JP2021038983A - Neutron measurement unit, neutron measurement device and neutron measurement method - Google Patents

Abstract

To provide a neutron measurement unit that can measure a dose of neutron beam emitted from a neutron source for a region having a predetermined spread in a short time without discrimination from γ-rays in the boron neutron capture therapy.SOLUTION: A neutron measurement unit 100 in the present invention includes a plate-shaped neutron converter 101 containing cadmium and a plate-shaped thermal phosphor 102 so as to be overlapped with each other by aligning the thickness directions T of both.SELECTED DRAWING: Figure 1

Description

The present invention relates to a neutron measuring unit, a neutron measuring device, and a neutron measuring method.

Boron neutron capture therapy (BNCT) is known as a next-generation radiotherapy method. BNCT is a therapeutic method in which α rays are generated by utilizing the reaction between boron isotopes and neutron rays, and the irradiation thereof destroys predetermined tumor cells. At the neutron source, γ-rays are generated along with the neutron rays required for the reaction, and both are irradiated to the tumor cells. Gamma rays have a different biological effect ratio from neutron rays, and γ rays also destroy cells other than predetermined tumor cells. Therefore, when performing BNCT, it is necessary to control the accuracy of neutron irradiation so that the amount of neutron rays to be irradiated is secured and the amount of γ-rays mixed in the neutron rays does not become too large. , Measurements that discriminate between neutron rays and γ-rays have been performed (Patent Document 1).

Japanese Unexamined Patent Publication No. 2018-24863

Patent Document 1 discloses a method for measuring neutron rays and γ-rays using a thermal phosphor containing aluminum oxide and beryllium oxide as main components. However, although such a thermal phosphor reacts with both neutron rays and γ-rays, its sensitivity to neutron rays is low, and it is difficult to sufficiently react with the amount of neutron rays used in BNCT. In BNCT for the human body, it is ^{necessary to perform measurements that discriminate between neutron rays and γ-rays in an area of 50 cm 2} or more, and if such measurements are performed one by one, the measurement time will increase. , There is a risk of exposure to the measurer.

In order to shorten the measurement time, a method has been proposed in which the distribution of the neutron irradiation dose in a wide range is captured at once by using an imaging plate and a radiomic film. However, since the dynamic range of the imaging plate does not correspond to the sensitivity required by BNCT, it is difficult to actually capture the distribution of the irradiation dose of the neutron beam. On the other hand, since the sensitivity of radiomic film varies depending on the irradiation dose, the accuracy of the distribution of the irradiation dose of the obtained neutron beam is low, and since it can be used only once, it is regarded as radioactive waste after use. turn into.

The present invention has been made in view of the above circumstances, and in boron neutron capture therapy, the amount of neutron rays emitted from a neutron source to a region having a predetermined spread without discrimination from γ-rays. It is an object of the present invention to provide a neutron measurement unit, a neutron measurement device, and a neutron measurement method capable of measuring a neutron in a short time.

In order to solve the above problems, the present invention employs the following means.

(1) The neutron measurement unit according to one aspect of the present invention includes a plate-shaped neutron converter containing cadmium and a plate-shaped thermal phosphor so as to be overlapped with each other by aligning the thickness directions of both. ..

(2) In the neutron measurement unit according to (1) above, it is preferable that the thermal phosphor has a thermal fluorescence characteristic showing an emission intensity peak at a temperature of 100 ° C. or higher.

(3) In the neutron measurement unit according to any one of (1) or (2), it is preferable that the thermal phosphor contains at least one of aluminum oxide and beryllium oxide.

(4) In the neutron measurement unit according to any one of (1) to (3), the thickness of the neutron converter is preferably 0.3 mm or more and 0.5 mm or less.

(5) In the neutron measurement unit according to any one of (1) to (4), the area of the region where the neutron converter and the thermal phosphor overlap in a plan view from the thickness direction. Is preferably 10 mm ² or more.

(6) In the neutron measurement unit according to any one of (1) to (5), the distance between the neutron converter and the thermal phosphor in the thickness direction is equal to or less than the range of β rays. It is preferable to have.

(7) The neutron measuring apparatus according to one aspect of the present invention is heated by the neutron measuring unit according to any one of (1) to (6) above, the heating means for heating the thermal phosphor, and the heating means. It is provided with a measuring means for measuring the intensity of light emission by the thermal phosphor.

