JPS61138445A - Proportional counter tube - Google Patents

Abstract

PURPOSE:To electrically shield a gastight wall against a positive electrode core line so as to prevent an error in measurement, by setting a grid electrode whose electric potential is not higher than that of the gastight wall, to lie midway between the gastight wall and the positive electrode core line. CONSTITUTION:A grid electrode 5 which is formed of many electric conductive lines which connect both side surfaces of a gastight wall 1 to each other, is set inside the gastight wall 1. This electrode 5 is formed cylindrically around a core line 3 as its axis, kept equipotential with the gastight wall 1, and a big space (s) is made between the wall 1 opposite to a window 4 of radiation incidence in relation to the core line 3, and the electrode 5. The space is not made at the window 4. In this way, most of the incident radiation taken from the window 4 excites gas molecules in the electrode 5, and disappears. A part of the radiation incident upon the wall 1 opposite to the window 4, generates fluorescent X-ray and Auger electron, but an error in measurement due to generation of X-ray or Auger electron can be prevented, as a big space (s) is made at the wall 1 opposite to the window 4.

Description

Detailed Description of the Invention A proportional counter can measure the radiation intensity of a desired energy out of one incident radiation by discriminating the pulse height of its output pulse. However, in some cases, a part of the incident radiation may reach the cathode of the counter. Fluorescent X-rays from the substances that make up the gas-tight wall are excited and generate free electrons due to the Auger effect.These free electrons and fluorescent X-rays excite gas molecules and are emitted. Since the main electrons are further gas-amplified and captured by the core wire of the anode, measurement errors will occur if the wave height of the output pulse approximates the wave height of the pulse generated by the radiation of the energy to be measured. Radiation with an energy different from that of the radiation source generates a pulse with a wave height that is the same as or similar to the output pulse due to the radiation beam with the energy, causing measurement errors. Therefore, the present invention attempts to prevent errors due to such causes. In the present invention, a part 1 of an airtight wall used as a cathode facing a radiation entrance window, that is, a part irradiated with radiation, is covered with a grid-like electrode to electrically shield it from the anode core wire. The grid electrode is kept at the same potential as the airtight wall or a lower potential, and the electrons generated at or near the cathode are prevented from being captured by the anode core wire. Since the radiation passes through the grid-like electrode and enters the airtight wall, fluorescent light or electrons due to the Auger effect are generated from this incident area.However, the airtight wall has a potential not higher than this. Because it is covered with a grid-like electrode, the majority of the Auger electrons are immediately absorbed by the airtight wall and disappear without being accelerated.Also, some of the fluorescent X-rays head toward the grid-like electrode. 1 By keeping the distance between the grid electrode and the airtight wall relatively large, most of the fluorescent X-rays collide with gas molecules and ionize them before passing through the grid electrode. ,! : Since the grid-shaped electrode has a potential that is at least not high relative to the airtight wall, the electrons generated by ionization travel toward the airtight wall and are absorbed by it. Some of the electrons drift at low speed in the space between the grid electrode and the hermetic wall, and are annihilated by recombination with ions within a short time.Therefore, they are caused by Auger electrons or fluorescent X-rays as mentioned above. This has the effect of preventing electrons from entering the polar core wire and generating output pulses, allowing accurate measurements. The output pulse generated due to the line cannot release this n. Figure 8 is a curve diagram for explaining the present invention in detail, as mentioned above.The horizontal axis represents the wave height of the output pulse of the counter tube, and hence the radiation energy E, and the vertical axis represents Taking the strength factor as an example, the curve P is an example of the relationship between the wave height E of the output pulse generated by the ionization of the gas in the pipe, that is, the strength factor.
, and a similar curve due to fluorescent X-rays or Auger electrons generated in the hermetic wall as described above is denoted by Q.

