling and disposal are easy.

According to a fourth aspect of the present invention, there is provided a method for fixing a potential of a shield,
By commonly grounding the conductive material constituting each layer, the built-in material of the shield functions to prevent a failure due to the occurrence of a storage phenomenon having a floating potential. When a magnetic material, a conductive material, or an insulating material is appropriately selected as a material of each shielding material layer according to the purpose of use, the material can also serve as a magnetic shield and an electrostatic shield.

[0021] The use of the multilayer shield in the beam transport tube according to claim 5 , the beam stopper according to claim 6 , and the collimator according to claim 7 , which is an element device of the radiation generation / utilization apparatus, This is an application example of the principle of the optical shielding method for improving performance.

[0022]

FIG. 1 shows a first embodiment of an optical shielding method relating to an X-ray shielding body having a multilayer structure. As shown in the figure, an X-ray beam 2 emitted from an X-ray source 1 is shielded by an optical shield 3 surrounding the X-ray beam. The optical shield 3 includes an interlayer gap 4, a multilayer shielding material layer 5,
And an absorbent material layer 6 covering the outer surface.
By selecting a material having a good scattering property as the material of the shielding material layer 5, the reflected scattered X-ray beam is repelled backward (toward the radiation source), and the energy is attenuated by multiple collisions in the interlayer gap 4 to reduce the energy. Can be efficiently captured in the material layer. In the vicinity of the outermost absorbent material layer 6, the energy of the scattered X-rays is also considerably reduced, so that the thickness of the material layer can be saved. The thickness of each shielding material layer 5 is considered to be about 1 mfp (mean free path) of a typical design X-ray energy (for example, incident X-ray energy).

FIG. 2 shows an example of the detailed structure of the optical shield.
The function is also described. First, the shielding material first layer 5a
Is an example using a single element constituent material, and usually uses a scattering material. However, when it is necessary to reduce the background radiation dose in the internal space on the radiation source side, an absorptive substance may be used as the first layer material. Next, what is shown in the shielding substance second layer 5b is an example in which a two-layer composite material of a scattering / absorbing substance is used. A scattering material plate is used on the X-ray incidence side to increase the reflection efficiency to the interlayer gap 4, and
X-rays that have been multiply scattered are captured by bringing a thin absorbing material plate into close contact later.

By employing the two-layer composite material, it is possible to greatly improve the shielding performance and to save the amount of the shielding material, as compared with the case where a single element material using a scattering material is used. It has been proved theoretically and experimentally (described later) in the course of consideration of the present invention. Next, the shielding material third layer 5
What is shown in c is an example of use of a three-layer composite component of a scattering / absorbing / scattering substance. This is characterized in that the reflection efficiency to the interlayer gap 4 at both ends of the composite component is increased.

The porous scattering / absorbing material 7 shown below the interlayer space 4 in FIG. 2 is for reflecting and capturing X-rays having reduced energy due to multiple reflections in the interlayer space 4. Is also one of the embodiments of the void layer installation according to the first aspect. In addition, the surface of the shielding material layer is made uneven so that X
Attempts to increase the line reflection efficiency are also within the scope of the present invention.

FIG. 3 shows an embodiment of the shielding material segment. The shielding material segment 8 is formed by integrating the above-described optical shielding body, in which a multi-layer shielding material layer 5 with an interlayer gap 4 is surrounded by an absorbing material 6. FIG. 3 shows an example in which a large shielding wall is formed by combining a large number of shielding material segments 8. Each shielding material segment 8 uses a filler 9 of an absorbing substance to prevent radiation leakage.

Such a shielding material segment 8 can be manufactured as a high-quality shielding board by combining a plate-like shielding material and producing it in a factory by the same method as that for building materials. In addition, the adoption of a detachable shield board has advantages such as easy repair, modification, and disposal of the shield facility. When the energy of the radiation is low, the thickness of the shielding material layer 5 becomes thin. Therefore, the shielding material segment 8 can be manufactured as a shielding sheet or a shielding tape combining a polyethylene sheet and an Al foil sheet. These are effective for radiation protection from gaps of radiation equipment.

