JP2023045462A - Radioactivity measurement device - Google Patents

Abstract

To provide a radioactivity measurement device that enables discriminating between a low-energy α-ray and β-ray and counting the α-ray and β-ray, and enables statistical data to be accumulated more quickly.SOLUTION: A radioactivity measurement device 100 comprises: a first integration circuit 21 that performs integration processing, with a first time constant T1, on electric pulse signals outputted from a detector 1, and outputs an integration pulse of a peak height value PH1; and a second integration circuit 22 that performs the integration processing, with a second time constant T2 (T2>T1), on the electric pulse signals, and outputs an integration pulse of a peak height value PH2. A discrimination unit 24 has a threshold that is represented as a function of the PH2 in a scatter diagram with a horizontal axis being the PH2 and a vertical axis being a ratio of the peak height values (PH2/PH1), and is configured to, when the ratio of the peak height values of the electric pulse signal is greater than the threshold, determine that the electric pulse signal is an α-ray, or, when the ratio of the peak height values thereof is smaller than the threshold, determine that the electric pulse signal is a β-ray, thereby, enabling discrimination between the low-energy α-ray and β-ray, and counting the α-ray and β-ray.SELECTED DRAWING: Figure 9

Description

The present application relates to a radioactivity measuring device.

Measurement of the amount of radioactivity present in the air is mainly performed to confirm that the air does not contain radioactivity emitted from nuclear facilities. For this reason, the radioactivity measurement equipment is equipped with α-rays mainly emitted by naturally occurring radioactivity, and β-rays emitted by both naturally occurring radioactivity and artificial radioactivity (radiated from nuclear-related facilities, etc.). and are required to be measured with one detector.

Conventionally, an α/β detector that combines a sensor that detects α rays and a sensor that detects β rays into one detector has been widely applied in nuclear power plants, environmental radiation monitoring systems, and the like. Since the output signal of the α/β detector is a mixture of the α-ray detection signal and the β-ray detection signal, the signal processing unit is applied with an α/β discrimination technique for distinguishing and measuring the α-rays and the β-rays. Aiming to improve the α/β discrimination technique, various α/β discrimination circuits have been proposed so far.

The α/β discriminating circuit realizes discrimination by utilizing the fact that the shape of the electrical pulse signal output by the α/β detector differs between α rays and β rays. In general, an α-ray electric pulse signal rises slowly, and a β-ray electric pulse signal rises sharply. Utilizing such characteristics, there is known a method for discriminating between α rays and β rays by passing an electrical pulse signal through a differentiating circuit and outputting the sharpness of the rise of the electrical pulse signal (see Patent Document 1. described as prior art).

In addition, as a simple discrimination method using the wide pulse width of α-rays, the electric pulse signal from the photomultiplier tube of the α/β detector is converted from analog to digital and integrated with two types of integration times. A method is used to discriminate α rays and β rays depending on whether or not exceeds a set value (threshold value).

JP-A-5-19061

However, in the discrimination method using a differentiating circuit, when the radiation energy of α-rays and β-rays is low, the crest height of the electrical pulse signal becomes low, making it difficult to distinguish between rising portions of α-rays and β-rays. In other words, the differentiating circuit is a high-pass filter, and the α-ray electric pulse signal, which rises slowly and is in a low frequency band, is attenuated when passed through the differentiating circuit. Therefore, in the case of low-energy α-rays with a low wave height of the electric pulse signal before passing through the differentiating circuit, there arises a problem that it cannot be read as a pulse after passing through the differentiating circuit.

In addition, even in the conventional integral type discrimination method, there is a problem that low-energy α-rays cannot be discriminated as pulses because of their low wave heights, and undistinguished waveforms are discarded as noise. In this way, with conventional radioactivity measuring devices, it is difficult to discriminate between low-energy α-rays and β-rays, especially α-ray electrical pulse signals. There was a problem that it took time to accumulate statistical data, and anomaly detection could not be executed immediately.

The present application discloses a technique for solving the above-mentioned problems, which enables discrimination and counting of low-energy α-rays and β-rays, and speeds up the accumulation of statistical data. An object of the present invention is to obtain a radioactivity measuring device.

The radioactivity measuring device disclosed in the present application has an α-ray sensor for detecting incidence of α-rays and a β-ray sensor for detecting incidence of β-rays. a detector for outputting an electric pulse signal by means of a detector; a first integration circuit for integrating the electric pulse signal output from the detector with a first time constant and outputting a first output pulse signal; a second integration circuit installed in parallel with the circuit for integrating an electrical pulse signal output from the detector with a second time constant larger than the first time constant and outputting a second output pulse signal; a comparison unit that calculates a peak value ratio based on the peak value of the first output pulse signal output from the first integration circuit and the peak value of the second output pulse signal output from the second integration circuit; , a threshold value set for each peak value of the second output pulse signal, and the electric pulse signal is detected as α-rays based on the ratio of the peak values output from the comparing unit and the threshold value; and a discriminating unit that discriminates which of the β rays.

According to the radioactivity measuring apparatus disclosed in the present application, the electric pulse signal is divided into α-rays and β-rays based on the ratio of the threshold value set for each peak value of the second output pulse signal and the peak value. By discriminating which is which, highly accurate discrimination is possible even when the energy of the α ray or β ray is low and the wave height of the electrical pulse signal is low. This makes it possible to count low-energy α-rays and β-rays, and speed up the accumulation of statistical data.

