JP2008232759A - Low-speed positron beam generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a small-sized low-speed positron beam generator capable of being merged with or installed in a semiconductor manufacturing apparatus or the like. <P>SOLUTION: A low-speed positron beam generator (1) is provided with an energy discriminator (3) for taking out a positron beam having desired energy from positron beams generated in a positron beam source (2) and decelerated by a moderator, a sample holding part (9) for holding a sample (11) to be measured, and an accelerating part (5) for accelerating a positron beam emitted from the energy discriminator (3) to irradiate the sample (11) to be inspected in a vacuum chamber. First permanent magnets (12, 13), generating magnetic field for conveying the positron beam on the sample (11) to be measured, are arranged in the vicinity of the sample (11) to be measured in the vacuum chamber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for generating a low-speed positron beam, and more particularly to a miniaturized low-speed positron beam generator.

  In recent years, a method using positron annihilation has been attracting attention as a method for non-destructively detecting a vacancy-type defect in the vicinity of a solid surface. Positron annihilation is a phenomenon in which positrons injected into a solid material annihilate with electrons captured by vacancy-type defects in the material and emit γ rays. By measuring and analyzing the lifetime of the positron, the energy distribution of the emitted γ-rays, the distribution of the emission angle, etc., it is possible to obtain important information about the lattice defects and the electronic structure of the material.

  Material analysis by positron annihilation is based on the characteristics such as non-destructive analysis of samples as described above and few restrictions such as conductivity and temperature of samples, semiconductors, metals, metal oxides, polymers, etc. It is possible to apply to a wide range of materials. As a result of evaluating various Si semiconductor device materials using this technique, it has been found that effective information can be provided to the field of material development (for example, see Non-Patent Documents 1 and 2).

  Various devices have been developed as materials evaluation devices using positron annihilation (see, for example, Patent Documents 1 and 2).

  FIG. 1 shows the structure of the defect evaluation apparatus disclosed in Patent Document 2. This apparatus includes a low-speed positron beam generator 100 and a detector 102 for detecting γ-rays generated from a sample to be measured held in the apparatus. As the detector, a semiconductor detector that absorbs γ rays and generates a current is used. Or it can also detect with the apparatus which generate | occur | produces fluorescence by irradiation of a gamma ray. The low-speed positron beam generator 1 selects a positron having a desired energy from among a low-speed positron emitted from the source section 103 and a low-speed positron emitted from the source section 103, including a source that generates positrons and a moderator that slows down the generated positrons. It comprises an energy discriminating unit 104 for taking out the energy, an accelerating unit 105 for accelerating and transporting the energy discriminated positron toward the sample, and a sample holding unit 106. The radiation source unit 103, the energy discriminating unit 104, the accelerating unit 105, and the sample holding unit 106 are configured by an integrated vacuum chamber.

  The energy discriminating unit 3 is usually composed of an E × B filter, and the E × B filter is actually composed of a parallel plate capacitor. However, if the parallel plate capacitor is used as it is, the distortion of the output positron beam is severe. Therefore, in order to prevent this, a capacitor having a structure in which a parallel plate is bent into a semicircular shape is usually used. The magnetic field B is generated by the electromagnetic coil 110 provided outside.

  In FIG. 1, 107 a and 107 b are shielding plates for preventing positrons having various energies emitted from the radiation source, other than energy discrimination and being used for measurement, from moving toward the sample portion. In general, it is composed of heavy metals such as Pb and W. Reference numeral 108 denotes an acceleration electrode, which accelerates a low-speed positron having an energy of about 100 eV, for example, to a desired energy in a range of, for example, 0 to 30 keV, and sets the sample 109 to be measured installed in the sample holder 106. For irradiating.

  In the low-speed positron beam generation apparatus 100 of FIG. 1, the vacuum chamber including the radiation source unit 103, the energy discriminating unit 104, the accelerating unit 105, and the sample holding unit 106 is provided with an electromagnetic coil 110 over the entire outer circumference thereof, and a vacuum A magnetic field is formed in the chamber. Positrons generated in the radiation source unit 103 are guided to the magnetic field and transported to the sample to be measured in the sample holding unit 106.

