JP5646308B2 - Radiation measurement equipment - Google Patents

Description

  The present invention relates to a radiation measurement apparatus using an ionization action, and more particularly to a radiation measurement apparatus that measures ions ionized by radiation emitted from a measurement object.

  In a nuclear facility, a radiation measurement device is used to observe the radioactivity of radioactive waste generated in the facility and to sort and store the waste for each radioactivity level.

  In these radiation measuring devices, the gas in the vicinity is ionized by radiation emitted from the measurement object such as waste, and ions are generated. The ions have a lifetime of several seconds to several tens of seconds, It exists in the vicinity of the measurement object. If the gas containing the generated ions is sucked and transferred to the ionization chamber, and the number of ions contained in the gas is measured as a current, the intensity of the radiation can be obtained (Patent Document 1).

  Since the number of ions generated by this ionization action is determined by the intensity of radiation and the size of the ionization space affected by the shape of the measurement object, the radiation intensity and ionization current for each shape of the measurement object in advance. By making this relationship correspond, the magnitude of the measured current can be converted into the radiation intensity.

  For example, in the radiation measuring apparatus disclosed in Patent Document 2, when the object to be measured is a pipe, the range of α rays and the recombination ratio of ions change depending on the length and diameter of the pipe. In addition, a correspondence diagram in which the length and diameter of the piping and the measurement sensitivity are associated with each other is created in advance, and the radiation intensity is corrected.

Japanese Patent No. 4131824 JP 2007-263804 A

However, the conventional radiation measuring apparatus described above has the following problems.
As a first problem, if the object to be measured matches the shape acquired in advance with the relationship between the radiation intensity and the ionizing current, it can be measured accurately, but if it does not match, the value complemented based on the correspondence table Even if is used, an error occurs in the measurement current, and an accurate radiation intensity cannot be obtained. Further, when the emission position of the radiation emitted from the measurement object has a spot-like distribution, if the time taken for the ions attracted to reach the ionization chamber varies depending on the emission position, an accurate radiation intensity is similarly obtained. There was a problem that it was not possible.

  As a second problem, since the amount of background ions in the gas is proportional to the volume of the measurement chamber that houses the measurement object, it is suitable for measurement objects when measuring a measurement object that is smaller than the measurement chamber. The background increases compared to a measurement chamber with a large volume, and the measurement accuracy decreases. Therefore, it is necessary to prepare a measurement chamber having a volume corresponding to the measurement object. However, it is possible to prepare multiple measurement chambers to cope with a wide variety of shapes, or to prepare a large measurement chamber and reduce the measurement chamber volume with a partition plate. Since the measurement chamber cannot be partitioned in the gas circulation direction, there is a problem that the shape of the measurement chamber is limited.

  As a third problem, when the measurement object surface is peeled off during measurement and separated from the object together with the circulating airflow, the measurement current greatly fluctuates. is necessary. Also, if the peeled contamination adheres to the measurement chamber or the ionization chamber, the background will rise when measuring a new measurement object, so it is necessary to take measures against such background abnormalities. It was.

  As a fourth problem, the amount of background ions in the gas varies depending on the environment. Therefore, if there is a difference between the background amount measured in advance and the background amount being measured, the measurement result is affected and the detection limit is limited. Deteriorate. In addition, since it is necessary to measure the background in a state where an object is not placed on the measurement line in advance, there is a problem that the total measurement time including the background measurement becomes long.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a radiation measuring apparatus capable of accurately measuring the radiation intensity of measurement objects having different shapes.

In order to solve the above problems, a radiation measurement apparatus according to the present invention includes a measurement chamber in which a measurement object is stored, an ion collector that collects ionized ions generated by radiation from the measurement object, and the measurement chamber And a gas circulation path that circulates gas through the ion collector, and an ion current measurement unit that measures an ion current value of ions collected in the ion collector, the shape data of the measurement object is An input shape data input unit, an ion transfer time calculation unit that calculates the transfer time of ionized ions from the upstream end of the measurement object to the ion collector based on the shape data, and the ion transfer time A correction coefficient calculation unit for obtaining a correction coefficient for correcting the ion current value from the ratio of the number of ions reduced by ion recombination in the gas and the shape data Wherein and a radiation dose conversion unit for converting the ion current to the radiation amount using the correction coefficient, provided with the ion current measuring unit on the upstream side and the downstream side of the measuring chamber, the circulation direction in said gas circulation path Switching means for switching between forward and reverse directions is provided .