1 is a block diagram showing a radioactivity measuring device according to Embodiment 1; FIG. 2 is a perspective view showing a detector of the radioactivity measuring device according to Embodiment 1. FIG. 3A and 3B are a sectional view showing an internal configuration of a detector and a sectional view showing a sensor section of the radioactivity measuring device according to Embodiment 1; FIG. 4 is a diagram for explaining the shape of an electrical pulse signal input to the gate integration type waveform discrimination circuit according to Embodiment 1; FIG. 4 is a diagram for explaining the relationship between the time constants of the first and second integrating circuits and the shape of the β-ray pulse signal according to Embodiment 1; FIG. 4 is a diagram showing integrated pulses caused by β-rays output by the first and second integrating circuits according to the first embodiment; FIG. 4 is a diagram for explaining the relationship between the time constants of the first and second integrating circuits and the shape of the α-ray pulse signal according to Embodiment 1; FIG. 4 is a diagram showing integrated pulses caused by α-rays output by the first and second integrating circuits according to the first embodiment; FIG. 4 is a scatter diagram obtained by two-dimensionally plotting the ratio of the output peak values of the first and second integrating circuits and the output peak value of the second integrating circuit according to Embodiment 1; FIG. 5 is a diagram showing the flow of processing of an electrical pulse signal in the gate integration type waveform discrimination circuit according to Embodiment 1; FIG. 2 is a scatter diagram obtained by two-dimensionally plotting naturally occurring total α radioactivity and total β radioactivity simultaneously measured in a normal environment using the radioactivity measuring device according to Embodiment 1. FIG. FIG. 4 is a schematic diagram illustrating the configuration of a gas monitor, which is a radioactivity measuring device according to Embodiment 2; FIG. 11 is a schematic diagram illustrating the configuration of a dust monitor, which is a radioactivity measuring device according to Embodiment 3;

Embodiment 1.
A radioactivity measuring device according to Embodiment 1 will be described below with reference to the drawings. FIG. 1 is a block diagram showing the functional configuration of a radioactivity measuring device according to Embodiment 1, FIG. 2 is a perspective view showing a detector of the radioactivity measuring device according to Embodiment 1, and FIG. , and a cross-sectional view of a portion indicated by AA' in FIG. 2, and FIG. 3B is a cross-sectional view showing the sensor portion of the detector. In addition, in each figure, the same code|symbol is attached|subjected to the same and a corresponding part.

The radioactivity measuring device 100 according to Embodiment 1 detects α-rays and β-rays emitted by a radioactive substance, and measures α-ray emitting radioactivity or β-ray emission as the amount of the radioactive substance emitting α-rays or β-rays. It is for evaluating radioactivity, and as shown in FIG. The gate integration type waveform discrimination circuit 2 also includes a preamplifier 20 , a first integration circuit 21 , a second integration circuit 22 , a comparison section 23 , a discrimination section 24 , and a high-voltage power supply 25 .

In addition, the device configuration of the radioactivity measuring device 100 is not limited to that shown in FIG. may be provided. Also, in the gate integration type waveform discrimination circuit 2, the comparing section 23 and the discriminating section 24 are shown separately, but the functions of the comparing section 23 and the discriminating section 24 may be realized by one device (circuit).

The detector 1 has an α-ray sensor for detecting incident α-rays and a β-ray sensor for detecting incident β-rays. Output. As shown in FIG. 2, the detector 1 has a cylindrical detector case 10 made of aluminum steel, and detects radiation incident through an entrance window 11c at the tip of the cylinder. When radiation enters inside the detector case 10 through the entrance window 11c, the sensor material emits light. The detector 1 converts this light emission quantity into an electric quantity and outputs it as an electric pulse signal P to the preamplifier 20 .

As shown in FIG. 3( a ), the detector 1 includes a sensor section 11 , a photomultiplier tube 12 and a divider circuit 13 inside a cylindrical detector case 10 . Further, as shown in FIG. 3B, the sensor unit 11 includes an incident window 11c having a thickness of about 10 micrometers and excellent light shielding performance, an α-ray sensor 11a that mainly reacts with α-rays, and a β-ray. β-ray sensor 11b, which mainly reacts, is overlapped.

When the α-rays pass through the entrance window 11c and reach the α-ray sensor 11a, the α-ray sensor 11a emits light, and the light passes through the β-ray sensor 11b and reaches the photocathode at the tip of the photomultiplier tube 12. do. When the β rays pass through the incident window 11 c and reach the β ray sensor 11 b , the β ray sensor 11 b emits light, and the light reaches the photocathode at the tip of the photomultiplier tube 12 . It should be noted that the β rays do not noticeably react even if they reach the α ray sensor 11a.

The light emitted by the α-ray sensor 11a or the β-ray sensor 11b generates a number of photoelectrons on the photocathode of the photomultiplier tube 12 in proportion to the amount of light. The photoelectrons are amplified by the voltage supplied from the high-voltage power supply 25 and the divider circuit 13 to generate an electric pulse signal P, which is output from the signal cable 14 to the preamplifier 20 . The detector 1 outputs an electric pulse signal P once each time an α ray or a β ray is incident.

Since α-rays have a range of only a few centimeters in the air and are very easy to stop, the entrance window 11c is thin enough to allow α-rays to pass through, and also has a light shielding function that blocks external light that causes electrical noise. Aluminum mylar or the like, which has excellent properties, is used. Silver-activated zinc sulfide (ZnS(Ag)) or the like, which is highly sensitive to charged particles, is used for the α-ray sensor 11a. Also, β-rays are relatively easily shielded, though not as much as α-rays. Therefore, a plastic scintillator is used for the β-ray sensor 11b so that it can be used without being placed in a protective case. In addition, the thickness of the plastic scintillator is set to several millimeters to make it insensitive to unnecessary gamma rays.

Since the detector 1 can simultaneously measure α-rays and β-rays, radioactivity that emits α-rays and β-rays, radioactivity that emits only α-rays, and radioactivity that emits only β-rays can be measured. can do. In addition, by adjusting the thickness of the plastic scintillator to be thin, the sensitivity to gamma rays is lowered, and when gamma rays are detected, an electric pulse signal P with an electric noise level is output, and the electric noise is removed together with the electric noise. .

