JP2002082170A - Ionization chamber type radiation detection device and ionization chamber inspecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect detection characteristics of an ionization chamber at a high dose rate, without having to use using a high-radiation source. SOLUTION: A low-radiation source 48 is arranged at a prescribed position. Then a low voltage is applied to the ionization chamber 12, by switching a normally-used high-voltage source 30 to a low-voltage power source 32 using a switch mechanism 34 of a power unit 14 and the voltage signal obtained, by converting the output current has its value recorded by a counting arithmetic part 18. According to a series of voltage signals which are recorded, it is decided whether detection characteristics of the ionization chamber 12 are proper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionization chamber type radiation detector and an inspection method of an ionization chamber, and more particularly to an inspection of an ionization chamber detection characteristic with respect to high dose rate radiation.

[0002]

2. Description of the Related Art In a facility handling radioactive materials, such as a nuclear power plant, an environmental radiation monitoring device is generally provided outside the facility or on the site of the facility to monitor radiation in and around the facility. As an environmental radiation monitoring device, a monitoring post for measuring an air gamma dose rate is known. The monitoring post includes an ionization chamber for detecting γ-rays, a NaI detector, etc.
Various modules for processing the measurement signals are stored in the office building on the rooftop.

[0003] A pressurized gas (for example, a rare gas) is sealed in an ionization chamber used for the monitoring post.
The enclosed gas is ionized due to the incidence of radiation,
The dose rate of the radiation is measured by collecting the generated charges.

[0004] The output current is proportional to the dose rate of the incident radiation. However, when an impurity gas leaks out of the inner surface of the container during use of the ionization chamber or a leak of the enclosed gas occurs, a detector is used. The output current from the ionizer decreases, and the performance of the ionization chamber deteriorates.

Therefore, in order to confirm whether the detection characteristics of the ionization chamber of the monitoring post have not changed,
It is necessary to perform an irradiation test periodically to check the output current of the ionization chamber. Regarding the detection characteristics of the ionization chamber in a region where the radiation dose rate is low, for example, when the absorbed dose rate is several μGy / h, a low radioactivity source such as ¹³⁷ Cs (3.7 MBq) is separated from the ionization chamber by a predetermined distance. It is installed at a location for inspection. Specifically, the inspection is performed by fixing the sealed radiation source at a height of, for example, 1 meter from the roof of the station building.

On the other hand, when inspecting the performance of an ionization chamber in a region where the radiation dose rate is high, for example, when the absorbed dose rate is 100 mGy / h, if the inspection is to be performed by the above-described method, ⁶⁰ Co (370 GBq) is placed near the monitoring post. And other high radiation sources must be installed. However, it is very dangerous to work with such a source and inspection near the station is practically impossible. For this reason, when using a high radioactivity source, it is necessary to move the ionization chamber to another facility that can handle it and conduct inspections.

[0007] However, it is very time-consuming and labor-intensive to remove the ionization chamber installed on the rooftop of the station building and perform the inspection using a high-radiation source that requires close attention. There are problems such as this.

The present invention has been made in view of the above problems, and has as its object to provide an ionization chamber type radiation detection apparatus and an ionization chamber capable of inspecting the detection characteristics of an ionization chamber at a high dose rate without using a high radiation source. An object of the present invention is to provide a method for inspecting a box.

[0009]

In order to achieve the above object, an ionization chamber type radiation detecting apparatus according to the present invention comprises: an ionization chamber for detecting radiation; a power supply for applying a voltage to the ionization chamber; Voltage switching means for switching the voltage, including, when inspecting the detection characteristics of the ionization chamber at a high dose rate using a radiation source that irradiates a low dose rate radiation, the applied voltage of the power supply to a low voltage It can be switched.

[0010] With the above configuration, the voltage applied to the ionization chamber is switched to a low voltage by the voltage switching means.
Using a source that irradiates the ionization chamber with low dose rate radiation,
It can inspect the detection characteristics of the ionization chamber at high dose rates.

As will be described later, the detection characteristics of the ionization chamber when the ionization chamber to which a high voltage is applied are irradiated with radiation at a high dose rate, and the detection characteristics when the ionization chamber to which a low voltage is applied are irradiated with radiation at a low dose rate. There is a correlation between the detection characteristics of the ionization chamber,
Based on this relationship, it is not necessary to irradiate the ionization chamber with high dose rate radiation in order to inspect the detection characteristics at high dose rates. That is, by using a low radiation source, irradiating the ionization chamber with a low dose rate of radiation, and lowering the applied voltage according to the dose rate and inspecting the detection properties, the detection properties at the high dose rate Can be inspected indirectly.

