JP4214176B2 - Neutron measurement system - Google Patents

Description

  The present invention relates to a neutron measurement system, and more particularly to a neutron measurement system that calculates a dose equivalent according to neutron energy.

  In nuclear fuel facilities, nuclear power plants, etc., neutron measuring devices are used for exposure management inside and outside the facilities. As a neutron measuring apparatus, for example, a survey meter is well known. A neutron measurement device generally uses a moderator made of a material containing a large amount of hydrogen atoms. The moderator is used to decelerate neutrons, and the decelerated neutrons (mainly thermal neutrons) are converted into scintillators or proportional counters. It is detected by a neutron sensor. A dose, dose equivalent, etc. are calculated from the detected value. A neutron measuring apparatus is required to detect neutrons over a wide energy range and to improve measurement accuracy. Furthermore, it is required to adopt a small and mobile configuration.

  The following Patent Document 1 shows a configuration in which neutron detectors are arranged at the front, middle, and rear of the moderator in the neutron flight direction to detect neutrons over a wide energy range. Further, this document describes that neutron energy is estimated from the mutual ratio of a plurality of detected values. Patent Documents 2 and 3 also show configurations for measuring neutrons over a wide energy range using a plurality of neutron detectors. The configurations described in Patent Documents 1 and 2 have a problem in terms of direction dependency, and in particular, there is a problem that neutrons flying from the side face cannot be measured with high accuracy. In the case of the configuration described in Patent Document 3, it is difficult to reduce the size.

JP-A-5-264739 JP 9-318759 A JP-A-6-258449

  As described above, it is desirable that the neutron measurement device is small and has good mobility.However, if the moderator is reduced and the size is reduced, the measurement accuracy on the high energy side will inevitably deteriorate. The energy estimation accuracy deteriorates. Further, a spatially flat sensitivity characteristic is desired, but there is a problem that direction dependency occurs. As described above, the request for miniaturization and the request for reliability of measurement are generally in a contradictory relationship. In particular, the neutron field is different for each facility, and it is required to ensure measurement accuracy even if the neutron field is different.

  An object of the present invention is to solve at least one of the plurality of problems described above. Specifically, an object of the present invention is to provide a radiation measurement system that has good mobility during measurement and can exhibit good measurement accuracy.

(1) The present invention includes a survey device that measures neutrons and outputs a measurement result, and a calibration device for calibrating the operation of the survey device, the survey device comprising a neutron detection unit, the neutron A calculation unit that calculates a measurement result from a detection value by a detection unit, and the calibration device includes a calibration neutron detection unit having energy sensitivity characteristics different from that of the neutron detection unit, and the calibration neutron detection unit. And a correction unit that executes processing for correcting the calculation conditions of the survey device in consideration of the detection value of

  According to the said structure, it is possible to perform a neutron measurement using the survey apparatus alone, after optimizing beforehand the calculation conditions in a survey apparatus using a calibration apparatus. Therefore, both mobility and sufficient measurement accuracy can be ensured. It is desirable that the survey apparatus is calibrated in an environment similar to a neutron field at an actual measurement site. In nuclear fuel facilities, etc., the neutron field is often considered to be generally uniform at each location inside and outside the facility.In such a case, if the survey device is calibrated using a calibration device at any location, The survey device alone can measure neutrons with good accuracy. On the other hand, neutrons can be measured with high accuracy in a state where the calibration device and the survey device are connected. Calibration can be performed periodically or when necessary (for example, when the neutron field changes). In a preferred example, the calibration apparatus includes a large neutron measurement apparatus that can detect fast neutrons and a computer that corrects the operating conditions of the survey meter using the measurement results. It is desirable to configure the large neutron measurement device and the computer so that they are electrically connected by a cable, but manually input the detection value or measurement result of the large neutron measurement device into the computer and use the input information. Correction calculation may be performed. Similarly, it is desirable that the calibration device and the survey device are electrically connected by a cable at the time of calibration, but the correction processing result by the correction unit in the calibration device is reflected in the operation of the survey device. As long as the electrical connection is not necessary. For example, when a relational expression correction value or function selection value is displayed as the correction processing result, the user can read the display value and manually input it to the survey apparatus. In that case, the survey apparatus executes a process of automatically correcting a calculation condition (preferably a relational expression described later) based on the input information. In any case, the correction unit executes a correction calculation process for correcting the operation of the survey apparatus, and more preferably executes a control for automatically correcting the operation of the survey apparatus based on the calculation result.

