JP7223420B2 - Temperature measuring device, temperature measuring method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law 2019 Spring Conference, Atomic Energy Society of Japan, March 20-22, 2019

The present invention relates to a temperature measuring device and a temperature measuring method for measuring the temperature of a sample without contact using resonance absorption of neutrons.

There are two types of methods for measuring the temperature of a sample: a contact type measurement method in which the sample and a temperature sensor are brought into contact with each other, and a non-contact type measurement method in which the temperature of the sample is measured in a non-contact state with the sample. In situations where it is difficult to bring the sample into contact with the temperature sensor, a non-contact measurement method is particularly preferred.

As a non-contact type measuring method, for example, a method of measuring temperature based on the intensity of thermal infrared rays emitted from a sample is widely used. On the other hand, when measuring the temperature of radioactive waste, for example, it is difficult to bring the sample into contact with the temperature sensor, and in addition, the sample may be covered with another material (such as a canister). , it is important to be aware of the temperature in the management of radioactive waste. In this case, since it is difficult to detect the thermal infrared rays emitted by the sample from the outside, it is difficult to detect the temperature of the sample with the thermal infrared rays.

Therefore, as a method for non-contact measurement of the temperature of the sample inside covered with the canister or the like, as described in Non-Patent Document 1, a method using X-rays that pass through the canister and the sample is known. It is In this measurement method, changes in the density of a sample with changes in temperature are recognized using transmitted X-rays. High-intensity synchrotron radiation is particularly preferably used as X-rays used as probes. However, in this method, the temperature can be measured only when the X-ray transmittance of the canister is sufficiently high, so there are large restrictions on the thickness and material of the canister.

On the other hand, in general, neutrons (rays) have a much higher transmittance to matter than X-rays. This is very effective because it loosens the restrictions on canisters that are For example, Non-Patent Documents 2 and 3 describe a temperature measurement method using a neutron beam as a probe. FIG. 8 is a diagram schematically showing the configuration of this measurement apparatus. Here, a neutron beam N0 with a wide range of energy (with a white spectrum) generated in a pulsed manner from the neutron source 100 hits the sample S. A neutron detector 90 detects the intensity of the neutron beam N1 that is irradiated to the sample S and passes through the sample S with high time resolution. It is an example of the measurement result in the neutron detector 90 used for calculating the temperature of the sample in this case. FIG. 9 shows the relationship between the flight time (detection time) and the detection intensity (neutron count) of neutrons emitted in pulses, and the neutrons that arrive earlier (on the side with the larger horizontal axis) have lower energy. It corresponds to high neutrons, and neutrons that arrive later (on the side with smaller horizontal axis) correspond to lower energy neutrons. Therefore, the characteristics of FIG. 9 correspond to the energy spectrum of the neutron beam N1. Here, only the sample S is shown in FIG. can be measured. Since neutrons have a higher material permeability than other radiations, many materials can be used as such materials.

Assuming that the neutron beam N0 has a white spectrum with a constant energy and the neutron beam N0 is detected by the neutron detector 90 as it is without the sample S present, as indicated by the dashed line in FIG. A temporally constant detection intensity reflecting the energy spectrum of is obtained. On the other hand, when the sample S is present, when the neutron beam N0 passes through the sample S, neutrons having energy specific to the resonance absorption of neutrons in the sample S (nuclides in the sample S) are particularly strongly absorbed. . Therefore, in the neutron beam N1 after passing through the sample S, strong absorption (decrease in detected intensity: dip) occurs during the flight time corresponding to the above-mentioned specific energy. This energy is about 4.3 eV when the sample S is made of Ta, for example.

When the temperature of the sample S changes, the position (energy: time of flight) of the minimum point of this dip does not change, but the shape (depth and width) of the dip is determined by the Doppler effect due to the thermal motion of atomic nuclei. temperature. For example, in FIG. 9, characteristic A corresponds to the resonance absorption of Ta at a temperature of 23.degree. Therefore, if the element (nuclide) contained in the sample S is specified and the difference in the shape of the dip can be recognized from the detection result of the neutron detector 90, the temperature of the sample S can be recognized. At this time, if the sample S contains multiple types of elements, this analysis can be performed for each element (nuclide). essentially the same temperature is calculated. For this reason, it is sufficient to select only one of these elements as this element. can be calculated.

