JPH06160595A - Low speed positron generator - Google Patents

Abstract

(57) [Summary] [Objective] To provide a slow positron generator with improved efficiency of slowing down positrons. [Structure] A moderator 13 is arranged behind the positron emission port 12, a radioisotope RI is arranged between the moderator 13 and the positron emission port 12, and positron e ⁺ emitted from the radioisotope RI is emitted. in slow positron generator which emitted from a positron emission port 12 is accelerated by an electric field the positrons emitted from moderator 13 surface decelerates the slow positron e ⁺ with entering the moderator 13, advance slow radioisotope RI It is characterized in that it is arranged outside the center of the beam transport path of the positron e ⁺ of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-speed positron generator which improves the efficiency of slowing down positrons.

[0002]

2. Description of the Related Art Positrons as antiparticles of electrons can be obtained from RI (radioisotope) such as β ⁺ -decaying ²² Na, ⁵⁵ Co and ⁶⁴ Cu.

The positrons incident on the material lose their energy by inelastically colliding with surrounding electrons and are decelerated to the thermal energy (kT) in a short time of about 10 ^-12 seconds. The thermalized positron annihilates with the electron with a lifetime of 10 ^-10 to 10 ^-7 seconds and emits γ-rays of about 511 [keV]. At this time, the energy and the momentum are preserved, so by observing the emitted γ-rays in detail, the state of the electron at the position where the positron disappears, the lattice defect of the substance, and the like can be known.

By the way, the penetration depth of high energy positrons into, for example, aluminum due to β ⁺ decay is 100 to 200.
Since it reaches [μm], in order to utilize positrons for surface and interface studies, it is necessary to slow them down and implant them into the sample in the state of uniform energy.

FIG. 4 is a conceptual diagram of a conventional rear surface reflection type slow positron generator used in a surface analyzer for analyzing the surface of a substance using slow positrons.

In the figure, the slow positron generator 1 is
The high-speed positron e ⁺ is arranged in the vacuum container 2 and in the center of the vacuum container 2 behind the positron emission port 3 (on the lower side of the figure) and diverges the positron e ⁺ to the rear.
A moderator 4 to the slow positron e ^+, provided between the moderator 4 and positrons emission opening 3, the grid 5 for accelerating the slow positron e ⁺ to a speed required for beam transport
And a magnetic force line generating means (not shown) arranged outside the vacuum container 2 for generating a magnetic force line parallel to the positron transport path for guiding the positron e ⁺ emitted from the moderator 4 to the positron emission port 3. Has been done.

When the positron e ⁺ emitted backward from RI enters the moderator 4, it is slowed down by the moderator 4 and returned to the surface by thermal diffusion to be emitted from the surface. The emitted positrons travel along the magnetic field lines B, are accelerated to the grid 5, and are emitted from the positron emission port 3. The positron e ⁺ emitted from the moderator 4 is transported to a sample (not shown).

[0008]

However, in the above-mentioned conventional low-speed positron generator, the RI arranged in front of the moderator 4 becomes a shadow, and the positron is seen from the center of the moderator 4 in the shadow. Since e ⁺ cannot be extracted, the efficiency of slowing down positrons becomes low.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a low-speed positron generator which improves the efficiency of speed reduction.

[0010]

In order to achieve the above object, the present invention provides a moderator behind a positron emission port and a radioisotope between the moderator and the positron emission port. In the slow positron generator, in which the positrons emitted from the radioisotope are incident on the moderator and are decelerated to slow positrons, the positrons emitted from the surface of the moderator are accelerated by an electric field and emitted from the positron exit, The isotopes are arranged outside the passage center of the slow positrons in advance.

[0011]

According to the above structure, since the radioisotope bypasses the center of the passage of the slow positron, it does not form a shadow of the radioisotope in the passage of the positron. Efficiency can be improved.

[0012]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram of an embodiment of the slow positron generator of the present invention.

In FIG. 1, the slow positron generator 10 is arranged on the side of the vacuum vessel 11 and on the side wall side (right side in the figure) behind the positron emission port 12 in the vacuum vessel 11 (downward direction in the figure). and RI diverging positron e ^+, is disposed perpendicular to the central axis of the positron emission port 12 at the rear of RI, positrons and moderator 13, and the moderator 13 to speed of the positron e ⁺ slow positron e ⁺ It is provided between the emission port 12 and the grid 14 for accelerating the low-speed positron e ⁺ to the velocity required for beam transport, and is arranged outside the vacuum vessel 11 to generate the magnetic field lines B converged on the positron transport path. It is composed of a magnetic field line generator (not shown). The positron e ⁺ emitted from the low speed positron generator 10 is transported to a sample (not shown).

For example, ²² Na (sodium) is used for RI, and the positron e ⁺ is emitted from one surface. FIG. 2 is an enlarged cross-sectional view of the RI container used in the slow positron generator shown in FIG.

