JPH05172611A - Radiation level meter calibration system - Google Patents

Abstract

PURPOSE:To enable conditions of vessel change to be simulated effectively without providing water to the vessel in a bar-shaped detection system by mounting an axis to a line source storage part position at both sides of the line source container and then setting the axis to a rotary mechanism and then rotating it forward and backward in reference to the axis. CONSTITUTION:A specific expression is established regarding a detector output between an exposure and a level to be measured and a detector output is obtained as a sum of a dose of gamma rays reaching a part exposed onto a liquid surface and gamma rays reaching through a liquid. Therefore, when an irradiation part of an irradiation beam can be changed arbitrarily in vessel empty state, a change in the liquid face can be handled equivalently. Namely, when a beam region of b0-u0 is displaced to b1-u1 with an irradiation angle theta being constant while maintaining the irradiation angle O to be constant, an equivalent effect where the liquid face is changed from 10 to 11 can be obtained. In the similar manner, by changing the irradiation beam region to b2-u2 and b3-u3, an effect when the liquid face is changed to levels in 12 and 13 can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration system for a .gamma.-ray rod detection level meter used mainly for measuring the liquid level in a vessel in the chemical industry field.

[0002]

2. Description of the Related Art Prior to describing the problems of the prior art relating to the present invention, a measuring method of this type currently used will be described with reference to the drawings.

FIG. 2 shows its general configuration. In the figure, 3 is usually called a vessel, and it is composed of several layers such as a container (usually a metal, a heat insulating material) that contains the object to be measured 4 (usually a solution or powder). 2 is a radiation source container that shields and stores a radioisotope (hereinafter referred to as RI), and 1 is a detector that is disposed opposite to 2 with 3 interposed therebetween. From the RI contained in the radiation source container, γ-rays are emitted toward the detector. Usually, RIs are distributed linearly in a large number (usually about 10) along the length direction of the vessel. Further, the γ rays from each RI are arranged so that they are concentrated at one point on the detector. In such a relationship, when the object to be measured is present on the line connecting the individual RI and the detector, the γ-rays are absorbed by the object to be measured to be in the cutoff state. The γ-ray beam reaches the detector. Therefore, when the level of the object to be measured in the vessel changes, the γ-ray reaching the detector changes like the characteristic shown in FIG. 2 (b). That is, the measurement target level in the vessel can be measured by measuring the γ-ray intensity with the detector.

In order to put the instrument into practical use in the above-mentioned measuring instrument for radiation application, the relationship between the radiation intensity (usually the counting rate) and the measured amount (liquid level in this example) is calibrated with a known value. (I.e., calibration) is required. This work is a necessary and important work in order to use the instrument accurately. Normally, an actual vessel will be used to fill water and the scale will be substantially determined. However, in reality, there are many cases where the above water filling test cannot be carried out due to various circumstances, and an effective and effective alternative is desired.

The calibration method differs depending on the measuring method of the instrument, but an example will be described by taking the method currently in practical use as an example.

When the level in the vessel container is continuously measured, the radiation sources are usually arranged in a shielded container in a distributed manner over several to ten measurement ranges as seen in the above-mentioned example. Further, the direction of the irradiation port of the shielding container is set so that the irradiation beams from the individual radiation sources are concentrated on the detection elements of the detector. In such a device configuration,
Since the measurement depends on the absorption of the irradiation beam from each radiation source by the vessel contents as described above, a calibration method based on the measurement principle is desired. That is, in the case of this method, as a structure in which a lead block capable of blocking the irradiation beam can be hung on each container irradiation port, when all the irradiation ports are blocked by the lead block, the solution in the vessel is full, In addition, when all of them are opened, the empty vessel state can be simulated. That is, by sequentially performing this from one irradiation port, the increase / decrease condition of the solution level in the vessel is simulated, and the simple calibration becomes possible.

Next, let us consider the case of the newly proposed measuring method.