Next, the gate integration type waveform discrimination circuit 2 that processes the electrical pulse signal P output from the detector 1 and discriminates it into α rays and β rays will be described. The preamplifier 20 amplifies and shapes the electrical pulse signal P. Although the preamplifier 20 is included in the gate integration type waveform discrimination circuit 2 in FIG. Further, when the electric pulse signal P is sufficiently large for the processing of the subsequent circuit, the preamplifier 20 may not have the amplifying function.

The shape of the electrical pulse signal P input to the gate integration type waveform discrimination circuit 2 will be described with reference to FIG. In FIG. 4, the horizontal axis is time, the vertical axis is voltage, and the pulse width is time width. The β-ray pulse signal 101 is the waveform of the electrical pulse signal P caused by the incidence of β-rays, and the α-ray pulse signal 201 is the waveform of the electrical pulse signal P caused by the incidence of α-rays. The heights of the β-ray pulse signal 101 and the α-ray pulse signal 201 are proportional to the energy of the α-rays or β-rays incident on the detector 1 .

As shown in FIG. 4, the β-ray pulse signal 101 has a sharp sharpness and a pulse width of about 20 nanoseconds, and the α-ray pulse signal 201 has a gentle sharpness and a long pulse width of about 200 nanoseconds. be. The specific numerical value of the pulse width varies depending on the settings of the preamplifier 20, the circuit constants of the first integration circuit 21 and the second integration circuit 22, and the like. Different digits are different.

The first integration circuit 21 integrates the electrical pulse signal output from the detector 1 with a first time constant and outputs a first output pulse signal. In Embodiment 1, the electrical pulse signal P output from the detector 1, amplified and shaped by the preamplifier is integrated with a first time constant T1 (see FIGS. 5(a) and 7(a)), An integration pulse P1, which is the first output pulse signal, is output.

The second integration circuit 22 is installed in parallel with the first integration circuit 21, and integrates the electrical pulse signal output from the detector 1 with a second time constant larger than the first time constant. A second output pulse signal is output. In Embodiment 1, the electric pulse signal P output from the detector 1 and amplified and shaped by the preamplifier is set to a second time constant T2 (FIGS. 5(b) and 7( b) is integrated in step (see b)), and an integrated pulse P2, which is a second output pulse signal, is output. The integral pulse P1 and the integral pulse P2 have peak values PH1 and PH2 that are proportional to the integral values.

The first integration circuit 21 and the second integration circuit 22 have the same circuit configuration, and circuit elements are selected so that only the time constant corresponding to the time for integration processing (hereinafter referred to as integration time) is different. For example, the first time constant T1 of the first integration circuit 21 is set to 30 ns, which encompasses approximately 20 ns of the pulse width of the β-ray pulse signal 101 (see FIG. 4). The width of the β-ray pulse signal 101 includes a time constant of approximately 30 nanoseconds even if there is some variation.

Also, the second time constant T2 of the second integration circuit 22 is set to 1 microsecond, which encompasses approximately 200 nanoseconds of the width of the α-ray pulse signal 201 (see FIG. 4). Although the width of the α-ray pulse signal 201 varies greatly from 200 nanoseconds, a time constant of approximately 1 microsecond is included. However, the value of the time constant is not limited to these, and can be changed as appropriate.

The relationship between the time constant and the crest value of the integrated pulse will be described with reference to the drawings. As described above, the crest values PH1 and PH2 of the integral pulses P1 and P2 are proportional to the integral value, and thus change depending on the value of the time constant, which is the integral time. Therefore, the crest value of the integral pulse can be adjusted by the time constant.

FIG. 5(a) shows the relationship between the first time constant of the first integration circuit and the shape of the β-ray pulse signal, and FIG. 5(b) shows the relationship between the second time constant of the second integration circuit and It shows the relationship with the shape of the β-ray pulse signal. As shown in FIGS. 5A and 5B, both the first time constant T1 of the first integration circuit 21 and the second time constant T2 of the second integration circuit 22 are It is set larger than the pulse width of the signal 101 . Therefore, the integration pulse P1 output from the first integration circuit 21 and the integration pulse P2 output from the second integration circuit 22 have substantially the same integrated value.

FIG. 6 shows integrated pulses caused by β rays output from the first and second integration circuits. In FIG. 6, the β-ray first integrated pulse 102 is the integrated pulse P1 caused by the β-ray output by the first integration circuit 21, and the β-ray second integrated pulse 103 is output by the second integration circuit 22. is the integrated pulse P2 caused by the β-rays. The peak value PH1 of the β-ray first integrated pulse 102 and the peak value PH2 of the β-ray second integrated pulse 103 are approximately the same.

FIG. 7(a) shows the relationship between the first time constant of the first integration circuit and the shape of the α-ray pulse signal, and FIG. 7(b) shows the relationship between the second time constant of the second integration circuit and It shows the relationship with the shape of the α-ray pulse signal. As shown in FIG. 7A, the first time constant T1 of the first integration circuit 21 is set smaller than the pulse width of the α-ray pulse signal 201, so that the α-ray pulse signal 201 is sufficiently integrated. cannot be processed.

On the other hand, as shown in FIG. 7B, the second time constant T2 of the second integration circuit 22 is set to be larger than the pulse width of the α-ray pulse signal 201, so that the α-ray pulse signal 201 is sufficiently can be integrated into Therefore, the integration pulse P1 output from the first integration circuit 21 and the integration pulse P2 output from the second integration circuit 22 are integrated values having a significant difference.

FIG. 8 shows integrated pulses caused by α-rays output from the first and second integration circuits. In FIG. 8, the α-ray first integrated pulse 202 is the integrated pulse P1 caused by the α-ray output by the first integration circuit 21, and the α-ray second integrated pulse 203 is output by the second integration circuit 22. is the integrated pulse P2 caused by the α-rays. A significant difference appears between the peak value PH1 of the α-ray first integrated pulse 202 and the peak value PH2 of the α-ray second integrated pulse 203, and PH2 is twice as large as PH1.