  As shown in FIG. 1, a conventional low-speed positron beam generating apparatus 100 is provided with an electromagnetic coil 110 over the entire length of the apparatus in order to form a magnetic field for transporting positrons. Therefore, the whole apparatus tends to be enlarged. Compared to other devices for evaluating the physical properties of semiconductors, such as an Auger analyzer, a fluorescent X-ray analyzer, etc., the trend toward larger devices is significant. Specifically, in the low-speed positron beam generator proposed in Patent Document 2, the beam line has a length of 3 to 5 m.

  On the other hand, in the semiconductor industry, development of highly functional materials is becoming indispensable in order to promote the high performance and high reliability of SoC. The physical property analysis using the low-velocity positron beam described above is an effective means for analyzing the physical properties of defects in materials. However, in order to evaluate a sample, the sample is once taken out from the manufacturing equipment into the atmosphere and used for γ-ray measurement. It is necessary to insert into a low-speed positron beam generator. Therefore, the sample cannot be evaluated during the semiconductor device manufacturing process.

  However, if the low-speed positron beam generator can be further reduced from its current size, the manufacturing process can be performed by installing this device in a semiconductor device manufacturing apparatus or other evaluation system, or by incorporating it in these devices. Can be monitored. As a result, the defect physical property analysis of the sample progresses, and an effective guideline can be given to the design and manufacture of the next-generation Si technology related material.

  Note that the evaluation principle, evaluation method, etc. of the vacancy-type defects due to positron annihilation are described in detail in Non-Patent Documents 1 and 2 or Patent Documents 1 and 2, so please refer to them. Since these are not the main part of the present invention, they will not be described here.

JP-A-7-270598 JP 2004-93224 A

"Basic behavior of positrons near the surface and material evaluation using them" Akira Uedo, Shoichiro Tanikawa, Materia 35, 140-146 (1996) “Evaluation of advanced semiconductor materials by positrons” Akiyoshi Uedo, Ryoichi Suzuki, Toshiyuki Ohira, Shoji Ishibashi, Applied Physics 74, 1223-1226 (2005)

  As described above, the downsizing of the low-speed positron beam generator is an indispensable requirement for coexistence of this apparatus with other material evaluation apparatuses or semiconductor device manufacturing apparatuses. It is not downsized enough.

  The present invention has been made in view of this point, and it is an object of the present invention to provide a low-speed positron beam generator that is miniaturized to the extent that it can coexist with other material evaluation apparatuses or semiconductor device manufacturing apparatuses.

  In order to solve the above problems, a first apparatus according to the present invention is an energy for extracting a positron beam having a desired energy from a positron beam generated by a positron source and slowed by a moderator in a vacuum chamber. In a low-speed positron beam generator comprising: a discriminator; a sample holding unit that holds a sample to be measured; and an acceleration unit for accelerating the positron beam emitted from the energy discriminator and irradiating the sample to be measured. A first permanent magnet for forming a magnetic field for transporting the positron beam onto the sample to be measured is disposed around the sample to be measured in the vacuum chamber.

  In the apparatus having the above configuration, the low-speed positron beam emitted from the energy discriminator and accelerated by the accelerating unit is transported by the first permanent magnet and applied to the sample to be measured. Therefore, it is not necessary to provide an electromagnetic coil for transporting the positron beam onto the sample to be measured at least around the sample holder outside the vacuum chamber. As a result, the entire slow positron beam generator can be reduced in size.

  In the low-speed positron beam generator, the energy discriminator has a first electromagnetic coil provided outside the vacuum chamber, and a shape that substantially fills a part of the space in the vacuum chamber, and An electrode part formed of a heavy metal as a material, and the electrode part is constituted by a first electrode and a second electrode, and the first and the second electrode are generated by the positron source and low in speed. You may make it form the space for the converted positron beam to pass and to go to the said acceleration part.

  The electrode portion may be made of Pb, W, or stainless steel.

  Furthermore, you may comprise the said acceleration part with the 2nd electromagnetic coil provided in the exterior of the said vacuum chamber, and the acceleration electrode formed in the said vacuum chamber.

  Alternatively, the accelerating unit may be constituted by a second permanent magnet installed in the vacuum chamber, and a negative voltage may be applied to the sample to be measured.

  Furthermore, a beam stabilization device for stabilizing the trajectory of the positron beam may be provided in front of the sample to be measured in the vacuum chamber.

  Furthermore, you may comprise the said 1st, 2nd permanent magnet with a ring-shaped permanent magnet.

