JPS5992373A - ionization chamber - Google Patents

Abstract

PURPOSE:To improve the yield of an ionization chamber by forming the surface of a radiation incidence flange which faces the inside of a case into a recessed spherical surface, and connecting it with a cylindrical edge part which is jointed with the lower end of the case by a curved surface with a large radius of curvature. CONSTITUTION:An upper flange 12 made of aluminum is welded airtightly to the upper end of the cylindrical case 11 made of aluminum for closure. Further, the lower end of the case 11 has the recessed spherical surface 13a which faces the inside of the case, and the circumferential edge part 16b is formed into a cylindrical surface connecting with the spherical surface by the curved surface 13c with the large radius of curvature. This radiation incidence flange 13 made of the aluminum plate is welded airtightly to the lower end part of the case 11. A terminal 14 made of an insulator of ceramics, etc., is fitted airtightly in the center of the upper flange 12 while piercing the flange airtightly, and a signal electrode 15 made of a conductive material is arranged concentrically with the center axial line of the case 11. The case 11 is evacuated through a discharge cylinder 16, pressurized ionized gas 7 is charged, and the case 11 is sealed airtightly.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an ionization chamber.

[Technical background of the invention and its problems]

Figure 1 shows a cross section of a typical ionization chamber. In Fig. 1, (1) is a terminal made of an insulator, which is made of a conductive metal-like upper flange (41) and is arranged through the center of the terminal in airtight contact.
are combined. (2) is a signal electrode that passes through the center of the terminal (1) and is airtightly joined to the terminal (1). (5) is a cylindrical case made of conductive metal, and has an upper flange (4) hermetically joined to its upper end. (6) is a radiation entrance flan: ) made of conductive metal and hermetically joined to the lower end of the case (5). These (41, (51, +
61 constitutes a high voltage electrode. (3) is the exhaust pipe, and the upper part 7
It is joined to the flange (4), and its terminal end is sealed airtightly after the inside of the case (5) is evacuated and filled with ionized gas. The case (5) is filled with ionized gas (the sword is pressurized to several atmospheres).

As shown in Fig. 2, when the radiation beam (9) from the radiation source (8) enters the ionization chamber tllK, the cis-isomer is ionized by the radiation that collides with the ionized gas, and the ion electrons (approximately the radiation dose (proportional) is generated and output as a current from the signal electrode (2).

Ionization chambers used in radiation thickness gauges are required to have high sensitivity in order to improve the performance of the thickness gauge. To avoid this, various efforts have been made to increase the detection sensitivity of the ionization chamber, but basically, it is necessary to allow as much radiation as possible to enter the ionization chamber, and to efficiently convert the incident radiation into ionizing current. Two things can be mentioned. For the former, the radiation entrance flange (6) should be made of a material that absorbs little radiation. For the latter, we need to increase the density of ionized gas (force (ionized molecules)) to increase the radiation capture rate, and to create an internal structure that can quickly collect ionized ions. The material with the lowest number can be made as thin as possible, and the latter can be made by increasing the pressure of the ionized gas and devising the structure of the signal electrode and high-voltage electrode.

However, when the pressure of the ionized gas is increased, the radiation entrance flange (6) also needs to be strong enough to withstand this pressure, so it must be made thicker. It is difficult to satisfy both at the same time.

Therefore, as a conventional technology, the radiation entrance flange (6)
In some cases, the required sensitivity is obtained by increasing the pressure of ionized gas using a metal plate with the least amount of radiation absorption, but metal plate has poor workability and is a toxic metal. In addition, because the welding technology has not been established, the product has a low yield and is expensive.

[Invention's purpose]

An object of the present invention is to provide an ionization chamber that eliminates the above-mentioned drawbacks.

[Summary of the invention]

The present invention provides a lower end of a cylindrical case made of a conductive material whose upper end is hermetically closed with an upper flange, the surface facing inside the case has a concave spherical shape, and the peripheral edge has a curved surface on the spherical surface. An aluminum radiation entrance flange formed on a connected cylindrical surface is hermetically connected to a high-voltage electrode and s-
A terminal made of an insulating material is airtightly attached to the center of the upper 7 langes on the mll, and a terminal made of an insulating material is airtightly passed through the terminals and is arranged concentrically with the central axis of the case and extends to the vicinity of the inner surface of the radiation entrance 7 langes. The desired objective was achieved by realizing an ionization chamber which is equipped with a signal electrode made of a conductive material and in which ionized gas pressurized to a required pressure is sealed in the case.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

An ionization chamber according to one embodiment of the present invention is shown in FIG. In Figure 3, the cylindrical case 1ll) is made of aluminum;
It has a stepped portion (tta) on its outer circumferential surface near its lower end, with a surface perpendicular to the central axis of the case facing downward.

The upper end of the case (11) is closed by an aluminum upper flange (13) hermetically joined by welding.