The integration circuit is a so-called low-pass filter, and for the α-ray pulse signal 201 that has a gentle rise and is in a low frequency band, the α-ray first integrated pulse 202 and the α-ray second integrated pulse 203 after passing through the integration circuit are noticeable. is not attenuated. Therefore, even when the α-rays incident on the detector 1 have low energy and the wave height of the α-ray pulse signal 201 is low, the first integrated pulse 202 of α-rays and the second integrated pulse of α-rays 203 are detected by the comparator 23 as waves. It is at a level where it is possible to find the ratio of the high price.

Note that the first integration circuit 21 and the second integration circuit 22 may each be configured by an analog circuit. Alternatively, analog-to-digital conversion (hereinafter referred to as AD conversion) may be performed before each integration circuit, and integration by numerical calculation may be performed by an FPGA (Field Programmable Gate Array) or CPU (Central Processing Unit).

The comparison unit 23 calculates the peak value based on the peak value of the first output pulse signal output from the first integration circuit 21 and the peak value of the second output pulse signal output from the second integration circuit 22. Find the ratio of In the first embodiment, the integration pulses P1 and P2 output from the first integration circuit 21 and the second integration circuit 22 are compared and processed to obtain the peak value PH1 of the integration pulse P1 and the peak value PH2 of the integration pulse P2. Find the ratio (PH2/PH1). Specifically, the peak values PH1 and PH2 are obtained as digital values and compared. When each integration circuit performs integration by numerical calculation, the ratio of integrated values is obtained directly.

The discriminating unit 24 has a threshold set for each peak value of the second output pulse signal, and discriminates the electric pulse based on the ratio of the peak values output from the comparing unit 23 and the threshold. Discriminate whether the signal is alpha or beta ray. The threshold value of the discriminating section 24 is PH1, which is the peak value of the integrated pulse P1 (first output pulse signal) obtained by the first integrating circuit 21, and PH1, which is the peak value of the integrated pulse P2 (first output pulse signal) obtained by the second integrating circuit 22. 2) is represented as a function of PH2 in a scatter diagram with PH2 on the horizontal axis and PH2/PH1 on the vertical axis.

A method of setting the threshold value of the discriminating section 24 will be described with reference to FIG. FIG. 9 is a scatter diagram obtained by two-dimensionally plotting the ratio of the output peak values of the first and second integrating circuits and the output peak value of the second integrating circuit. As shown in FIG. 9, the horizontal axis represents peak values PH1 and PH2 respectively derived from integration pulses P1 and P2 successively input to the comparison unit 23 from the first integration circuit 21 and the second integration circuit 22. is represented on a scatter diagram with PH2 and the vertical axis is PH2/PH1, two groups are formed.

The threshold D is expressed as a function of PH2 on this scatter diagram, the group in the region where PH2/PH1 is larger than the threshold D is the α-ray group 211, and the PH2/PH1 is smaller than the threshold D. A group in the region becomes the β-ray group 111 . Based on this scatter diagram, the discriminating unit 24 determines that the electrical pulse signal is α rays when PH2/PH1 is greater than the threshold value D, and when PH2/PH1 is smaller than the threshold value D It can be determined that the electric pulse signal is a β ray.

As another threshold setting method, a threshold correspondence table in which a threshold is set for each crest value PH2 of the second output pulse signal can be created based on the scatter diagram of FIG. At that time, it is also possible to divide regions according to the level of the peak value PH2 of the second output pulse signal and create a threshold value correspondence table for regions in which both the β-ray group 111 and the α-ray group 211 exist. good.

For example, in FIG. 9 , only the β-ray group 111 exists and the α-ray group 211 does not exist in the area where the crest value PH2 on the horizontal axis is small (this is defined as the first area). Therefore, an integral pulse having a peak value PH2 in the first region can be determined to be a β ray without comparing the peak value ratio with the threshold value D. FIG. Moreover, when the level of the peak value PH2 is higher than that in the first region, there is a second region in which both the β-ray group 111 and the α-ray group 211 are present. For the integral pulse having the peak value PH2 in the second region, the ratio of the peak values is compared with the threshold value D to determine whether it is an α ray or a β ray.

In the third region where the level of the peak value PH2 of the second output pulse signal is higher than that in the second region, only the α-ray group 211 exists and the β-ray group 111 does not exist. Therefore, an integrated pulse having a peak value PH2 in the third region can be determined to be an α-ray without comparing the ratio of the peak values with the threshold value D. FIG. In this way, the level of the peak value PH2 is divided into the first region, the second region, and the third region. You can create a table with

Even with the α-ray pulse signal 201 having a low wave height caused by low-energy α-rays, there is a significant difference between the integrated values of the integral pulses P1 and P2, and PH2 is sufficiently larger than PH1 (twice in FIG. 8). or higher). For this reason, a threshold value is set for each peak value PH2 of the integral pulse P2, and α rays and β rays are discriminated based on the ratio of the peak values output from the comparator 23 and the threshold value. can be discriminated and counted even for α-rays, and the number of α-rays used as statistical data can be increased.

Furthermore, the discriminating unit 24 has an α-ray counter and a β-ray counter. and outputs to the counting unit 3 an α-ray discrimination signal to which the digital information of the total α-ray count and a β-ray discrimination signal to which the digital information of the total β-ray count is inputted.

The α-ray counter and the β-ray counter accumulate the number of α-rays and the number of β-rays, respectively, in a constant period, obtain the total counts of α-rays and β-rays at the end of accumulation in each period, and obtain the α-ray discrimination signal and β-rays. A line discrimination signal is transmitted to the counting unit 3 . After transmission, the total counts of the α-ray counter and the β-ray counter are reset.

