JP2009209437A - Hollow sintered metal compact, bubbler for neutron source liquids metallic targets using it, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bubbler for a neutron source liquid metal target capable of withstanding an impact erosion damage because a macroscopic negative pressure accompanying the discontinuous deformation at the liquid/solid boundary along an inner wall of a vessel during rapid deformation of a vessel structural material from a difference in acoustic impedance of a liquid/solid metal takes place and so-called cavitation occurs, and also, the impact erosion damage composed of micropit groups are generated at the solid boundary subjected to the microscopic damage accompanying cavitation breakdown. <P>SOLUTION: A raw material for hollow which substantially diffuses or volatilizes by sintering is used and the raw material for hollow is removed by sintering. The set hollow metal sintered compact is obtained by press and sintering steps. The hollow metal sintered compact is installed as the bubbler in the prescribed position of the mercury target vessel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid metal target for a neutron source in which a high-energy proton beam is incident on a liquid metal to generate high-intensity pulsed neutrons by a nuclear fragmentation reaction and the liquid metal itself is used as a coolant.

  First, Japanese Patent Laid-Open No. 6-174970 discloses an invention by the present applicant as “molybdenum pipe and manufacturing method thereof”. In this invention, in order to provide inexpensively a molybdenum pipe that can be used as a ferrule of an optical connector, a weight that fixes one end of a nylon thread is fixed to the inner bottom part of the rubber, and an upper end of the nylon thread is fixed to a fixed part. The rubber is filled with molybdenum powder, the rubber is closed with a die, and this is hydraulically pressed to obtain a pressed body. The press body is then baked to remove the nylon thread to form an inner hole and sintered. After this, a method for obtaining a molybdenum pipe by pipe drawing is shown. In this invention, when the hydraulic press is performed, the rod is bent due to the shrinkage of the rubber, and a straight hole cannot be obtained. In addition, a plurality of holes essential for use as a bubbler cannot be prepared.

  For example, Japanese Patent Laid-Open No. 2001-259753 describes a method for performing press working on the production of a hollow part as “a method for producing a hollow part”. When manufacturing a hollow part, a hollow metal material filled with an incompressible fluid in a hollow interior is pressed into a predetermined outer shape, and then the incompressible fluid inside the hollow is discharged. . As a result, the material flow mechanism of the hollow metal material during pressing is the same as that of the solid material, and the fluid that is the internal filler is much more fluid than the solid such as metal due to its characteristics. . In the present invention, the material requires a lot of fluidity and cannot be applied when press working cannot be applied.

  According to Japanese Patent Laid-Open No. 2006-297412, “for manufacturing hollow-shaped parts”, a forging material in which an internal pressure-holding metal is inserted into a cylindrical member made of steel or a bottomed cylindrical member is forged to form a predetermined outer shape. After that, a method is shown in which the forged product is heated to a temperature equal to or higher than the melting point of the internal pressure holding metal to melt and remove the internal pressure holding metal to obtain a hollow part made of steel. In this case, it is necessary to melt and remove the internal metal. It can be easily imagined that hole clogging occurs when trying to obtain a narrow diameter.

  Further, the technical contents shown as “fine deep hole machining method” in Japanese Patent Laid-Open No. 9-285905 and “ultra fine pipe electrode and electrode device for electric discharge machining” in Japanese Patent Laid-Open No. 2000-94219 are used to machine a small number of highly fine holes. This technique is not suitable for processing a large amount of holes as a bubbler in terms of time and cost.

  As for the bubbler, a bubbler using a sintered porous metal is used in “bubbler” of Japanese Patent Application Laid-Open No. 2002-083777. JP 2001-131754 discloses a bubbler for vaporizing a thin film deposition sample. Neither invention is a technology that can be applied to a liquid metal for a spallation neutron target capable of controlling the bubble shape and number.