The method for inspecting an ionization chamber is particularly useful when the ionization chamber is fixedly installed outdoors, for example, for inspecting an ionization chamber used for the above-mentioned monitoring post. In this case, the high dose rate refers to, for example, the level of the dose rate at which the ionization chamber needs to be moved to a conventional facility for inspection.

Preferably, the apparatus further includes low voltage variable means for varying a low voltage applied to the ionization chamber. This makes it possible to inspect the detection characteristics of the ionization chamber at a high dose rate in detail. In addition, the apparatus further includes a pass / fail determination unit that determines pass / fail of detection characteristics of the ionization chamber based on an output current of the ionization chamber.

In order to achieve the above object, an ionization chamber inspection method according to the present invention comprises a step of irradiating the ionization chamber with radiation at a low dose rate, and a step of lowering a voltage applied to the ionization chamber from a normal operating voltage. Switching to voltage and detecting the output current of the ionization chamber.

According to the above configuration, while irradiating the ionization chamber with radiation at a low dose rate, the voltage applied to the ionization chamber is switched from a normal operating voltage to a low voltage, and the output of the ionization chamber is reduced. By detecting the current, the detection characteristics of the ionization chamber at a high dose rate can be inspected based on the current.

Preferably, the first inspection includes a first inspection step of inspecting a detection characteristic of the ionization chamber at a low dose rate, and a second inspection step of inspecting a detection characteristic of the ionization chamber at a high dose rate. The step includes: a first irradiation step of irradiating the ionization chamber with radiation at a low dose rate; and a first detection step of applying a high voltage to the ionization chamber and detecting an output current of the ionization chamber. The second inspection step includes irradiating the ionization chamber with radiation at a low dose rate, and applying a low voltage to the ionization chamber to detect an output current of the ionization chamber. 2 detection steps.

According to the above configuration, in the first inspection step, a high voltage is applied to the ionization chamber while irradiating the ionization chamber with radiation at a low dose rate, and the radiation dose rate of the radiation is measured from the ionization chamber. And the detection characteristics of the ionization chamber at a low dose rate can be inspected based on the output current. Also,
In the second inspection step, a low voltage is applied to the ionization chamber while irradiating the ionization chamber with radiation at a low dose rate, an output current at the dose rate of the radiation is detected from the ionization chamber, and a high current is detected based on the output current. It is possible to inspect the detection characteristics of the ionization chamber at the dose rate.

[0018]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a view showing an entire configuration of a monitoring post 10 provided with an ionization chamber type radiation detecting apparatus according to an embodiment of the present invention. The monitoring post 10 is a facility for monitoring the radiation environment at the installation location.

First, the configuration of the monitoring post 10 and the operation during monitoring will be described. The ionization chamber type radiation detection apparatus includes an ionization chamber 12, a power supply unit 14 for applying a voltage to the ionization chamber 12, an electrometer 16 for converting an output current from the ionization chamber 12 into a voltage signal, and a voltage signal from the electrometer 16. The monitoring post 10 further includes a recording medium 22 and a transmitter 24. The counting post 18 calculates the dose rate and the like, and the display unit 20 outputs the result of the calculation by the counting post. In addition, the ionization chamber 12 and the electrometer 16 are provided on the monitoring post office building. The counting operation unit 18 and the like are provided in the station building.

The ionization chamber 12 comprises, for example, a spherical collector electrode 26 and a spherical container electrode 28 surrounding the collector electrode 26. Since the container electrode 28 is formed in a substantially spherical shape, radiation can be detected in all directions. A pressurized rare gas is sealed inside the container electrode 28, and when radiation is incident, the gas sealed inside is ionized. A high voltage is applied to the ionization chamber 12 to collect electric charges generated by the ionization and take out the ionization chamber 12 as an output current. The container electrode 28 has, for example, a radius of 30 cm and a capacity of 14 l, and has a pressure of 4 at, for example.
m Ar gas is sealed. However, the shape of the ionization chamber 12 and the type of gas filling are not limited to those described in the present embodiment. As the filling gas, a nitrogen gas or the like to which electrons and the like once ionized are unlikely to adhere may be used.