(8) The neutron measuring method according to one aspect of the present invention is a neutron measuring method using the neutron measuring device according to any one of (1) to (6) above, and is used in the neutron measuring unit. On the other hand, the first step of irradiating a neutron beam from the neutron converter side, converting the neutron beam into ionizing radiation in the neutron converter, and absorbing the ionizing radiation into the thermal phosphor, and the above-mentioned absorbing the ionizing radiation. The amount of the neutron beam irradiated to the neutron measurement unit by integrating the second step of heating the thermal phosphor and emitting light in a predetermined temperature region and the intensity of the light emission in the temperature region. It has a third step of estimating.

According to the present invention, in boron neutron capture therapy, the amount of neutron rays emitted from a neutron source is measured in a short time with respect to a region having a predetermined spread without discrimination from γ-rays. It is possible to provide a neutron measurement unit, a neutron measurement device, and a neutron measurement method.

It is a perspective view of the neutron measurement unit which concerns on one Embodiment of this invention. It is sectional drawing of the neutron measuring apparatus which concerns on one Embodiment of this invention. It is a graph which shows the glow curve of the thermal phosphor which concerns on the comparative example of this invention. It is a graph which superimposes the glow curve of FIG. 3 and the glow curve of the thermal phosphor which concerns on Example 1 of this invention. It is a top view which shows typically the structure of the neutron measurement unit which concerns on Example 2 of this invention. It is an image which shows the distribution of a strong light emitting part and a weak light emitting part in the thermal phosphor after irradiation of Example 2. FIG. It is a graph which compares the strong light emitting part and the weak light emitting part of the thermal phosphor of FIG. 6 with a gray value.

Hereinafter, the neutron measurement unit, the neutron measurement device, and the neutron measurement method according to the embodiment to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. Absent. Further, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

FIG. 1 is a perspective view of a neutron measurement unit 100 according to an embodiment of the present invention. The neutron measurement unit 100 is mainly composed of a plate-shaped neutron converter 101 containing cadmium and a plate-shaped thermal phosphor 102, and both are provided so as to be overlapped with each other with the thickness direction T aligned. ing.

In the neutron measurement unit 100, first, the neutron converter 101 is irradiated with _{neutron rays (thermal neutron rays) L 1} and γ rays L ₂ generated from a neutron source (not shown) such as an accelerator or a reactor. Subsequently, the irradiated neutron beam L _{1 is converted into ionizing radiation L 3} such as β-rays, γ-rays, and X-rays in the neutron converter 101, and is emitted from the neutron converter 101. Of these, the ionizing radiation L ₃ is irradiated to the thermal phosphor 102 and absorbed. Further, the γ-ray L ₂ irradiated to the neutron converter 101 is attenuated and emitted in the neutron converter 101, and the emitted γ-ray L ₄ is also irradiated to the thermal phosphor 102 and absorbed.

The neutron converter 101 uses at least one ^{of the cadmium isotopes 106} Cd, ¹⁰⁸ Cd, ¹¹⁰ Cd, ¹¹¹ Cd, ¹¹² Cd, ¹¹³ Cd, ¹¹⁴ Cd, and ¹¹⁶ Cd, which are inexpensive and easy to increase the area. It is contained as a main component. The neutron converter 101 may contain more ¹¹⁰ Cd, ¹¹¹ Cd, ¹¹² Cd, and ¹¹³ Cd having a large neutron reaction cross section from the viewpoint of increasing the probability that the neutron beam collides with cadmium and is converted into γ ray. preferable. The neutron converter 101 may contain, for example, isotopes of Gd, Li, and B as components other than cadmium.

The thickness 101b of the neutron converter is preferably 0.3 mm or more and 0.5 mm or less, and more preferably about 0.4 mm, from the viewpoint of increasing the probability of converting the neutron beam into γ-ray and emitting it. If the neutron converter 101 is thinner than 0.3 mm, the content of cadmium as a medium for converting neutral rays to γ-rays is low, so the probability that neutron rays will collide with cadmium is low, and the conversion to γ-rays is sufficient. I can't do it. As a result, the amount of γ-rays absorbed by the thermal phosphor 102 is reduced. On the other hand, if the neutron converter 101 is thicker than 0.5 mm, the converted γ-rays are prevented from being emitted to the outside, and some γ-rays are self-absorbed in the neutron converter 101. The amount of γ-rays absorbed by the phosphor 102 is reduced.

The thermal phosphor 102 is a ceramic containing a material having thermal fluorescence characteristics as a main component, and when heat is applied in a state where the energy of ionizing radiation such as β-rays, γ-rays, and X-rays is stored, the stored energy is stored. Part of the light is emitted as light. The thermal fluorescence characteristics in the present embodiment are preferably those that emit light only in a predetermined temperature range, and more preferably those that show a emission intensity peak in a temperature range of about 100 ° C. or higher.

The thermofluorescent material preferably has high thermofluorescence characteristics with respect to ionizing radiation derived from neutrons, and examples _{thereof include oxides such as aluminum oxide (Al 2} O ₃ ) and beryllium oxide (BeO). .. From the viewpoint of increasing the absorption efficiency of ionizing radiation, the thermal phosphor 102 preferably contains at least one of aluminum oxide and beryllium oxide. As the material contained in the thermal phosphor 102, aluminum oxide, which is easy to handle, is preferable to beryllium oxide. When the thermal phosphor 102 contains aluminum oxide, it may further contain chromium. When an appropriate amount of chromium is contained, the thermal fluorescence sensitivity and fading characteristics are improved.

In particular, aluminum oxide has a high spatial resolution for radiation, and can make the image of the distribution of the obtained irradiated line clear. Further, since aluminum oxide does not have water absorption, it can be used in a water phantom (in water) that is less affected by environmental factors, and highly accurate measurement can be realized. Further, aluminum oxide has a high uniformity and a simple structure as compared with other materials having thermal fluorescence characteristics, and has a short half-life after activation, so that it can be used repeatedly. , There is no risk of radioactive waste being generated. Further, since aluminum oxide has a wide dynamic range (ratio of the maximum signal to the minimum signal that can be detected), it can absorb ionizing radiation with high efficiency. For these reasons, aluminum oxide is most preferable as the material contained in the thermal phosphor.

The thickness 102b of the thermal phosphor is preferably 0.3 mm or more and 2.0 mm or less. When making the thermal phosphor emit light, it is necessary to heat the entire thermal phosphor 102 or the portion absorbing ionizing radiation, and if the thickness exceeds 2.0 mm, the temperature rising time becomes long, which is not preferable. .. When the thickness 102b of the thermal phosphor is less than 0.3 mm, a part of the irradiated ionizing radiation is not absorbed and is transmitted, the emission intensity with respect to the irradiation dose is reduced, and the robustness is also lowered. To do.

When a plurality of thermal phosphors made of the same material are joined together, even if their main surfaces form one surface, the irradiation state changes at the joint, so that the thermal phosphor 102 is integrated. It is preferable to have.

In FIG. 1, in order to explain the configuration and operation of the neutron generation unit 100, the neutron converter 101 and the thermal phosphor 102 are shown to be largely separated from each other, but in reality, the facing surfaces of the two are opposed to each other. Are arranged in close contact with each other so that they are in close contact with each other. Specifically, it is assumed that the distance D between the neutron converter 101 and the thermal phosphor 102 in the thickness direction T of both is equal to or less than the range D of β rays emitted from the neutron converter 101. In order to correctly detect the distribution of the irradiation dose, the neutron converter 101 and the thermal phosphor 10 are substantially parallel to each other so that the distance from the neutron converter 101 is substantially uniform over the entire irradiated surface. It is preferable that they are arranged so as to be.

In FIG. 1, one main surface 101a of the neutron converter and one main surface 102a of the thermal phosphor have similar areas to each other and almost completely overlap each other in a plan view from the thickness direction T. Although the case is illustrated, the present embodiment is not limited to this case. That is, the areas of the two main surfaces 101a and 102a may be different from each other, and at least a part of the two main surfaces 101a and 102a, preferably at least a part including the center, may overlap each other. ..

In a plan view from the thickness direction T, the area of the region where the main surface 101a of the neutron converter and the main surface 102a of the thermal phosphor overlap ^{is preferably 10 mm 2} or more. However, assuming the case of irradiating a predetermined target such as a tumor cell, it is preferable to have an area larger than the area where the target is distributed. When it is assumed that it is applied to BNCT targeting the human body, this area is ^{preferably 50 cm 2} or more, and more preferably 200 cm ² or more.