On the other hand, in connection with the method of manufacturing the composite component material of the shielding material layer 5, not only a mere combination structure of a plate or a sheet material but also, for example, Al or F
Use of a multilayer composite component manufactured using the latest thin film lamination technology, such as vapor deposition of a thin film of e, also falls within the scope of the present invention. In addition, the conductive material constituting the shielding material layer 5 or the like incorporated in the shielding structure has a floating potential if left as it is, and may cause a trouble such as occurrence of a discharge phenomenon due to storage of electricity. This obstruction can be prevented by grounding each conductive material in common. This is also within the scope of the present invention.

FIGS. 4 to 6 show examples of application of the optical shielding method to element devices of a radiation generating / using apparatus.

First, FIG. 4 shows a beam transport tube 1 such as an accelerator.
This is an example applied to 0. The beam transport tube 10 has a double tube configuration in which the inside of the inner tube is evacuated, and a high-energy X-ray or charged particle beam 11 runs inside the tube. A part of the beam diverged while the X-ray / particle beam travels in the transport tube collides with the inner tube and scatters and emits X-rays. By setting the space between the outer tubes of the transport tube 10 to the above-described interlayer gap 4, shielding material layer 5, and absorbent material 6, the beam transport tube 10
Can also serve as a radiation shield.

FIG. 5 shows an example in which the present invention is applied to a beam stopper for X-rays or the like having a high energy exceeding 1 MeV.
In this case, since the material penetrating power of the incident X-ray beam 2 is strong,
Only in front of the beam irradiation surface, an absorptive shielding material 12 of a heavy element such as Pb or W is used to reduce the transmission power of incident X-rays at a short distance. The side gaps deviated from the beam irradiation surface and the scattered X-rays with reduced energy at the terminal end employ the above-described interlayer voids 4, shielding material layers 5, and absorptive materials 6 in the outer peripheral portion of the main force. The overall size of the stopper is reduced.

FIG. 6 shows an example applied to a collimator of an X-ray CT apparatus. High-speed electron beam 13
To generate high-energy X-rays. A collimator 16 is provided to emit the high-energy X-ray beam 2 in a specified direction. This collimator 16
Must also shield high energy transmitted X-rays,
An absorptive shielding substance of a heavy element such as b or W is used.
On the other hand, in order to shield the scattered X-rays, the periphery of the collimator 16 is covered with the above-described interlayer gap 4, the shielding material layer 5, and the absorbing material 6, thereby forming an efficient shielding system as a whole.

Hereinafter, experimental examples will be described. In order to verify the principle of the optical shielding method, the following experiment was performed.

FIG. 7 shows the configuration of the experimental system. A high voltage of 150 kV is applied to the X-ray tube of the X-ray generator 17,
An X-ray beam 2 having a maximum of 150 keV was generated and incident on the optical shield 3. The optical shield 3 includes an interlayer gap 4, a multilayer shielding material layer 5, and an absorbing material layer 6 covering the outer surface. In order to measure the dose of the X-ray beam 2 having passed through the optical shield 3, a PN junction type silicon semiconductor detector 18 and an X-ray film 19 were arranged.

As the material of the shielding material layer 5, Al was selected as the scattering material and Fe was selected as the absorbing material, and the composite component was an Al / Fe composite component. The thickness of each shielding material layer 5 was 1 mfp at an X-ray energy of 150 kV.

First, using a three-layer pure Al shield,
FIG. 8 shows the results of the void effect confirmation test. As the Al shielding material layer was brought into close contact with the interlayer gap, the X-ray dose rate passing through the shielding body was reduced, and it was confirmed that there was a void effect.

Next, a test for confirming the optical shielding effect of the multilayer shielding body was carried out by examining a pure Al shielding body, a pure Fe shielding body,
1 / Fe composite shield (1st layer is pure Al layer)
We carried out about kind.

Table 1 shows the measured values of the X-ray dose rate ratio after passing through various shields, measured with a semiconductor detector and an X-ray film, and theoretically calculated values calculated in advance. These measurement results were in good agreement with the results of the theoretical prediction, demonstrating the effectiveness of the optical shielding effect. In addition, good scattering performance of the scattering / absorbing composite component, which is one of the features of the present invention, was also clarified.