  Preferably, a calculation condition related to the estimation of neutron energy in the calculation unit is corrected. Preferably, the neutron detection unit includes a plurality of survey neutron detection units having different energy sensitivity characteristics, and the calculation unit calculates a ratio of a plurality of detection values by the plurality of survey neutron detection units, Means for calculating a conversion coefficient based on a relational expression depending on neutron energy from a ratio of the plurality of detected values; and means for calculating the measurement result using the conversion coefficient, wherein the relational expression is corrected. The The above relational expression may be held in the form of a mathematical expression or may be configured in the form of a table. The relational expression may be corrected by correcting the contents of the relational expression itself or by selecting an optimum relational expression from a plurality of relational expressions. There are various other correction methods.

  Preferably, the relational expression is based on an energy estimation function for estimating neutron energy from a ratio of the plurality of detected values, and a conversion coefficient determination function for obtaining a conversion coefficient from the neutron energy, and the energy estimation function Is corrected. The energy estimation function and the conversion coefficient determination function may be configured as independent mathematical expressions or tables, or may be configured as an integrated mathematical expression or table. In any case, an appropriate conversion factor corresponding to the neutron energy is obtained from the ratio.

  Preferably, the neutron detection unit includes a first survey neutron detection unit having a first energy sensitivity characteristic, and a second sensitivity having a main sensitivity on a higher energy region side than the main sensitivity in the first energy sensitivity characteristic. A second survey neutron detector having energy sensitivity characteristics, wherein the calibration neutron detector has a sensitivity at least higher than that of the second energy sensitivity characteristics at the high energy region side. 3 energy sensitivity characteristics. The calibration neutron detector has a role of complementing the detection capabilities of the first and second survey neutron detectors, and is preferably sufficiently good and has flat energy sensitivity characteristics over a wide energy range. Any material having good sensitivity at least in the high energy region can be used.

  Preferably, the first survey neutron detection unit includes a first speed reduction member having a first size, and a first neutron sensor provided in the first speed reduction member, The second survey neutron detection unit includes a second moderator member having a second size larger than the first size, a second neutron sensor provided in the second moderator member, The calibration neutron detection unit includes a third speed reduction member having a third size larger than the second size, and a third neutron sensor provided in the third speed reduction member; ,including.

  Preferably, the first speed reduction member has a small diameter cylindrical shape, the second speed reduction member has a large diameter cylindrical shape, and the first speed reduction member and the second speed reduction member are mutually connected. It is provided with a form in which the central axes are matched to each other.

(2) The present invention is a portable survey device that measures neutrons and calculates a dose equivalent, and prior measurement of neutrons in a neutron field that can be regarded as the neutron field at the time of actual measurement prior to actual measurement by the survey device. And a calibration device that calibrates the operation of the survey device, wherein the survey device includes first and second survey neutron detectors having different energy sensitivity characteristics, and the first and second surveys. And a calculation unit that calculates a dose equivalent based on the first and second detection values by the neutron detection unit, and the calibration device is at least more than the first and second survey neutron detection units. In consideration of the detection value by the calibration neutron detection unit having energy sensitivity characteristics with good sensitivity on the high energy region side and the calibration neutron detection unit, the calculation unit A correction unit that executes a process for correcting a calculation condition of a dose equivalent to be calculated. In the preliminary measurement, the operation of the survey apparatus is calibrated using the calibration apparatus, and the actual measurement is performed. In this case, neutrons are measured using a calibrated survey device alone.

  Preferably, the survey apparatus includes a speed reducer having a configuration in which a small diameter portion and a large diameter portion are combined, a first scintillator that is provided in the small diameter portion and emits light upon incidence of neutrons, and in the large diameter portion. A second scintillator that emits light upon incidence of neutrons, and a photomultiplier that is disposed with a light-receiving surface entering the large-diameter portion and receives light from the first and second scintillators. The small-diameter portion and the first scintillator constitute the first survey neutron detector, and the large-diameter portion and the second scintillator serve as the second survey neutron detector. Constitute.

  As described above, according to the present invention, it is possible to provide a radiation measurement system that has good mobility during measurement and can exhibit good measurement accuracy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram showing the overall configuration of a neutron measurement system according to the present invention. This neutron measurement system is used to measure neutrons inside and outside a facility in a nuclear power plant, a nuclear fuel processing facility, or the like.

