JP2008256404A - Thermofluorescent dose measuring element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quantitatively evaluate a radiation amount with one thermofluorescent dose measuring element by distinguishing gamma rays and neutron rays from the other radiations. <P>SOLUTION: Tb<SB>4</SB>O<SB>7</SB>powder of 0.06 wt.%, Sm<SB>2</SB>O<SB>3</SB>powder of 0.03 wt.% and Gd<SB>2</SB>O<SB>3</SB>powder of 0.36 wt.% are added to CaF<SB>2</SB>powder and uniformly mixed. The mixed powder is filled into a mold and is subjected to pressure forming in a disc shape. It is further sintered at 1100°C for two hours in air atmosphere to obtain a sintered body of a thermofluorescent dose measuring element. When each radiation of ultraviolet rays, X-rays, gamma rays and neutron rays is applied to the sintered body and a glow peak curve 1 is evaluated, peaks of the ultraviolet rays and the X-rays are observed near 100°C, while those of the gamma rays and the neutron rays are observed near 150°C. This shows that the peaks of gamma rays and neutron rays can be distinguished from those of other radiations even in a mixed radiation field. Moreover, the radiation amount of each radiation can be quantitatively evaluated from the area of the part enclosed by the glow peak curve and a heating temperature axis 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermofluorescence dosimetry element that classifies line types such as ultraviolet rays and neutron rays and quantitatively evaluates the amount of irradiation.

As a thermofluorescence dosimetry element, there is an element obtained by adding a rare earth element such as terbium Tb, samarium Sm or gadolinium Gd to a base material such as calcium fluoride CaF ₂ or lithium fluoride LiF. These additive elements are energized by irradiation with radiation such as ultraviolet rays, X-rays, gamma rays, and neutron rays. This excited state differs depending on the type of additive element. For example, Gd has high sensitivity to ultraviolet rays, neutron rays, and the like, and is easily excited by irradiation with these radiations. Gd excited by the irradiation delivers excitation energy to Tb (energy transition), and Gd itself returns to the original stable energy state (ground state).

  The Tb that has received this excitation energy stably maintains the above excited state for at least several days. When the temperature of the thermoluminescent dosimetry element in this excited state is raised from room temperature to about 300 ° C., the excited Tb is Returning to the ground state, light emission corresponding to the energy difference between the excited state and the ground state occurs at that time (see Patent Documents 1 and 2).

JP 7-97570 A Japanese Patent No. 3250192

  It has been found that the temperature at which this luminescence is most intense (thermofluorescence glow peak temperature) varies depending on the type of the additive element and the radiation line type, and the type of additive element and the combination thereof depending on the radiation line type to be measured. Is appropriately selected.

  This thermofluorescence dosimetry element is sometimes worn by workers at work sites that handle radiation, etc., and is used to measure the exposure of workers when a radiation leakage accident occurs. . In this case, it is important in the accident processing to know not only the dose of the worker but also what type of radiation or the like was exposed. Therefore, it is necessary to assume in advance what kind of radiation is likely to be exposed and to use a thermofluorescence dose measuring element corresponding to the radiation type.

  Among the above-mentioned radiations, gamma rays and neutron rays have a high transmission ability with respect to the shielding material, so that the adverse effects on the human body are much greater than other radiations such as ultraviolet rays and X-rays. Therefore, it is desired to develop a thermofluorescence dosimetry element that can evaluate gamma rays and neutron rays separately from other radiation.

  As described above, it is necessary for the thermofluorescence dosimetry element to appropriately select the type of thermofluorescence dosimetry element to be used corresponding to the specific radiation line type. Therefore, in a site where a plurality of types of radiation are handled (a site where there is a risk of exposure to a plurality of types of radiation), several types of thermofluorescence dosimetry elements must be used in combination.

  Accordingly, an object of the present invention is to classify a plurality of radiation types, particularly gamma rays and neutron rays, from other radiations and to quantitatively evaluate the irradiation dose with one thermofluorescence dosimetry element.

In order to solve the above-mentioned problems, the present invention adds a Tb, Sm, and Gd oxide at an appropriate ratio to a CaF ₂ base material to constitute a thermofluorescence dose measuring element. is there. Specifically, the amount of each additive is 0.01 to 0.2% by weight of Tb ₄ O ₇ , 0.01 to 0.2% by weight of Sm ₂ O ₃ , and Gd ₂ O _3. Is preferably in the range of 0.01 to 1% by weight.

  If a plurality of additives are added simultaneously as described above, measurement sensitivity can be obtained for a plurality of radiation line types. Moreover, the thermofluorescence glow peak of each line type can be clearly separated by setting the addition ratio. For this reason, even when a mixed radiation field in which a plurality of radiations are mixed, in particular, when gamma rays and neutron rays are mixed with other radiation, the above-described line type (gamma rays and neutrons) is obtained with one thermofluorescence dosimetry element. Line and other line types) can be separated, and the dose can be evaluated quantitatively for each of the above classifications.