The high-voltage power supply 25 supplies power to the detector 1 as a power supply, but is often arranged on the side of the gate integration type waveform discrimination circuit 2, so it is included in the gate integration type waveform discrimination circuit 2 in FIG. ing. The power supply from the high voltage power supply 25 is normally supplied to the preamplifier 20 circuitry. A capacitor as a so-called coupling capacitor is installed on the input side of the circuit of the preamplifier 20 so that a high voltage is not applied to the output side of the preamplifier 20 .

The flow of processing the electrical pulse signal in the gate integration type waveform discrimination circuit 2 will be described with reference to the flow chart of FIG. When the electric pulse signal P is input from the detector 1 to the gate integration type waveform discrimination circuit 2, if the gate integration type waveform discrimination circuit 2 has a preamplifier 20, the dynamic range of the gate integration type waveform discrimination circuit 2 is matched. The pulse wave height is adjusted by amplifying the electric pulse signal P so that the pulse wave height is adjusted (step S1).

Subsequently, the electric pulse signal P is input to the first integration circuit 21 and the second integration circuit 22 (step S2). AD conversion is performed when the integrating circuit is realized by numerical calculation. Next, the electrical pulse signal P is integrated by the first integration circuit 21 and the second integration circuit 22 (step S3).

Next, the integration pulse P1 output from the first integration circuit 21 and the integration pulse P2 output from the second integration circuit 22 are input to the comparator 23 (step S4). Subsequently, the peak values PH1 and PH2 of the integrated pulses P1 and P2 are respectively detected in the comparator 23, and the ratio (PH2/PH1) of the peak values of the two integrated pulses P1 and P2 is calculated (step S5). Next, the discrimination unit 24 compares the peak value ratio (PH2/PH1) with the threshold value D (step S6).

If PH2/PH1 is greater than the threshold value D (step S6: Yes), it is determined that the electrical pulse signal P is caused by alpha rays, and 1 is added to the alpha ray counter (step S7a). . If PH2/PH1 is smaller than the threshold value D (step S6: No), it is determined that the electrical pulse signal P is caused by β rays, and 1 is added to the β ray counter (step S7b). . Finally, the discriminating unit 24 aggregates the quantities of α-rays and β-rays per unit time and outputs them to the counting unit 3 (step S8).

The counting unit 3 counts the α-ray discrimination signal and the β-ray discrimination signal, which are the discrimination results of the discriminating unit 24, each for a preset counting time. Furthermore, the α-ray count rate is calculated by dividing the α-ray integrated value, which is the count result of the α-ray discrimination signal, by the counting time, and the β-ray integrated value, which is the count result of the β-ray discrimination signal, is divided by the counting time. to calculate the β-ray count rate.

For example, an α-ray discrimination signal and a β-ray discrimination signal are transmitted from the discrimination section 24 every minute, and the α-ray count information recorded in the α-ray discrimination signal and the β-ray discrimination signal are recorded in the counting section 3 for 60 minutes, for example. and the β-ray count information provided are respectively added. That is, based on 60 α-ray discrimination signals and β-ray discrimination signals received in 60 minutes, the sum of α-ray count information and β-ray count information is calculated and held as an α-ray integrated value and a β-ray integrated value.

Furthermore, the α-ray count rate and the β-ray count rate are calculated by dividing the α-ray integrated value and the β-ray integrated value by the counting time (60 minutes in the above example), respectively. In the above examples, the unit of the α-ray count rate and the β-ray count rate is counts per minute (cpm), but when divided by seconds, it becomes counts per second (cps).

Further, the counting unit 3 multiplies the α-ray count rate by a preset α-ray sensitivity constant to calculate α-ray emitting radioactivity, and multiplies the β-ray count rate by a preset β-ray sensitivity constant. β-ray emitting radioactivity is calculated. Sensitivity coefficients for α rays and β rays are preset and held in the counting unit 3 . The units of α-ray radioactivity and β-ray radioactivity are both becquerels (Bq).

Furthermore, the counting unit 3 multiplies the α-ray emission radioactivity calculated based on the α-ray count rate by a preset αβ abundance ratio to calculate the β-ray radioactivity correlated with the α-ray, and calculates the β-ray count The net β-ray radioactivity may be calculated by subtracting the β-ray radioactivity correlated with α-rays from the β-ray emitting radioactivity calculated based on the rate. The αβ abundance ratio at the installation location is preset and held in the counting unit 3 .

Unless the environment is a special environment such as a nuclear fuel facility, when the radioactivity measuring device 100 is installed in an environment including a nuclear-related facility such as a nuclear power plant, the detected α-ray radioactive material is naturally derived. . On the other hand, the radioactive substances of β-rays are naturally derived in the normal environment, but in the nuclear accident environment, radioactive substances derived from the accident are added to the naturally derived radioactive substances. Therefore, it is important to measure natural α-ray radioactivity and β-ray radioactivity in normal times.

FIG. 11 is a scatter diagram obtained by two-dimensionally plotting naturally-derived total α radioactivity and total β radioactivity simultaneously measured in a normal environment using the radioactivity measuring device 100 . In FIG. 11, the horizontal axis is the total α-ray radioactivity concentration, the vertical axis is the total β-ray radioactivity concentration (both units are Bq/m ³ ), and G is the data group. As shown in Figure 11, naturally occurring α radioactivity and β radioactivity are in a proportional relationship, and the degree of this proportionality (slope T) is called the αβ abundance ratio. A proportional relationship is also maintained.

As mentioned above, α-ray radioactivity is a naturally occurring radioactive substance unless it is in a special environment such as a nuclear fuel plant. ability can be evaluated. Furthermore, by subtracting the naturally occurring β-ray radioactivity from the measured β-ray radioactivity, only the β-ray radioactivity derived from the nuclear accident can be determined.