In the figure, ²² Na is Pt (platinum).
Alternatively, it is attached to a W (tungsten) plate 20 and is housed in a disc-shaped container 21 made of Ti (titanium), and one surface of the container 21 has a thickness of about a thickness having a function of a positron e ⁺ diffusion window. It is covered with a Ti thin film 22 of 5 [μm].
The positron e ⁺ diverges from the container 21 in the direction of the arrow through the Ti thin film. Although ²² Na was used in this example,
The present invention is not limited to this, and radioactive isotopes such as ⁵⁵ Co and ⁶⁴ Cu may be used.

The moderator 13 is a plate-shaped single crystal having no lattice defect, for example, a copper single crystal [Cu (111)].
Is used.

The magnetic force line generating means is adapted to generate a magnetic force line B that converges from the surface of the moderator 13 (upper side in the drawing) to the positron emission port 12.

Although the grid 14 is formed in a mesh shape in this embodiment, it is not limited to this and may be formed in, for example, a ring shape as long as the speed of the slow positron e ⁺ can be accelerated.

Next, operation of the embodiment will be described.

The positron e ⁺ from the radioisotope RI diverges backward and enters the surface of the moderator 13, enters the moderator 13 and is decelerated to become a low-speed positron, and the moderator 1
Slow positron e ⁺ is forward from the surface of 3 (upward direction in the figure)
Emit to. At this time, since the radioisotope RI is arranged so as to bypass the center of the passage of the slow positron e ⁺ , the deceleration of the portion which is conventionally shaded by the radioisotope RI (in the beam transport path). Since the slow positron e ⁺ from the material 13 can also be taken out and the magnetic field lines B are converged from the position of the moderator 13 to the position of the positron emission port 12, (a new shadow is generated due to the detour of the radioactive isotope RI. The low-speed positron e ⁺ from the moderator 13 (in the part where
To the sample side. Therefore, the slow positron e ⁺ can be efficiently extracted.

FIG. 3 shows a second slow positron generator according to the present invention.
It is a conceptual diagram of the Example of.

The difference from the first embodiment shown in FIG. 1 is that the moderator 13 is arranged so as to be inclined with respect to the central axis of the beam transport path (positron emission port 12) and the magnetic field B is The point is that it is parallel to the beam transport path as in the past.

In the figure, the positron e ⁺ diverges rearward from RI and is incident on the surface of the moderator 13, and the low-speed positron e ⁺ is emitted forward (upward in the figure) from the surface of the moderator 13. At this time, the radioactive isotope RI is a slow positron e
Since it is arranged outside the center of the ⁺ transport path, it does not form a shadow of the radioisotope RI (in the beam transport path), so deceleration is performed using the conventional magnetic field generator. Slow positron e ⁺ from material 13
Can be taken out efficiently.

Although the magnetic field lines B are parallel to the beam transport path in this embodiment, they may be formed so as to converge like the magnetic field lines B shown in FIG.

As described above, in this embodiment, the moderator 13 is disposed behind the positron emission port 12, the radioisotope RI is disposed between the moderator 13 and the positron emission port 12, and the radioisotope thereof is disposed. The positron e ⁺ diverging from the RI enters the moderator 13 and is decelerated as well as the slow positron e ^+.
In a slow positron generator in which positrons emitted from the surface of the moderator are accelerated by an electric field and emitted from the positron emission port 12, the radioisotope RI is arranged outside the center of the beam transport path of the slow positron e ^{+ in} advance. Therefore, it is possible to realize a low-speed positron generator with improved efficiency of slowing down positrons by eliminating the formation of a shadow of the radioisotope RI in the positron beam transport path.

Although the moderator 13 is formed in a plate shape in the drawing, it is not limited to this and may be formed in a curved shape.

[0028]

In summary, according to the present invention, the moderator is arranged behind the positron emission port, the radioisotope is arranged between the moderator and the positron emission port, and the radioisotope diverges. In a slow positron generator in which a positron is injected into a moderator and decelerated into a low-speed positron, the positron emitted from the surface of the moderator is accelerated by an electric field and emitted from a positron exit port. Since it is arranged outside the center of the passage, it is possible to realize a low-speed positron generator with improved efficiency of slowing down positrons.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an embodiment of a slow positron generator of the present invention.

FIG. 2 is an enlarged cross-sectional view of a radioisotope container used in the slow positron generator shown in FIG.

FIG. 3 is a conceptual diagram of a second embodiment of the slow positron generator of the present invention.

FIG. 4 is a conceptual diagram of a conventional back-reflection-type slow positron generator used in a surface analyzer that analyzes the surface of a substance using slow positrons.

[Explanation of symbols]

 10 Low-speed positron generator 11 Vacuum container 12 Positron emission port 13 Moderator 14 Grid

Claims (1)

[Claims] 1. A moderator is disposed behind the positron emission port,
A radioisotope is placed between the moderator and the positron emission port, and the positron emitted from the radioisotope enters the moderator and is decelerated into a low-speed positron that is emitted from the moderator surface. In a slow positron generator for accelerating an electron with an electric field to emit the positron from a positron emission port, the radioisotope is arranged in advance outside the passage center of the slow positron.