"Development of three-dimensional X-ray thermography technology capable of non-destructively measuring the temperature inside an object", Hitachi, Ltd. HP, URL: https://www. hitachi. co. jp/rd/news/topics/2018/0926. html Tetsuya Kai, Kosuke Hiroi, Yusha Su, Takenao Shinohara, Joseph D.; Ｐａｒｋｅｒ、Ｙｏｓｈｉｈｉｒｏ Ｍａｔｓｕｍｏｔｏ、Ｈｉｒｏｔｏｓｈｉ Ｈａｙａｓｈｉｄａ、 Ｍａｒｉｋｏ Ｓｅｇａｗａ、Ｔａｋｅｓｈｉ Ｎａｋａｔａｎｉ、Ｋｅｎｉｃｈｉ Ｏｉｋａｗａ、 Ｓｈｕｏｙｕａｎ Ｚｈａｎｇ、 ａｎｄ Ｙｏｓｈｉａｋｉ Ｋｉｙａｎａｇｉ、「Ｒｅｌｉａｂｉｌｉｔｙ Ｅｓｔｉｍａｔｉｏｎ ｏｆ Ｎｅｕｔｒｏｎ Ｒｅｓｏｎａｎｃｅ Ｔｈｅｒｍｏｍｅｔｒｙ Ｕｓｉｎｇ Ｔａｎｔａｌｕｍ ａｎｄ Ｔｕｎｇｓｔｅｎ」、Ｐｈｙｓｉｃｓ Ｐｒｅｃｅｄｉａ（２０１７年）、Ｖｏｌｕｍｅ． 88, 306 pages A. S. Tremsin, W.; Kockelmann, D. E. Pooley, W. B. Feller, "Spatially Resolved Remote Measurement of Temperature by Neutron Resonance Absorption", Nuclear Instruments and Methods in Physics Research Section A. May 2005, Vol. 18, 15 pages

When calculating the temperature from the shape (depth, width) of the dip in FIG. 9, it is necessary to recognize the decrease in the detection intensity (neutron count) in the dip from the background value I0 in FIG. Become. Therefore, along with I0, it is necessary to accurately recognize the decrease value ID from I0 at the minimum point of the dip. is required to be large. However, I0 is the intensity of neutrons in the non-resonant region (having energy sufficiently separated from the energy of resonance absorption), which corresponds to the intensity of the probe neutron beam N0, so I0 is always a large value. whereas the ID caused by resonance absorption in sample S may be small. Therefore, it is actually difficult to sufficiently increase the ratio ID/I0, and the accuracy of temperature calculation is not sufficient. Furthermore, when a plurality of elements are contained in the sample S, I0 is also affected by other elements other than the element forming the target dip, so the value of I0 itself to be adopted in the calculation is also uncertain. exists. Therefore, actually, in the temperature measurement method using neutrons as described above, the resolution ΔT/T of the absolute temperature T to be measured is 5% or more (for example, about 20K at 400K), and the temperature measurement accuracy is it wasn't enough.

That is, it has been desired to measure the temperature of a sample in a non-contact manner and with high accuracy by utilizing neutron resonance absorption in the sample.

The present invention has been made in view of such problems, and an object of the present invention is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
A temperature measuring device according to the present invention is a temperature measuring device for measuring the temperature of a sample in a non-contact manner by using resonance absorption of neutrons in the sample, wherein the spectrum of the energy range including the energy generated by the resonance absorption in the sample and a neutron source that generates a pulsed neutron beam composed of neutrons having a An indicator to which a neutron beam is irradiated, and a detection unit that detects a time-of-flight spectrum that is a time-dependent change in the intensity of a prompt gamma ray accompanying the resonance absorption from the indicator or a scattered neutron beam off the optical axis of the neutron beam. and an analysis unit that calculates the temperature of the sample from the time-of-flight spectrum.
In the temperature measuring device of the present invention, the indicator is configured to contain a common nuclide with the sample.
In the temperature measurement device of the present invention, the analysis unit calculates an integral value of a difference between the time-of-flight spectrum and a reference spectrum stored in advance, and calculates the temperature based on the integral value. do.
In the temperature measurement method of the present invention, the indicator containing the plurality of nuclides is used for the sample containing a plurality of nuclides having different resonance absorption energies in the temperature measurement device, and each of the plurality of nuclides is characterized in that the temperature is calculated with respect to
The temperature measurement method of the present invention is characterized in that the plurality of nuclides are separately contained in a plurality of separate portions of the sample, and the temperature is calculated for each portion.

Since the present invention is configured as described above, the temperature of a sample can be measured in a non-contact manner and with high accuracy using neutron resonance absorption in the sample.

It is a figure showing composition of a temperature measuring device concerning an embodiment of the invention. It is a figure explaining the time-of-flight spectrum measured by the detection part in the temperature measuring device which concerns on embodiment of this invention. It is an example of the time-of-flight spectrum obtained with the temperature measuring device according to the embodiment of the present invention. It is an example of enlarging the vicinity of the resonance absorption energy of Ta in the time-of-flight spectrum obtained by the temperature measuring device according to the embodiment of the present invention. FIG. 5 is a diagram showing an example of shapes at two temperatures near the resonance absorption energy of Ta in the time-of-flight spectrum obtained by the temperature measuring device according to the embodiment of the present invention; 4 shows the temperature dependence of evaluation values calculated from time-of-flight spectra in the example of the present invention. It is a figure which shows the structure in the case of performing the measurement with respect to the two separate samples by the temperature measuring device which concerns on embodiment of this invention. 1 is a diagram showing the configuration of a conventional temperature measurement device using neutron resonance absorption; FIG. FIG. 2 is a diagram schematically showing measurement results for calculating the temperature of a sample with a conventional temperature measuring device;

A temperature measuring device according to an embodiment of the present invention will be described below. FIG. 1 is a diagram showing the configuration of this temperature measuring device 1. As shown in FIG. In this temperature measuring device 1, a neutron source 100 that emits a white spectrum, pulsed neutron beam N0 is used, and the neutron beam N0 is irradiated to a sample S0 whose temperature is to be measured. This point is the same as the configuration in FIG. However, the neutron beam N1 after passing through the sample S0 is irradiated to the indicator S1 whose material composition is known. A gamma ray detector (detection unit) 20 is provided at a location outside the optical axis of the neutron beams N0 and N1 around the indicator S1. Gamma rays are detected.

The γ-rays detected here are prompt γ-rays G emitted immediately after the neutron beam N1 is resonantly absorbed in the indicator S1. Therefore, similar to the neutron detector 90, if this γ-ray is detected with a high time resolution and its change over time is detected, this characteristic will show the resonance of neutrons in the indicator S1 as in FIG. Absorption effects are reflected. On the other hand, the neutron beam N1 is also affected by resonance absorption of neutrons in the sample S0, as shown in FIG. The data analysis unit (analysis unit) 30 is, for example, a personal computer, and calculates the temperature of the sample S0 by performing calculations described later from the output of the γ-ray detector 20 .

Here, for example, when the element (accurately, the nuclide) constituting the sample S0 and the element (exactly, the nuclide) constituting the indicator S1 are the same, in the neutron beam N0, in the sample S0, the neutron In line N1, at indicator S1, resonance absorption occurs at the same energy. FIG. 2 schematically shows changes over time in the intensity of γ-rays detected by the γ-ray detector 20 or the intensity of neutrons passing through the indicator S1 in this case. Here, since the γ-rays detected are prompt γ-rays G, the passage of time on the horizontal axis in FIG. 2 corresponds to the neutron flight time (energy) of the neutron beam N1 in FIG. is the time-of-flight spectrum of G. Such measurements for prompt γ-rays G can be performed because the neutron beam N0 is emitted in a pulsed manner.

In FIG. 2, if the sample S0 does not exist (if there is no resonance absorption in the sample S0), the indicator S1 is directly irradiated with the neutron beam N0. Since this situation is equivalent to the case where the sample S in FIG. 8 becomes the indicator S1, the energy spectrum of the neutrons transmitted through the indicator S1 is the characteristic A , B, the same characteristic C is obtained. If the γ-rays detected by the γ-ray detector 20 are only the prompt γ-rays G due to this resonance absorption, the detection result of these γ-rays will be a peak corresponding to the energy of resonance absorption instead of a dip in FIG. As shown, the characteristic D is the inverse of the characteristic C.

However, in the configuration of FIG. 1, the indicator S1 is irradiated with the neutron beam N1 after passing through the sample S, and in this neutron beam N1, there is resonance absorption at the same energy as the resonance absorption in the indicator S1. . Therefore, in the configuration of FIG. 1, the number of neutrons forming the vicinity of the peak in the characteristic D decreases like the dips in the characteristics A and B of FIG. , the energy of the local minimum of this dip is equal to the energy of the characteristic D peak. For this reason, the characteristics detected by the gamma ray detector 20 in the configuration shown in FIG. The characteristic E is substantially symmetrical on both sides of the minimum point (energy of resonance absorption) such that the intensity becomes zero.

In the characteristics of FIG. 9, the majority of the detection results are regions not related to resonance absorption (the background value I0), and among them, the region related to resonance absorption (the decrease value from I0 is the dip where ID is). part) were present and generally the ratio ID/I0 was small. On the other hand, in characteristic E in FIG. 2, only the vicinity of the portion corresponding to the dip due to resonance absorption is recognized, and there is no background component unrelated to resonance absorption. On the other hand, from the results of FIG. 9, there is a component dependent on the temperature of the sample S0 in the portion corresponding to the dip whose intensity was recognized in the characteristic E. Therefore, the time-of-flight spectrum (the shape of the characteristic E in FIG. 2) measured by the γ-ray detector 20 has temperature dependence, and the temperature of the sample S0 can be calculated by analyzing this. .

The results of actual measurements performed with the configuration shown in FIG. 1 will be described. As the neutron source 100, J-PARC (Japan Atomic Energy Agency) neutron nuclear reaction measurement apparatus (BL04: ANNRI) is used, the sample S0 is 40 μm, the indicator S1 is Ta with a thickness of 100 μm, and neutrons The distances from source 100 were 24.5 m and 27.9 m, respectively. As the γ-ray detector 20, a combination of a scintillator (NaI) and a photomultiplier tube was used. More precisely, two γ-ray detectors of this combination were installed at angles of 90° and 125° with respect to the optical axes of neutron rays N0 and N1, and measurement was performed to detect prompt γ-rays, respectively.

The temperature of the indicator S1 was room temperature (23°C: unheated), and the temperature of the sample S0 was room temperature, 100, 200, 300, 400, and 500°C. FIG. 3 shows the above measurement results by the γ-ray detector 20. FIG. Here, there are many dips or peaks corresponding to multiple resonance absorption energies (time of flight: TOF) of Ta nuclei. FIG. 4 is an enlarged view of a portion corresponding to 4.3 eV, which is the resonance absorption energy of Ta nuclei. This measurement result has the shape of the characteristic E in FIG. 2, and this characteristic fluctuates according to the temperature of the sample S0. In particular, in this measurement result, as the temperature rises, the central minimum point becomes shallower and the heights of the peaks on both sides thereof change. Therefore, the temperature of the sample S can be calculated from this measurement result.

A method for calculating the temperature of the sample S0 from this characteristic can be set as appropriate. For example, in the results of FIG. 4, the characteristic at a temperature of 23° C. is used as known standard data (reference spectrum), the variation from this characteristic is quantified and calculated as an evaluation value, and this evaluation value is converted to temperature. method is possible. FIG. 5 is a diagram illustrating an example in which this technique is applied when the temperature is 500.degree. It can be confirmed that such a difference in characteristics between the two is more pronounced in FIG. 5 than in FIG. In FIG. 5, the characteristic at 500° C. is larger than the standard data in the central dip portion and smaller than the standard data in the peak portions on both sides. Therefore, the integrated value of the hatched portion in FIG. 5 can be used as this evaluation value.

FIG. 6 shows the results of similarly calculating the evaluation values (integrated values) for temperatures other than 500° C. and showing the relationship with the temperature of the sample S0. Since good linearity is observed between this evaluation value and temperature, the temperature can be calculated from this numerical value with high accuracy. Specifically, the temperature resolution ΔT/T is 1 to 2% in the temperature range shown here, and ΔT is about 5°C at 500°C.

Therefore, the data analysis unit 30 in FIG. 1 quantifies the measurement result of the γ-ray detector 20 as described above, and calculates the temperature of the sample S0 based on this. Note that the method for calculating the temperature as described above is only an example, and methods other than the above methods can also be used as methods for calculating (estimating) the temperature using the temperature dependence of the characteristics in FIG. . For example, the temperature may be calculated by pre-storing the above measurement results at a plurality of temperatures and comparing these results with the actual measurement results.

In the above measurement, since both the sample S0 and the indicator S1 are composed of the same element (Ta), the measurement has symmetrical peaks before and after the resonance absorption energy, as shown by characteristic E in FIG. The results were obtained. However, even different elements may have close resonance absorption energies. In this case, as an element constituting the indicator S1, an element that is not included in the sample S0 but has a close resonance absorption energy may be used instead.