The display 4 displays the counting results and engineering values calculated by the counting section 3 . Specifically, the α-ray count rate and the β-ray count rate calculated by the counting unit 3, the α-ray radioactivity and the β-ray radioactivity, or both of them may be displayed. Alternatively, the measured β-ray radioactivity minus the naturally-occurring β-ray radioactivity may be displayed. If necessary, the counter 3 or the display 4 may be provided with an alarm function so that an alarm is issued when the counting rate exceeds the alarm set value.

As described above, according to the radioactivity measuring apparatus 100 according to Embodiment 1, based on the threshold value D set for each peak value PH2 of the integral pulse P2 and the peak value ratio (PH2/PH1), By discriminating whether the electrical pulse signal P is α-rays or β-rays, highly accurate discrimination is possible even when the energy of α-rays or β-rays is low and the wave height of the electrical pulse signal P is low. This makes it possible to count low-energy α-rays and β-rays, and speed up the accumulation of statistical data.

In addition, by using the threshold D expressed as a function of PH2 in a scatter diagram with PH2 on the horizontal axis and PH2/PH1 on the vertical axis, it is possible to discriminate and count even low-energy α-rays, The number of α-rays used as statistical data can be increased.

Further, since the counting unit 3 obtains the α-ray count rate and the β-ray count rate, the radioactivity can be managed by the radioactivity measuring device 100 alone. In addition, by calculating the α-ray emitting radioactivity and the β-ray emitting radioactivity in the counting unit 3, the level of the measured value with respect to the regulation value by law can be known instantaneously. Furthermore, since only radioactivity released from managed nuclear facilities can be evaluated, it is possible to quickly confirm the measured values subject to legal control, and management that can reduce the burden on administrators. system is obtained.

Embodiment 2.
In Embodiment 2, a radioactivity measurement device (generally called a gas monitor) provided with a gas sampler in addition to the radioactivity measurement device 100 according to Embodiment 1 will be described. FIG. 12 is a schematic diagram illustrating the configuration of a gas monitor according to Embodiment 2. FIG.

A gas monitor 500 according to Embodiment 2 includes a detector 1 , a gate integration type waveform discrimination circuit 2 , a counting section 3 , a display (not shown), and a gas sampler 510 . Note that the components other than the gas sampler 510 are the same as those of the radioactivity measuring apparatus 100 according to the first embodiment, and thus descriptions thereof are omitted here.

The gas sampler 510 has a gas container 512 that takes in a gas to be measured (usually in the atmosphere) and a gas suction mechanism 516 connected to the gas container 512 . The detector 1 is installed in the gas container 512 of the gas sampler 510 and detects α-rays and β-rays emitted from radioactive substances contained in the gas taken into the gas container 512 . The gas monitor 500 may include at least the gas sampler 510 and the detector 1, and the gate integration type waveform discrimination circuit 2, the counting unit 3, and the display may be built in or installed in the gas monitor 500. , may be installed outside the gas monitor 500 .

As shown in FIG. 12 , the gas sampler 510 includes a gas inlet 511 and gas outlet 517 , a gas container 512 , a shielding material 518 , and a gas suction mechanism 516 . The inlet 511 takes in the gas to be measured and the outlet 517 exhausts the measured gas. The gas container 512 stores gas to be measured, and the detector 1 is installed therein. A shielding material 518 is provided around the gas container 512 to prevent γ-rays not to be measured from entering the gas container 512 and the detector 1 .

The gas suction mechanism section 516 has a vacuum pump 513 , a flow meter 514 and a control section 515 . The vacuum pump 513 sucks the gas to be measured and takes it into the gas container 512 . A flow meter 514 measures the flow rate of the gas flowing into the gas sampler 510 . Controller 515 controls both vacuum pump 513 and flow meter 514 .

In the example shown in FIG. 12, the vacuum pump 513 is provided on the discharge port 517 side of the gas sampler 510, but a compressor or blower for discharging gas may be provided on the suction port 511 side. As equipment for the gas system, an air filter for removing dust contained in the gas, a pressure gauge for monitoring the pressure of the gas system, or a heating device for removing moisture from the gas may be provided.

For the gas container 512 and the piping system, for example, stainless steel or reinforced plastic material is used as a base material, and corrosion countermeasures are implemented as necessary for surfaces that come into contact with the gas. The shielding material 518 is made of lead, iron, or the like, which has a high specific gravity. However, these materials are not particularly limited.

The operation of gas monitor 500 will be described. The gas to be measured sucked from the suction port 511 of the gas sampler 510 is stored in the gas container 512 and is sufficiently diffused. The volume of the gas container 512 and the gas flow rate are adjusted so that the detector 1 can detect uniform gas α-rays and β-rays. The gas to be measured stays in the gas container 512 for the time required for measurement, passes through the flow meter 514 , and is discharged from the discharge port 517 through the vacuum pump 513 . The flow rate data read by the flowmeter 514 is transferred from the control section 515 directly or through the counting section 3 to the host computer 1000 as data for evaluating the volume of the gas to be measured per unit time.

Also, the gas monitor 500 can be installed as an exhaust stack monitor for nuclear facilities. Specifically, an air sampling nozzle and an exhaust nozzle installed in the exhaust stack are connected to the intake port 511 and the exhaust port 517, respectively, and the air in the exhaust stack is used as the gas to be measured.

When the gas monitor 500 is operated as an exhaust stack monitor, the counting section 3 obtains the β-ray counting rate and outputs it to the host computer 1000 in the same manner as in the conventional exhaust stack monitor. Furthermore, by obtaining the α-ray count rate and outputting it to the host computer 1000, it is possible to provide information on naturally occurring radioactivity, and the host computer 1000 can determine whether or not the β-ray count rate increased due to nuclear factors. can determine whether When used as an exhaust stack monitor, the β-ray count rate may be obtained in the same manner as the conventional product, but engineering values such as the amount of radioactivity and radioactivity concentration may be calculated and provided.