  In order to solve the above problems, the second apparatus according to the present invention is an energy for extracting a positron beam having a desired energy from a positron beam generated by a positron source and slowed by a moderator in a vacuum chamber. In a low-speed positron beam generator comprising: a discriminator; a sample holding unit that holds a sample to be measured; and an acceleration unit for accelerating the positron beam emitted from the energy discriminator and irradiating the sample to be measured. The energy discriminator includes a first electromagnetic coil provided outside the vacuum chamber, and an electrode portion having a shape that substantially fills a part of the space in the vacuum chamber and formed of heavy metal as a material. And the electrode part is composed of first and second electrodes, and is generated by the positron source between the first and second electrodes, and Wherein the-speed positron beam to form a space for passing toward the accelerating portion.

  In the second apparatus, the energy discriminating unit is configured by an E × B filter including a magnetic field generated by an external electromagnetic coil and an electric field formed between the first and second electrodes. Yes. At this time, the electrode part composed of the first and second electrodes has a shape that substantially fills the internal space of the energy discriminating part, and is made of a heavy metal that absorbs the positron beam. Therefore, this energy discriminating unit has a function of filtering a positron beam having various energies and a shielding function of absorbing a positron beam other than a positron beam having a necessary energy. As a result, the conventionally required shielding plate is unnecessary, which contributes to the downsizing of the low-speed positron beam generator.

  In addition, the energy discriminating part has a structure in which the interior space is almost filled with a positron shield, so that positrons generated in all directions in the radiation source can be almost completely prevented from leaking to the sample holder. Can do. As a result, it is not necessary to increase the distance from the energy discriminator to the sample holder and absorb unnecessary positrons that form background noise during measurement at this portion. This makes it possible to further reduce the size of the low-speed positron beam generator. The background noise is generated when unnecessary positrons not used for measurement reach the sample holder and collide with an internal substance to form annihilation γ rays, which are detected by a detector. . Therefore, if unnecessary positrons can be completely shielded, the background noise is reduced.

  In the second apparatus, the electrode portion may be made of Pb, W, or stainless steel.

  According to the first apparatus, the positron beam emitted from the energy discriminating unit is transported onto the sample to be measured by the first permanent magnet provided around the sample to be measured. Of the electromagnetic coils outside the vacuum chamber, at least the electromagnetic coil around the sample holder is not necessary. As a result, the entire apparatus can be reduced in size as compared with the conventional apparatus. In addition, if the electromagnetic coil which comprised the acceleration part with the conventional apparatus is replaced with the permanent magnet different from the 1st permanent magnet arrange | positioned in a vacuum chamber, the whole apparatus can be reduced more in size. At this time, if the accelerating portion is grounded and the sample to be measured is set to a negative potential, the positron beam is accelerated toward the sample to be measured, so that it is not necessary to provide an accelerating electrode inside the accelerating portion. In addition, the second device also eliminates the need for a shielding plate and eliminates the need to consider the occurrence of background noise, so that the entire device can be further downsized.

  As a result of the above, the apparatus according to the present invention can be added to or incorporated in a semiconductor device manufacturing apparatus or other evaluation system, so that it is possible to evaluate materials during the manufacturing process of semiconductor devices and the like. Contributes greatly to the development of functional materials.

  The inventors considered that the existence of an electromagnetic coil that forms a magnetic field for transporting the positron beam onto the sample to be measured is the most obstacle to downsizing the low-speed positron beam generator. This is because the electromagnetic coil cannot be housed in the vacuum chamber, and the size of the device is increased accordingly. Therefore, it was considered that a part of the electromagnetic coil was replaced with a permanent magnet and placed in a vacuum chamber. Since the permanent magnet generates a strong magnetic field with a smaller volume than the electromagnetic coil, the entire apparatus can be downsized accordingly.

  As a result of various experiments, it has been found that by arranging a permanent magnet around the sample to be measured, the positron beam can be stably transported onto the sample to be measured even if the electromagnetic coil around the sample chamber is removed. It was. The apparatus of the present invention is constructed based on this discovery.

  By replacing the electromagnetic coil around the sample to be measured with a permanent magnet, the entire apparatus can be miniaturized. On the other hand, background noise tends to increase in γ-ray detectors. Background noise is a positron generated by a positron source, other than the positron beam used for measurement, enters the sample chamber and collides with the internal material to generate annihilation gamma rays, which are detected by the detector. Caused by

  Therefore, in order to completely shield positrons other than those incident on the energy discriminator, it is necessary to provide a relatively large shielding structure instead of the conventional simple shielding plate. However, the size of the device increases accordingly. Therefore, the present inventors considered that an E × B filter provided for energy discrimination has a shielding function for unnecessary positrons, thereby eliminating the need for a shielding structure. The E × B filter described in the following embodiments has been invented based on such an idea.