  In FIG. 1, in this embodiment, the neutron measurement system includes a survey meter 10 that functions as a survey device, an auxiliary measurement device 12 that separately detects neutrons to correct the operating conditions of the survey meter 10, and detection by the auxiliary measurement device 12. And a system controller 14 that corrects the operating conditions of the survey meter 10 using values and the like. Here, the system controller 14 and the auxiliary measuring device 12 constitute a calibration device as a whole. In FIG. 1, the system controller 14 and the auxiliary measuring device 12 are configured separately, but they may be integrated. In the neutron measurement system shown in FIG. 1, the operating conditions of the survey meter 10, specifically the calculation conditions as described later, are corrected using the auxiliary measuring device 12 and the system controller 14. In addition, the neutron can be measured by itself using the survey meter 10. Of course, normal neutron measurement can also be performed in a state where the survey meter 10, the auxiliary measuring device 12, and the system controller 14 are electrically connected to each other. In that case, the auxiliary measuring device 12 functions as a neutron measuring device like the survey meter 10.

  The survey meter 10 has a configuration that can be carried by an operator, and constitutes a portable neutron measurement device. The survey meter 10 includes a detection unit 15 (first detection unit 16 and second detection unit 18) and a measurement unit 20. A battery (not shown) is built in the measurement unit 20, and neutrons can be measured while gripping and moving a grip 21 provided in the measurement unit 20. That is, as described above, the survey meter 10 measures neutrons alone and outputs measurement results such as dose equivalent as described later.

  The first detection unit 16 and the second detection unit 18 constitute a detection unit 15, the first detection unit 16 constitutes a small diameter portion, and the second detection unit 18 constitutes a large diameter portion. As will be described later, the first detector 16 has a main sensitivity mainly for the slow neutrons 26, and the second detector 18 has a main sensitivity mainly for the medium speed neutrons 28. The first detection unit 16 and the second detection unit 18 both have a cylindrical moderator, and the first detection unit 16 has a size of, for example, 3.5 cmφ × 3.5 cm, The part 18 has a size of 10 cmφ × 7.5 cm, for example. A neutron sensor composed of a scintillator is embedded in each of the detection units 16 and 18. It should be noted that the numerical values given in this specification are merely examples, and other numerical values can be adopted.

  As described above, the auxiliary measurement device 12 also functions as a normal neutron measurement device, and the auxiliary measurement device 12 includes a third detection unit 22 and a measurement unit 24. The 3rd detection part 22 has a moderator with a larger size than said 2nd detection part, for example, has a size of 20 cmphi * 20cm. As will be described later, a neutron sensor composed of a scintillator or a semiconductor detector is embedded in the moderator in the third detector 22, and the third detector 22 is good for the fast neutron 30. Sensitivity.

  The measurement unit 24 in the auxiliary measurement device 12 incorporates an electronic circuit as in the measurement unit 20 described above, and the measurement unit 24 calculates a dose equivalent based on the detection value of the third detection unit 22. Can do. In the present embodiment, a battery is built in the measurement unit 24, but of course power may be supplied from an external power source or the like.

  The system controller 14 is configured by a personal computer in the example shown in FIG. 1, and the system controller 14 and the auxiliary measuring device 12 are electrically connected by a cable 12A. Similarly, the system controller 14 and the survey meter 10 are electrically connected by a cable 10A. As will be described in detail later, the system controller 14 has a function of correcting the calculation conditions in the survey meter 10 based on the detection value of the auxiliary measuring device 12 and the like. Specifically, it has a function of correcting an energy estimation function used in estimation of neutron energy or a relational expression including the function. An interface circuit for performing electrical communication with the system controller 14 is provided in the measurement unit 24, and this also applies to the measurement unit 20. An interface circuit for communicating between the measurement unit 20 and the measurement unit 22 is built in the system controller 14. It is also possible for the user to read the detected value or measured value displayed on the auxiliary measuring device 12 and manually input the value to the system controller 14. Further, when the correction processing result is obtained in the system controller 14, the information is displayed, and the user reads it and inputs it manually into the survey meter 10, and the operating condition of the survey meter 10 is automatically determined based on the input information. You may make it correct | amend. However, if each device is connected to each other by a cable as in the present embodiment, the burden on the user can be reduced, and quick and accurate correction can be performed.

  FIG. 2 is a block diagram showing the components of the neutron measurement system shown in FIG.

  As described above, the survey meter 10 includes the detection unit 15 and the measurement unit 20. The detection unit 15 is configured by a first detection unit 16 and a second detection unit 18, and the first detection unit 16 is configured by a moderator 32 having a cylindrical shape and a neutron sensor 34 embedded near the center thereof. Yes. The second detector 18 includes a cylindrical moderator 36 and a neutron sensor 38 embedded in the vicinity of the center of the moderator 36. As shown in FIGS. 1 and 2, the first detection unit 16 and the second detection unit 18 are provided in a state of being connected to each other. In the present embodiment, as described later with reference to FIG. 9, The moderators in the respective detectors 16 and 18 are arranged in an integrated state with their axis centers coinciding with each other. In each of the detection units 16 and 18, the moderators 32 and 36 have a cylindrical shape. Therefore, as will be described later, when the front side of the survey meter 10 is viewed, the direction dependency, that is, the direction-dependent sensitivity fluctuation is generated. It can be improved, and a substantially uniform sensitivity characteristic is obtained over a so-called 2π range.

  The measurement unit 20 includes signal processing circuits 40 and 42, a calculation unit 48, an input device 51, and a display device 53. The signal processing circuits 40 and 42 are circuits for processing the output signals from the neutron sensors 34 and 38. In FIG. 2, counters 44 and 46 provided in the signal processing circuits 40 and 42 are illustrated. Has been. In addition to the counters 44 and 46, the signal processing circuits 40 and 42 have a preamplifier, a wave height discriminator, and the like. A signal output from the neutron sensor 34 is counted by the counter 46, and a count value (detection value) obtained thereby is output to the calculation unit 48. Similarly, the counter 44 counts the signal output from the neutron sensor 38 and outputs the count value (detection value) to the calculation unit 48. A coincidence circuit or the like may be provided as necessary.

  The calculation unit 48 is configured by an electronic circuit such as a microprocessor. In this embodiment, the calculation unit 48 calculates a ratio of count values, estimates neutron energy based on the ratio, and further corresponds to the neutron energy. A function for determining a conversion coefficient, a function for calculating a dose equivalent from one or both count values using the conversion coefficient, and the like. A relational expression for obtaining a conversion coefficient from the ratio of the count values is stored on a memory 49 provided in the calculation unit 48. This relational expression 49 may be a mathematical function or a table. Various user commands can be given to the calculation unit 48 using the input device 51, and a dose equivalent that is a measurement result output from the calculation unit 48 is displayed on the display unit 53. Incidentally, the measurement result may be output to the outside by a wireless method or a wired method.

  As described above, the auxiliary measuring device 12 includes the third detection unit 22 and the measurement unit 24, and the third detection unit 22 includes a large moderator 52 and a neutron sensor 54 embedded in the vicinity of the center. ing. The measurement unit 24 includes a signal processing circuit 56, a calculation unit 60, an input device 62, and a display device 64. Similar to the signal processing circuits 40 and 42 described above, the signal processing circuit 56 includes a preamplifier, a wave height discriminator, and the like. In FIG. 2, a counter 58 provided therein is clearly shown. The counter 58 counts the output signal from the neutron sensor 54 and outputs the count value to the calculation unit 60.

  The calculation unit 60 has a function of calculating a dose equivalent by multiplying a predetermined conversion coefficient based on the input count value. When a calibration process by prior measurement performed prior to the actual measurement process is performed, the calculation unit 60 transmits the input count value to the system controller 14 via the cable 12A. An input device 62 is connected to the calculation unit 60, and a display 64 for displaying values such as dose equivalent is connected.

  Although the single neutron sensor 54 is provided in the auxiliary measuring device 12 in FIG. 2, a plurality of neutron sensors may be provided, or a plurality of detection units may be used.

  Although the auxiliary measuring device 12 is the same neutron measuring device as the survey meter 10, it has a larger size than the survey meter 10, and carrying it is a heavy burden considering its size and weight. Therefore, in this embodiment, the neutron measurement with the survey meter 10 alone is realized after correcting the operating conditions for the survey meter 10 using the auxiliary measuring device 12. This provides mobility and good measurement accuracy.

  The system controller 14 includes a calculation unit 66, an input device 68, a display device 70, an external storage device 72, and the like. The calculation unit 66 estimates the neutron spectrum at that time based on the count value output from the auxiliary measuring device 12 and the two count values output from the survey meter 10, and from the shape or state of the neutron spectrum, the survey meter 10 is corrected. This function is represented as a relational expression calibration unit 67 in FIG. In this way, the state of the neutron field was investigated from the three detection values obtained by the three detection units, and then the relational expression was corrected. As described later, it was output from the auxiliary measurement device 12. The contents of the relational expression may be corrected or selected directly from the count value. That is, in calibrating the operating conditions of the survey meter 10, only the count value obtained by the auxiliary measuring device 12 may be used, or the two count values output from the survey meter 10 may be further considered as described above. Good. In any case, by considering the count value obtained by the auxiliary measuring device 12, the operating condition is fitted to the actual neutron field even in a situation where the measurement accuracy cannot be sufficiently maintained by the survey meter 10 alone. Therefore, there is an advantage that neutrons can be measured by a survey meter alone under always optimal conditions.