According to the gas monitor 500 according to Embodiment 2, the same effect as the radioactivity measuring apparatus 100 according to Embodiment 1 is obtained, and the volume of the measurement gas can be obtained from the flow rate information per unit time from the flow meter 514. By dividing the radioactivity by the measured gas volume, the α-ray and β-ray radioactivity concentrations can be obtained with high accuracy even for low-energy α-rays and β-rays. In addition, when the gas monitor 500 is used as an exhaust stack monitor, it is possible to more accurately determine whether to issue an alarm in the host computer 1000 when the β-ray count rate increases.

Embodiment 3.
In Embodiment 3, a radioactivity measurement apparatus (generally called a dust monitor) provided with a dust sampler in addition to the radioactivity measurement apparatus 100 according to Embodiment 1 will be described. FIG. 13 is a schematic diagram illustrating the configuration of a dust monitor according to Embodiment 3. FIG.

A dust monitor 600 according to Embodiment 3 includes a detector 1 , a gate integration type waveform discriminator 2 , a counter 3 , a display (not shown), and a dust sampler 610 . Note that the constituent elements other than the dust sampler 610 are the same as those of the radioactivity measuring apparatus 100 according to the first embodiment, and thus descriptions thereof are omitted here.

The dust sampler 610 has a dust collection filter paper 612 that allows air containing dust to be measured to pass therethrough and collects the dust, and a dust collection mechanism section 616 that feeds air into the dust collection filter paper 612 . The detector 1 is installed in the dust sampler 610 and detects α rays and β rays emitted from radioactive substances contained in dust collected by the dust collection filter paper 612 . The dust monitor 600 may include at least the dust sampler 610 and the detector 1, and the gate integration type waveform discrimination circuit 2, the counting unit 3, and the display may be built in or installed in the dust monitor 600. Alternatively, it may be installed outside the dust monitor 600 .

As shown in FIG. 13 , the dust sampler 610 includes an inlet 611 , an outlet 617 , a dust collection filter paper 612 , a dust collection mechanism 616 , a shielding material 618 , a filter paper winding mechanism 621 and a filter paper feed mechanism 622 . The intake port 511 takes in air containing dust to be measured, and the exhaust port 617 exhausts measured air. The dust collection filter paper 612 allows air containing dust to be measured to pass therethrough and collects the dust. The detector 1 is installed close to the dust collection portion of the dust collection filter paper 612 .

The dust collection mechanism section 616 includes a vacuum pump 613 , a flow meter 614 and a control section 615 . A vacuum pump 613 sucks air containing dust to be measured, and a flow meter 614 measures the flow rate of the air flowing into the dust sampler. A control unit 615 controls a vacuum pump 613 , a flow meter 614 and a filter paper feeding mechanism 622 . The shielding material 618 is provided around the dust collection filter paper 612 and the detector 1 to prevent γ rays not to be measured from entering the dust collection filter paper 612 and the detector 1 .

The dust collection filter paper 612 may be fixed filter paper or long filter paper, and FIG. 13 shows the case of long filter paper. In the case of long filter paper, a filter paper winding mechanism 621 and a filter paper feeding mechanism 622 are installed outside the shielding material 618, and the dust collecting filter paper 612 is fed from the filter paper feeding mechanism 622 side to the filter paper winding mechanism 621 side. The filter paper winding mechanism 621 has a structure that continuously winds the dust collection filter paper 612 at a low speed and a structure that instantaneously winds the dust collection filter paper 612 by several centimeters at regular intervals. A drive motor for the filter paper winding mechanism 621 is provided in the dust collecting mechanism section 616 .

A compressor or the like may be used as the vacuum pump 613 used for inflowing air into the dust collection filter paper 612 . Also, an air filter, a pressure gauge, a heating device, or the like may be provided as equipment for the dust monitor system. The material of the piping system and the shielding material 618 is the same as that of the second embodiment, so the description is omitted.

Operation of the dust monitor 600 will be described. Air containing dust to be measured is sucked from the suction port 611 of the dust sampler 610 and passed through the dust collection filter paper 612 to collect the dust on the dust collection filter paper 612 . The sucked air passes through the flow meter 614 and is exhausted from the exhaust port 617 through the vacuum pump 613 . The flow rate data read by the flowmeter 614 is transferred from the control section 615 of the dust collection mechanism section 616 directly or through the counting section 3 to the host computer 1000 as data for evaluating the volume of air to be measured per unit time.

Also, the dust monitor 600 can be applied to a normal monitoring system of a preventive action preparation zone (PAZ) set within a radius of about 5 kilometers from a nuclear power reactor facility. The α-ray radioactivity concentration and the β-ray radioactivity concentration calculated from the flow rate information of the flow meter 614 in the counting unit 3 can distinguish α-rays and β-rays even if they are low-energy α-rays and β-rays. Furthermore, since it can be distinguished from electrical noise, it is possible to shorten the time required to accumulate statistical data of α rays and β rays. For this reason, it is possible to achieve a performance effect that is sufficiently applicable as a normal monitoring system that requires a radioactivity concentration of 1 becquerel or less per 1 cubic meter in one-hour radioactivity concentration measurement as a detection limit.

According to the dust monitor 600 according to Embodiment 3, the same effect as that of the radioactivity measuring apparatus 100 according to Embodiment 1 is obtained, and the volume of measured air can be determined from the information of the flow rate per unit time from the flow meter 614. Therefore, by dividing the radioactivity by the measured air volume, the α-ray radioactivity concentration and the β-ray radioactivity concentration can be obtained with high accuracy even for low-energy α-rays and β-rays.