On the other hand, for example, when the sample S0 is composed of a compound or mixture of two elements (nuclides) having different resonance absorption energies, and the indicator S1 is similarly composed of a compound or mixture of these two elements, The temperature can be calculated by performing the above analysis in the vicinity of the two different resonance absorption energies of these two kinds of elements. However, in this case, in principle, a common temperature is calculated as the temperature of the sample S0 in either result. Therefore, it is sufficient to use at least one element contained in the sample S0 as the element forming the indicator S1. This setting is easy if the origin of the sample S is known in advance. Alternatively, when the sample S is unknown, if a time-of-flight spectrum obtained by the γ-ray detector 20 has a portion like the characteristic E in FIG. It is possible to estimate the possible elements (nuclides) that will be

Also, for example, as the configuration is described in FIG. 7, two separate samples S01 and S02 may be provided at the same time. Here, the sample S01 contains the element (nuclide) X1, the sample S02 contains the element (nuclide) X2, the sample S01 does not contain the element X2, and the sample S02 does not contain the element X1. shall be Since the neutron beam N0 used as a probe needs to pass through both samples S01 and S02, these are arranged in series with respect to the neutron beam N0. With this configuration, part of the neutron beam N0 is resonantly absorbed by the element X1 in the sample S01 to become the neutron beam N01, and part of this neutron beam N01 is resonantly absorbed by the element X2 in the sample S02 to become the neutron beam N1. Become. Here, for example, the sample S02 can be assumed to be radioactive waste, and the sample S01 can be assumed to be a canister.

Here, the neutron beam N1 in this case reflects both the influence of the resonance absorption of the element X1 and the element X2. Therefore, if the element X1 and the element X2 have different resonance absorption energies, the above analysis can be performed on the time-of-flight spectra near the respective resonance absorption energies. The temperature of element X2 (sample S02) can be calculated individually. At this time, in the time-of-flight spectrum obtained as described above, there is no background component as indicated by the dashed line in FIG. The temperatures of S01 and sample S02 can be calculated with high accuracy. Although the number of samples is two in FIG. 7, the same applies to the case of three or more samples. That is, in the temperature measurement method using the temperature measurement device described above, the temperature can be measured for each of a plurality of elements (nuclides) contained in the sample. Therefore, when the sample is composed of a plurality of separate parts, the temperature of each part can be calculated by one measurement.

In the above example, the γ-ray detector (detection unit) 20 detected prompt γ-rays G immediately after neutron resonance absorption, and the temporal change in the detected intensity was obtained as a time-of-flight spectrum. However, other than the intensity of the neutrons transmitted through the indicator S1, other than the prompt γ-rays G may be detected as long as the state of resonance absorption of neutrons in the indicator S1 can be similarly detected. For example, a neutron detector may be used as the detector to detect the intensity of scattered neutrons at the indicator S1. In this case, it is particularly necessary to prevent neutrons that have passed through the sample from being detected. It is preferable to set it as the structure which a detector detects.

In the above example, the gamma ray detector and the neutron detector used as the detector to acquire the time-of-flight spectrum have the characteristics shown in FIG. 4 separately for each temperature. A device having such a time resolution can be used as appropriate. Further, the shape and configuration of the indicator are appropriately set so that prompt γ-rays and scattered neutrons as described above can be detected.

1 Temperature measuring device 20 γ-ray detector (detection unit)
30 data analysis unit (analysis unit)
90 Neutron detector 100 Neutron source G Prompt gamma rays N0, N01, N1 Neutron rays S, S0, S01, S02 Sample S1 Indicator

Claims (5)

A temperature measuring device that measures the temperature of a sample in a non-contact manner using resonance absorption of neutrons in the sample,
a neutron source for generating a pulsed neutron beam composed of neutrons having a spectrum in an energy range including the energy generated by the resonance absorption in the sample;
an indicator that includes a nuclide that causes the resonance absorption in the energy region in which the resonance absorption occurs in the sample, and that is irradiated with the neutron beam after passing through the sample;
a detection unit that detects a time-of-flight spectrum, which is a time-dependent change in the intensity of the prompt γ-ray accompanying the resonance absorption from the indicator or the scattered neutron beam deviating from the optical axis of the neutron beam;
an analysis unit that calculates the temperature of the sample from the time-of-flight spectrum;
A temperature measuring device comprising: 2. The temperature measuring device according to claim 1, wherein said indicator includes a common nuclide with said sample. 3. The analysis unit according to claim 1, wherein the time-of-flight spectrum and an integral value of a difference from a reference spectrum stored in advance are calculated, and the temperature is calculated based on the integral value. temperature measuring device. 4. The temperature measuring device according to any one of claims 1 to 3, wherein the indicator containing a plurality of nuclides is used for the sample containing a plurality of nuclides having different resonance absorption energies. ,
A temperature measuring method, wherein the temperature is calculated for each of the plurality of nuclides. 5. The temperature measuring method according to claim 4, wherein the plurality of nuclides are separately contained in a plurality of separate portions of the sample, and the temperature is calculated for each portion.

Images