The neutron measurement of the present embodiment can be performed by the following procedure. First, the neutron converter side 101 of the neutron measurement unit 100 _{is irradiated with the neutron beam L 1} , and the neutron converter 101 converts the neutron beam L _{1 into ionizing radiation L 3} such as β ray, γ ray, and X ray. The ionizing radiation L ₃ is absorbed by the thermal phosphor 102 (first step).

FIG. 2 is a cross-sectional view of the neutron measuring device 200 according to the embodiment of the present invention. The neutron measuring device 200 mainly includes the neutron measuring unit 100 of FIG. 1, the heating means 103 of the thermal phosphor 102 constituting the neutron measuring unit 100, and the measuring means for measuring the intensity of light emission by the thermal phosphor 102. It includes 104 and a container (dark box) 105 that shields light from the outside. Here, the illustration of the neutron converter 101 is omitted. The heating means 103 is mainly composed of a known heater 103A and a temperature control device 103B thereof. The measuring means 104 is mainly composed of an image pickup device 104A such as a CCD camera and a control device 104B for controlling the image pickup device 104A and analyzing the obtained image. The thermal phosphor 102 and the heater 103A are housed inside the dark box 105.

After the first step, the heat phosphor 102 absorbs the ionizing radiation L _3, on the heater 103A neutron measuring apparatus 200, as the surface of the ionizing radiation is incident (the illuminated surface) faces the imaging apparatus 104A side Install. In that state, the heater 103A is heated by using the temperature control device 103B to heat the thermal phosphor 102 and emit light in a predetermined temperature range (second step).

Subsequently, an image of the thermal phosphor 102 in the light emitting state is acquired by using the imaging device 104A, and the acquired image is sent to the analyzer 104B, where the intensity of light emission in the temperature region is integrated and the subject corresponding to the light emission intensity is integrated. by calculating the radiation dose estimates the dose of neutron radiation L ₁ irradiated to neutron measuring unit 100 (third step). The irradiation dose calculated here includes the dose of surplus γ-rays, but since the ratio of the dose is smaller than 1/100, the calculated dose of neutron rays is almost neutron-derived ionization. a dose of radiation L _3, which can be actually viewed as a dose of neutron radiation L ₁ emitted from the neutron source.

As described above, according to the neutron measurement unit 100 according to the present embodiment, the measurement of the dose of neutron radiation L ₁ generated from the neutron source, rather than neutron radiation itself, via reaction with neutrons and cadmium The obtained ionizing radiation L ₃ is absorbed by the thermal phosphor 102. The ionizing radiation (particularly β-ray) L ₃ derived from the neutron beam is absorbed by the thermal phosphor 102 with higher efficiency than the surplus γ-ray L _{2 inevitably generated from the neutron source.} A thermal phosphor that has absorbed ionizing radiation can exhibit high intensity light emission in a predetermined temperature range.

As will be described later as an example, the _{emission intensity of the ionizing radiation L 3} derived from the neutron beam is about 100 times or more the emission intensity of the surplus γ-ray L _{2 that is inevitably generated.} Therefore, the obtained emission intensity can be considered to be due to the contribution of ionizing radiation L _3. Therefore, the dose of only the _{ionizing radiation L 3} absorbed by the thermal phosphor 102 can be easily measured from the obtained emission intensity _{without discriminating the contribution of the surplus γ-ray L 2.} Based on this measurement result, of the radiation generated by neutron source, actually (in this case the thermal phosphor 102) irradiated body can be calculated dose of neutron radiation L ₁ irradiated to.

Neutron measuring unit of the present embodiment, the dose of neutron radiation L ₁ emitted from a given neutron source, the two-dimensional distribution of the irradiation dose in the irradiated surface of the heat phosphor 102, to accurately grasp be able to. This makes it possible to appropriately perform verification of a treatment plan and accuracy control of neutron irradiation assuming that a region having a predetermined area such as a living body is treated by irradiating a neutron beam.

Further, even when the treatment area is wide, the distribution information of the irradiation dose can be acquired at the same time by increasing the area of the irradiation surface of the neutron converter and the thermal phosphor. Therefore, as compared with the conventional case where the treatment area is divided into a plurality of minute areas and the measurement is performed for each minute area, the number of irradiations of radiation can be reduced and the exposure probability of the measurer is greatly reduced. be able to.

Hereinafter, the effects of the present invention will be made clearer by examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

(Comparison example)
In the above embodiment, with the neutron converter removed, the thermal phosphor was directly irradiated with neutron rays and γ-rays generated from the neutron source. The irradiation time was about 1.5 hours. As the thermal phosphor, one containing about 99% of aluminum oxide and about 0.05 w% of Cr, having an area of the main surface (irradiated surface) of 100 mm ² and a thickness of 0.7 mm was used.

After the irradiation, the emission intensity of the heated thermal phosphor was measured. FIG. 3 is a graph showing the glow curve obtained by the measurement. The horizontal axis of the graph shows the temperature (° C.), and the vertical axis of the graph shows the relative thermal fluorescence intensity.

(Example 1)
Neutron measurement was performed according to the above embodiment, and the neutron beam and γ ray generated from the neutron source were irradiated to the thermal phosphor via the neutron converter. The irradiation time was about 1.5 hours. As the neutron converter, a natural cadmium plate was used, and a neutron converter having a main surface (irradiated surface) with an area of 100 mm ² and a thickness of 0.5 mm was used. As the thermal phosphor, the same one as in the comparative example was used.

After the irradiation, the emission intensity of the heated thermal phosphor was measured. FIG. 3 is a graph showing the glow curve obtained by the measurement of the comparative example. FIG. 4 is a graph showing the glow curve obtained by the measurement of Comparative Example and the glow curve obtained by the measurement of Example 1 superimposed.

From the graph of FIG. 3, it can be seen that the thermal phosphor of the comparative example emits light in the temperature range of 200 ° C. to 400 ° C., and the emission intensity becomes maximum when the temperature reaches 300 ° C. From the graph of FIG. 4, the thermal phosphor of Example 1 also emits light in the same temperature range as in Comparative Example, and the emission intensity is maximized at the same temperature. This result shows that the thermal phosphor of Comparative Example and the thermal phosphor of Example 1 have the same thermal fluorescence characteristics. In other words, it can be seen that the measurements are made under the same conditions except for the presence or absence of the neutron converter.

On the other hand, when the numerical values of the emission intensities are compared, the maximum emission intensity of the thermal phosphor of Example 1 is 100 times or more the maximum emission intensity of the thermal phosphor of the comparative example. Comparing the glow curves by the amount of light emitted by integrating in the range of 200 ° C. to 400 ° C. (corresponding to the shaded portion surrounded by the horizontal axis of the graphs of FIGS. 3 and 4 and the glow curve), Example 1 There is a higher difference in magnification between the amount of light emitted and the amount of light emitted in the comparative example. This is because the absorption rate (easiness of absorption) of the converted neutron-derived ionizing radiation with respect to the thermal phosphor is dramatically increased compared to the absorption rate of the unconverted neutron beam itself. It is thought that it is because of it.

Therefore, it can be seen that the obtained emission intensity can be considered to be due to the contribution of ionizing radiation. Therefore, only the ionizing radiation absorbed by the thermal phosphor without discriminating the contribution of excess γ-rays from the obtained emission intensity. The dose of can be easily measured. Based on this measurement result, among the neutron rays generated by the neutron source, the dose of the neutron beam actually irradiated to the irradiated object (here, the thermal phosphor) can be calculated.

(Example 2)
FIG. 5 is a plan view schematically showing the configuration of the neutron measurement unit according to the second embodiment. As the neutron converter and the thermal phosphor, those having the same composition as in Example 1 were used. Neutron converter major surface 101a, the area of the main surface 102a of the thermal phosphor, respectively and 1600mm ^2, 6400mm ^2, in a plan view from both the thickness direction, as shown in FIG. 5, the neutron converter 101, thermoluminescence It was arranged so as to overlap the central portion of the body 102. In this state, neutron irradiation was performed for 20 minutes. In this case, the portion of the thermal phosphor 102 that overlaps with the neutron converter 101 is irradiated with γ-rays mixed in the neutron field and ionizing radiation such as γ-rays and β-rays in which the neutron rays are converted by the neutron converter. Therefore, the portion that does not overlap with the neutron converter 101 is directly irradiated with the neutron beam and the γ-ray mixed in the neutron field.