The power supply unit 14 for applying a voltage to the ionization chamber 12 includes a high-voltage power supply 30 for supplying a voltage at the time of use and a low-voltage power supply 32 for testing the detection characteristics of the ionization chamber 12 at a high dose rate. A high-voltage power supply 30 and a low-voltage power supply 32 are controlled by a switch mechanism 34 provided in the power supply unit 14.
Is switchable. During normal use of the apparatus, a voltage of, for example, −1000 V is applied to the container electrode 28 by the high-voltage power supply 30. The applied voltage of the low-voltage power supply 32 is, for example, −several volts, and the voltage value can be changed.

One end of a conducting wire 36 is connected to the collecting electrode 26, and the other end of the conducting wire 36 is drawn out of the ionization chamber 12 from the container electrode 28 via an insulator 38. The output current taken out of the ionization chamber 12 via the conducting wire 36 is converted into a voltage signal by the electrometer 16 and input to the counting operation unit 18. The electrometer 16 includes an operational amplifier 40, a resistor 42, and a capacitor 44. The resistor 42 and the capacitor 44 are used as a feedback element. For example, the resistance value can be switched stepwise from 1.5 TΩ to 1.5 × 10 MΩ.
Has a capacitance of 5 pF. The magnitude of the voltage signal output from the electrometer 16 is determined by the average current of the collected electric charge and the resistance of the resistor 42, and the time constant of the pulse of the voltage signal is determined by the resistance of the resistor 42 and the capacitance of the capacitor 44. It is determined by the product of Therefore, if the resistor 42 and the capacitor 44 are used as feedback elements as described above, a voltage signal corresponding to the average current of the collected charges can be obtained. Here, an amplifier, a waveform shaping circuit, and the like may be provided at a stage preceding the counting operation unit 18 as appropriate.

The counting operation section 18 includes an electrometer 16
Calculate radiation dose rate etc. based on the voltage signal from
The calculation result is output to the display 20, the recording medium 22, and the transmitter 24. Further, in the example shown in FIG.
, And the count calculation unit 18 and the determination unit 46 are realized on a microcomputer. However, a case where the quality determination is performed artificially without specially providing the determination unit 46 is also one embodiment of the present invention.

The display 20 is provided at the front of the monitoring post or the like, and displays the detected radiation dose rate and the like. The recording medium 22 is a memory for storing dose rate data and the like from the counting operation unit 18. In this way, data on the radiation environment can be analyzed in detail at a later date. Transmitter 2
4 transmits dose rate data and the like to a remote monitoring center (not shown) and the like. In this way, the radiation environment can be grasped at a remote place.

Next, the low dose rate of the ionization chamber 12 (for example, several μm)
Before describing the method of inspecting the detection characteristics at Gy / h) and a high dose rate (for example, 100 mGy / h), the detection characteristics at the time of normal operation and at the time of deterioration of the ionization chamber 12 will be described.

FIG. 2 is a diagram showing the relationship (saturation characteristic) between the applied voltage and the output current to the ionization chamber 12 when the dose rate of the radiation applied to the ionization chamber 12 is fixed. The horizontal axis represents the magnitude of the voltage applied to the ionization chamber 12, and the vertical axis represents the output current of the ionization chamber 12. The solid line indicates the saturation characteristics when the ionization chamber 12 is normal, and the dashed line indicates the ionization chamber 12.
When the detection characteristic of the sample is deteriorated, for example, the saturation characteristic is shown when an impure gas flows out from the inner surface of the container or a leak of the sealed gas occurs.

When the detection characteristics of the ionization chamber 12 are normal, as the applied voltage is increased from the low voltage side, the ionization chamber 1
The output current of No. 2 increases (see the A recombination region in the figure).
However, when the applied voltage is further increased, the output current saturates at a certain value, and even when the applied voltage is further increased, the output current value does not change much within a certain range (see the B saturation region in the figure). This is because, in a region where the applied voltage is low, the electric field generated in the ionization chamber 12 is weak, so that the speed of ions generated by ionization is low, and the collector electrode 26 or the container electrode 28
Before the ions arrive at the positive and negative ions.
This is known as recombination. That is, as the applied voltage is increased, the speed of the ions increases, and the ratio of the ions before they reach the electrodes decreases, so that the output current increases. When the applied voltage is further increased, almost all of the ions generated by ionization can be collected on the electrode, and the output power reaches the saturation value without further increasing. An output current in this saturation region is called a saturation current.