As shown in FIG. 1, reference numeral 6 designates a radiation source, which is basically a single radiation source, and the irradiation beam is widened as shown in the figure. Unlike the conventional point detection, the detector of 5 has a line shape (bar shape) along the length direction of the vessel.
Becomes Therefore, the measurement results obtained by this method have various characteristics such as continuous characteristics (generally exponential function) and continuous characteristics as shown in FIG. It will be the method you have. However, since there is only one source and a wide-angle beam, it is difficult to apply the conventional calibration method as it is because of the apparatus configuration, and an effective means instead of this is required. Among them, when the vessel is empty, the empty (0%) and full (100%) states are measured,
The middle is done only by selecting a function meter (exponential function) 2
Point calibration method (substantially one-point calibration that measures only space time)
There is. However, the two-point calibration is not a proper method because it is a rough calibration method as it is a method that simply depends on a function meter without any examination of the intermediate points.

[0009]

As described above, in the case of the rod-shaped detection method, basically, there is one radiation source and a wide-angle beam (opens at a certain angle downward from the horizontal plane). Therefore, unlike the conventional method, a lead block cannot be attached to the container irradiation port to simulate the liquid level change.

The problem to be solved by the present invention is to propose an effective calibration method capable of simulating the condition of the vessel level change even in such a rod-shaped detection method without flooding the vessel like the conventional method.

[0011]

In order to achieve the above-mentioned object, a shaft is attached to the position of the radiation source storage portion on both sides of the radiation source container, and the shaft can be set in a rotating mechanism to rotate back and forth around the axis. The structure is as follows.

By changing the mounting position angle of the container body, the range of the beam irradiating the detection element can be changed, and an effect equivalent to the level change of the liquid in the vessel can be provided.

The rotation is manually performed by the handle. The rotation position can be easily set by the scale plate attached to the device and its angle can be set, so that reproducibility of the effect can be easily ensured.

[0014]

In order to achieve the above object, it is basically necessary to be able to simulate changes in the liquid level in the vessel. For this reason,
It suffices that the irradiation beam on the rod-shaped detection surface changes due to the level change, and the same effect as if the irradiation beam is absorbed by the vessel contents is provided.

First, a rotating shaft is attached to both sides of a container for storing the radiation source so that the container can rotate around the radiation source storage position. The container irradiation port has a slit structure that is tapered downward so that the beam can be irradiated at a wide angle.

The rotating shaft on the container side is attached to the connecting portion of the rotating mechanism. The rotating mechanism has a handle so that it can be rotated manually, and a reduction mechanism is attached so that it can be easily rotated by hand. The inclination angle from the horizontal plane can be directly read by the scale plate attached to the device. Therefore, the rotational position can be reset easily and accurately.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method proposed by the present invention will be described below with reference to FIGS.

First, the device configuration will be described. 1 of FIG.
Are installed as shown along the level direction of the vessel to be measured by the rod-shaped detector. In the figure, the portion receiving the irradiation beam is the rod-shaped detection element portion. A portion 3 in FIG. 1 is a storage tank commonly referred to as a vessel that stores the measurement target 4 (liquid, powder, slurry, etc.), and is generally a metal cylindrical container. The shielding container 6 which houses the radiation source is arranged at an upper position facing the detector with the vessel in between. In the operating state in which the shutter is opened, the entire detection element is placed as shown in the figure. It can be illuminated by a beam that opens downward. In such a device configuration, the change in the liquid level in the vessel is measured by the degree to which the irradiation beam from the radiation source is absorbed by the measurement target in the vessel. Now, the following relational expression is generally established between the irradiation dose and the measurement target level.

[0019]

[Equation 1]

Here, y: detector output C: counting efficiency per detector unit length (cps) / (mr /
h) · cm I ₀ : γ at the same height as the source on the detector (x = 0)
Line intensity x: Distance from the source height to the bottom
(Cm) h: Liquid level (cm) D: Tank diameter (cm) μm: Mass absorption coefficient of liquid (cm ² / g) ρ: Density of liquid (g / cm ³ ) t: γ-ray passage in liquid Length (cm) H: Detector length (cm) In Equation 1, the first term represents the dose portion that is not absorbed by the absorber, and the second term represents the dose portion that is absorbed by the absorber.