  Various embodiments of the present invention will be described below with reference to the drawings. In addition, in each following figure, since the same code | symbol shows the same or similar component, the overlapping description is not performed.

[First Embodiment]
2A is a diagram showing a schematic configuration of the low-speed positron beam generator 1 according to the first embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line AA ′ in FIG. FIG. In FIG. 2A, reference numeral 2 denotes a radiation source section provided in the vacuum chamber. For example, a radiation source holding a radioactive isotope such as ²² Na, and a moderator for slowing down positrons emitted from this radiation source. It consists of and. Reference numeral 3 denotes an E × B filter constituting the energy discriminator, and 4 denotes an aperture for allowing the positron beam emitted from the E × B filter 3 to pass to the acceleration unit 5. A ring-shaped or donut-shaped (hereinafter referred to as ring-shaped) permanent magnet 6 is disposed on the acceleration portion side of the aperture 4.

  Reference numeral 7 denotes an electromagnetic coil mounted outside the vacuum chamber, and is formed so as to cover the radiation source portion 2, the E × B filter 3, the aperture 4 and the permanent magnet 6. The magnetic field generated by the electromagnetic coil 7 is such that, in the radiation source unit 2, more positrons radiated from the radiation source in all directions are directed toward the E × B filter 3, and the E × B filter. 3, a magnetic field B necessary for filtering is formed, and on the output side of the aperture 4, positrons are easily emitted from the E × B filter 3 to the acceleration unit 5. The configuration of the E × B filter 3 will be described later with reference to FIG.

  In FIG. 2 (a), reference numeral 8 denotes an accelerating tube constituting the accelerating portion 5, and includes a plurality of accelerating electrodes 8a, 8a,. Moreover, electromagnetic coils 8b and 8b for acceleration are provided outside. Reference numeral 9 denotes a sample chamber constituting a sample holding unit, and a part 9 a thereof is connected to the acceleration tube 8 via a bellows 10. The bellows 10 is inserted to protect the acceleration unit 8 from damage due to mechanical vibration. In the sample chamber 9, a sample 11 to be measured is arranged on the orbit of the positron beam.

  Reference numeral 12 denotes a permanent magnet disposed in the vicinity of the sample 11 to be measured, and has a ring shape. Reference numeral 13 denotes a ring-shaped permanent magnet provided in the sample chamber 9 behind the sample to be measured 11 (between the sample to be measured 11 and a γ-ray detector not shown). In addition, both 12 and 13 can be comprised with the normal permanent magnet which uses neodymium (Nd) etc. as a material. As described above, the inventors of the present invention are that these permanent magnets 12 and 13 provided around the sample 11 to be measured sufficiently replace the function of the electromagnetic coil provided around the sample chamber in the conventional apparatus. It was confirmed. Therefore, in the apparatus shown in FIG. 2, no electromagnetic coil is provided around the sample chamber 9.

  The sample chamber 9 has an exhaust port 14 and is connected to a vacuum pump (not shown) to evacuate the radiation source unit 2, the energy discriminating unit including the E × B filter 3, the acceleration unit 5, and the sample chamber 9. Positron annihilation experiments are performed in a vacuum.

  Hereinafter, the structure of the E × B filter 3 will be described with reference to FIG. The E × B filter 3 of the present embodiment has a cylindrical shape that substantially fills the space in which the E × B filter 3 of the vacuum chamber is disposed. In FIG. 2B, reference numeral 20 denotes an inner wall of a vacuum chamber that houses the E × B filter 3. The E × B filter 3 includes a first electrode 21 and a second electrode 22 as illustrated. The opposing surfaces of the first electrode 21 and the second electrode 22 have a concentric semicircular shape, and a space 23 through which a positron beam passes is formed between the first and second electrodes. Therefore, a desired electric field E can be formed in the space 23 through which the positron beam passes by applying a voltage to the first and second electrodes 21 and 22.