In order to further clarify the separation of the thermoluminescent glow peak, the amount of each additive is 0.05 to 0.07 wt% for Tb ₄ O ₇ and 0.02 to 0 for Sm ₂ O ₃ . It is more preferable that 0.04% by weight and Gd ₂ O _{3 be} in the respective ranges of 0.3 to 0.4% by weight.

The thermofluorescence dosimetry element is prepared by uniformly mixing the raw materials CaF ₂ , Tb ₄ O ₇ , Sm ₂ O ₃ and Gd ₂ O ₃ powders and then putting them in a mold, It is obtained by applying pressure to form a molded body, and further sintering the molded body in a heating furnace heated to 1000 to 1200 ° C.

  According to the present invention, the above-mentioned line types (gamma rays and neutron rays and other line types) can be classified with a single thermofluorescence dosimetry device, and the dose can be quantitatively evaluated for each of the above classifications.

Example 1
CaF ₂ powder (purity 99.99%, rare metallic), 0.06 wt% Tb ₄ O ₇ powder (purity 99.99%, rare metallic), 0.03% wt Sm ₂ O ₃ powder (Purity 99.99%, rare metallic) and 0.36 wt% Gd ₂ O ₃ powder (purity 99.99%, Mitsuwa Chemicals) are mixed uniformly, and this mixed powder is filled into a mold. Then, it was pressure-molded into a disk shape having a diameter of 6 mm and a thickness of 1 mm. This molded body was placed in a platinum crucible and sintered in the air atmosphere at 1100 ° C. for 2 hours to obtain a sintered body of a thermoluminescent dose measuring element.

(Example 2)
The thermofluorescence dosimetry device obtained in Example 1 was irradiated with ultraviolet rays (wavelength 253.7 nm, irradiation intensity of about 0.4 J / min · cm ² ) using a low-pressure mercury lamp as a light source for a maximum of 180 seconds. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 300 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak at the time of the temperature increase was measured.
In this case, as shown in FIG. 1A, a thermofluorescent glow peak was observed around 100 ° C. In addition, no conspicuous peak was observed except for the temperature.
In this graph, the area of the portion 3 formed by the glow peak curve 1 and the heating temperature axis 2 is obtained, and this area and the area corresponding to the above-described area when a known amount of ultraviolet rays are irradiated using the thermoluminescent dose measuring element. Can be estimated.
Further, as shown in FIG. 1B, the thermofluorescence intensity continued to increase linearly with respect to the irradiation time until the irradiation time reached 180 seconds, and the thermofluorescence intensity did not reach saturation. From this, it can be said that this thermofluorescence dosimetry device can quantitatively measure the amount of ultraviolet rays for at least 180 seconds under this ultraviolet ray intensity.

(Example 3)
The thermofluorescence dosimetry device obtained in Example 1 was irradiated with X-rays (0.15 C / min · kg) for a maximum of 120 seconds, respectively. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 240 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak during the temperature increase was measured.
In this case, as shown in FIG. 2A, a thermofluorescence glow peak was observed at around 100 ° C. as in the case of irradiation with ultraviolet rays in Example 1. In addition, no conspicuous peak was observed except for the temperature.
In this graph, the area of the portion 3 formed by the glow peak curve 1 and the heating temperature axis 2 is obtained, and this area and the area corresponding to the above-mentioned area when a known amount of X-rays are irradiated using the thermoluminescent dose measuring element Can be estimated.
In addition, as shown in FIG. 2B, the thermofluorescence intensity continued to increase linearly with respect to the irradiation time until the irradiation time was 120 seconds, and the thermofluorescence intensity did not reach saturation. From this, it can be said that this thermofluorescence dosimetry element can quantitatively measure the X-ray dose for at least 120 seconds under this X-ray intensity.

Example 4
The thermofluorescence dosimetry device obtained in Example 1 was irradiated with 11.5 μSv of gamma rays using cobalt 60 as a radiation source. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 300 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak at the time of the temperature increase was measured.
In this case, as shown in FIG. 3, a thermoluminescent glow peak was observed at around 150 ° C. In addition, although the thermofluorescence intensity was slightly higher in the temperature range of 250 ° C. or higher, no particularly conspicuous peak was observed.
In this graph, the area of the portion 3 formed by the glow peak curve 1 and the heating temperature axis 2 is obtained, and this area and the area corresponding to the above-mentioned area when a known amount of gamma rays are irradiated using the thermoluminescent dose measuring element. Can be used to estimate the irradiated gamma dose.

(Example 5)
The thermofluorescence dosimetry device obtained in Example 1 was irradiated with 4.18 mSv of neutron beam. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 300 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak at the time of the temperature increase was measured.
In this case, as shown in FIG. 4, a thermofluorescent glow peak was observed around 150 to 160 ° C. In addition, although the thermofluorescence intensity was slightly higher in the temperature range of 250 ° C. or higher, no particularly conspicuous peak was observed.
In this graph, the area of the portion 3 formed by the glow peak curve 1 and the heating temperature axis 2 is obtained, and this area and the area corresponding to the above-mentioned area when a known amount of neutron beam is irradiated using the thermoluminescent dose measuring element. The neutron dose irradiated can be estimated.

