JPH0584900U - Moderator for slow positron production - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to efficiently convert fast positrons to slow positrons. In the moderators 10 and 20 for decelerating high energy positrons to low energy positrons, tungsten tapes 12 and 2 as plate-shaped moderators are used.
By bending or combining two, the passage through which the high-speed positrons pass is formed so that multiple hexagons (circles) are aggregated, so that the area where the high-speed positrons that are about to diverge collide with the side wall of the moderator. The feature is that the number of high-speed positrons can be efficiently converted into low-speed positrons.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a moderator for producing slow positrons for decelerating high energy positrons and converting them into low energy positrons.

[0002]

[Prior Art]

Positrons as antiparticles of electrons can be obtained from R I (radioisotope) such as β ⁺ -decaying ²² Na, ⁵⁵ Co, and ⁶⁴ Cu.

The positrons incident on the substance inelastically collide with surrounding electrons to lose energy, and are decelerated to 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. Since energy and momentum are preserved at this time, the state of the electron at the position where the positron disappears can be known by observing the emitted γ-rays in detail.

By the way, since the penetration depth of high-energy positrons due to β ⁺ decay reaches 100 to 200 μm, in order to utilize positrons for surface and interface studies, it is necessary to slow down the positrons and implant them into a sample. There is.

FIG. 3 is a conceptual diagram of a radiation source unit used in an apparatus for analyzing the surface of a substance using slow positrons.

[0006] In the figure, the source unit, in a vacuum chamber 1, is arranged ²² Na as RI, high energy on the front surface (right side of figure) of the ²² Na, obtained by beta ⁺ decay ( A moderator 2 is arranged for converting (decelerating) positrons of high speed into positrons of low energy (low speed). The moderator 2 is composed of a tungsten ribbon, and an electrode (grid) 3 for extracting the decelerated positron from the surface of the tungsten ribbon is arranged on the front surface of the tungsten ribbon. A predetermined voltage is applied to this grid 3. The positron e ^{+ that} has passed through the grid 3 is made incident on a sample (not shown) through an accelerating tube for accelerating to a velocity required for analysis.

Here, the moderator 2 will be described in more detail.

FIG. 4 is a plan view of a moderator used in the radiation source section shown in FIG.

As shown in the figure, the moderator 2 is formed by attaching a ring-shaped frame 4 and a plurality of (9) tungsten ribbons 5 in the holes of the frame 4. These tungsten ribbons 5 are attached to the frame so as to be perpendicular to the paper surface, parallel to each other and at equal intervals (about 1.5 mm).

In this moderator 2, ²² Na is arranged on the central axis of the frame 4 and in the vicinity of ²² Na. When the fast positron e ⁺ passes from one side of the moderator 2 (for example, the back side of the paper surface) to the other side (front side of the paper surface), it collides with the side wall (perpendicular to the paper surface) of the tungsten ribbon 5 and the low speed positron e ⁺ You can get it.

[0011]

[Problems to be solved by the device]

However, since the tungsten ribbons 5 are arranged in a comb shape as shown in FIG. 5, some of the high-speed positrons generated from ²² Na do not collide with the tungsten ribbon 5 (especially the horizontal component) and spread. Since it passes through, the efficiency of slowing down high-speed positrons becomes poor. FIG. 5 is a schematic diagram showing the positional relationship between the positron and the moderator tungsten ribbon.

Therefore, an object of the present invention is to solve the above problems and to provide a moderator capable of efficiently converting a high-speed positron into a low-speed positron.

[0013]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention provides a moderator for decelerating high energy positrons into low energy positrons by bending or combining plate-shaped moderators such as tungsten to form positron passages. It is formed as a set of multiple polygons or circles.

[0014]

[Action]

 According to the above configuration, a plate-shaped moderator is bent or combined with respect to a high-speed positron that is about to diverge, and the passage of the positron is formed so that a plurality of polygons or circles are aggregated. The area that collides with the side wall of is increased, and high-speed positrons can be efficiently converted into low-speed positrons.

[0015]

【Example】

 Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view of a moderator for producing slow positrons of the present invention.

As shown in FIG. 1, the moderator 10 includes a hexagonal shape having a plurality of positron passages (37 pieces) in a ring-shaped frame 11 in which a tungsten tape 12 as a moderator is bent several times. Are formed so as to aggregate (in a honeycomb shape).

The frame 11 is made of a metal having a diameter of about 16 mm and a height of about 8 mm and can withstand a high temperature, and a substantially hexagonal hole is formed inside.

The thickness of the tungsten tape 12 is about 25 μ, and a commercially available one is used. Although tungsten is used as the moderator material in this embodiment, other materials such as iridium may be used as long as they can slow down high-speed positrons.