  Incidentally, as the moderators 32, 36, and 52 in each of the detection units 16, 18, and 22 described above, a material containing a large amount of hydrogen atoms can be used, and for example, high-density polyethylene having a specific gravity of 0.95 can also be used. . In addition, when a neutron sensor is arranged inside each moderator, energy sensitivity characteristics and spatial sensitivity characteristics vary depending on the arrangement position. Therefore, a more suitable position is found by experiment, and each neutron sensor is located there. It is desirable to arrange.

  Next, the spatial sensitivity characteristic of the survey meter 10 will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, when the neutron incident direction 76 is defined with respect to the detection center axis 74, the incident angle θ is defined. FIG. 4 shows the relative sensitivity in relation to the incident angle θ. In FIG. 4, black circles indicate characteristics when fast neutrons are incident on the first detector 16, black triangles indicate characteristics when thermal neutrons are incident on the first detector 16, and white circles indicate 2 shows characteristics when fast neutrons are incident on the detector 18, and a white triangle indicates characteristics when thermal neutrons are incident on the second detector 18.

  As shown in FIG. 4, in the survey meter 10 of the present embodiment, the first detection unit 16 is configured in a cylindrical shape, and the second detection unit 18 is also configured in a cylindrical shape. The characteristics are almost flat. That is, even when neutrons are incident from the side direction, good sensitivity can be exhibited as in the front direction.

  FIG. 5 shows the energy sensitivity characteristics of the detection units 16, 18, and 22. That is, the horizontal axis in FIG. 5 indicates neutron energy, and the vertical axis indicates sensitivity. Reference numeral 80 indicates the energy sensitivity characteristic of the first detection unit 16, reference numeral 82 indicates the energy sensitivity characteristic of the second detection unit 18, and reference numeral 84 indicates the energy sensitivity characteristic of the third detection unit 22. . As shown in the figure, the first detector 16 has a main sensitivity on the low energy side, and the second detector 18 has a main sensitivity on medium energy. Further, the third detection unit 22 has a main sensitivity on the high frequency side. In estimating the neutron energy, the ratio (ratio) between the count value of the first detection unit 16 and the count value of the second detection unit 18 is obtained, and the neutron energy is estimated according to the ratio. As is clear from the characteristics, there is a possibility that the difference in the ratio is not sufficiently generated in the high energy range, and as a result, the energy estimation error increases. On the other hand, in this embodiment, the ratio or intensity of high-energy neutrons is evaluated using the count value obtained by the third detection unit 22, and the energy estimation function is corrected thereby, thereby increasing the energy estimation accuracy on the high-energy side. Has been improved. As a result, even when neutron measurement is performed using the survey meter 10 alone, neutron measurement accuracy can be sufficiently ensured over a wide energy range.

  FIG. 6 shows the relationship for estimating the neutron energy from the ratio of the two count values in the survey meter 10 and further determining the conversion coefficient from the neutron energy. The left half of the horizontal axis represents the ratio of the two count values. When the count value of the first detector 16 is C1, and the count value of the second detector 18 is C2, the ratio is C1 / C2. expressed. The right half of the horizontal axis in FIG. 6 represents the conversion coefficient. This conversion coefficient is a coefficient multiplied by the detected value of neutrons, and the dose equivalent can be obtained by the multiplication.

  The vertical axis in FIG. 6 represents the average neutron energy. Reference numeral 86 represents an energy estimation function for determining the neutron energy from the ratio of the count values, and a plurality of functions 86A, 86B, 86C are illustrated as specific contents. That is, energy estimation that is optimal for the actual neutron field by correcting the shape of the function on the high-energy side, or by selecting one of the functions, particularly in relation to the abundance of high-energy neutrons It is possible to specify the function and estimate the neutron energy using the specified function.

  Reference numeral 88 represents a conversion coefficient determination function, and the conversion coefficient is uniquely determined from the estimated neutron energy. Therefore, when the calibration process based on the pre-measurement is executed prior to the actual measurement process, the optimum energy estimation function is specified, and for example, the energy estimation function 86B shown in FIG. 6 is specified. Then, when the ratio of the count values is obtained as A, for example, the point B corresponding to A is specified on the function 86B, and thereby the neutron energy is uniquely determined. Then, the point C corresponding to the point B is specified on the conversion factor determination function 88, and D can be obtained as a conversion factor from the point C.