  The E × B filter 3 has only a positron beam having a desired energy by the interaction between the magnetic field B generated by the external electromagnetic coil 7 and the electric field E formed between the first and second electrodes 21 and 22. Select to pass through. The shape including the length of the E × B filter 3 is determined by performing a trajectory calculation of the positron beam. The radiation source unit 2 is arranged at a position off the center of the E × B filter 3, and the output unit of the E × B filter 3 is provided at the center. This is because only the positron beam having a desired energy is taken out by changing the trajectory by the E × B filter 3. By passing the positron beam emitted from the E × B filter 3 further through the aperture 4, a positron beam flying along the central axis of the vacuum chamber can be formed.

  The E × B filter 3 including the electrodes 21 and 22 is formed using a heavy metal such as lead (Pb), tungsten (W), and stainless steel as a material. As a result, the E × B filter 3 itself has a function as a positron shield, and the positron beam having various energies generated by the radiation source unit 2 other than passing through the E × B filter 3. The positron beam will be almost completely shielded. Therefore, unlike the conventional apparatus shown in FIG. 1, the apparatus according to the present embodiment does not require the provision of a positron shield separate from the E × B filter 3, and the apparatus can be downsized accordingly.

  Further, the E × B filter 3 can almost completely prevent the leakage of high energy positrons that cause background noise. Therefore, the length of the acceleration unit 5 is unnecessarily increased, and high energy positrons are generated in this portion. A configuration such as absorption is unnecessary. Therefore, the apparatus can be further downsized.

  From the above results, the apparatus of this embodiment can make the beam line much shorter than the conventional low-speed positron beam generator. In one example, an apparatus having a length L of FIG. 2 of approximately 1 m could be configured. This is a significant reduction in size compared to conventional devices having a length of 3-5 m.

[Second Embodiment]
FIG. 3A is a diagram showing a configuration of a low-speed positron beam generator 30 according to the second embodiment of the present invention, and FIG. 3B is a cross-sectional view along the line AA ′ in FIG. is there. The apparatus of the present embodiment is almost the same as the apparatus 1 according to the first embodiment shown in FIG. 2 except that a gate valve 32 is provided between the acceleration unit 5 and the sample chamber 9. ing. The gate valve 32 is inserted so as not to expose the radiation source unit 2 to the atmosphere when the vacuum of the sample chamber 9 is broken for replacement of the sample 11 to be measured.

  According to this embodiment, the beam line becomes longer by the provision of the gate valve 32, but the total length is increased by the configuration of the E × B filter 3 and the effect of the ring-shaped permanent magnet 12 provided around the sample 11 to be measured. A low speed positron beam generator of about 1.1 m could be constructed.

[Third Embodiment]
FIG. 4 is a diagram showing a configuration of a slow positron beam generator 40 according to the third embodiment of the present invention. 4A is a configuration diagram of the entire apparatus, and FIG. 4B is a cross-sectional view along the line AA ′ of FIG. The apparatus of the present embodiment is a modification of the apparatus of the second embodiment shown in FIG. 3, and is the second in that a beam stabilization device 42 is provided between the positron beam acceleration unit 5 and the permanent magnet 12. This is different from the apparatus of the embodiment. The beam stabilizing device 42 is composed of, for example, two parallel plate capacitors provided in the x-axis and y-axis directions, and has a function of correcting and stabilizing the orbit of the positron beam by adjusting the voltage applied to the electrodes. ing.

  By providing the gate valve 32 between the accelerating unit 5 and the permanent magnet 12, the positron beam trajectory can be adjusted by adjusting the voltage applied to the beam stabilizing device 42 even when the distance between the gate valve 32 is somewhat longer. Can be corrected and can be accurately incident on the sample 11 to be measured. The beam stabilization device 42 may be provided in the device according to the first embodiment shown in FIG.

[Fourth Embodiment]
FIG. 5 is a diagram showing a configuration of a low-speed positron beam generation apparatus 50 according to the fourth embodiment of the present invention. FIG. 5A shows the overall configuration of the apparatus 50, and FIG. A sectional view taken along line AA ′ of FIG. The device according to the present embodiment is different from the devices according to the first to third embodiments in the structure of the acceleration unit 52. The acceleration unit 52 of the present embodiment is characterized in that a plurality of ring-shaped permanent magnets 56, 56... Are arranged inside the acceleration tube 54, and no electromagnetic coil is provided outside the vacuum chamber of the acceleration unit 52.