  According to the present invention, it is possible to accurately measure the radiation intensity of measurement objects having different shapes.

1 is an overall configuration diagram of a radiation measurement apparatus according to a first embodiment. The lineblock diagram of the radiation measuring device concerning a 2nd embodiment. The lineblock diagram of the radiation measuring device concerning a 3rd embodiment. The whole block diagram of the radiation measuring device which concerns on 4th Embodiment. The whole block diagram of the radiation measuring device which concerns on 5th Embodiment. The correspondence figure of the shape of piping and the measurement sensitivity in the conventional radiation measuring device.

Hereinafter, embodiments of a radiation measuring apparatus according to the present invention will be described with reference to the drawings.
[First Embodiment]
A radiation measuring apparatus according to a first embodiment of the present invention will be described with reference to FIG.
(Constitution)
The radiation measurement apparatus according to the first embodiment is connected to a measurement chamber 3 in which a measurement object 1 and a sample stage 2 are housed, a gas convergence nozzle 4 provided on the outlet side of the measurement chamber 3, and a gas convergence nozzle 4. The flow velocity measuring unit 12 and the ion collecting unit 5, and the circulation device 7 including a fan for circulating the air in the measurement chamber 3 through the gas circulation path 6.

The radiation measurement unit includes an ion current measurement unit 8 for measuring the current value of the ions collected by the ion collection unit 5, a radiation dose conversion unit 19 for converting the measured ion current into a radiation dose, and a measurement target A shape data input unit 9 for inputting the shape data of the object 1, an ion transfer time calculation unit 10 for calculating the time for ions generated in the measurement chamber to move to the ion collection unit together with air, and while the ions move From the recombination of ions, the rate of decrease in the number of ions is calculated, the collected ion amount correction coefficient calculation unit 11 in the ion collection unit 5, and the flow rate measurement unit 12 for calculating the flow rate of the circulated air. Composed.
In the first embodiment, the measurement object 1 is a substantially straight pipe, and the pipe is placed on the sample table 2 in parallel with the air flow flowing in the measurement chamber.

(Function)
The principle and operation of the radiation measuring apparatus configured as described above will be described.
When α rays are emitted from α radionuclides such as uranium adhering to the surface of the measurement object 1, the air is ionized within the range of the α rays and ions are generated. The generated ions are sent to the ion collector 5 through the gas converging nozzle 4 together with the air that is blown and circulated by the circulation device 7. Further, the air makes a round through the gas circulation path 6 to the measurement chamber 3. At this time, the number of ions decreases with time and disappears due to recombination, or is collected there if a filter is installed in the circulation device 7.

  The ion collector 5 usually has an electrode structure to which a voltage is applied, and a current corresponding to the amount of ions is generated by collecting ions on the electrode. This current is measured by the ion current measuring unit 8, and the current value measured by the radiation dose conversion unit 19 is converted into a radiation dose by arithmetic processing.

  As a general method of calculation processing at this time, a conversion coefficient for converting from current to radiation dose for each shape of an object to be measured is obtained in advance by a calibration test, and a correspondence table between the shape and the conversion coefficient is prepared in advance. The measured current value is converted into the radiation dose with reference to the conversion coefficient corresponding to the input shape data. Note that the conversion coefficient may be a combination of sensitivity correction coefficients for each shape with respect to a reference conversion coefficient.

  This conversion coefficient or sensitivity correction coefficient decreases due to ion recombination before ions generated by the ionizing action of α rays reach the electrode of the ion collector 5, so that ions move from the ion generation position to the electrode. Depends on time.

The relationship between the recombination of ions and the number of ions is expressed by the following equation in which the number of ions generated by α rays and the number of background ions are modeled respectively (Patent Document 2).

Here, the relationship between the conversion coefficient and the number of ions when the measurement object 1 is the pipe shown in FIG. 1 will be described.
Normally, the position where alpha rays are generated on the pipe surface is unknown, so when evaluating the radiation dose to the safe side, such as when carrying out inspection from the radiation control area, the conversion factor at the position where the sensitivity is expected to be the lowest is calculated. Use. In FIG. 1, a conversion coefficient that is assumed to be an α ray generation position, that is, contamination is present at the upstream end portion of the measurement object 1 indicated by a. The number of ions that decrease by recombination before the ions generated in a reach the electrode position b of the ion collector 5 depends on the distance from a to b if the ion moving speed is constant, and the position of a If the difference is different, the number of ions to be reduced is also different, so the conversion coefficient is also changed.

  At this time, if there is a conversion coefficient having the same length as that of the measurement object 1 in the conversion coefficient correspondence table, the distance from a to b is the same, and therefore correct conversion can be performed. When there is no length conversion coefficient, a conversion coefficient having a shape closest to the length of the measuring object 1 is selected in the conventional method.

  In this case, if the difference between the distance from a to b and the length of the selected shape is large, correct conversion cannot be performed and the error increases. Further, although it is possible to calculate a conversion coefficient having the same length as the object by interpolation of the correspondence table, it is necessary to prepare a large amount of conversion coefficients in the correspondence table in order to suppress errors.

  On the other hand, in the first embodiment, first, the length of the measuring object 1 is input by the shape data input unit 9. The input means may be a manual input by an operator or a method of automatically reading the length. The input length information is sent to the ion transfer time calculator 10. Here, the distance from a to b is calculated based on the length information of the measurement object 1 input first. In addition, in FIG. 1, b is shown by the position of the entrance of the ion collection part 5, but if it is constant, it will not specifically limit.

  Next, the ion transfer time calculation unit 10 calculates the flow rates of the measurement chamber 3, the gas converging nozzle 4, and the flow rate measurement unit 12 from the flow rate of the air circulated in the circulation device 7, and moves ions from a to b. Calculate time. The flow rate is obtained from the flow velocity measured by the flow velocity measuring unit 12, but when the flow rate of the air circulated in the circulation device 7 is adjusted to be constant in advance, the flow rate may be used.

  Next, the correction coefficient calculation unit 11 obtains the ion current reduction rate due to ion recombination from the ion movement time, and selects the shape closest to the measurement object 1 from the conversion coefficient correspondence table used in the radiation dose conversion unit 19. Then, an ion current decrease rate due to recombination of ions in the selected shape is obtained, an ion current correction coefficient is calculated from the ratio with the ion current decrease rate at the measurement object 1, and the radiation dose conversion unit 19 calculates the correction coefficient. Enter.

When the measurement object is a pipe, the conversion coefficient correspondence table used here is obtained from a correspondence table in which the diameter of the pipe having the reference length is associated with the measurement sensitivity (not shown). Note that pipes used in nuclear power plants and the like are usually pipes having a plurality of predetermined diameters, and if a correspondence table is created using the diameters, a conversion factor corresponding to the actual pipes can be obtained. Can do.
Moreover, it is good also as a correction coefficient of the conversion factor of a radiation dose instead of the correction coefficient of an ion current.

  Next, air is circulated by the circulation device 7 in a state where the measurement object 1 is housed in the measurement chamber 3. The circulated air is ionized by α rays generated from the measurement object 1, and the generated ions are transferred to the ion collector 5 together with the air, and the ions are collected by the electrodes. The ion current is measured by the ion current measurement unit 8 and the current value is input to the radiation dose conversion unit 19. The input current value is corrected with the correction coefficient input from the correction coefficient calculation unit 11 into the shape data of the correspondence table, converted into the radiation dose by the conversion factor of the correspondence table, and displayed or recorded.

(effect)
As described above, according to the first embodiment, by using the actual length of the measurement object, the radiation intensity of the measurement object having a different shape can be accurately and efficiently measured.

[Second Embodiment]
A radiation measurement apparatus according to a second embodiment of the present invention will be described with reference to FIG.
(Constitution)
In the radiation measuring apparatus of the second embodiment, ion collectors 5-1 and 5-2 are arranged before and after the measurement chamber 3, and a control unit 13 for reversing the blowing direction of the circulation device 7 is provided. In FIG. 2, the radiation measurement unit is omitted.

(Function)
The operation of the radiation measuring apparatus configured as described above will be described.
First, let the direction which blows with the circulation apparatus 7 be a forward direction shown with a dotted-line arrow. In this state, a state similar to that shown in FIG. 1 is obtained, and the conversion coefficient used is calibrated based on the time required for ions to move from a to b. In the ionic fluid transfer type measurement, since the air in the measurement chamber is collectively transferred to the ion collecting unit and measured, the generation position of α rays on the surface of the measurement object cannot be detected.

  Here, assuming that the α-ray generation position is at the downstream end c of the measurement object 1, the ions generated at c reach b of the ion collector 5-1 at a shorter distance than the upstream end a. Therefore, the amount of annihilation due to recombination of ions is small, the measured ion current becomes large, and the converted radiation dose is overestimated.

  In the present embodiment, after the radiation intensity is measured by the ion collector 5-1, the air flow direction of the circulation device 7 is reversed by the control unit 13, so that the air flow direction is opposite to the forward direction as indicated by the solid line arrow. The reverse direction. The controller 13 may be a method of inverting the circulation device 7 or a method of switching the connection direction of the gas circulation path 6 using a valve.

  As a result, the ions generated at c move to b ′ of the ion collector 5-2, so that the moving distance c-b ′ becomes longer than c-b. For example, the arrangement of the measuring object 1 is measured. If it is arranged at the center of the chamber 3, the amount of annihilation due to recombination of ions is the same as when it moves from a to b.

  When the circulation direction of the air is the forward direction of the dotted arrow, the ion collector 5-1 calculates the ion current measured by the ion collector 5-2 when the circulation direction is the solid arrow of the reverse direction. When the radiation dose is converted by the ions generated at the position c with the conversion constant calibrated at the position a by, for example, averaging the values, only the forward blast indicated by the dotted arrow is used. Compared with the measured current value, the ratio of overestimation is reduced and the error can be reduced by calculating the measured current value in the reverse direction blowing together.

(effect)
According to the second embodiment, even if spot-like contamination is present at an arbitrary position of the measurement object, errors due to overestimation can be reduced, so that the radiation intensity of the measurement object can be more accurately and accurately. It can be measured efficiently.

[Third Embodiment]
A radiation measurement apparatus according to a third embodiment of the present invention will be described with reference to FIG.
(Constitution)
In the radiation measuring apparatus according to the third embodiment, an ion adsorption filter 14 is arranged on the upstream side of the measurement object 1 housed in the measurement chamber 3. In FIG. 3, the radiation measurement unit is omitted.

(Function)
The operation of the radiation measuring apparatus configured as described above will be described.
Background ions generated in the measurement chamber 3 include those caused by radon existing in the natural environment, and those caused by environmental γ rays and cosmic rays caused by other natural nuclides. This background ion amount depends on the volume of the measurement chamber 3. When the measurement object 1 is small, the measurement chamber 3 has a larger volume than the measurement object 1.

Therefore, in the third embodiment, by arranging the ion adsorption filter 14 on the upstream side of the air flow with respect to the measurement object 1, background ions generated on the upstream side of the ion adsorption filter are adsorbed. The volume of the measurement chamber 3 is apparently reduced and the generated background ions are reduced, and the ions are transferred to the ion collector 5 together with the ionized ions caused by the α rays generated in the measurement object 1.
Thereby, since background noise is reduced as compared with the case where the ion adsorption filter 14 is not disposed, it is possible to measure to a lower signal level.

(effect)
According to the third embodiment, even when measuring a small measurement object with respect to the volume of the measurement chamber, the background can be reduced, so that the detection sensitivity can be improved. The radiation intensity of the measurement object can be measured more accurately and efficiently.

[Fourth Embodiment]
A radiation measurement apparatus according to a fourth embodiment of the present invention will be described with reference to FIG.
(Constitution)
The radiation measuring apparatus according to the fourth embodiment reads an ion current value storage unit 15 that sequentially stores the ion current values measured by the ion current measurement unit 8, and reads the stored ion current values. Ion current value fluctuation detection unit 16 that detects measurement abnormality, BG current value storage unit 17 that sequentially stores the background current (BG current) value measured by the ion current measurement unit 8, and the stored BG current value And a BG current value fluctuation detection unit 18 for detecting a background abnormality from a change in the BG current value is added.

(Function)
The operation of the radiation measuring apparatus configured as described above will be described.
First, before storing the measuring object 1 in the measuring chamber 3, the BG current is measured in advance. This is for calculating the ionization ion current value by the net α ray by subtracting the BG current value from the current value measured after the measurement object 1 is accommodated. The measured BG current value is sequentially stored in the BG current measurement value storage unit 15. The timing of BG measurement, the period to be stored, and the number of measurements are not particularly limited as long as a change in BG current can be detected. For example, after measuring the BG current before measuring a certain measurement object, the measurement object 1 is stored in the measurement chamber 3 and measurement is started.

  At this time, when the radioactive substance adhering to the surface of the measuring object 1 is peeled off and attached to the sample table 2, or the peeled radioactive substance is transferred to the ion collecting part 5 together with air and the ion collecting part 5 is contaminated. In the next BG measurement, the BG current increases due to this contamination. Usually, a plurality of measurements are performed by one BG current measurement to obtain a variation error, but a single measurement value may be used if the error is evaluated in advance.

  Next, the BG current value stored in the ion current measurement value variation detection unit 16 is read and compared. For example, the latest BG current value and the previous BG current value are read out, and the threshold value is a value that significantly varies with respect to the error. The threshold value and the fluctuation range of the BG current are compared, and the fluctuation range exceeds the threshold value. If an alarm is output or displayed. Alternatively, instead of the previous BG current, a BG current value in an arbitrary fixed period may be read out and compared with a current value in a portion where the fluctuation of the BG current is flat or an average current value in a fixed period.

  Next, the measurement object 1 is accommodated in the measurement chamber 3 to perform the main measurement. The ion current value measured by the ion current measurement unit 8 is stored in the ion current measurement value storage unit as a numerical value for each sampling performed by the ammeter. The sampling time and sampling number for storing the ionic current value are not particularly limited as long as the fluctuation of the ionic current can be detected.

  During the actual measurement at a certain point in time, if the radioactive material adhering to the surface of the measurement object 1 is peeled off and flows out of the measurement chamber together with the circulating airflow and adheres to the gas circulation path 6 or the like, The ion current value is greatly reduced. Usually, the measurement time for one time is about several tens of seconds, and the average current during this period is obtained. Sampling measurement by the ammeter is performed in a shorter time, and the change at this time is recorded.

  Next, the recorded current value for each sampling is read by the ion current value fluctuation detection unit 16 and averaged in an arbitrary section. When each section is compared and a significant variation is detected with respect to the variation error of the section average value, an alarm is output or displayed.

(effect)
According to the fourth embodiment, since it is possible to detect an abnormality when secondary contamination occurs due to peeling of contamination on the surface of the measurement target being measured, the radiation intensity of the measurement target is more accurately and accurately detected. It can be measured efficiently.

[Fifth Embodiment]
A radiation measurement apparatus according to a fifth embodiment of the present invention will be described with reference to FIG.
(Constitution)
The radiation measurement apparatus according to the fifth embodiment has a configuration in which a plurality of measurement chambers 3, gas converging nozzles 4, and ion collection units 5 are provided, and individual ion current measurement units 8 are provided in each ion collection unit.

(Function)
The operation of the radiation measuring apparatus configured as described above will be described.
The measurement object 1 is accommodated in one of the plurality of measurement chambers 3 shown in FIG. Note that the number of measurement chambers and the number of measurement chambers in which measurement objects are stored can be appropriately increased or decreased.

  In this state, air is blown by the circulation device 7 to send air to each measurement chamber, and the current is measured by the ion current measuring unit connected to each ion collecting unit 5. The measured current value is output to the radiation dose conversion unit 19 and is connected to the measurement chamber 3 that does not contain the measurement object 1 from the ionic current value on the side connected to the measurement room 3 that houses the measurement object 1. The net current value is obtained by subtracting the ion current value on the side of the current side, and converted to the radiation dose.

(effect)
According to the present embodiment, since the BG measurement can be performed simultaneously with the main measurement and the net current value can be obtained without measuring the BG current in advance, the radiation intensity of the measurement object can be measured more accurately and efficiently. be able to.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, combinations, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Measurement object, 2 ... Sample stand, 3 ... Measurement chamber, 4 ... Gas convergence nozzle, 5-1, 5-2 ... Ion collection part, 6 ... Gas circulation path, 7 ... Circulation apparatus, 8 ... Ion Current measurement unit, 9 ... shape data input unit, 10 ... ion transfer time calculation unit, 11 ... correction coefficient calculation unit, 12 ... flow velocity measurement unit, 13 ... circulation direction reversal unit, 14 ... ion adsorption filter, 15 ... ion current value Storage unit 16 ... Ion current value fluctuation detection unit 17 ... BG current value storage unit 18 ... BG current value fluctuation detection unit 19 ... Radiation dose conversion unit.

Claims (6)

A measurement chamber in which a measurement object is stored, an ion collector that collects ionized ions generated by radiation from the measurement object, a gas circulation path that circulates gas in the measurement chamber and the ion collector, and the ion collection In a radiation measurement apparatus having an ion current measurement unit that measures an ion current value of ions collected in the unit,
A shape data input unit for inputting the shape data of the measurement object, and an ion transfer time calculation for calculating the transfer time of ionized ions from the upstream end of the measurement object to the ion collector based on the shape data A correction coefficient calculation unit for obtaining a correction coefficient for correcting the ion current value from the shape data and the ratio of the number of ions that are reduced by recombination of ions in the gas within the transfer time, and the correction coefficient and a radiation dose conversion unit which converts the radiation dose of the ion current value using,
A radiation measuring apparatus characterized in that the ion current measuring unit is provided on the upstream side and the downstream side of the measurement chamber, and switching means for switching the circulation direction between forward and reverse directions is provided in the gas circulation path . A measurement chamber in which a measurement object is stored, an ion collector that collects ionized ions generated by radiation from the measurement object, a gas circulation path that circulates gas in the measurement chamber and the ion collector, and the ion collection In a radiation measurement apparatus having an ion current measurement unit that measures an ion current value of ions collected in the unit,
A shape data input unit for inputting the shape data of the measurement object, and an ion transfer time calculation for calculating the transfer time of ionized ions from the upstream end of the measurement object to the ion collector based on the shape data A correction coefficient calculation unit for obtaining a correction coefficient for correcting the ion current value from the shape data and the ratio of the number of ions that are reduced by recombination of ions in the gas within the transfer time, and the correction coefficient A radiation dose conversion unit that converts the ion current value into a radiation dose using an ion current, an ion current value storage unit that sequentially stores the ion current value measured by the ion current measurement unit, and the ion current value for each predetermined section A radiation measurement apparatus comprising: an ion current value fluctuation detection unit that obtains an average value of the ion current and monitors the fluctuation of the average value. The measurement object is a substantially straight pipe, the shape data radiation measuring device according to claim 1 or 2, wherein the a length and diameter of the pipe. Radiation measuring apparatus according to any one of claims 1 to 3, characterized in that a partition plate made of an ion adsorption filter on the upstream side of the measuring chamber. A background current value storage unit for storing a background current periodically measured without storing a measurement object in the measurement chamber, and a background current value fluctuation detection unit for monitoring the fluctuation of the background current value are provided. radiation measuring apparatus according to any one of claims 1 to 4, characterized in that the. Wherein a plurality of measurement chambers, radiation measuring device according to any one of claims 1 to 5, characterized in that a ion current measuring unit for each measurement chamber.

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