JPS5824903B2 - Multilayer electrode type ionization chamber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer electrode type ionization chamber with improved sensitivity and responsiveness.

For example, in a radiation ionization chamber used for a thickness gauge, as shown in FIG. A thin film of stainless steel or the like is adhered to the radiation entrance window 4, an end plate 5 is provided at the other end, and a sensitive gas is sealed inside.

Then, the window 4 is made to face a radiation source (not shown), and the radiation source and the window 4 are
A sample is inserted between the electrodes 1 and 2, a high voltage is applied to both electrodes 1 and 2, and the ionization current of the sensitive gas is measured to measure the thickness of the sample.

In addition, in the figure, 6 and 7 indicate lead wires, and 8 indicates the radiation incident direction.

By the way, when the energy of the radiation source, such as X-rays or r-rays, is low, the absorption in the window 4 is very large and the output decreases. Therefore, in order to increase the output, the ionization chamber must be made larger or the intensity of the radiation source must be increased. It needs to be bigger.

However, in consideration of the response speed of the ionization chamber, it is necessary to increase the applied voltage or decrease the pressure of the sensitive gas, which is also a cause of a decrease in sensitivity.

The sensitivity of the ionization chamber is directly related to the accuracy of thickness measurement when the radiation sources are the same, and the higher the sensitivity, the better.

Furthermore, when the thickness gauge is used in the rolling process of iron plates, the response speed is preferably as fast as possible from measuring the thickness to controlling the thickness.

Therefore, an ionization chamber with excellent sensitivity and responsiveness is desired.

This invention was made to meet the above-mentioned needs, and it is a multilayer electrode type ionization chamber that can increase the sensitivity of the ionization chamber, speed up the response measurement, improve measurement accuracy, and facilitate the process control of a manufacturing line, for example. The purpose is to provide the box.

That is, in this invention, an aluminum member is used for the radiation entrance window, and signal extraction electrodes and high voltage impression electrodes are arranged alternately in multi-layer concentric circles along the radiation entrance direction, and the sensitive gas A multilayer electrode type ionization chamber is characterized in that it is encapsulated with:

Hereinafter, one embodiment of the ionization chamber according to the present invention will be described with reference to FIG. 2, in which the same parts as in FIG. 1 are designated by the same reference numerals.

This invention differs from the conventional example in that an aluminum member plate 4a is used for the radiation entrance window to reduce absorption on the window surface, and 6 freezing electrodes are arranged concentrically in a plurality of cylinders 2a, 2b, 2c.
Divide each cylinder 2a + 2b + 2c into a disk 2d
The disk 2d is connected to the lead wire 6 via the insulator 3, and the high voltage application electrode is placed concentrically around the aluminum window 4a in the cylinder 9a.

9b is attached, and each cylinder 9a, 9b is the cylinder 2b.

It has a structure inserted between 2b and 2c.

Therefore, the radiation 8 passes through the window 4a and the electrodes 2a, 2
When reaching between b, 2c and 9a, 9b, a sensitive gas such as xenon gas is ionized.

A bias voltage is applied to the electrodes 2a, 2b, 2c and 9a, 9b to produce a current output.

Note that when aluminum is used for the window 4a, for example, when the window thickness of stainless steel (SUS304) is 0.5 mm, the window thickness of aluminum (A5084) is 0.93 m.
Corresponds to m.

The transmittance of 60 Key r-rays with stainless steel 0.5 mm is 64%, and the transmittance with aluminum 0.93 mm is 93, which is a very good transmittance of 1.46.
Double the sensitivity.

(However, since the absorption coefficient differs depending on the quality and energy of the radiation, here we will discuss r-rays of 60Kev from Am"".

) Also, regarding the response speed, the electrode spacing is determined by sandwiching the concentric cylinders between each electrode.
In the configuration shown in Figure 2, the electrode spacing is 115
become.

When the electrode spacing is 115, the time taken for ionized ions to travel from the anode to the cathode becomes 1/25, so the charge accumulation time can be shortened to 1/25.

This speeds up the response time of the ionization chamber, which naturally speeds up the response time of the entire measurement system.

Therefore, according to the present invention, it is possible to provide an ionization chamber that has improved sensitivity and responsiveness, and is lightweight and easy to handle by using aluminum for the window.

It should be noted that the larger the number of cylinders used for the electrodes, the more advantageous it is that the annual voltage and sensitive gas pressure can be reduced.

In addition to xenon gas, rare gases such as alcone and krypton, carbon dioxide gas, and nitrogen gas can also be used as sensitive gases.

Further, in this invention, a thickness gauge has been described as an example of the application of the ionization chamber, but the invention is not limited to this and can be applied to other applications.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a conventional ionization chamber, and FIG. 2 is a longitudinal sectional view showing one embodiment of the ionization chamber according to the present invention. 1... Cylindrical anode, 2... Collector electrode, Meter... Insulator, 4
...Window, 5...End plate, 6.7...Lead wire, 8.
...Radiation incident direction.

Claims (1)

[Claims] 1. An aluminum member is used for the radiation entrance window, and signal extraction electrodes and voltage year electrodes are arranged alternately in a multilayer concentric circle along the radiation entrance direction, and a sensitive gas is sealed. A multilayer electrode type ionization chamber featuring: