JP7395428B2 - Dust radiation monitor and dust radiation measurement method - Google Patents

Description

Embodiments of the present invention relate to a dust radiation monitor and a dust radiation measurement method.

When performing work in a radiation controlled area, the concentration of radioactive substances contained in the air in the work area (radioactivity per unit volume, hereinafter also referred to as "dust concentration") is measured and safety monitoring of the area is carried out. It is essential to do this at all times. A device that accomplishes this is a dust radiation monitor. To measure dust concentration, piping is laid from the sampling point to the measuring device, the gas sucked in by a pump is collected with filter paper, and a radiation detector placed opposite the filter paper detects the radiation emitted from the filter paper. A common method is to count the pulsed electrical signals output from the sensor and calculate the dust concentration based on that.

However, for example, in a work area where buildings and equipment are being dismantled, a large amount of dust may be stirred up during the work, and gas containing high concentrations of radioactive materials may be inhaled temporarily or for a certain period of time. obtain. At this time, since the radiation detector frequently detects radiation, it is assumed that each pulse-shaped electrical signal outputted from the radiation detector occurs frequently and overlaps, making accurate counting difficult. In other words, if the dust concentration exceeds the upper limit of measurement for a measuring device, there is a concern that the measuring device will become saturated and monitoring will become difficult, and a solution is needed.

On the other hand, in radiation measurement systems, there is a known technology that evaluates the radiation dose based on the radiation count rate when the radiation dose is low, and based on the average current within a predetermined time when the radiation dose is high. It is being

Japanese Unexamined Patent Publication No. 61-62886 Japanese Patent Application Publication No. 2003-35779

However, there is no known technique for continuously measuring the dust concentration over a wide measurement range from a low concentration region to a high concentration region when the dust concentration changes significantly.

Embodiments of the present invention aim to enable uninterrupted and continuous measurement of dust radiation over a wide measurement range, even when the dust concentration changes significantly.

A dust radiation monitor according to an embodiment of the present invention includes a dust collection container through which a gas containing dust flows, a filter attached to the dust collection container to collect the dust and transmit the gas, and the filter. a radiation detector that detects radiation emitted from the dust collected by the dust and outputs an electrical signal; a counting processing circuit that calculates a radiation counting rate based on the output of the radiation detector; an average current processing unit that calculates an average current within a predetermined time of output; the counting rate obtained by the counting processing circuit; and the average current obtained by the average current processing unit. A dust radiation monitor comprising: a concentration calculation unit that calculates a dust concentration of a count rate concentration calculation unit that calculates a count rate concentration corresponding to the dust concentration in the gas; and a count rate concentration calculation unit that calculates a count rate concentration corresponding to the dust concentration in the gas, and a an average current concentration calculation section that calculates an average current concentration corresponding to the dust concentration, and an output of the count rate concentration calculation section that is higher than a predetermined low concentration reference value, and an output of the average current concentration calculation section that calculates the low concentration a weighted average calculation unit that calculates a weighted average of the count rate concentration and the average current concentration when the concentration is lower than a predetermined high concentration reference value that is higher than a reference value; Weighting is performed such that the closer the concentration is to the low concentration reference value, the greater the weighting rate to the count rate concentration, and the closer the average current concentration is to the high concentration reference value, the greater the weighting rate to the average current concentration. wherein the weighting factor for the count rate concentration is 1 when the count rate concentration is equal to the low concentration reference value and zero when the average current concentration is equal to the high concentration reference value. , is characterized by.

Further, the dust radiation measuring method according to the embodiment of the present invention includes a dust collecting step of transmitting a gas containing dust through a filter and collecting the dust, and a step of collecting the dust, and collecting the radiation emitted from the dust collected by the filter. a radiation detection step of detecting with a radiation detector and outputting an electrical signal; a counting processing step of calculating a radiation counting rate based on the output of the radiation detector; and an average of the output of the radiation detector within a predetermined time. an average current calculation step of calculating a current, and calculating a count rate concentration corresponding to the dust concentration in the gas based on the count rate, assuming that the count rate and the dust concentration in the gas are proportional. a count rate concentration calculation step; and an average current concentration for calculating an average current concentration corresponding to the dust concentration in the gas based on the average current, assuming that the average current and the dust concentration in the gas are proportional. calculating the count rate concentration when the count rate concentration is higher than a predetermined low concentration reference value and the average current concentration is lower than a predetermined high concentration reference value higher than the low concentration reference value; A dust radiation measurement method comprising: a weighted average calculation step of calculating a weighted average with the average current concentration, wherein the weighted average is such that the closer the count rate concentration is to the low concentration reference value, the lower the count rate concentration is. The weighting rate to the count rate concentration is large, and the closer the average current concentration is to the high concentration reference value, the higher the weighting rate to the average current concentration is.The weighting rate to the count rate concentration is: Set to 1 when the count rate concentration is equal to the low concentration reference value, set to 0 when the average current concentration is equal to the high concentration reference value, and set to 0 when the count rate concentration is equal to or lower than the low concentration reference value. The count rate concentration is the dust concentration in the gas, and if the average current concentration is equal to or higher than the high concentration reference value, the average current concentration is the dust concentration in the gas, and the count rate concentration is the low concentration. If the average current concentration is higher than a reference value and lower than the high concentration reference value, the weighted average is set as the dust concentration in the gas.

According to embodiments of the present invention, dust radiation can be continuously measured without interruption over a wide measurement range even when the dust concentration changes significantly.

FIG. 1 is a block diagram showing the configuration of an embodiment of a dust radiation monitor according to the present invention. FIG. 2 is a flowchart showing the procedure of an embodiment of a dust radiation measuring method using the dust radiation monitor of FIG. 1. FIG. FIG. 2 is a diagram for explaining a method of calculating dust concentration in an embodiment of the dust radiation monitor according to the present invention, in which the horizontal axis is the true duct concentration, and the vertical axis is the dust concentration instruction value. 2 is a flowchart showing a procedure for determining a low concentration reference value, a high concentration reference value, and a weighting rate relational expression in an embodiment of the dust radiation measurement method using the dust radiation monitor of FIG. 1. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dust radiation monitor and a dust radiation measuring method according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a dust radiation monitor according to the present invention. This dust radiation monitor includes a dust collection container 12, a suction pump 13, a filter paper (filter) 14, a radiation detector 15, an amplifier circuit 16, a counting processing circuit 17, an average current processing section 18, and a concentration calculation unit. 19.

A gas introduction pipe 21 and a gas discharge pipe 22 are connected to the dust collection container 12, and a suction pump 13 is attached to the gas discharge pipe 22. Filter paper 14 is attached to dust collection container 12. A gas (for example, air) 11 containing dust to be measured is introduced into the dust collection container 12 from the gas introduction pipe 21, passes through the filter paper 14, is sucked by the suction pump 13, and is discharged from the gas exhaust pipe 22. be discharged. Dust contained in the gas 11 is collected by the filter paper 14. The filter paper 14 has countless fine holes and is made of paper or resin material. A filter paper winding device (not shown) is attached to the dust collection container 12, and a new portion of the filter paper 14 is exposed to the gas 11 every time radiation detection is completed at a predetermined time (for example, several minutes to several hours). is configured to be

The radiation detector 15 converts the radiation emitted from the dust collected by the filter paper 14 into an electrical signal, and includes a scintillator 25 that detects radiation (for example, β rays) and emits light, and a scintillator 25 that detects radiation (for example, β rays) and emits light, and a scintillator 25 that detects radiation (for example, β rays) and emits light. It has a photomultiplier tube 26 that outputs a corresponding electric signal. When the radiation 24 is incident on the radiation detector 15, the scintillator 25 generates a slight fluorescence. The light emitted from the scintillator 25 enters the photomultiplier tube 26 to generate photoelectrons, the number of electrons is amplified several hundred to tens of thousands of times, and the photoelectron multiplier tube 26 outputs it as a pulsed electrical signal. be done. The radiation detector 15 has a closed housing and is configured to prevent light from entering from the outside.

The amplifier circuit 16 is connected to the radiation detector 15 via a cable 30 and amplifies the electrical signal output from the photomultiplier tube 26.

The counting processing circuit 17 performs wave height discrimination processing to remove signals below a set threshold based on the output of the amplifier circuit 16, counts the number of electrical signals per unit time, and calculates the counting rate (per unit time). (number of pulses).

The average current processing unit 18 calculates an average current value that is the average of the electrical signal output from the amplifier circuit 16 within a predetermined time.

The concentration calculation unit 19 outputs the dust concentration based on the output of the counting processing circuit 17 and the output of the average current processing unit 18, and includes a count rate concentration calculation unit 33, an average current concentration calculation unit 34, and a weighted It has an average calculation section 35 and an output selection section 36.

The count rate concentration calculation unit 33 calculates the dust concentration by multiplying the count rate R, which is the output of the counting processing circuit 17, by a conversion coefficient. The calculation for calculating the dust concentration is based on the following equation (1), for example. In equation (1), C is the dust concentration, R is the counting rate, η is the detection efficiency specific to the detector, Q is the average flow rate of the gas passing through the filter paper 14, t is the elapsed time for dust collection, and D is the filter paper 14 Inherent collection efficiency. When using this equation (1), the conversion coefficient is D·η/(Q·t). Note that (Q·t) is the volume of gas that has passed through the filter 14 within the dust elapsed time.

C=D・η・R/(Q・t) ... (1)
The dust concentration obtained by the count rate concentration calculation unit 33 is herein referred to as "count rate concentration." When the dust concentration is relatively low, the count rate concentration is used as the duct concentration.

The average current concentration calculating section 34 calculates the dust concentration by multiplying the output of the average current processing section 18 by a coefficient. This coefficient indicates the relationship between the average current and the counting rate, and is assumed to be obtained in advance. The dust concentration obtained by the average current concentration calculating section 34 is referred to as "average current concentration" here. When the dust concentration is relatively high, the average current concentration is used as the duct concentration.

The output of the count rate concentration calculation section 33 and the output of the average current concentration calculation section 34 are both input to the weighted average calculation section 35 and the output selection section 36. The weighted average calculation unit 35 calculates a weighted average of the count rate concentration and the average current concentration when the count rate concentration is higher than a predetermined low concentration reference value and the average current concentration is lower than a predetermined high concentration reference value. , and outputs the result to the output selection section 36. The high concentration reference value is higher than the low concentration reference value. A method for calculating the high concentration reference value, low concentration reference value, and weighted average will be described later using FIGS. 3 and 4.

The output selection unit 36 outputs the count rate concentration as a duct concentration when the count rate concentration is below the low concentration reference value, outputs the average current concentration as the duct concentration when the average current concentration is above the high concentration reference value, When the count rate concentration is higher than the low concentration reference value and the average current concentration is lower than the high concentration reference value, the output of the weighted average calculation section 35 is output as the duct concentration.

FIG. 2 is a flow diagram showing the procedure of an embodiment of a dust radiation measuring method using the dust radiation monitor of FIG. 1.

First, the gas 11 containing dust is transmitted through the filter 14 and the dust is collected (dust collection step S11). Next, the radiation detector 15 detects radiation emitted from the dust collected by the filter 14 and outputs an electrical signal (radiation detection step S12).

Next, the counting processing circuit 17 calculates a radiation counting rate based on the output of the radiation detector 15 (counting processing step S13). Further, the average current processing unit 18 calculates the average current of the output of the radiation detector 15 within a predetermined time (average current calculation step S14).

Next, on the assumption that the count rate and the dust concentration in the gas are proportional, the count rate concentration calculation unit 33 calculates the count rate concentration corresponding to the dust concentration in the gas based on the count rate and the volume of the gas. Calculate (count rate concentration calculation step S15). Further, the average current concentration calculation unit 34 calculates the average current concentration corresponding to the dust concentration in the gas based on the average current and the volume of the gas, assuming that the average current and the dust concentration in the gas are proportional. (average current concentration calculation step S16).

Next, when the count rate concentration is higher than a predetermined low concentration reference value and the average current concentration is lower than a predetermined high concentration reference value which is higher than the low concentration reference value, the weighted average calculation unit 35 calculates the count rate A weighted average of the concentration and the average current concentration is calculated (weighted average calculation step S17).

Next, the output selection unit 36 selects one of the count rate concentration, average current concentration, and weighted average and outputs it as the dust concentration in the gas (concentration measurement result output step S18). Here, if the count rate concentration is below the low concentration standard value, the count rate concentration is selected as the dust concentration in the gas, and if the average current concentration is above the high concentration standard value, the average current concentration is selected as the dust concentration in the gas. Select as the dust concentration. Furthermore, when the count rate concentration is higher than the low concentration reference value and the average current concentration is lower than the high concentration reference value, the weighted average is selected as the dust concentration in the gas.

Here, a method for determining the dust concentration over a wide range using the count rate concentration and the average current concentration will be explained using FIG. 3.

FIG. 3 is a diagram for explaining a method of calculating dust concentration in an embodiment of the dust radiation monitor according to the present invention, in which the horizontal axis is the true duct concentration and the vertical axis is the dust concentration indication value. .

The count rate density produced by the counting processing circuit 17 has high accuracy at relatively low counting rates, and the average current density produced by the average current processing unit 18 has high precision at relatively high counting rates. In the counting processing circuit 17, when the counting rate is high, that is, when a large amount of radioactive material is collected on the filter paper 14, the frequency of pulsed electrical signals becomes very high, and the accuracy is increased by superimposing each electrical signal. This makes accurate counting difficult and reduces accuracy. Furthermore, the average current processing unit 18 has low accuracy because it performs averaging using a pulsed electrical signal at a relatively low counting rate.

As shown in FIG. 3, the instruction value C1 of the count rate concentration by the counting processing circuit 17 matches the true dust concentration when the true dust concentration is relatively low below the low concentration reference value CL. Therefore, when the true dust concentration is relatively low below the low concentration reference value CL, the count rate concentration instruction value C1 can be set as the true dust concentration. When the true dust concentration exceeds the low concentration reference value CL, the count rate concentration instruction value C1 indicates a value lower than the true dust concentration.

The average current concentration instruction value C2 by the average current processing unit 18 matches the true dust concentration when the true dust concentration is relatively high, equal to or higher than the high concentration reference value CH. Therefore, when the true dust concentration is relatively high, equal to or higher than the high concentration reference value CH, the instruction value C2 of the count rate concentration can be set as the true dust concentration. When the true dust concentration is lower than the high concentration reference value CH, the count rate concentration instruction value C2 indicates a value higher than the true dust concentration.

For the intermediate region between CL and CH, the weighted average of the indicated value C1 of the count rate concentration by the counting process and the indicated value C2 of the average current concentration by the average current is calculated using the following equation (2), and this weighted average is calculated as the dust Let it be the concentration.

C=k・C1+(1-k)・C2... (2)
Here, k is a weighting rate to the count rate concentration, is a function of the count rate concentration instruction value C1 and the average current concentration instruction value C2, and has a value from zero to one. The weighting rate for the average current concentration is (1-k). When the count rate concentration instruction value C1 is equal to the low concentration reference value CL, k=1, and when the average current concentration instruction value C2 is equal to the high concentration reference value CH, k=0. In the intermediate region from CL to CH, the weighting rate k to the count rate concentration becomes smaller as the indicated value C1 of the count rate concentration becomes larger and as the indicated value C2 of the average current concentration becomes larger.

Next, a procedure for determining the low concentration reference value, high concentration reference value, and weighting rate relational expression necessary for performing the above processing will be explained using FIG. 4. FIG. 4 is a flowchart showing a procedure for determining a low concentration reference value, a high concentration reference value, and a weighting rate relational expression in an embodiment of the dust radiation measurement method using the dust radiation monitor of FIG.

In determining these values and relational expressions, first, using the dust radiation monitor shown in FIG. S12 and counting process step S13 (see FIG. 2) are performed. Thereby, the relationship between the count rate and the dust concentration is determined (count rate dust concentration relationship acquisition step S51). Thereby, a curve of the dust concentration instruction value C1 can be obtained by the counting process shown in FIG. 3.

Similarly, using the dust radiation monitor shown in FIG. ). Thereby, the relationship between the average current and the dust concentration is determined (average current dust concentration relationship acquisition step S52). Thereby, the curve of the dust concentration instruction value C2 according to the average current shown in FIG. 3 can be obtained.

Note that the gas with a known dust concentration used in the above-mentioned count rate dust concentration relationship acquisition step S51 and the gas with a known dust concentration used in the average current dust concentration relationship acquisition step S52 are partially or completely common. There may be. Furthermore, in the case where gases having a known dust concentration are common, the dust collection step S11 and the radiation detection step S12 in the count rate dust concentration relationship acquisition step S51 and the average current dust concentration relationship acquisition step S52 are each a common step. It can be done.

Next, a low concentration reference value CL is determined as the point at which the curve of the dust concentration instruction value C1 obtained by the counting process in FIG. 3 begins to deviate from the straight line passing through the origin with a slope of 1 (low concentration reference value determination step S53). The curve of the dust concentration instruction value C1 obtained by the counting process is a straight line passing through the origin with a slope of 1 in the region below the low concentration reference value CL.

Similarly, the high concentration reference value CH is determined as the point at which the curve of the concentration instruction value C2 based on the average current in FIG. 3 begins to deviate from the straight line passing through the origin with a slope of 1 (high concentration reference value determination step S54). The curve of the concentration instruction value C2 based on the average current is a straight line passing through the origin with a slope of 1 in the region of the high concentration reference value CH or higher.

Next, in FIG. 3, in the region (intermediate region) where the true dust concentration is between the low concentration reference value CL and the high concentration reference value CH, a formula for the weighting rate k that satisfies formula (2) is determined ( Weighting rate relational expression determination step S55).

Here, the weighting rate k is a function of the dust concentration instruction value C1 obtained by the counting process and the concentration instruction value C2 obtained by the average current, and the curve of the true dust concentration C and the dust concentration instruction value C1 obtained by the counting process in FIG. The relational expression can be determined from the relationship of the curve of the concentration instruction value C2 with the average current.

According to the embodiment described above, even if the dust concentration changes significantly, dust radiation can be measured continuously over a wide measurement range without interruption.

In the embodiment of the dust radiation monitor described above, the counting processing circuit 17, the average current processing section 18, and the concentration calculation section 19 can be realized by hardware such as an electronic circuit, but some or all of them can be implemented by an electronic computer. It can also be realized by software.

[Other embodiments]
Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

11... Gas (air), 12... Dust collection container, 13... Suction pump, 14... Filter paper (filter), 15... Radiation detector, 16... Amplification circuit, 17... Counting processing circuit, 18... Average current processing section, 19 ... Concentration calculation section, 21 ... Gas introduction pipe, 22 ... Gas discharge pipe, 24 ... Radiation, 25 ... Scintillator, 26 ... Photomultiplier tube, 30 ... Cable, 33 ... Counting rate concentration calculation section, 34 ... Average current concentration calculation Part, 35... Weighted average calculation part, 36... Output selection part

Claims (4)

A dust collection container that circulates gas containing dust;
a filter that is attached to the dust collection container and that collects the dust and allows the gas to pass through;
a radiation detector that detects radiation emitted from the dust collected by the filter and outputs an electrical signal;
a counting processing circuit that calculates a radiation counting rate based on the output of the radiation detector;
an average current processing unit that calculates an average current of the output of the radiation detector within a predetermined time;
a concentration calculation unit that calculates the dust concentration in the gas based on the counting rate obtained by the counting processing circuit and the average current obtained by the average current processing unit;
A dust radiation monitor having:
The concentration calculation section is
a count rate concentration calculation unit that calculates a count rate concentration corresponding to the dust concentration in the gas based on the count rate, assuming that the count rate and the dust concentration in the gas are proportional;
an average current concentration calculation unit that calculates an average current concentration corresponding to the dust concentration in the gas based on the average current, assuming that the average current and the dust concentration in the gas are proportional;
When the output of the count rate concentration calculation section is higher than a predetermined low concentration reference value, and the output of the average current concentration calculation section is lower than a predetermined high concentration reference value that is higher than the low concentration reference value, the a weighted average calculation unit that calculates a weighted average of the count rate concentration and the average current concentration;
Equipped with
In the weighted average, the closer the count rate concentration is to the low concentration reference value, the greater the weighting rate to the count rate concentration, and the closer the average current concentration is to the high concentration reference value, the greater the weighting rate to the average current concentration. is weighted to increase the count rate concentration, and the weighting rate to the count rate concentration is 1 when the count rate concentration is equal to the low concentration reference value, and the average current concentration is equal to the high concentration reference value. be zero when equal to,
A dust radiation monitor featuring: If the count rate concentration is below the low concentration reference value, output the count rate concentration as a dust concentration in the gas;
If the average current concentration is equal to or higher than the high concentration reference value, output the average current concentration as a dust concentration in the gas,
When the count rate concentration is higher than the low concentration reference value and the average current concentration is lower than the high concentration reference value, the weighted average is output as the dust concentration in the gas. that you are
The dust radiation monitor according to claim 1, characterized in that: a dust collection step of transmitting a gas containing dust through a filter and collecting the dust;
a radiation detection step of detecting radiation emitted from the dust collected by the filter with a radiation detector and outputting an electric signal;
a counting processing step of calculating a radiation counting rate based on the output of the radiation detector;
an average current calculation step of calculating an average current of the output of the radiation detector within a predetermined time;
a count rate concentration calculation step of calculating a count rate concentration corresponding to the dust concentration in the gas based on the count rate, assuming that the count rate and the dust concentration in the gas are proportional;
an average current concentration calculation step of calculating an average current concentration corresponding to the dust concentration in the gas based on the average current, assuming that the average current and the dust concentration in the gas are proportional;
When the count rate concentration is higher than a predetermined low concentration reference value and the average current concentration is lower than a predetermined high concentration reference value that is higher than the low concentration reference value, the count rate concentration and the average current concentration a weighted average calculation step of calculating a weighted average of
A dust radiation measurement method comprising:
In the weighted average, the closer the count rate concentration is to the low concentration reference value, the greater the weighting rate to the count rate concentration, and the closer the average current concentration is to the high concentration reference value, the greater the weighting rate to the average current concentration. The weighting rate for the count rate concentration is set to 1 when the count rate concentration is equal to the low concentration reference value, and when the average current concentration is equal to the high concentration reference value. Set to zero when equal,
If the count rate concentration is below the low concentration reference value, the count rate concentration is set as the dust concentration in the gas,
If the average current concentration is equal to or higher than the high concentration reference value, the average current concentration is set as the dust concentration in the gas,
When the count rate concentration is higher than the low concentration reference value and the average current concentration is lower than the high concentration reference value, the weighted average is set as the dust concentration in the gas;
A dust radiation measurement method characterized by: A count rate dust concentration in which the relationship between the count rate and the dust concentration is determined by performing the dust collection step, the radiation detection step, and the counting processing step for each of at least three types of gases with known dust concentrations. a relationship acquisition step;
An average current dust that calculates the relationship between the average current and the dust concentration by performing the dust collection step, the radiation detection step, and the average current calculation step for each of at least three types of gases with known dust concentrations. a concentration relationship acquisition step;
a reference value determining step of determining the low concentration reference value and the high concentration reference value based on the relationship between the counting rate and the dust concentration and the relationship between the average current and the dust concentration;
a weighting rate relationship that determines a weighting rate relational expression for determining the weighting rate as a function of the counting rate and the average current, based on the relationship between the counting rate and the dust concentration and the relationship between the average current and the dust concentration; a formula determination step;
The dust radiation measuring method according to claim 3, further comprising:

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