Assuming that the peak part X in curve A is due to the radiation of the measurement target to be detected, and the peak part y is due to the incident radiation of a wavelength other than the measurement target, pulses with wave heights from E8 to E are detected. By doing this, the radiation intensity of the object to be measured can be known. In this case, if the aforementioned fluorescent X-rays or Auger electrons produce an output as shown by curve Q, the combined output waveform will be as shown by the broken line, The shaded area is added to the output as an error. The error in the parentheses changes depending on the nature of the incident radiation, for example, an increase or decrease in the peak portion y, so it is impossible to predict and correct this. In other words, the present invention This has the effect of removing errors that cannot be easily corrected and allowing accurate measurements to be made. FIG. 1 is a vertical cross-sectional view of an embodiment of the present invention, and FIG. In the -A cross-sectional view, ionized gas at an appropriate pressure is sealed inside the rectangular cylindrical casing formed by the airtight wall 1, or this casing is connected to an ionized gas source. This airtight wall through which atmospheric pressure ionized gas flows is made of an electrical conductor lFi (insulators i and 2 are provided on both end faces of the opening, and an anode core wire 3 is suspended between these and a part of the side wall is used for detection. The radiation entrance window 4 is formed of a film that transmits the radiation.The proportional counter tube as described above also has a lattice-like structure made of a large number of electrical conductor wires connecting the two end faces inside the airtight wall l. An electrode 5 is provided.The lattice electrode 5 is formed into a cylindrical shape with the core wire 3 as an axis as shown in the figure, and is held at the same potential as the airtight wall l, and the window 4 is opposite to the core wire 3. A relatively large gap 8 is provided between the side airtight wall and the electrode 5 - and the window portion is not provided with the grid electrode 5. Therefore, most of the radiation incident from this nitrogen is formed in a cylindrical shape. The gas molecules are excited inside the grid-like electrode 5 and are annihilated, and the oL radiation is detected as a pulse current sent out from the core wire 3 in the same way as in a conventional proportional counter tube. Fluorescent X-rays and Auger electrons are generated as described above, but since a relatively large gap 1 is provided in this area, measurement errors due to this may occur as described above. can be prevented.

FIG. 3 is a longitudinal cross-sectional view of another embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along line B-B. The airtight wall 11c forms a cylindrical casing, and the core wire 3 is stretched along the axis of the cylindrical casing. It is a bridge. A planar lattice electrode 5 is provided on the part of the cylindrical casing facing the window 4 by an electric conductor connecting both bottoms ml, and a gap is carved between this electrode and the airtight wall l. It is. Also, Figure 5 is a proportional counter having a substantially cylindrical airtight wall l, similar to Figures 3 and @4, but an axial groove 6 is formed in the airtight wall in the portion facing the 4th part. By increasing the gap 1 in this manner, the operation of the present invention is further ensured. Further, FIG. 6 is a longitudinal cross-sectional view showing an embodiment in which the present invention is applied to a pillbox type proportional counter tube, and FIG. It has the same effect as the example. In each of the above embodiments, the grid-like electrode 5 is connected to the airtight wall l and held at the same potential as n, but there is no need to apply a negative potential to the airtight wall by intervening I@. It is clear that the effects of the present invention can be more reliably obtained by

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, FIG. 2 is a five-way sectional view of FIG. 1, and FIG. 3 is a longitudinal sectional view of another embodiment of the invention.
FIG. 4 is a sectional view taken along line BB in FIG. 3, and FIG. 5 is a further embodiment of the present invention.
= Cross-sectional view of the same part as FIG. 4 in another embodiment, No. 6
The figure is a longitudinal cross-sectional view of an embodiment of the present invention in a pillbox type proportional counter, FIG. 7 is a plan view of a portion of the embodiment of FIG. 6, and FIG. 8 is a curve diagram explaining the present invention in detail. It is. In the figure, 1 is an airtight wall, 2 is an insulator, and 3 is a core wire to 4.
5 is a radiation entrance window, 5 is a grid electrode, and 6 is a groove.

Claims (1)

[Claims] The airtightness is achieved by arranging a lattice-shaped electrode to which a potential is at least not higher than that of the airtight wall between the airtight wall and the anode core wire in a portion facing the radiation entrance window and receiving radiation incident from the window. A proportional counter characterized in that a wall is electrically shielded from the anode core wire.