In the level meter based on the above measurement principle, in order to use this for the main operation in the field, it is necessary to set the scale (calibration curve) in advance.
In general, water is filled in the vessel before the operation of the apparatus to obtain the calibration curve. However, due to various circumstances, the water filling test may not be possible, and a means for performing an effective equivalence test is desired.

The present invention proposes an effective method for coping with such a demand. That is, as is clear from Equation 1, the detector output is the sum of the γ-ray dose reaching the portion above the liquid surface and the γ-ray dose reaching through the liquid. Therefore, if the irradiation portion of the irradiation beam can be arbitrarily changed in the empty vessel state, the change in the liquid surface can be treated equivalently. That is, in FIG. 1, the beam area (irradiation angle θ) sandwiched between the normal beam divergences b _{0 to} u ₀ with the irradiation angle θ kept constant is kept constant b.
_When the liquid level is changed from ₁ to u ₁ , the liquid level can obtain an effect equivalent to changing from l ₀ to l ₁ . Similarly, b _{2 to} u ₂ , b
It is possible to obtain the effect of changing the liquid surface to the l ₂ and l ₃ levels by changing the irradiation beam area from _{3 to} u ₃ .

The device shown in FIG. 3 is proposed as a device capable of creating such conditions. In the figure, 6 is a radiation source container for accommodating a radiation source, 7 is a support base for supporting 6, 8 is a bearing portion for receiving the rotation axis of the container, 9 is a reduction mechanism, 10 is a rotating handle, 11 is an opening / closing shutter for the container, Reference numeral 12 is a scale plate for reading the rotation angle. As described above, the rotation axis of the container is attached to both sides of the container such that the position of the radiation source is the center, and the container body is rotated around this axis in the front and rear directions in the irradiation direction. .. The rotation is performed by a manual handle, but the rotation can be easily given because a reduction mechanism is attached. Once the position is set, it is locked to prevent the position from changing during calibration. With the attached scale plate, the amount of displacement from the initial setting position can be read immediately and the conditions can be easily set again.

[0024]

The main effects of the present invention are listed below.

(1) When obtaining a calibration curve in a γ-ray level meter using the rod-shaped detection method, an equivalent effect can be given even if a water filling test cannot be performed, and the condition setting can be easily and accurately realized. it can.

(2) The calibration work only requires setting the angle of the container, and the work can be performed safely.

(3) The angle of the container is set only in the upward direction of the irradiation beam, and the exposure due to the unnecessary beam is in the direction away from the person, and there is no particular problem.

(4) The calibration conditions can be set arbitrarily and easily, and the resetting of the conditions can be easily performed by the scale plate, so that the working efficiency is remarkably improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration and a detection characteristic of a conventional level meter system.

FIG. 2 is a diagram showing a device configuration and a detection characteristic of a level meter system using a rod-shaped detector.

FIG. 3 is a view showing a shielding container equipped with a rotation mechanism.

[Explanation of symbols]

1 ... Detector, 2 ... Circular shielding container, 3 ... Vessel, 4 ...
Vessel contents, 5 ... Rod-shaped detector, 6 ... Wide-angle beam type shielding container, 7 ... Container supporting device, 8 ... Bearing part, 9 ... Reducer part, 10 ... Rotating handle, 11 ... Shutter lever, 1
2 ... Scale plate.

Claims (1)

[Claims] 1. A shielded container in which a detector has a rod-like shape in a vessel level length direction and is arranged so as to sandwich the vessel, is a radiation level meter in which radiation is irradiated at a wide angle over the entire length of the detector. As a structure that can rotate up and down around the source storage position in the irradiation direction, the radiation level meter is characterized in that the radiation beam direction can be changed arbitrarily without performing a water filling test when the vessel is empty, and the same effect as the water filling test can be obtained. Calibration method.