A method of manufacturing the moderator 10 will be described below.

For example, the tungsten tape 12 is folded inward from the start position S in the drawing five times (120 degrees) on each side, and a substantially hexagonal shape H is formed.₁And the tungsten tape 12 is bent outward for approximately one side (180 degrees), and then folded inside for 5 times (120 degrees) for each side to produce an approximately hexagonal shape H.₂To form. Hexagonal H₂After forming, the tungsten tape 12 is folded outward for approximately one side (180 degrees) and folded back four times for each side (120 degrees).₁Hexagon H with one side as one side₃First, the hexagon H formed by forming₁Hexagonal H around the center_Four, H_Five, H ₆ ... H₃₇Are formed in sequence. When the tungsten tape 12 is folded back to form 37 hexagons up to the end position E and housed in the frame 11, the moderator 10 is formed. In addition, these multiple hexagons H₁~ H₃₇The inside of the becomes a passage through which positrons pass.

The moderator 10 thus formed is arranged near the ²² Na inside the vacuum container 1 (FIG. 3) described above so that the ²² Na is on the central axis of the frame 11.

Next, the operation of the embodiment will be described.

In FIG. 3, the tungsten tape 12 of the moderator 10 was bent to form a passage of positrons so that a plurality of polygons gathered for a high speed positron emitted from ²² Na and trying to diverge. , The area of collision with the side wall of the tungsten tape 12 is increased, which is larger than that when the conventional comb-shaped tungsten ribbon 5 (Figs. 4 and 5) is used (the leakage of the horizontal component is reduced), and the high-speed positron Can be efficiently converted into slow positrons.

In the present embodiment, the tungsten tape 12 is used to form 37 hexagons, but the invention is not limited to this, and polygons such as triangles, squares and octagons may be formed. Also, the number may be changed as necessary.

FIG. 2 is a plan view of a second embodiment of the moderator for producing slow positrons of the present invention.

1 is different from the moderator shown in FIG. 1 in that the plate-shaped speed reducer shown in FIG. 1 is bent to form a polygonal (hexagonal) aggregate, whereas the plate-shaped speed reducer is formed. This is the point where the aggregate was formed by combining (circles).

Similarly to the above, the moderator 20 is formed by combining a plurality of (37) tungsten tapes 22 bent in a substantially circular shape in a ring-shaped frame 21 in which a substantially hexagonal hole is formed. There is. This moderator 20 is also provided in the vacuum container 1 (FIG. 3) described above. ^{twenty two} Near Na,^{twenty two}The Na is arranged on the central axis of the frame 21.

When a high-speed positron is incident on the moderator 20, the positron that is about to diverge collides with the side surface of the tungsten tape 22 and the high-speed positron can be efficiently converted into a low-speed positron. Although the holes of the frame 21 are substantially hexagonal in the present embodiment, the holes are not limited to this. Although the tungsten tape 22 has a circular shape, it may have an oval shape.

In the above, in the moderators 10 and 20 for decelerating high-energy positrons to low-energy positrons, the tungsten tapes 12 and 22 as plate-shaped moderators are bent or combined to form high-speed positrons. Since the passage through which the positrons pass is formed so that multiple hexagons (circles) are aggregated, the area where the high-speed positrons that are about to diverge collide with the side wall of the moderator increases, and the high-speed positrons are efficiently transmitted It can be converted into low-speed positrons.

[0031]

[Effect of the device]

 In summary, according to the present invention, in the moderator for decelerating high energy positrons into low energy positrons, a plate moderator such as tungsten is bent or combined to form a plurality of positron passages. Since it is formed as a set of polygons or circles, fast positrons can be efficiently converted into slow positrons.

[Brief description of drawings]

FIG. 1 is a plan view of a first embodiment of a moderator for producing slow positrons according to the present invention.

FIG. 2 is a plan view of a second embodiment of the moderator for producing slow positrons of the present invention.

FIG. 3 is a conceptual diagram of a radiation source unit used in an apparatus for analyzing a surface of a substance using low-speed positrons.

FIG. 4 is a plan view of a moderator used in the radiation source unit shown in FIG.

FIG. 5 is a schematic diagram showing a positional relationship between a positron and a tungsten ribbon of a moderator.

[Explanation of symbols]

 10,20 Moderator 11,21 Frame 12,22 Tungsten tape

Claims (1)

[Scope of utility model registration request] 1. A moderator for decelerating high-energy positrons into low-energy positrons by bending or combining plate-shaped moderators such as tungsten so that positron passages have a plurality of polygonal or circular shapes. A moderator for producing slow positrons characterized by being formed as a set.