When the ionization chamber 12 is deteriorated, for example, when an impure gas spouts from the inner surface of the container, the concentration of the impurity gas in the ionization chamber 12 increases, and the ions recombine more than in the normal state. The percentage increases. Therefore, in order for the output current to reach the saturation current, it is necessary to apply a higher voltage than normal. In FIG. 2, the output current at the applied voltage V ₀ has reached the saturation current in the normal state, but the output current has decreased at the time of deterioration, and a loss from the saturation current (see a in the figure) is seen.

The behavior of the saturation characteristic shown in FIG. 2 basically does not depend on the magnitude of the dose rate of the radiation applied to the ionization chamber 12. That is, as the applied voltage increases, the output current of the ionization chamber 12 increases, and when the applied voltage is further increased, the output current saturates at a certain value. However, since the number of ions generated by ionization is proportional to the dose rate,
The value of the saturation current is proportional to the dose rate.

Next, the change in the output current of the ionization chamber 12 when the radiation dose rate is changed will be described with reference to FIG.
Here, a normal operating voltage (high voltage: 10) is applied to the ionization chamber 12.
00V) is applied. The horizontal axis indicates the absorbed dose rate of the radiation applied to the ionization chamber 12, and the vertical axis indicates the output current of the ionization chamber 12. The solid line indicates the case where the detection characteristics of the ionization chamber 12 are normal, and the dashed line indicates the case where the detection characteristics of the ionization chamber 12 are deteriorated.

When the detection characteristics of the ionization chamber 12 are normal, the output current is proportional to the dose rate of the incident radiation (dose rate linearity). The output current at each dose rate is a saturation current. On the other hand, an alternate long and short dash line indicates a case where the detection characteristics of the ionization chamber 12 are deteriorated. The output current is almost proportional to the dose rate on the low dose rate side, but the dose rate linearity is reduced on the high dose rate side. This is because the impurity gas concentration in the ionization chamber 12 increases and the output current is reduced by the amount of loss from the saturation current (see b in the figure).
Is caused. On the high dose rate side, the proportion of the loss is increased because the rate of recombination of ions depends on its density, and the proportion of recombination increases as the density of ions increases.

Therefore, in general, in order to inspect the detection characteristics of the ionization chamber 12 at a predetermined dose rate, a working voltage is applied to the ionization chamber 12, and the ionization chamber 12 is irradiated with a radiation source corresponding to a target dose rate, and the ion beam is irradiated therefrom. May be detected to check whether the output current has reached the saturation current.

FIG. 4 shows a process of inspecting the detection characteristics of the ionization chamber at a low dose rate, for example, an absorption dose rate of several μGy / h. First, a low-radiation radiation source 48 (see a dotted line in FIG. 1), for example, ¹³⁷ Cs (3.7 MBq) or the like is arranged at a predetermined position, and the radiation is irradiated onto the ionization chamber 12 at a low dose rate (S101). . Here, the radiation source 48 is fixed, for example, at a position one meter from the roof of the station building. Next, the high voltage power supply 30
With the use voltage applied to the ionization chamber 12, the output current from the ionization chamber 12 is detected by the electrometer 16 (S102). The electrometer 16 converts the output current into a voltage signal, and based on the converted signal, determines whether the detection characteristics of the ionization chamber 12 are good or not based on a predetermined reference (S103). As a determination method, for example, if the ratio of the loss from the detected saturation current to the saturation current is within ± 5%, it is determined that the detection characteristics are normal. Otherwise, the ionization chamber 12 is deteriorated. Should be determined. The determination result is output to the display 20, the recording medium 22, the transmitter 24, and the like.

In inspecting the detection characteristics, if the value of the dose rate to be inspected is sufficiently low, a radiation source corresponding to the target dose rate may be used, but if the target dose rate is high (for example,
00mGy / h), there are cases where a high-dose-rate source cannot be used directly, in which case the above method cannot be used.

However, when the ionization chamber 12 to which the working voltage is applied is irradiated with radiation at a high dose rate, the detection characteristics of the ionization chamber 12 are as follows.
There is a correlation with the detection characteristics of the ionization chamber 12 when irradiating low dose rate radiation to the ion beam, and the detection characteristics of the ionization chamber 12 are inspected using a low dose rate source without using a high dose rate source. be able to.