In recent years, the importance of neutron beam research has been increasing rapidly, and plans for next-generation spallation neutron sources are the United States (SNS program), EU (ESS program), and Japan (High Energy Agency-JAEA integrated program). It is being advanced in. The three major plans in the world plan to inject a proton beam of several MW, which has not been experienced yet, into the target in order to obtain a high-intensity neutron flux. The energy of the proton beam here is 1 to 3 GeV. is there. In general, a target of several MW class has a heat generation in the target reaching several hundred MkW / m ³ , so that liquid mercury that can be used as a coolant can be used in combination with the current method of cooling a solid metal with water. Adoption has been decided.
Figure 1 schematically shows the environment where the liquid mercury target is exposed. When a MW-class pulse proton beam enters the mercury target, an expansion wave is generated in the liquid mercury due to sudden heat generation, but the expansion wave becomes a pressure wave and propagates through the mercury at a speed of sound. Then, a shocking load is applied to the container wall surface. Also, due to the difference in acoustic impedance between liquid / solid metal, a macroscopic negative pressure accompanying discontinuous deformation occurs at the liquid / solid interface along the inner wall of the container during rapid deformation of the container structural material. This negative pressure establishes a condition that causes so-called cavitation near the liquid interface, so impact erosion damage consisting of micropits, that is, pitting damage, at the solid side interface that has received microscopic local impact due to cavitation bubble collapse. Occurs. Since the pulsed proton beam is incident at 25 Hz, impact erosion is a factor that determines the lifetime of the solid metal container. Therefore, in order to improve the operational stability of the neutron source and the durability of the target vessel, it is important to understand the impact erosion behavior, design the vessel structure that accurately evaluates and considers damage, and develop damage suppression technology. is there.
JP-A-6-174970 JP 2001-259753 A JP 2006-297412 A JP 9-285905 A JP 2000-94219 A JP 2002-083777 A JP 2001-131754 A

  Although high-power neutron sources are being developed worldwide, liquid mercury has begun to be used as a target material for generating neutrons because it is advantageous for removing heat generated by the incidence of proton beams. The US SNS (Spallation Neutron Source) started operation in 2006 with an actual mercury target.

  In Japan, the construction of a pulsed neutron source using a liquid mercury target is advancing at the J-PARC (Japan Proton Accelerator Research Complex) facility for generating and using proton beams. Figure 1 schematically shows the environment where the liquid mercury target is exposed. When a MW-class pulse proton beam enters the mercury target, an expansion wave is generated in the liquid mercury due to sudden heat generation, but the expansion wave becomes a pressure wave and propagates through the mercury at a speed of sound. Then, a shocking load is applied to the container wall surface. For this reason, control technologies for ensuring the soundness and long life of the structure including the coexistence with structural materials in liquid mercury are currently being researched and developed. One technique for ensuring structural integrity is to prevent material corrosion and impact erosion damage. Impact erosion damage is predicted to cause significant damage as pitting damage. (Masatoshi Futagawa, “Shock Corrosion by Proton Beam-Excited Pressure Wave in Pulsed Neutron Source Mercury Target” Journal of the Atomic Energy Society of Japan, Vol.47, No.8 p14-19 (2005)) Develop innovative technology to absorb shock waves. It has been foreseen since the 1990s that shock absorption by bubbles has been effective in preventing damage to pitting (K. Skala and G. Bauer, “ON THE PRESSURE WAVE PROBLEM IN LIQUID METAL TARGETS FOR PULSED SPALLATION NEUTRON SOURCES ”, PSI Proceedings 95-02, Vol.II, pp.559-571 (1995cc)).