  As shown in FIGS. 1 to 4, the thermofluorescence glow peaks of gamma rays and neutrons are shifted from the thermofluorescence glow peaks of ultraviolet rays and X-rays by about 50 ° C. Therefore, for example, even in a mixed radiation field in which X-rays and gamma rays are mixed, both line types can be clearly separated.

  In addition, as described above, no conspicuous peak other than the specific thermofluorescent glow peak is observed in any line type. Therefore, even when ultraviolet rays and X-rays overlap with gamma rays and neutron rays, As long as the temperature can be specified, the line type can be specified by the temperature.

The above-mentioned thermofluorescence glow peak changes the temperature and height of the peak position and the appearance of multiple peaks when the type and amount of the additive element changes. , Tb ₄ O ₇ is preferably 0.01 to 0.2% by weight, Sm ₂ O ₃ is 0.01 to 0.2% by weight, and Gd ₂ O ₃ is preferably 0.01 to 1% by weight. .
Further, in order to clearly distinguish the above line types, 0.05 to 0.07 wt% of Tb ₄ O ₇ , 0.02 to 0.04 wt% of Sm ₂ O ₃ , and Gd ₂ O ₃ are used. It is more preferable to set it as 0.3 to 0.4 weight%.

  This thermofluorescence dosimetry device has a high sensitivity to radiation with a relatively low intensity such as ultraviolet rays in sunlight. Therefore, this thermofluorescence dosimetry element can also be used as an ultraviolet sensor.

(Comparative example)
CaF ₂ powder (purity 99.99%, manufactured by Rare Metallic), 0.06 wt% Tb ₄ O ₇ powder (purity 99.99%, manufactured by Rare Metallic) and 0.36 wt% Gd ₂ O _Three powders (purity 99.99%, manufactured by Mitsuwa Chemicals Co., Ltd.) were uniformly mixed, and this mixed powder was filled into a mold and pressure-molded into a disk shape having a diameter of 6 mm and a thickness of 1 mm. This molded body was placed in a platinum crucible and sintered in the air atmosphere at 1100 ° C. for 2 hours to obtain a sintered body of a thermoluminescent dose measuring element.
The thermofluorescence dosimetry device was irradiated with ultraviolet rays (wavelength: 253.7 nm, irradiation intensity: about 0.4 J / min · cm ² ) using a low-pressure mercury lamp as a light source for a maximum of 180 seconds. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 300 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak at the time of the temperature increase was measured.
In this case, as shown in FIG. 5A, thermoluminescent glow peaks were observed at two locations near 90 to 100 ° C. and 250 ° C.

Further, the thermofluorescence dose measuring element was irradiated with 11.5 μSv of gamma rays using cobalt 60 as a radiation source. Furthermore, the thermofluorescence dosimetry device after irradiation was heated from room temperature to 300 ° C. at a rate of 20 ° C./min, and the thermofluorescence glow peak at the time of the temperature increase was measured.
In this case, as shown in FIG. 5B, a large peak was observed near 250 ° C., and a small peak was also observed near 150 ° C.
Thus, in any case irradiated with ultraviolet rays or gamma rays, thermofluorescent glow peaks are observed in two places, and the peaks around 250 ° C. are overlapped. Therefore, it is difficult to evaluate the two separately. .

In Example 2, (a) is a glow peak curve and (b) is a graph showing the irradiation time dependence of thermofluorescence intensity of a thermofluorescence dosimetry element irradiated with ultraviolet rays. In Example 3, (a) is a glow peak curve and (b) is a graph showing the irradiation time dependence of thermofluorescence intensity of a thermofluorescence dosimetry element irradiated with X-rays. In Example 4, the graph which shows the glow peak curve of the thermofluorescence dosimetry element irradiated with the gamma ray In Example 5, the graph which shows the glow peak curve of the thermofluorescence dosimetry element irradiated with the neutron beam In a comparative example, (a) is a graph showing a glow peak curve of a thermofluorescence dosimetry element irradiated with ultraviolet rays and (b) is irradiated with gamma rays.

Explanation of symbols

1 Glow peak curve 2 Heating temperature axis 3 Glow peak curve and heating temperature axis

Claims (3)

CaF ₂ sintered containing 0.01 to 0.2% by weight of Tb ₄ O ₇ , 0.01 to 0.2% by weight of Sm ₂ O ₃ , and 0.01 to 1% by weight of Gd ₂ O ₃ Thermoluminescent dosimetry element consisting of body. Tb ₄ O ₇ and 0.05 to 0.07 wt%, the _Sm 2 _{O 3} 0.02 to 0.04% by weight, and, CaF ₂ containing _Gd 2 _{O 3} 0.3 to 0.4 wt% A thermofluorescence dosimetry element made of a sintered body. 1000 CaF ₂ containing 0.01 to 0.2 wt% Tb ₄ O ₇ , 0.01 to 0.2 wt% Sm ₂ O ₃ , and 0.01 to 1 wt% Gd ₂ O ₃ The manufacturing method of the thermofluorescence dosimetry element obtained by sintering at -1200 degreeC.

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