In addition, since even low-energy α-rays and β-rays can be handled as effective data, statistical data can be accumulated in a relatively short period of time. Even if the relatively short time is set to, for example, 1 hour, it is possible to measure radioactivity concentration, which is a sufficient detection limit of 1 becquerel or less per cubic meter, particularly for α-ray radioactivity. Therefore, it is possible to provide the dust monitor 600 that can be applied as a normal dust monitor.

While this disclosure describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more of the embodiments may vary from particular embodiment to embodiment. The embodiments are applicable singly or in various combinations without being limited to the application. Accordingly, numerous variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, modification, addition or omission of at least one component, extraction of at least one component, and combination with components of other embodiments shall be included.

INDUSTRIAL APPLICABILITY The present application can be used as a radioactivity measuring device, a gas monitor, and a dust monitor for measuring radioactivity contained in the atmosphere.

1 detector, 2 gate integration type waveform discriminator, 3 counter, 4 indicator, 10 detector case, 11 sensor unit, 11a α-ray sensor, 11b β-ray sensor, 11c entrance window, 12 photomultiplier tube, 13 Divider circuit 14 Signal cable 20 Preamplifier 21 First integration circuit 22 Second integration circuit 23 Comparison unit 24 Discrimination unit 25 High voltage power supply 100 Radioactivity measuring device 101 β-ray pulse signal 102 β ray first integrated pulse, 103 β-ray second integrated pulse, 111 β-ray group, 201 α-ray pulse signal, 202 α-ray first integrated pulse, 203 α-ray second integrated pulse, 211 α-ray group, 500 gas monitor, 510 Gas sampler, 511 suction port, 512 gas container, 513 vacuum pump, 514 flow meter, 515 control unit, 516 gas suction mechanism unit, 517 discharge port, 518 shielding material, 600 dust monitor, 610 dust sampler, 611 suction port, 612 Dust collection filter paper 613 Vacuum pump 614 Flow meter 615 Control part 616 Dust collection mechanism part 617 Discharge port 618 Shielding material 621 Filter paper winding mechanism 622 Filter paper feeding mechanism 1000 Host computer

Claims (9)

A detector that has an α-ray sensor that detects incident α-rays and a β-ray sensor that detects incident β-rays, and outputs an electric pulse signal according to the detection results of each of the α-ray sensor and the β-ray sensor. and,
a first integration circuit that integrates the electrical pulse signal output from the detector with a first time constant and outputs a first output pulse signal;
It is installed in parallel with the first integration circuit and integrates the electrical pulse signal output from the detector with a second time constant larger than the first time constant to output a second output pulse signal. a second integration circuit;
Comparison for obtaining a peak value ratio based on the peak value of the first output pulse signal output from the first integration circuit and the peak value of the second output pulse signal output from the second integration circuit Department and
a threshold value set for each peak value of the second output pulse signal, and the electric pulse signal is alpha rays based on the ratio of the peak values output from the comparing unit and the threshold value; a discrimination unit that discriminates which of the β rays,
A radioactivity measuring device comprising: The discriminating unit determines that the electrical pulse signal is α-rays when the peak value ratio is greater than the threshold, and determines that the electrical 2. The radioactivity measuring apparatus according to claim 1, wherein the pulse signal is determined to be β rays. The threshold value of the discriminating section is PH1 for the crest value of the first output pulse signal output from the first integration circuit, and PH1 for the peak value of the second output pulse signal output from the second integration circuit. 3. The radioactivity measuring device according to claim 1 or 2, characterized in that, when the peak value is PH2, it is represented as a function of PH2 in a scatter diagram in which the horizontal axis is PH2 and the vertical axis is PH2/PH1. . The discriminating unit counts the number of electrical pulse signals determined to be α rays and the number of electrical pulse signals determined to be β rays for each unit time, and receives digital information on the total number of α ray counts. 4. The radioactivity measuring apparatus according to any one of claims 1 to 3, which outputs a β-ray discrimination signal and a β-ray discrimination signal to which digital information on the total number of β-ray counts is input. further comprising a counting unit for counting each of the α-ray discrimination signal and the β-ray discrimination signal output from the discrimination unit in a preset counting time;
The counting unit calculates an α-ray count rate by dividing the α-ray integrated value, which is the result of counting the α-ray discrimination signal, by the counting time, and calculates the α-ray integrated value, which is the result of counting the β-ray discrimination signal. 5. The radioactivity measuring apparatus according to claim 4, wherein the β-ray counting rate is calculated by dividing by the counting time. The counting unit multiplies the α-ray count rate by a preset sensitivity constant for α-rays to calculate α-ray emitting radioactivity, and multiplies the β-ray count rate by a preset sensitivity constant for β-rays to obtain β-rays. 6. The radioactivity measuring device according to claim 5, wherein the emitted radioactivity is calculated. The counting unit multiplies the α-ray emission radioactivity calculated based on the α-ray count rate by a preset αβ abundance ratio to calculate the β-ray radioactivity correlated with the α-ray, and the β-ray count rate 7. The radioactivity measuring device according to claim 6, wherein the net β-ray radioactivity is calculated by subtracting the β-ray radioactivity correlated with the α-ray from the β-ray emission radioactivity calculated based on the above. further comprising a gas sampler having a gas container that takes in the gas to be measured;
8. The detector according to any one of claims 1 to 7, wherein the detector is installed in the gas sampler and detects alpha rays and beta rays emitted from radioactive substances contained in the gas taken into the gas container. or the radioactivity measurement device according to item 1. Further comprising a dust sampler having dust collection filter paper for passing air containing dust to be measured and collecting the dust,
8. The detector is installed in the dust sampler and detects alpha rays and beta rays emitted from radioactive substances contained in the dust collected by the dust collection filter paper. Radioactivity measuring device according to any one of.

Images