  Due to the difference in acoustic impedance of liquid / solid metal, macroscopic negative pressure accompanying discontinuous deformation occurs at the liquid / solid interface along the inner wall of the container during rapid deformation of the container structural material. Because of this negative pressure, so-called cavitation conditions are established in the vicinity of the liquid interface, so impact erosion damage consisting of micropits, that is, pitting damage, is caused at the solid side interface that has received microscopic local impact due to cavitation collapse. Arise. Since the pulsed proton beam is incident at 25 Hz, impact erosion is a factor that determines the lifetime of the solid metal container. Therefore, in order to improve the operational stability of the neutron source and the durability of the target vessel, it is important to understand the impact erosion behavior, design the vessel structure that accurately evaluates and considers damage, and develop damage suppression technology. is there. Although it has been foreseen that the bubble is effective in absorbing the shock, the generation method, introduction method, and appropriate input amount have not been shown. In the present invention, the introduction method and the appropriate amount were considered, and the lifetime and capacity of the target were optimized.

  In the present invention, a hollow material that substantially diffuses or volatilizes by sintering can be used, and the hollow material can be removed by sintering to obtain a hollow metal sintered body set by pressing and sintering processes. (FIG. 2). A bubbler characterized by the use of a hollow metal sintered body can provide a bubbler with a small diameter and an external shape that has never been designed before, and enough bubbles to absorb shock waves. Can be obtained. Thereby, the target life can be extended and the operational stability of the neutron source can be improved. In addition, as shown in FIG. 3, a plurality of hollow materials can be arranged in an arbitrary arrangement, so that it is possible to freely design a bubbler hole arrangement, to generate a flow in a certain direction, or to generate a spiral bubble. By using these, it is possible to establish a highly reliable liquid metal target system that has a long life and little container damage due to impact erosion damage.

  Particularly, the hollow metal sintered body used as the bubbler of the present invention has a through-hole having a hole diameter of φ100 μm or less, a length of 3 mm or more, and an aspect ratio (length / hole diameter) of 30 or more. I have it. In the present invention, the hole diameter of the aspect ratio is a hole diameter obtained by an arbitrary cross section perpendicular to the discharge portion direction from the gas introducing portion of the bubbler, and is a value obtained by averaging the hole diameters of the respective holes, When the cross section is other than a circle, the diameter when converted to a circle having the same area is used. The length of the aspect ratio is the shortest distance from the gas inlet to the outlet of the bubbler (corresponding to the thickness of the bubbler). When the hollow hole has undulations or bends, that is, the length is substantially long. Even in this case, the aspect ratio is 30 or more.

According to the present invention, a bubbler having fine holes can be obtained. Moreover, the target for neutron sources using the bubbler can be constructed.
Here, the bubbler thus obtained can be produced not only in a straight direction in the length direction but also in an arbitrary shape. This is due to the fact that glass fibers having a free shape can be produced. Thereby, the bubbler which implement | achieved the combination of the hole which made bending, the wave | undulation, direction, etc. for controlling the flow of a bubble arbitrary is producible. Further, the number of holes is not substantially limited. And it is very simple and easy to manufacture, and if it is manufactured by machining, it is possible to easily realize very complicated and expensive processing. In addition, it is possible to produce a unique bubbler at a low cost, which is not possible with conventional manufacturing methods, such as holes that are not constant in diameter and that have a stepped shape, that is, holes with different inner diameters connected to each other. It becomes possible.

  In the present invention, liquid mercury for a neutron source has been mainly described. However, as a method for manufacturing a hollow member, it can be widely used industrially, and a bubble of a small size that has not been possible so far as a bubbler. Can be formed. In addition, in this explanation, the explanation is limited to only the mercury target that is under construction in the next stage, but it can be used for liquid targets such as lead bismuth.

  By utilizing the diffusion or volatilization by sintering according to the first invention of the present application, pressing a material having a melting point lower than the melting point of the sintered metal, and removing the hollow material by sintering. According to the hollow metal sintered body obtained by forming two or more hollow holes in the process of pressing and sintering, it is possible to industrially stabilize a die that was impossible by industrial machining. It becomes possible to produce.

  A metal characterized in that, in the hollow metal sintered body according to the second, third, and fourth inventions of the present application, a hollow shape and an arrangement thereof are arbitrarily set, and a minute hollow hole that enables manufacturing processing is provided. According to the sintered body, it is possible to produce a hollow metal that has a small diameter and that can be freely designed.

