JPS6127076Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an end-window type proportional counter used for X-ray detection.

When using an end-window type proportional counter, the counting rate will gradually change over time from the start of X-ray detection operation, and it will take 10~10 seconds to stabilize.
After about 20 minutes, when the X-ray injection is stopped, it returns to its original state in a short time, and when the X-ray is re-entered, the same process occurs again until it reaches a stable state for a long time. Moreover, the change in the counting rate over time is not constant, both in the increasing direction and in the decreasing direction. The present invention was made with the aim of eliminating the above-mentioned instability observed in end window type counters.

FIG. 1 shows an example of the above-mentioned change, in which the vertical axis represents the count rate, that is, the X-ray intensity, and the horizontal axis represents time. The cause of the above-mentioned change is thought to be in the support structure of the core wire. Figure 1a is data for the counter having the structure shown in Figure 2a, Figure 2b is the data shown in Figure 2b, Figure 2c is
is the data for the counter shown in FIG. 2c. In the data in Figure 1a, the counting rate is at the time of X-ray incidence.
After 500 seconds from 92OKCPS, it increased by about 0.7% to 927Kcps, and after a pause of 1000 seconds from 500 seconds and when the X-rays were re-injected from 1500 seconds, the change followed exactly the same process. The other data b and c are the results of experiments using a similar time schedule. In the data in Figure 1b, a decrease of 0.11% over time is seen, and in data c, the fluctuation is up and down in a range of 0.1%, with no tendency for gradual increase or gradual decrease. In the data above, the X-ray intensity is the counting rate.
This is a case of 1000Kcps or less, and the rate of change increases as the X-ray intensity increases. Figure 1 b'c' shows this. The data in Figure 1 b' and c' are obtained when the X-ray intensity was increased to about 2400 Kcps in the same counter as in Figure 1 b and c, and the type in Figure 2 c is based on the data in Figure 1 c. was recognized as relatively good, but
As the line intensity increases, it begins to show a gradual increasing tendency, and after 250 seconds it already shows a gradual increase of more than 0.09%, and if this is extended to 500 seconds, it is expected to reach about 0.2%.

Let us consider the causes of the above-mentioned fluctuations with reference to FIG. In FIG. 2, 1 is an outer cylinder, 2 is a core wire, and the outer cylinder is grounded, and a positive high voltage is applied to the core wire. For this reason, the core wire must be held insulated from the outer cylinder. Reference numeral 3 denotes a window provided in the end member of the outer cylinder, which is covered with foil such as beryllium, and X-rays enter through this window. The window 3 has an oblong shape that is long in the direction perpendicular to the plane of the drawing. In the type shown in FIG. 2a, the core wire 2 is welded to a metal wire frame 4 that straddles the window 3 with a glass insulating material 5. This structure gives the structure shown in FIG. 1a. The reason for this is that the glass insulator 5 is located directly on the center line of the counter tube, which is directly irradiated with X-rays. Initially, the glass insulator 5 is at a potential close to that of the core wire 2, but due to the incidence of X-rays, the gas inside the tube When the electrons are ionized, some of the electrons adhere to the glass insulator 5.
This adhesion does not become a core wire current, resulting in a decrease in the count. As time passes, a considerable amount of electrons adhere to the glass insulator 5, and the potential decreases, preventing the incidence of electrons, and the counting rate becomes stable at a point where it increases. When the incidence of X-rays is stopped, the electrons attached to the glass insulator 5 leak through the glass as a conduction current, and the state returns to its original state. In FIG. 2b, the core wire has a glass insulating seat 5' formed on the inner surface of the outer cylinder 1, and a support 4' is erected on this and held at the end of the support. In this structure, the glass insulating seat 5' is located at a position where the incident X-rays do not hit, but ions are incident on this seat initially at the same potential as the outer tube 1, and the potential becomes positive. Therefore, on the X-ray incident end side of the counter, the potential gradient from the core wire toward a part of the outer tube (seat 5') becomes weaker, and the amplification effect due to gas ionization is reduced at this point. Although this range is small in terms of the volume of the entire counter, it has the effect of reducing the counting rate. This may be the reason why the data shown in Figure 1b is obtained. The type shown in Fig. 2c has a glass insulating material 5" welded to the middle of the column 4", and although the insulating material 5" is not in a place directly exposed to X-rays as shown in Fig. 2a, enters the counter tube in the form of a slightly divergent wire bundle, so a portion of the outer circumferential portion of the wire bundle enters a portion of the insulating material 5''. Therefore, although the tendency is weak, it should show the same change tendency as the structure in Figure 2a, and this is shown in Figure 1c'.