  The ring-shaped permanent magnets 56, 56... Form a magnetic field for transporting the positron beam emitted from the aperture 4 of the energy discriminating portion in the direction of the sample 11 to be measured. The positron beam cannot be accelerated to the desired energy by itself. In the present embodiment, the sample to be measured 11 is set to a negative potential in order to accelerate the positron beam. In this case, the acceleration unit 52 needs to be grounded. As a result, a potential difference is formed between the aperture 4 and the sample 11 to be measured, and the positron beam flying between them is accelerated.

  As shown in the figure, the beam stabilizing device 42 is arranged near the sample 11 to be measured, thereby correcting and stabilizing the trajectory of the positron beam so that the beam accurately enters the sample 11 to be measured. However, the beam stabilization device 42 is not always necessary.

  According to the apparatus of the present embodiment, the electromagnetic coil 7 formed in the portion of the E × B filter 3 can be left and all other electromagnetic coils can be removed, so the low-speed positron beam generator 50 can be further downsized. It becomes possible.

The figure which shows schematic structure of the conventional low-speed positron beam generator. The figure which shows schematic structure of the low-speed positron beam generator based on the 1st Embodiment of this invention. The figure which shows schematic structure of the slow positron beam generator based on the 2nd Embodiment of this invention. The figure which shows schematic structure of the slow positron beam generator based on the 3rd Embodiment of this invention. The figure which shows schematic structure of the slow positron beam generator based on the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low-speed positron beam generator 2 Radiation source part 3 ExB filter 4 Aperture 5 Acceleration part 7 Electromagnetic coil 8 Acceleration tube 8a Acceleration electrode 8b Electromagnetic coil 9 Sample chamber 10 Bellows 11 Sample to be measured 12, 13 Permanent magnet 20 Vacuum chamber Inner walls 21, 22 First and second electrodes 23 Space

Claims (9)

In the vacuum chamber,
An energy discriminator for extracting a positron beam having a desired energy among positron beams generated by a positron source and slowed by a moderator;
A sample holder for holding the sample to be measured;
In a low-speed positron beam generator comprising an accelerating unit for accelerating the positron beam emitted from the energy discriminator and irradiating the sample to be measured,
A low-speed positron beam generating apparatus, wherein a first permanent magnet for generating a magnetic field for transporting the positron beam onto the sample to be measured is disposed around the sample to be measured in the vacuum chamber. .   2. The low-speed positron beam generator according to claim 1, wherein the energy discriminator substantially fills a part of a space in the vacuum chamber and a first electromagnetic coil provided outside the vacuum chamber. And an electrode portion formed of a heavy metal as a material, the electrode portion being composed of first and second electrodes, and being generated by the positron source between the first and second electrodes, and A low-speed positron beam generation apparatus, characterized in that a space for passing a low-speed positron beam to travel toward the acceleration unit is formed.   3. The low-speed positron beam generator according to claim 2, wherein the electrode section is made of any one of Pb, W, and stainless steel.   4. The low-speed positron beam generation apparatus according to claim 1, wherein the acceleration unit includes a second electromagnetic coil provided outside the vacuum chamber, and an acceleration electrode formed in the vacuum chamber. And a low-speed positron beam generator.   4. The low-speed positron beam generation apparatus according to claim 1, wherein the acceleration unit includes a second permanent magnet installed in the vacuum chamber, and further, the acceleration unit is grounded and the acceleration unit is grounded. A low-speed positron beam generator, wherein a sample to be measured is set to a negative potential.   6. The low-speed positron beam generator according to claim 1, wherein a beam stabilization device for stabilizing the trajectory of the positron beam is provided in front of the sample to be measured in the vacuum chamber. A low-speed positron beam generator.   The slow positron beam generator according to any one of claims 1 to 6, wherein the permanent magnet is a ring-shaped permanent magnet. In the vacuum chamber,
An energy discriminator for extracting a positron beam having a desired energy among positron beams generated by a positron source and slowed by a moderator;
A sample holder for holding the sample to be measured;
In a low-speed positron beam generator comprising: an acceleration unit for accelerating the positron beam emitted from the energy discriminator and irradiating the sample to be measured;
The energy discriminator is
A first electromagnetic coil provided outside the vacuum chamber; and an electrode portion having a shape that substantially fills a part of the space in the vacuum chamber and formed of heavy metal as a material. The portion is composed of first and second electrodes, and a space is formed between the first and second electrodes for the positron beam generated by the positron source and slowed to pass toward the acceleration portion. A low-speed positron beam generator, characterized in that   9. The low-speed positron beam generator according to claim 8, wherein the electrode portion is made of any one of Pb, W, and stainless steel.

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