Furthermore, the lower end of the case aυ has a concave spherical surface (13a) facing inward, and the peripheral edge (13b) is formed into a cylindrical surface connected to the spherical surface by a curved surface (13) with a large radius of curvature. The radiation entrance flange (13) is made of aluminum plate and its peripheral edge (13b) is hermetically joined to the lower end of the case 60 by welding. It constitutes an electrode.

A terminal I made of an insulating material such as ceramic is airtightly attached to the center of the upper 7 flange fitting. A signal electrode (5) is arranged and extends to the vicinity of the inner surface of the radiation and incident sensor. Then, after exhausting the inside of the case 0υ, an ionized gas (
7), tip the end of the exhaust pipe and attach the case (1).
υ is hermetically sealed.

The ionization chamber of the embodiment of the present invention configured as described above applies a predetermined voltage between the high voltage electrode and the signal electrode (1, as in Figure 2, allows radiation to enter the radiation entrance flange (E)) Then, the gas is ionized by the radiation colliding with the ionized gas (7) and ion electrons are generated, which are output from the signal electrode (l) as a current proportional to the radiation dose.
By measuring this current, the incident dose per unit time can be determined.

The radiation incidence 7 flange 0 is not shaped like a flat plate, but is formed into a sphere 1ni (13a) with a concave surface facing inside the case, and a cylindrical peripheral edge portion is joined to the lower end of the case (11). (13b) and the spherical surface (13a) are connected by a curved surface (13c) with a large radius of curvature, so even if the plate thickness is reduced, sufficient strength can be obtained and radiation absorption can be reduced. This eliminates the need to use beryllium,
It becomes possible to increase the sealing pressure of ionized gas. With these, detection sensitivity can be increased. Since it does not use beryllium, there is no need to worry about toxicity, and because it uses aluminum, it has good workability and there are no welding difficulties, so the product yield is significantly improved and the price is lower.

In addition, there is a stepped part (lla) with the surface perpendicular to the case circle facing downward.
By providing the stepped portion (lla), the ionization chamber can be stably fixed using the stepped portion (lla) as a seating surface. In addition, instead of providing the step (lla), the upper flange member is made in a shape that protrudes outward from the outer peripheral surface of the case 01) in the shape of a flange.
The ionization chamber may be fixed using this brim-shaped protruding surface as a seat surface.

〔Effect of the invention〕

As detailed above, according to the present invention, the radiation entrance flange is formed into a spherical surface with a concave surface facing the inside of the case, and the cylindrical peripheral edge joined to the lower end of the case and the spherical surface are connected to each other. 4 Since the shape is connected by curved surfaces with a large radius of curvature, sufficient strength can be obtained even if the plate thickness is reduced. As a result, the following effects can be obtained.

[1] The radiation entrance flange can be made thin using aluminum, which can reduce radiation absorption, and (7) The structure has high strength, so the personal pressure of ionized gas can be increased. , the detection sensitivity is improved.

[2] Since there is no need to use beryllium, a toxic metal, problems with workability and welding are solved, and product yields are improved and prices are reduced.

[3] By providing a stepped section on the outer circumferential surface of the case with the right-angled surface facing downward, or by making the upper flange protrude outward from the outer circumferential surface of the case in a flange shape, these can be used as seating surfaces for the ionization chamber. can be stably fixed.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing a conventional general ionization chamber, Fig. 2 is an explanatory view showing a state in which radiation enters the IM and acid phase from a radiation source, and Fig. 3 is an ionization chamber of an embodiment of the present invention. FIG. 7 Ionized gas 11 Case i1a Step part 12 Upper flange 13 Radiation incidence flange 13a Spherical surface 13'b Peripheral end
t3C curved surface 714 ・Terminal 15
Signal electrode 16 Exhaust stack agent Patent attorney Inoue - Male

Claims (1)

[Scope of Claims] (1) A cylindrical case made of a conductive material whose upper end is hermetically closed with an upper flange has a spherical shape with a concave surface facing the inside of the case, and a peripheral edge thereof. a high-voltage electrode formed by an aluminum radiation incidence flange formed on a cylindrical surface connected to the spherical surface by a curved surface and hermetically joined; a terminal made of an insulating material airtightly attached to the center of the upper flange; and this terminal. a signal electrode made of a conductive material that airtightly penetrates the case, is arranged concentrically with the central axis of the case, and extends to the vicinity of the inner surface of the radiation entrance flange; Enclosed ionization chamber 5
1(2) The ionization chamber according to claim 1, wherein the ionization chamber has a stepped portion on the outer peripheral surface of the case, with a surface perpendicular to the central axis of the case facing downward. (3) The ionization chamber according to claim 1, wherein the upper flange is formed in a shape that projects outward from the outer circumferential surface of the case in the shape of a brim.