  In the present embodiment, as shown in FIG. 6, the energy estimation function and the conversion coefficient determination function are provided independently as the relational expressions, and the former is corrected. The functions may be integrated into one relational expression, and the contents of the relational expression may be corrected. In any case, under the situation where neutrons are actually measured by correcting the operational characteristics of the survey meter 10 in advance under the same neutron field conditions as in the actual measurement site in consideration of the measurement results by the auxiliary measurement device 12. It is possible to construct an optimal calculation condition in step (b).

  Next, the operation of the system will be described with reference to FIG. In FIG. 7, S <b> 10 indicates a calibration process by prior measurement, which is expressed as a function 100 of the calculation unit 66. Symbol S12 represents an actual measurement process, which is represented as a function 108 of the calculation unit 48. The calculation unit 66 has a function 102 for estimating a neutron spectrum, a function 106 for correcting the relational expression 112, and a function 104 for calculating a dose equivalent, as indicated by reference numeral 100. .

In the estimation 102 of the neutron spectrum, three count values C1, C2, and C3 by the three detectors 16, 18, and 22 are used. Here, the energies of fast neutrons, medium neutrons and slow neutrons are defined as E1, E2 and E3, and each of the detectors 16, 18, and 22 at a certain energy E _i (i = 1, 2, 3). When the sensitivity is expressed as R1 (Ei), R2 (Ei), and R3 (Ei) and the neutron fluence at the energy Ei is defined as φ (Ei), the following relational expression is established.
[Equation 1]
C1 = R1 (E1) × φ (E1)
+ R1 (E2) × φ (E2)
+ R1 (E3) × φ (E3) (1)
C2 = R2 (E1) × φ (E1)
+ R2 (E2) × φ (E2)
+ R2 (E3) × φ (E3) (2)
C3 = R3 (E1) × φ (E1)
+ R3 (E2) x φ (E2)
+ R3 (E3) × φ (E3) (3)

  The arithmetic unit 66 calculates the energy distribution of the neutron fluence that is unknown information, that is, the neutron spectrum, by mathematically processing the above calculation formula according to the spectrum analysis method. Of course, the neutron spectrum or its pattern may be obtained using a table or the like without using mathematical calculation.

  When the neutron spectrum is estimated as indicated by reference numeral 102 in FIG. 7, it is indicated by reference numeral 104 by considering the neutron spectrum based on one or more of the count values C1, C2, and C3. The dose equivalent can be calculated with high accuracy. Further, based on the spectrum thus estimated, the relational expression 112 can be corrected as indicated by reference numeral 106. In other words, it is possible to determine in which energy category the neutron component is large or small based on the result of spectrum analysis, and optimize the contents of the relational expression 112 in consideration of such a situation in the current neutron field. be able to. Specifically, the energy estimation function 86 can be derived using, for example, an inverse problem solving method, or the energy estimation function most suitable for the current neutron field is selected from a plurality of energy estimation functions. Is possible.

  After the relational expression is optimized as described above, in the actual measurement step S12, the calculation unit 48 obtains the ratio of the two count values C1 and C2 as indicated by reference numeral 110, and the relational expression 112 is obtained from the ratio. Based on this, the conversion coefficient D is obtained as described with reference to FIG. And as shown by the code | symbol 114, a dose equivalent is calculated by multiplying a conversion factor using either the count value C1, C2, or both.

  Therefore, in the calibration step S10 by prior measurement, the entire neutron measurement system is organically coupled, and as a result, the calculation conditions of the survey meter 10 are optimized. In the actual measurement step S12, the survey meter 10 is moved from the neutron measurement system. The neutron will be separated and high-precision measurement of neutrons will be executed. In this case, since the relational expression 112 is corrected to the optimum content, it is possible to appropriately perform energy estimation even in the presence of high-energy neutrons and increase the calculation accuracy of the dose equivalent.

  As described above, the survey meter 10 is smaller in terms of weight and size than the auxiliary measuring device 12 as described above, and even such a measuring device is corrected by the measurement result by the auxiliary measuring device 12. Therefore, highly accurate neutron measurement is realized.

  In the operation example shown in FIG. 7, the state of the neutron field in a situation that can be regarded as a measurement site is actually estimated. However, in the operation example shown in FIG. 8, the relational expression is simply selected in the calibration step by the preliminary measurement shown in S 10. (See reference numeral 116), and such a configuration can also be adopted. That is, after a plurality of relational expressions are registered in advance, one of the relational expressions is specified based on the count value C3 and used as the corrected relational expression 112 in the actual measurement step S12. Even in this case, there is an advantage that the actual measurement can be performed using an appropriate relational expression reflecting the measurement result of the auxiliary measuring device 12.