FIG. 6 is an image showing the distribution of a portion (strongly emitting portion) 102A that emits strong light and a portion (weakly emitting portion) 102B that hardly emits light in the thermal phosphor 102 after irradiation. FIG. 7 is a graph for comparing the emission intensities of the strong light emitting portion 102A and the weak light emitting portion 102B in the portion of the thermal phosphor 102 of FIG. 6 where the straight line C is attached by a gray value. The horizontal axis of the graph shows the distance (pixels) from one end of the thermal phosphor 102 shown in FIG. The vertical axis of the graph shows the gray value in the image of the thermal phosphor 102 of FIG.

As can be seen from FIGS. 6 and 7, the portion of the thermal phosphor 102 that does not overlap with the neutron converter 101 and is directly irradiated is the weak light emitting portion 102B, whereas it overlaps with the neutron converter. The portion irradiated via the neutron converter is a strong light emitting portion 102A. Since ionizing radiation such as γ-rays and β-rays converted by the neutron converter is irradiated in a range slightly outward from the strong light emitting part 102A when viewed from the neutron source side, the strong light emitting part 102B is strongly emitted. Even in the vicinity of the light emitting portion 102A, weak light emission corresponding to that amount is observed. Except for the contribution of the spread and irradiated ionizing radiation, it is considered that almost no light emission is observed in the vicinity of the strong light emitting portion 102A.

Therefore, the amount of light emitted by the strong light emitting portion 102A is substantially several hundred times or more larger than the amount of light emitted by the weak light emitting portion 102B, which is a sufficiently detectable amount. Therefore, the dose of the irradiated neutron beam can be estimated with high accuracy. Since the irradiation dose at each position of the thermal phosphor can be measured by one neutron beam irradiation regardless of the irradiation area, the distribution information of the irradiation dose can be obtained in a short time.

From these results, when detecting a neutron beam using the emission of a thermal phosphor in a region having a predetermined spread, the neutron beam is irradiated through the neutron converter as compared with the conventional method of irradiating without the neutron converter. It can be seen that the method of the present invention is extremely effective.

100 ... Neutron measurement unit 101 ... Neutron converter 101a ... Neutron converter main surface 101b ... Neutron converter thickness 102 ... Thermal phosphor 102a ... Thermal phosphor main surface 102b ... ··································································································································································. Device 104B ... Control device 105 ... Dark box 200 ... Neutron measuring device D ... Distance between neutron converter and thermal phosphor L ₁ ... Neutron beam L ₂ , L ₄ ... γ ray L ₃ ... Ionizing radiation T ... Neutron converter, thickness direction of thermal phosphor

Claims (8)

A neutron measurement unit characterized in that a plate-shaped neutron converter containing cadmium and a plate-shaped thermal phosphor are provided so as to be overlapped with each other by aligning the thickness directions of the two. The neutron measurement unit according to claim 1, wherein the thermal phosphor has a thermal fluorescence characteristic showing an emission intensity peak at a temperature of 100 ° C. or higher. The neutron measurement unit according to claim 1 or 2, wherein the thermal phosphor contains at least one of aluminum oxide and beryllium oxide. The neutron measurement unit according to any one of claims 1 to 3, wherein the thickness of the neutron converter is 0.3 mm or more and 0.5 mm or less. The aspect according to any one of claims 1 to 4, wherein the area of the region where the neutron converter and the thermal phosphor overlap in a plan view from the thickness direction is 10 mm ^{2 or more.} Neutron measurement unit. The neutron measurement unit according to any one of claims 1 to 5, wherein the distance between the neutron converter and the thermal phosphor in the thickness direction is equal to or less than the range of β rays. The neutron measurement unit according to any one of claims 1 to 6.
A heating means for heating the thermal phosphor and
A neutron measuring device comprising: a measuring means for measuring the intensity of light emission by the heated thermal phosphor. A neutron measurement method using the neutron measurement unit according to any one of claims 1 to 6.
The first step of irradiating the neutron measuring unit with a neutron beam on the neutron converter side, converting the neutron beam into ionizing radiation in the neutron converter, and absorbing the ionizing radiation into the thermal phosphor.
The second step of heating the thermal phosphor that has absorbed the ionizing radiation and causing it to emit light in a predetermined temperature range, and
A neutron measurement method comprising a third step of estimating the amount of the neutron beam irradiated to the neutron measurement unit by integrating the intensity of the light emission in the temperature region.