  According to the fifth aspect of the present invention, a bubbler of a spallation neutron source liquid metal target characterized in that a hollow body is cut out and gas is passed as a through hole. A bubbler whose external shape can be freely designed can be obtained.

  According to the bubbler for a spallation neutron source liquid mercury target according to the sixth invention of the present application, characterized in that the hole diameter is a diameter of φ100 μm or less and a length of 3 mm or more. A bubbler capable of obtaining effective bubbles while maintaining the structure as a container can be produced.

  According to the seventh aspect of the present invention, a bubbler for a spallation neutron source liquid metal target characterized in that 90% or more of the generated bubbles are bubbles of 100 μm or less. Bubbles having an effect of absorbing shock can be generated.

  According to the eighth aspect of the present invention, a bubble structure for a spallation neutron source liquid target characterized by arranging a hollow structure with 200 or more holes is generated. can do.

  The target container (FIG. 7) does not become large, and the dimensions of the container excluding the piping part are approximately 800 mm in length, approximately 500 mm in width, and approximately 100 mm in height. In the present invention, it is important that bubbles be 0.1% by volume or more in mercury. This is determined by the mercury flow rate and the gas injection flow rate, and the gas injection flow rate is a parameter (gas injection flow rate) that determines the size of the bubble. If it is low, a fine bubble is formed). The number of holes of 200 or more arranged in the hollow structure is the number necessary for injecting 0.1% by volume of 100 μm bubbles. If the mercury flow rate in the target container increases, the number of holes needs to be increased, but there is no problem if the number of holes is 200 or more. Note that there is no existing bubbler that can inject a 100 mm bubble into a liquid metal at 0.1% by volume or more.

  According to the ninth aspect of the present invention, the liquid target bubbler is characterized in that, among the metals in the liquid after passing through the bubbler, the bubble has a volume of 0.1% by volume or more. Bubbles can be generated that lead to bubble construction.

  A bubbler for a spallation neutron source liquid metal target according to the tenth invention of the present application can be easily formed into an arbitrary shape around the hole of the bubbler and can easily control the bubble shape as compared with the case of a planar shape. According to this, it is possible to generate a bubble leading to the construction of a bubble having a shock absorbing ability.

  According to the eleventh aspect of the present invention, two or more bubblers are arranged, and the arrangement is other than the proton beam incident surface, and the bubbler for the spallation neutron source liquid metal target on the upstream side of the liquid metal is efficiently bubbled. It is possible to introduce an effective shock absorption, which is completely different from the arrangement at one place.

  According to the twelfth and thirteenth inventions of the present invention, there is provided a bubble target for a spallation neutron source liquid target having a lifetime of 2000 hours or more, characterized by containing 0.1% by volume or more of gas in mercury in the target container. According to the present invention, it is possible to extend the replacement work that has been frequently performed in the past, and to reduce the radioactive waste as a result in addition to the direct effects brought about by the extension of the lifetime.

