JPS6154489A - Multiple line type 2pi gas flow counter tube for large area ray source - Google Patents

Abstract

PURPOSE:To prevent a charge from being accumulated on the surface of a sample and to nearly eliminate count variation in every measurement by forming a lower cathode which is used as a sample mount in a special shape and providing another sample mount. CONSTITUTION:The sample 5 for measurement is mounted on a lower sample base 8. The sample base 8 is made of a material which contains a small amount of alpha-eay radiating elements and placed on the sample base 8 so that its measurement sample surface and cathode 4 are at an interval of 3-6mm.. An alpha-ray measuring device separates the cathode 4 and measurement sample 5 from each other and consists of an anode 3, multiple line type cathode 4, and sample base, so alpha particles radiated by the sample are emitted between the cathode and anode without boding disturbed by the diverse cathode 4 practically, thereby ionizing counter gas. Positive charges produced by the ionization are acquired by the upper cathode 2 and lower multiple line type cathode 4, so stable counting is performed without accumulating any positive charge on the sample surface practically even when the sample is a molding having no conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-wire type 2π gas flow counter for a large area radiation source that measures the amount of alpha rays (hereinafter referred to as α rays) radiation.

In recent years, as integrated circuits have become more highly integrated and densely packed, it has become known that alpha rays emitted from uranium, thorium, etc. contained in containers that store integrated circuits can cause malfunctions in integrated circuits. As the material for the container, it is important to select a material that emits extremely low amounts of α-rays. Therefore, it is desired to develop means and devices that can easily and quickly evaluate the amount of α-ray radiation of these materials down to the low-level α-ray region.

Conventionally, as a low-level α-ray radiation detector, as shown in FIG.
．． A multi-wire type 2π gas flow counter is known, which comprises a cathode 3 made of a stainless steel wire and an anode 3 made of a thin stainless steel wire stretched at approximately equal intervals between the cathodes so as to be parallel to both cathode plates.

(For example, "Applied Physics" Vol. 33, No. 5, 1964) During measurement, this device places the sample to be measured directly on the lower cathode, and the counting gas is introduced into the box-shaped container through the gas inlet 6 and then exited. A high DC voltage (for example, 2 kV) is applied between the anode and the cathode while being continuously led out through the lower cathode, and the α rays emitted from the surface of the sample placed on the lower cathode are detected.

The measurement principle of this detector is that when alpha rays are emitted from the measurement sample, ionization (-order ionization) of the counting gas occurs, and the electrons generated by ionization move toward the anode and the cations move toward the cathode, but the electric field around the anode Because the electrons are extremely large, they are accelerated to high speeds, and these accelerated electrons further ionize surrounding gas molecules (secondary ionization), and these secondary ions are further accelerated and ionize surrounding gas molecules, a so-called electron avalanche phenomenon. wake up The instantaneous current obtained by this phenomenon is converted into a voltage pulse, which is further multiplied by 1 in an external circuit to count the number of emitted α particles.

However, when measuring by placing the sample on the top surface of the conventional lower underground hole, although this is not noticeable when the sample is a powder sample, the sample may be a ceramic molded body or a plastic molded body that does not have conductivity. In this case, as the measurement continues, positive charges accumulate on the sample surface (electrostatic phenomenon), which causes the accurate detection of α-ray radiation amount, which results in an increase in the number of counts for each measurement of the same sample. This has the disadvantage that j is significantly different.

In view of this situation, the present inventors based on a known multi-wire type 2π gas flow proportional counter for large-area radiation sources, and as mentioned above, there is no charge accumulation on the sample surface and there is almost no variation in counts from measurement to measurement. As a result of conceptual studies, we discovered that all of the above objects could be satisfied by creating a special shape for the lower cathode, which was conventionally used as a sample holder, and providing a separate sample Q holder, and developed the present invention. I was able to complete it.

That is, the present invention provides a multi-wire type 2π gas flow counter for absolute measurement of alpha rays emitted from a large-area radiation source, in which the configuration of the counter is such that a cathode plate is inserted from above into a box-shaped container having a counting gas introduction outlet. The present invention provides a multi-wire 2π gas flow counter for a large-area radiation source, which is characterized by being arranged with a multi-wire anode, a multi-wire cathode, and a sample stage.

In addition, in the present invention, a large area radiation source is at least 100 c
Refers to powder or granular materials, or even molded objects, having an area of n (or more).