FIG. 5 shows the saturation characteristics of the ionization chamber 12 and the low dose rate (several μGy) when a voltage near the working voltage (high voltage: 1000 V) is applied at a high dose rate (100 mGy / h).
/ H) illustrates the saturation characteristics of the ionization chamber 12 when a low voltage (several V) is applied. The horizontal axis is the ionization chamber 1
2, the vertical axis indicates the output current of the ionization chamber 12. The solid line is the saturation characteristic at the time of normal operation, and the dotted line is the saturation characteristic at the time of deterioration. Above right, absorbed dose rate is 100m
Part of the saturation characteristic at Gy / h is shown. On the other hand, the lower left shows the saturation characteristics when the absorbed dose rate is several μGy / h. As can be seen from the figure, the saturation characteristics when applying high dose rate radiation and applying high voltage are similar to the saturation characteristics when applying low dose rate radiation and applying low voltage. It can be seen that there is a correlation between the two.

When the applied voltage is 1000 V, the saturation current I ₁ is an output current in a normal state, and a loss δI ₁ (see c in the figure) from the saturation current due to recombination occurs in a degraded state.
On the other hand, on the low voltage side, the saturation current obtained under normal conditions is defined as I _2, and the loss from the saturation current when deteriorated is represented by δI ₂
(See d in the figure) By properly selecting the value of the voltage, the ratio of the saturation current to the loss δI ₁ / I ₁ and δI ₂ / I ₂ can be made equal. Conversely, I
₂ and δI ₂ , the absorbed dose rate is 100 mGy /
h. The detection characteristics of the ionization chamber 12 at an applied voltage of 1000 V can be inspected.

Hereinafter, for simplicity, the above correlation will be specifically examined in an ionization chamber in which a voltage is applied between parallel plate electrodes. The ratio δI / I between the saturation current I of the ionization chamber and the loss δI from the saturation current due to recombination is given by the following equation.

[0040]

## EQU1 ## δI / I = (α · N ₀ · d ² ) / (6 · w ₊ · w ₋ ) (1) where δI is positive when loss occurs. Here, α is the recombination coefficient, N ₀ is the ion generation rate per unit time, d is the distance between the electrodes, w ₊ is the speed of positive ions, and w _- is the speed of negative ions. The velocity w ± of the positive / negative ions is determined by the electric field E in the ionization chamber, the gas pressure P in the ionization chamber, and the mobility μ ± of the positive / negative ions, and the relation of w ± = μ ± E / P There is. Here, the ion generation rate N ₀ per unit time is proportional to the absorbed dose rate, and the electric field is expressed as voltage and E = V
Note that δI / I is proportional to absorbed dose rate and inversely proportional to V ² . Working voltage 1000V
When it is desired to measure δI / I at a high dose rate, for example, an absorbed dose rate of 100 mGy / h, the same δI / I can be measured using a low-activity source. For example, if the absorbed dose rate is 0.3 μGy / h, the same δI / I can be measured by reducing the applied voltage to about 1.7 V by simple calculation.

Equation (1) holds true only in the ionization chamber having the parallel plate electrodes, and the ratio δI / I of the saturation current I of the ionization chamber and the loss δI from the saturation current due to recombination is obtained. Generally, the relationship that the ratio increases when the absorbed dose rate increases and decreases when the applied voltage, that is, the electric field in the ionization chamber increases, generally holds regardless of the shape of the ionization chamber.

Therefore, in order to inspect the detection characteristics of the ionization chamber 12 at a high dose rate without using a high dose rate radiation source, the ionization chamber 12 is irradiated with a low dose rate radiation source and the applied voltage is used. The output current of the ionization chamber 12 may be detected by switching from the voltage to the low voltage, and may be compared with the normal output current when the ionization chamber 12 is irradiated with a low dose rate radiation source.

FIG. 6 shows a process for inspecting the detection characteristics of the ionization chamber at a high dose rate, for example, at an absorbed dose rate of 100 mGy / h, without using a high radiation source. First, a low-radiation source 48 (see the dotted line in FIG. 1), for example, ¹³⁷ Cs
(3.7 MBq) or the like is placed at a predetermined position, and the radiation is applied to the ionization chamber 12 at a low dose rate (S201). here,
As the low-radiation source 48, the same source as that used when inspecting the detection characteristics of the ionization chamber at the low dose rate described above may be used. Next, while the power supply of the ionization chamber 12 is switched from the high voltage power supply 30 to the low voltage power supply 32 by the switch mechanism 34, the output current from the ionization chamber 12 is detected by the electrometer 16 (S202). The counting operation unit 18 records the voltage signal from the electrometer 16 (S203). Next, the applied voltage is changed (S2
04) The voltage signal associated with the change is sequentially recorded by the counting operation unit 18. Based on the record, the quality of the detection characteristics of the ionization chamber 12 is determined based on a predetermined reference (S205), and the result is displayed on the display 20 and the recording medium 2 (S205).
2. Output to the transmitter 24.