Hereinafter, the present invention will be described in more detail.
Example 1
In FIG. 4, the press process in preparation of a hollow metal sintered compact is shown. A standard powder of molybdenum powder having an average particle diameter of 5 μm was used. Here, 10 g of molybdenum powder is put into a φ25 mm mold, preliminarily pressed with a punch at 5 MPa, and the punch is once extracted to obtain a flat surface. In the preliminary press, the smaller the pressure, the less likely the interface cracks with the high press pressure in the next step, and for example, only a punch may be placed. The rest can be arbitrarily set according to the required degree of straightness of the hole. A hollow material corresponding to the target hole diameter is disposed on the flat surface. For example, in any of nylon yarns φ0.2 mm, φ0.3 mm, quartz glass, and Pyrex φ0.1 mm glass, a hole diameter as a bubbler could be secured as an experiment described later (FIG. 5). Further, after preliminary pressing, an equal amount of 10 g of powder was added and pressed at 200 MPa. Thereafter, when sintering was performed in hydrogen at 1800 ° C. for 10 hours, a density of 9.8 g / cm ³ , which is 95% or more of the theoretical density, was obtained. In any case, the above-mentioned material disappeared by sintering, and the through-hole was secured over the entire length of the hole embedded so as to satisfy the use condition as a bubbler. The hole diameter and length were the same as the sintered shrinkage of the pressed body. The holes thus prepared could be used for bubbling. When a soft material such as nylon was selected, the hole was flattened into an oval shape by the press pressure, but this did not hinder the use as an actual bubbler. Further, if an isotropic means such as CIP is used as a pressing method, deformation of the hole can be prevented. By arbitrarily cutting out from the hole thus obtained, it can be used as a bubbler. This means that a nozzle having an arbitrary shape can be secured at an arbitrary position by applying the powder metallurgy method even when producing a nozzle having a complicated shape. Such a hole having an aspect ratio of 30 or more cannot be manufactured by machining with the current technology.
(Example 2)
Similar results could be obtained using stainless steel. Similarly, a hole of a predetermined shape can be prepared by pressing 20 g of powder into a φ25 mm die in the same process as in Example 1 at 124 MPa, 581 MPa, and 678 MPa, and embedding φ0.1 mm glass fiber. (FIG. 6).

  At a press pressure of 124 MPa, a density of 68.5% was obtained by sintering at 1000 ° C. for 1 hour at a press body density of 59.4%. After pressing for 2 hours at 67.34% and 1200 ° C for 1 hour after sintering for 1 hour at 1030 ° C in a pressed body having a pressed body density of 59.1%, the third time at 90.81% and 1300 ° C for 1 hour. A density of 95.4% was obtained after sintering.

  Also, after pressing for the second time of 87.06% and 1200 ° C for 1 hour at a press body density of 74.77% and 1030 ° C for 1 hour at a pressing pressure of 581 MPa, 96.10% and 1300 ° C for 1 hour, respectively. A density of 97.65% was obtained after the third sintering of time. Further, the press body density is 76.84% at a pressing pressure of 678 MPa, 89.24% by sintering for 1 hour at 1030 ° C., 97.52% after 1 second sintering at 1200 ° C., 1 at 1300 ° C. A density of 97.60% was obtained after the third sintering of time. From these results, it was found that the press body pressure has a correlation with the sintered density and is greatly related to the initial density increase.

In the case of Mo, a pressed body (pressing pressure 387 MPa), which had a density of 70%, became a density of 92% by sintering at 1875 ° C. for 1 hour.
As described above, the bubbler can be manufactured regardless of the material as long as it is a material that can be processed by powder metallurgy.
(Example 3)
With the method as described above, even in a single-screw mold press, it becomes possible to open a plurality of holes by arranging a number of fibers, and more holes can be formed by pressing in multiple layers. Can be opened. For example, 200 holes can be easily prepared by stacking 10 layers of fibers arranged in one layer so that the holes are parallel to each other by filling and pressing a small amount of powder.

CIP can be used when making more complicated holes. Many and arbitrary shapes can be arranged, and bubbles can be generated in a spiral shape.
Moreover, the hollow hole can be produced not only in a straight direction in the length direction but also in an arbitrary shape. This is because not only straight glass fibers but also free shapes can be produced. Thereby, the bubbler which implement | achieved the combination of the hole which made the bending, the wave | undulation, direction, etc. for controlling the flow of gas, ie, a bubble, can be produced. Further, as described above, there is no limit on the number of holes. In addition, manufacturing is extremely simple and easy, and shapes that are impossible by machining are industrially possible. Here, the diameter is not constant, which is impossible with the conventional manufacturing method, and any shape such as a step, taper, barrel, or drum shape, and a hole with any inner diameter connected can be made. It is possible to produce a characteristic metal hollow body that has not been made so far.