The apparatus of the present invention will be explained in more detail below.

1A and 1B are a schematic front view and a schematic side view of a multi-wire 2π gas flow counter according to the present invention, respectively;
is a box-shaped container, 2 and 4 are cathodes, 3 is an anode, 5 is a sample,
Reference numeral 6 indicates a counting gas inlet, 7 indicates an outlet for the gas, and 8 indicates a sample stage.

In the present invention, the material of the cathode 2 is a conductive material with a low content of alpha-ray emitting elements, and the material is not particularly limited, but for example, it may be made of plastic or ultra-high purity metal such as copper or aluminum that is vacuum-calculated. , ultra-high purity metal plated plate or carbon fiber molding machine, etc. are suitable.

In addition, the shape of the cathode 2 may be one in which a conductive material with a small content of alpha-ray emitting elements is processed into stripes on a plane parallel to the Heisei or anode thin wire, but in the latter case, stripes should be processed in order not to reduce the counting efficiency. The total area of the material needs to be processed so that it has a total area that is two or more of the total area of the plate.

The fine anode wire 3 in FIG. 1 has a wire diameter of 10 to 200 μm, preferably 30 to 80 μm, and is made of a conductive material with a small content of α-ray emitting elements. Further, since the thin wire needs to be stretched so as not to loosen, a material having a certain degree of tensile strength is preferable. Such materials include stainless steel, copper, and the like. Although there is no particular restriction on the spacing between the thin wires constituting the anode 3, it is usually set to 2 to 3 cm, and the spacing between the anode and cathode is usually set in the range of 1 to 2 cm. The line spacing and the spacing between each electrode may be fixed, but may also be variable from the outside using a screw mechanism or the like.

The lower cathode 4 may also be made of a conductive material with a low content of alpha-ray emitting elements, and may be made of the same material as the anode). Wire diameter: 50~1
00μm is preferable, and the line spacing is 5 to 2Qmm.
They may be stretched in parallel or in a cross pattern. If the line spacing exceeds 20 yen, the function as a cathode will deteriorate and the counting efficiency will decrease, which is not preferable. On the other hand, if it is narrower than 5, the alpha rays emitted from the measurement sample are obstructed and prevented from entering the counting region, which lowers the counting efficiency and increases the alpha ray background of the detector, which is not preferable.

In the apparatus of the present invention, a measurement sample 5 is placed on a sample stage 8 below the cathode 4. The sample stand is also made of a material with a low content of α-ray emitting elements, such as an acrylic resin plate, and the distance between the measurement sample and the cathode 4 is such that the measurement sample is placed on the sample stand and the distance between the measurement sample surface and the cathode 4 is 3 to 5 inches. It will be set up so that

In the present invention, the electrodes are mounted using a jig and a box-shaped container.In order to reduce the α-ray bank ground of the detector itself as much as possible, a plastic material with a low α-ray emitting element content is used, or a metal material with a low α-ray emitting element content is used. It is desirable to use a coating coated with a coating agent (for example, copper, aluminum, etc.) with a small amount.

The α-ray measuring device of the present invention described in detail above separates the cathode 4 and the measurement sample 5, and is configured as an anode 3 - multiwire cathode 4 - sample stage 8, so that α particles emitted from the sample are multiwire. The positive charge generated by the ionization is emitted between the cathode and the anode substantially unhindered by the cathode 4 of the equation, and ionizes the counting gas.
Even if the sample is a molded object with no conductivity, stable counting is possible without substantially causing accumulation of positive charges on the sample surface, and its industrial value is It's a huge deal.

[Brief explanation of the drawing]

1A and B are schematic front and side views of a multi-wire 2π gas flow counter of the present invention, and FIGS. 2 A and B are schematic front and side views of a conventionally known multi-wire 2π gas flow counter. It is a diagram. In the figure, 1 is a box-shaped container, 2.4 is a cathode, 3 is an anode, 5 is a sample 6 is a counting gas inlet, 7 is a counting gas outlet 8, and the sample stage is not shown.

Claims (1)

[Claims] Multi-wire system 2π for absolute measurement of α-rays emitted from large-area sources
The gas flow counter is characterized in that the counter is configured such that a cathode plate, a multi-wire anode, a multi-wire cathode, and a sample stage are arranged from above in a box-shaped container having a counting gas inlet and outlet. Multi-wire 2π gas flow counter for large area radiation source