[0039]

[Table 1]

[0040]

According to the present invention described above, unlike the conventional shielding method based on particulate handling, a multilayer shielding body including a void having an optical characteristic such as reflection and absorption of radiation is employed. Therefore, the radiation energy incident on the shield is dispersed throughout the shield while lowering the energy by means of scattering materials and voids, and then absorbed and confined by an absorbent material to minimize leakage to the outside. It is possible to improve the shielding performance over the conventional method by adopting this optical shielding, and the range of choice of the type and arrangement of the shielding substance is expanded,
We can expect improvement of economic efficiency.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a radiation shield of the present invention.

FIG. 2 is a partial sectional view showing a detailed structure of FIG.

FIG. 3 is a side view showing a partial cross section of a shielding material segment in which a plurality of optical shielding bodies are combined, as one of application examples of the radiation shielding body of the present invention.

FIG. 4 is a perspective view showing a beam transport tube employing the radiation shield of the present invention.

FIG. 5 is a sectional view showing a radiation beam stopper employing the radiation shield of the present invention.

FIG. 6 is a sectional view showing an X-ray CT apparatus collimator employing the radiation shield of the present invention.

FIG. 7 is a sectional view showing an experimental system for verifying the principle of the optical shielding method of the present invention.

FIG. 8 is a characteristic diagram showing the results of a test for confirming the void effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray source, 2 ... X-ray beam, 3 ... Optical shield, 4 ...
Interlayer gap, 5: shielding material layer, 6: absorbing material layer, 7: porous scattering / absorbing material, 8: shielding material segment, 9: filler, 10: beam transport tube, 11: charged particle beam, 12
... absorbing shielding material, 13 ... electron beam, 14 ... target material, 16 ... collimator.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21F 3/00 G21K 1/02

Claims (7)

(57) [Claims] 1. A radiation shield comprising a multilayer shielding material surrounding a radiation source, wherein each of said shielding material layers is made of a radiation scattering material or an absorption material.
Single-element constituent material, radiation scattering material and absorbing material
A radiation shield formed of a composite material having a combination of qualities and having a vacuum or gas gap layer between the respective shield material layers. 2. The radiation shield according to claim 1, wherein the outermost layer of the multilayer shielding material layer is made of an absorbing material. 3. A radiation shield comprising a multilayer shielding material surrounding a radiation source, wherein each shielding material layer is formed by combining a number of shielding material segments, and each of the shielding material segments Is
A radiation shield, wherein a vacuum or gas void layer is provided between the multilayer shielding material layers, and the multilayer shielding material layer is formed by covering the periphery of the multilayer shielding material layer with an absorbing material. 4. The method according to claim 1, wherein when each of said shielding material layers is formed of a conductive material, each conductive material is commonly grounded. Radiation shield. 5. A double tube structure comprising an outer tube and an inner tube, wherein the inside of the inner tube is evacuated, and a high energy X-ray or a charged particle beam runs through the inner tube. Alternatively, in a beam transport tube in which a part of a beam diverged while a charged particle beam travels collides with the inner tube to scatter and emit X-rays, a space between the outer tube and the inner tube is between multilayer shielding material layers. A beam transport tube, which is provided with a vacuum or gas void layer and is formed of a radiation shielding material in which a multilayer shielding material layer is covered with an absorbing material. 6. A radiation absorbing shielding material is provided on a beam irradiation surface to capture and absorb a high-energy primary X-ray or particle beam, and to capture and absorb a secondary beam which collides and scatters with the absorbing material. In the beam stopper having a double structure provided on the side surface portion deviated from the beam irradiation surface, the outer peripheral portion of the terminal end portion, the side portion deviated from the beam irradiation surface, the outer peripheral portion of the terminal end portion. The shielding material layer is provided with a vacuum or gas gap layer between the multilayer shielding material layers, and is formed of a radiation shielding material in which the multilayer shielding material layer is covered with an absorbing material. And beam stopper. 7. A collimator for colliding an electron beam with a target material and emitting a generated high-energy X-ray beam in a specified direction, wherein a vacuum is provided around the collimator between the multilayer shielding material layers.
Alternatively, a collimator provided with a gas void layer and covered with a radiation shielding material formed by covering a multilayer shielding material layer with an absorbing material.