The pass / fail judgment may be made without changing the applied voltage. In this case, if the ratio of the loss from the detected saturation current to the saturation current is within ± 5%, the detection characteristics are normal. It is determined that there is, and if not, the ionization chamber 12
May be determined to be degraded. When the applied voltage is changed, the voltage may be compared with a known voltage signal obtained when the ionization chamber 12 is normal, or based on a graph shape, for example, a slope of a series of voltage signals obtained with the change in the applied voltage. Is also good. In this embodiment, the pass / fail determination is performed by the determination unit 46. However, a case where the determination is performed artificially is one aspect of the present invention.

In the present embodiment, the detection characteristics of the ionization chamber at a high dose rate were examined using a low radiation source.
In general, by changing the applied voltage while irradiating the ionization chamber with radiation of a predetermined dose rate, the detection characteristics of the ionization chamber at an arbitrary dose rate can be inspected.

The switching of the voltage power supply by the switch of the power supply unit 14 may be performed manually.
The control may be performed by using.

The ionization chamber type radiation detector and the ionization chamber inspection method described above are not limited to the ionization chamber for gamma ray measurement, but can be applied to any ionization chamber as long as it utilizes the ionization effect of the sealed gas. .

[0048]

As described above, according to the ionization chamber type radiation detection apparatus and the ionization chamber inspection method of the present invention, the ionization chamber detection characteristics at a high dose rate can be obtained by using a high radiation source. Can be inspected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a monitoring post provided with an ionization chamber type radiation detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a saturation characteristic of an ionization chamber.

FIG. 3 is a diagram showing detection characteristics of an ionization chamber.

FIG. 4 is a flowchart showing a process of inspecting the detection characteristics of the ionization chamber at a low dose rate.

FIG. 5 is a diagram showing a correlation between the saturation characteristics of the ionization chamber at a high dose rate and those at a low dose rate.

FIG. 6 is a flowchart showing a process of inspecting a detection characteristic of an ionization chamber at a high dose rate.

[Explanation of symbols]

Reference Signs List 10 monitoring post, 12 ionization chamber, 14 power supply unit, 16 electrometer, 18 counting operation unit, 20 display, 22 recording medium, 24 transmitter.

Claims (5)

[Claims] 1. An ionization chamber for detecting radiation, a power supply for applying a voltage to the ionization chamber, and voltage switching means for switching a voltage applied to the power supply, comprising: An ionization chamber type radiation detection apparatus, wherein the applied voltage of the power supply is switched to a low voltage when inspecting the detection characteristics of the ionization chamber at a high dose rate using the apparatus. 2. The ionization chamber type radiation detection apparatus according to claim 1, further comprising: a low voltage variable unit that varies a low voltage applied to the ionization chamber. 3. The ionization chamber-type radiation detection device according to claim 1, further comprising a pass / fail determination unit that determines pass / fail of a detection characteristic of the ionization chamber based on an output current of the ionization chamber. Ionization chamber type radiation detector. 4. An ionization chamber inspection method for inspecting the detection characteristics of an ionization chamber at a high dose rate, comprising: irradiating the ionization chamber with radiation at a low dose rate; and applying a voltage to the ionization chamber. Switching from a normal operating voltage to a low voltage to detect an output current of the ionization chamber. 5. A first inspection step for inspecting a detection characteristic of the ionization chamber at a low dose rate, and a second inspection step for inspecting a detection characteristic of the ionization chamber at a high dose rate.
An inspection step, wherein the first inspection step includes: a first irradiation step of irradiating the ionization chamber with radiation at a low dose rate; and applying a high voltage to the ionization chamber to output the ionization chamber. A first detection step of detecting a current; a second irradiation step of irradiating the ionization chamber with radiation at a low dose rate; and applying a low voltage to the ionization chamber. A second detection step of detecting an output current of the ionization chamber.