  The calibration step S10 based on the preliminary measurement can be performed at the start of the survey, can be performed prior to each measurement, or can be performed only when a change occurs in the neutron field.

  Next, a specific configuration example of each of the detection units 16 and 18 in the survey meter 10 will be described with reference to FIG. In FIG. 9, the shield container 90 is a hollow container made of a material such as aluminum, and the front side of the shield container 90 has a slightly tapered shape. A photomultiplier tube (PMT) 92 is disposed in the shield container 90. As is well known, the photomultiplier tube converts light reaching the light receiving surface 92A into an electric signal.

  In the example shown in FIG. 9, the moderator 32 in the first detector 16 is composed of two moderators 32A and 32B. The moderator 32B exists in the shield container 90, and the moderator 32A exists outside the shield container 90. The moderator 36 in the second detector 18 is composed of moderators 36A and 36B. The moderator 36B exists in the shield container 90, and the moderator 36A exists outside the shield container 90. Here, the moderator 32A and the moderator 36A constitute an integrated member, and similarly, the moderator 32B and the moderator 36B constitute an integrated member. That is, the shield container 90 is made of aluminum or the like, functions as a member for light shielding or physical protection, and hardly affects neutrons. Accordingly, the moderator 32 functions as a moderator for the neutron sensor 34 as a whole, and similarly, the moderator 36 functions as a moderator for the neutron sensor 38 as a whole.

  Each of the neutron sensors 34 and 38 is constituted by a solid scintillator, that is, when neutrons (mainly thermal neutrons) decelerated by a moderator are incident, light is thereby emitted, and the light is detected by a photomultiplier tube 92. . Here, as the photomultiplier tube 92, one having two light receiving surfaces 92A and 92B is used. The light generated by the neutron sensor 34 is guided to the light receiving surface 92A by the light guide 94, and the neutron sensor 38 is directly joined on the light receiving surface 92B. That is, light from the neutron sensor 34 is guided to the light receiving surface 92A, and light from the neutron sensor 38 is guided to the light receiving surface 92B, respectively, and is generated by the two neutron sensors 34 and 38 using one photomultiplier tube. Light can be received.

  As shown in FIG. 9, each of the first detection unit 16 and the second detection unit 18 has a cylindrical shape as described above, and is integrally coupled with the central axes thereof coincided with each other. . With such a configuration, good sensitivity characteristics almost independent of the incident angle as shown in FIG. 4 are obtained. Therefore, even when neutrons are incident from the side, the neutrons can be detected with good sensitivity.

  Incidentally, in the above-described embodiment, the dose equivalent of neutrons is calculated, but it may be a dose equivalent rate, or may be a dose or a dose rate or the like. In the above embodiment, the relational expression is corrected. However, when it is necessary to correct the operating condition of the survey meter using the third neutron measuring apparatus, various application examples of the present invention can be considered. For example, even when the dose or dose equivalent is not calculated, more accurate energy estimation can be realized by applying the above-described method, and the above-described method is also applied when performing various measurements. By correcting the operating conditions, more accurate measurement can be realized.

  According to the neutron measurement system according to the above-described embodiment, the operating conditions of the neutron measurement apparatus that can be used alone in the system are corrected using the high-precision measurement function of the entire system, and then the neutron measurement apparatus It is possible to realize neutron measurement with high mobility and high accuracy.

It is a conceptual diagram which shows the whole structure of the neutron measurement system which concerns on this invention. It is a block diagram which shows the whole structure of the neutron measurement system which concerns on this invention. It is a figure for demonstrating the incident angle of a neutron. It is a figure which shows the relationship between the incident angle of neutron and relative sensitivity. It is a figure which shows the energy sensitivity characteristic of each detector. It is a figure which shows the relationship between a neutron energy estimation function and a conversion factor determination function. It is a figure which shows an example of the operation example of a system. It is a figure which shows the other example of the operation example of a system. It is a figure which shows the structural example of each detection part in a survey meter.

Explanation of symbols

  10 survey meters, 12 auxiliary measurement devices, 14 system controllers, 15 detection units, 16 first detection units, 18 second detection units, 20 measurement units, 22 third detection units, 24 measurement units, 48, 60, 66 calculation units, 67 Relational expression calibration unit, 86 energy estimation function, 88 conversion coefficient determination function.