The above explanation of the cause of count rate instability is a tentative assumption, and it cannot be confirmed that it is correct, but the position and size of the insulating material that insulates between the core wire 2 and the outer cylinder 1 are involved. This is admittedly true. Based on the above considerations, the present invention provides an end window type counter as described in the following embodiments.

FIG. 3 shows an embodiment of the present invention. 1 is the outer cylinder,
2 is a core wire, and 3 is an X-ray entrance window. A support 7 is erected on the end member 6 on the X-ray incident side, the tip is bent toward the center of the tube, and immediately after bending, the support 7' is secured with a glass insulating material 8.
are welded to hold the core wire 2 at the end of the support 7'.
The distance of the glass insulating material 8 from the center of the counter tube is selected as follows. When the X-rays entering the X-ray entrance window 3 enter through something like a solar slit, they can be regarded as a parallel ray bundle, so there is no particular problem.
When placing a counter behind the slit where the X-rays diffracted by the curved crystal converge, the incident X-rays become a divergent ray bundle, so even in this case, prevent the X-rays from hitting the insulating material 8. There is a need. The curved crystal for spectroscopy has a width of 4 to 5 cm, and the distance from this crystal to the X-ray convergence point is about 20 cm, which is the size of a typical X-ray spectrometer. The angle is approximately 15° and 7.5° on one side. Therefore, in Fig. 3, a line inclined 7.5° upward from the horizontal line is drawn from the upper edge of the window 3 toward the inside of the counter tube, and the insulating material 8 is positioned closer to the outer cylinder than the point where this line intersects with the support 7'. Must be.

FIG. 4 shows another embodiment of the present invention in which the support 7 is welded with an insulating material 8 at a position closer to the base than the position where the support 7 is bent around the center of the pipe.

FIG. 5 shows actual measurement data for the embodiment shown in FIG. 3 above. A is the data when the X-ray intensity is 1000 Kcps or less, and b is the data when the X-ray intensity is 3400 Kcps. Although the time schedules for a and b are different, they can be extrapolated from the change trends and compared with each other, and the changes do not show a biased tendency such as gradual increase or gradual decrease, and the change width is 0.05.
It can be seen that it is 0.09%, which is better than any of the data shown in FIG.

As mentioned above, the end window type proportional counter tube of the present invention is one in which the core wire struts are connected with an insulating material at a position completely hidden by the window when viewed from the incident X-ray, and the inner surface of the outer tube is covered with an insulating material. Since no insulating material is provided in the area where the incident X-rays enter the tube, stability over time is improved, and the structure is no more complicated than the conventional example.

[Brief explanation of the drawing]

Figure 1 is the measurement data of the conventional example, Figure 2 is a longitudinal cross-sectional side view of the conventional example, Figures 3 and 4 are longitudinal cross-sectional side views of main parts of different embodiments of the present invention, and Figure 5 is the implementation of the present invention. Measurement data by example is shown. 1...Outer cylinder, 2...Core wire, 3...X-ray entrance window,
6... Pipe end member, 7, 7'... Support column, 8... Insulating material.

Claims (1)

[Scope of utility model registration request] The end of the core wire on the X-ray entrance side is held by a support placed on the tube end member provided with an An end-window type proportional counter with an insulating material added in the shadow of the X-ray entrance window.