  Moreover, since a hollow state cannot be obtained as a through-hole at the stage of pressing and sintering, it can be cut into an arbitrary shape by a technique that does not crush holes. For example, shape processing to a bubbler in a state in which a through hole is secured can be performed by wire electric discharge machining or the like. Further, the bubbler thus obtained can be welded or attached as a flange to an effective location of the target stainless steel container. In this way, the connection with the gas introduction part is made possible, and helium gas is introduced.

As shown in the above-described embodiments, these bubblers exhibit an effect in a state where there are sufficiently many holes, and it is effective to perform bubbling with 200 or more holes. This bubble can obtain an impact buffering effect with a bubble of 0.1% by volume or more, can reduce damage to the target container, and can have a life of 2000 hours or more. If the bubble is introduced in an amount of 0.01% by volume or less, the impact absorbing effect cannot be obtained. In particular, the size of the bubble is important, and a state in which most bubbles of 100 microns or less occupy is necessary. If the spallation neutron source liquid metal target has no more than 200 holes, the volume effect cannot be obtained sufficiently.
Example 4
By using the bubbler produced by the above process, the wear on the target container is significantly reduced.

By introducing helium gas as the introduction gas, shock waves can be effectively reduced without deteriorating mercury.
On the other hand, since mercury has poor wettability with the bubbler material, the gas discharged from the bubbler adheres to the bubbler material, making it difficult to control the bubble shape. The group of inventors of the J-PARC Center investigated the behavior of gases and gas bubbles in mercury by experiments and numerical analysis, and optimized the bubbler profile by utilizing the mercury flow in the mercury target. The bubble shape can be controlled.

  If the area around the hole of the bubbler is flat, it cannot be expected to tear off the gas due to the flow of mercury, but the hollow metal sintered body produced in this process can be easily formed into an arbitrary shape. Can be processed. By making the mercury flow rate 5 m / s and the bubbler outer shape convex, it becomes possible to introduce 100 μm bubbles into the mercury. Since the bubbler produced by the above steps can be easily formed into an arbitrary shape, it can be processed into an optimum bubbler shape.

  7 and 8 show the bubble trajectory obtained by the numerical analysis and the position of the bubbler. By installing bubblers at the two locations shown in Fig. 7 and Fig. 8, it is possible to efficiently send bubbles to the vicinity of the proton beam entrance surface where the target vessel of the mercury target is heavily worn and to the position where the generated pressure wave is high. It is. Since the bubbler produced in this step can be installed at any position by welding, flange connection, or the like, the bubbler can be installed at an optimum position in the mercury target.

  That is, as shown in FIG. 7, the bubbler of the present invention is installed at the position of the container opening away from the side on which the proton beam of the mercury target container is incident, and after the liquid mercury has passed through this bubbler, the proton When the beam is incident and the inside of the incident surface where the wear of the container is severe is passed, the pressure wave generated when the proton beam is incident is absorbed and relaxed by the bubbles injected into the liquid mercury when passing through the bubbler. Damage is prevented. In addition, as shown in FIG. 8, the bubbler of the present invention is installed near the inside of the mercury target container where the proton beam is incident, and after passing liquid mercury through the bubbler, the proton beam is incident and irradiated. When passing through a position where the pressure wave becomes high, bubbles injected into the liquid mercury when passing through the bubbler absorb and relax the pressure wave generated when the proton beam is incident, thereby preventing impact damage to the container.

Industrial application fields

  The present invention relates to a hollow sintered metal in which a large number of fine holes are arbitrarily combined in a metal, in which bending, undulation, direction and the like are arbitrarily combined, and a bubbler using the hollow sintered metal. Is. This production method can be widely used industrially as a hollow metal production method. Moreover, this bubbler can be used not only for mercury targets but also for liquid metal targets such as lead bismuth.

It is the figure which showed the environment by the pulsed proton beam incidence of a liquid metal target. It is the figure which showed the state which embedded the raw material for hollows in the sintered compact raw material in the process of producing a hollow metal sintered compact. It is the figure which showed the example of embedding arrangement | positioning of the raw material for hollows at the time of producing a hollow metal sintered compact in the case of generating many bubbles and the case where a spiral bubble is generated. It is the figure which showed the method of installing the raw material for hollows in metal powder, when producing a hollow metal sintered compact. It is the figure which showed the hollow part (hole) produced when using molybdenum as a metal sintered compact. It is the figure which showed the hollow part (hole) produced when using stainless steel (SUS316L) as a metal sintered compact. It is the figure which installed a bubbler in a mercury target, estimated the locus | trajectory of a bubble, and showed that a bubble could be efficiently inject | poured into a site | part with a severe damage of a container. It is the figure which showed that the bubble locus | trajectory was estimated in the mercury target, the bubble locus | trajectory was estimated, and a bubble could be efficiently inject | poured into the position where a pressure wave is high.

Claims (14)

A hollow material having a melting point lower than the melting point of the sintered metal, which is diffused or volatilized by sintering, is pressed in the sintered metal powder, the hollow material is removed by sintering, and two or more hollow holes are pressed. A hollow metal sintered body formed by a sintering process. The hollow metal sintered body according to claim 1, wherein the hollow metal sintered body has a minute hollow hole that allows a hollow shape and its arrangement to be arbitrarily set and manufactured. The hollow metal sintered body according to claim 2, wherein the hollow hole shape is accompanied by bending and undulation. The hollow metal sintered body according to claim 2, wherein the hollow metal sintered body is a hollow in which holes having different shapes and diameters are connected. A spallation neutron source for generating bubbles in the liquid metal in the liquid metal target by cutting out the hollow metal sintered body according to any one of claims 1 to 4 and allowing a gas to pass through the fine hollow hole as a through hole. Bubbler for liquid metal targets. 6. The spallation neutron source liquid metal according to claim 5, wherein the hole diameter is a diameter of φ100 μm or less, a length of 3 mm or more, and a through hollow hole having an aspect ratio (length / hole diameter) of 30 or more. Target bubbler. 6. The bubbler for a spallation neutron source liquid metal target according to claim 5, wherein 90% or more of the generated bubbles are 100 μm or less. A bubbler for a spallation neutron source liquid metal target, wherein the hollow structure according to claim 7 is provided with 200 or more holes. 6. The bubbler for a spallation neutron source liquid metal target according to claim 5, wherein the bubble has a volume of 0.1% by volume or more of the liquid metal after passing through the bubbler. 6. The bubbler for a spallation neutron source liquid metal target according to claim 5, wherein the periphery of the hole of the bubbler can be easily formed into an arbitrary shape, and the bubble shape can be easily controlled as compared with a planar shape. . The bubbler for a spallation neutron source liquid metal target according to any one of claims 5 to 7, wherein two or more bubblers are arranged and arranged on the upstream side of the liquid metal other than the proton beam incident surface. . The spallation neutron source liquid according to any one of claims 5 to 7, characterized by containing 0.1 vol% or more gas in mercury in the target container and having a lifetime of 2000 hours or more. Bubbler for metal targets. The metal powder is put into a mold for obtaining an arbitrary bubbler shape, the metal powder is pre-pressed, a fiber-shaped hollow material is placed on the pressed metal powder, and the metal powder is placed thereon. Press again and insert the hollow material into the metal powder, take out the resulting molded body from the mold and sinter at a temperature above the melting point of the hollow material and below the melting point of the metal powder. A method for producing a bubbler for a spallation neutron source liquid metal target comprising a hollow metal sintered body having fine hollow holes in a sintered compact by diffusing or volatilizing a material. The method according to claim 13, wherein the metal powder is molybdenum or stainless steel, and the hollow material is a nylon thread, a quartz glass thread or a pyrex thread.

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