Claims (8)

A survey device that detects neutrons and outputs a measurement result, and a calibration device for calibrating the operation of the survey device,
The survey device
A neutron detection unit that detects neutrons and outputs detection values;
Based on a detection value by the neutron detection unit, a calculation unit that calculates a measurement result according to calculation conditions;
Have
The calibration device is
The neutron detection unit has an energy sensitivity characteristic different from that of the neutron detection unit, detects a neutron in a neutron field at the time of calibration, and outputs a detection value;
A correction unit that executes processing for correcting calculation conditions in the calculation unit of the survey apparatus, using at least the detection value of the calibration neutron detection unit during the calibration,
Have
The calculation condition is a condition for calculating dose, dose rate, dose equivalent or dose equivalent rate as the measurement result,
During the actual measurement after the calibration, the measurement result is calculated according to the corrected calculation condition in the survey device.
A neutron measurement system characterized by that. The apparatus of claim 1.
Neutron measuring system wherein the operation condition is corrected by the correction unit includes neutron energy estimation function for determining the neutron energy, it is characterized. The apparatus of claim 1 .
The neutron detection unit includes a plurality of survey neutron detection units having different energy sensitivity characteristics,
The computing unit is
Means for calculating a ratio of a plurality of detection values by the plurality of survey neutron detection units;
From the ratio of the plurality of detected values, a means for obtaining a conversion coefficient based on a relational expression depending on neutron energy;
Means for calculating the measurement result using at least one of a plurality of detection values output from the plurality of survey neutron detection units, and the conversion factor;
Including
The measurement result is the dose equivalent,
The conversion coefficient is a coefficient for obtaining the dose equivalent from at least one of a plurality of detection values output from the plurality of survey neutron detection units,
The calculation condition includes the relational expression,
The relational expression includes an energy estimation function for estimating neutron energy from a ratio of the plurality of detection values, and a conversion coefficient determination function for obtaining a conversion coefficient from the neutron energy,
The neutron measurement system, wherein the energy estimation function is corrected. The apparatus of claim 1.
The neutron detection unit is
A first survey neutron detector having a first energy sensitivity characteristic;
A second survey neutron detector having a second energy sensitivity characteristic having a main sensitivity on a higher energy region side than a main sensitivity in the first energy sensitivity characteristic;
Consists of
The neutron measurement system according to claim 1, wherein the calibration neutron detector has a third energy sensitivity characteristic having a better sensitivity at least on the high energy region side than the main sensitivity in the second energy sensitivity characteristic. The apparatus of claim 4.
The first survey neutron detection unit includes:
A first deceleration member having a first size;
A first neutron sensor provided in the first deceleration member;
Including
The second survey neutron detector is as follows.
A second deceleration member having a second size larger than the first size;
A second neutron sensor provided in the second deceleration member;
Including
The calibration neutron detector is
A third deceleration member having a third size larger than the second size;
A third neutron sensor provided in the third deceleration member;
A neutron measurement system comprising: The apparatus of claim 5.
The first deceleration member has a small diameter cylindrical shape,
The second deceleration member has a large-diameter cylindrical shape,
The neutron measurement system according to claim 1, wherein the first speed reduction member and the second speed reduction member are provided in such a manner that their center axes coincide with each other. A portable survey device that measures neutrons and calculates a dose equivalent, and prior to actual measurement by the survey device, prior measurement of the neutron is performed in a neutron field that can be considered similar to the neutron field at the time of the actual measurement. A calibration device for calibrating the operation,
The survey device
First and second survey neutron detectors having different energy sensitivity characteristics;
A calculation unit that calculates a dose equivalent based on the first and second detection values by the first and second survey neutron detection units;
Have
The calibration device is
A calibration neutron detector having an energy sensitivity characteristic at least at a higher energy region than the main sensitivity in the energy sensitivity characteristic of each of the first and second survey neutron detectors;
In consideration of the detection value by the calibration neutron detection unit, a correction unit that executes processing for correcting the calculation condition of dose equivalent in the calculation unit,
Have
During the preliminary measurement, the operation of the survey device is calibrated using the calibration device,
In the actual measurement, the neutron measurement system is characterized in that neutrons are measured using a calibrated survey device alone. The apparatus of claim 7.
The survey device
A speed reducer having a configuration in which a small diameter portion and a large diameter portion are combined;
A first scintillator that is provided in the small-diameter portion and emits light by the incidence of neutrons;
A second scintillator provided in the large-diameter portion and generating light emission upon incidence of neutrons;
A photomultiplier tube that is disposed with a light-receiving surface entering the large-diameter portion and receives light from the first and second scintillators;
Including
The small diameter part and the first scintillator constitute the first survey neutron detection part,
The neutron measurement system, wherein the large-diameter portion and the second scintillator constitute the second survey neutron detector.

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