JPH06214030A - Diamond thermoluminescence dosemeter and its manufacture - Google Patents

Abstract

PURPOSE:To provide sufficient thermoluminescence sensitivity even with a synthetic diamond containing a specified value or more of nitrogen impurities by providing a diamond having, in the crystal, a luminescence center having an absorption coefficient in a determined wavelength accompanied by absorption and emission of light within a specified range. CONSTITUTION:A diamond sample manufactured by a superhigh pressure and high temperature synthesis containing 120ppm of nitrogen which is thermally treated at 9OO deg.C has a thermoluminescence intensity about 100 times, compared with an untreated crystal, and the thermal treatment temperature at which the thermoluminescence intensity starts to increase is about 6OO deg.C. This temperature is coincident to the temperature at which a luminescence center starts to generate, and by generating the luminescence center in the diamond crystal in this way, the thermoluminescence intensity is improved, and high sensitivity can be provided. Until the absorption coefficient at wavelength 580nm of the luminescence center reaches 10cm<-1>, the thermoluminescence intensity is linearly increased and saturated, and with 20cm<-1> or more, it is gradually lowered. Thus, to provide a highly sensitive thermoluminescence, the absorption coefficient of the luminescence center is desirably set to 8cm<-1> to 25cm<-1>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond thermoluminescence dosimeter and a method for manufacturing the same, and particularly to high energy photons (X-rays and γ rays) and high energy particle beams (electrons, neutrons, protons, α particles, etc.). TECHNICAL FIELD The present invention relates to a diamond thermoluminescence dosimeter for measuring a radiation dose and the manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, as one of methods for measuring a radiation dose, a method using thermoluminescence of a substance (fluorescence emitted when the substance is heated) is known. Thermoluminescent substances have the property of emitting thermoluminescence upon irradiation with radiation (X-rays, γ-rays, etc.), and the principle thereof is considered as follows. That is, the electrons or holes excited by the radiation are captured by the lattice defects in the crystal. This trapped state remains stable at room temperature. However, the electrons or holes bound by heating are released from the trap center and trapped again in another lattice defect (emission center). Electrons (holes) finally return to the ground state at this emission center, but light emission occurs in this process. If the relationship between the radiation dose and the luminescence intensity is known,
The radiation dose can be measured by measuring the thermoluminescence intensity. The characteristics required when using a thermoluminescent substance in a dosimeter are high sensitivity to radiation dose, good linearity between radiation dose and luminescence intensity, and electrons trapped at room temperature (holes). ) Has a long life.

At present, substances practically used as thermoluminescence dosimeters include LiF, CaF ₂ and CaSO _4.
and so on. The fact that diamond is a thermoluminescent substance is described in the Industrial Diamond Review (July 1977 page 239).
Examples of utilizing diamond in a nuclear radiation dosimeter utilizing this property are disclosed in JP-A-61-270298 and JP-A-2-52277. Among them, JP-A-61-270298 discloses a synthetic diamond having a nitrogen concentration of 100 ppm or less as a thermoluminescent substance. In addition, JP-A-2-5227
7 discloses that it is effective to subject diamond to an electron beam irradiation treatment in order to improve the sensitivity of thermoluminescence and the linearity with respect to dose.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
1-270298 discloses that diamond is used as a thermoluminescent substance by controlling the nitrogen concentration in the diamond. That is, the sensitivity of thermoluminescence is affected by impurities in diamond, and the sensitivity of thermoluminescence decreases as the nitrogen concentration increases. Specifically, when the nitrogen concentration is 100 ppm, the thermoluminescence sensitivity is about 10 ⁻³ times as high as when it is 1 ppm. In consideration of such a point, in JP-A-61-270298, the concentration of nitrogen contained in diamond is defined as 100 ppm or less.

However, industrially produced diamond is produced at a high pressure and a high temperature under the iron group (Fe, Ni, C).
o) It is a diamond synthesized by using a metal or an alloy thereof using a catalyst. The diamond obtained by such ultra-high pressure and high temperature synthesis usually contains 100 ppm or more of nitrogen as an impurity, and such a diamond is classified as Ib type. The use of such an Ib type industrial diamond in a thermoluminescence dosimeter has been a problem in the prior art in that the sensitivity is lowered.

The present invention has been made in order to solve the above problems, and the object of the inventions described in claims 1 to 5 is sufficient even in a normal industrial synthetic diamond containing 100 ppm or more of nitrogen impurities. It is to provide a diamond thermoluminescence dosimeter capable of obtaining excellent thermoluminescence sensitivity and a manufacturing method thereof.

[0007]

The diamond thermoluminescence dosimeter according to the first and second aspects is provided with a diamond having a luminescent center having absorption and emission of light in its crystal. The absorption coefficient at the wavelength of 580 nm of the emission center is 8 cm ^-1 or more and 25 cm ^-1 or less.

[0008] Diamond thermo lumi according to claims 3-5
The manufacturing method of the luminescence dosimeter is 30 pp of Ib type nitrogen.
1 to 4M for diamonds containing m to 200ppm
Electron beam with energy of eV 0.4 × 10¹⁸Pieces / cm²
1.3 x 10 or more¹⁸Pieces / cm ²Irradiate with the following dose
Step, and the diamond above 600 ℃ 1400 ℃
And a step of performing heat treatment under the lower temperature condition.

[0009]

In the diamond thermoluminescence dosimeter according to the first and second aspects, the thermoluminescence intensity is improved because the diamond crystal has an emission center accompanied by absorption and emission of light. In addition, the emission center of 580n
Since the absorption coefficient at the wavelength of m is set to 8 cm ^-1 or more and 25 cm ^-1 or less, it is possible to obtain a dosimeter in which the thermoluminescence intensity is high to some extent, and to obtain a diamond thermoluminescence dosimeter with high thermoluminescence sensitivity. You can The details of having a luminescent center in the diamond crystal and having an absorption coefficient of the luminescent center of 8 cm ^-1 or more and 25 cm ^-1 or less will be described below.

First, it was clarified in the present invention that the presence of the luminescent center (NV center) dramatically improves the thermoluminescence intensity of diamond. Figure 1
It is a glow curve (correlation diagram) showing the temperature dependence of thermoluminescence intensity. With reference to FIG. 1, a curve A is a diamond sample produced by ultrahigh pressure high temperature synthesis containing 120 ppm of Ib type nitrogen, which is in an untreated state. Also B
Is a sample obtained by irradiating the same diamond crystal as A with an electron beam at a dose of 1 × 10 ¹⁸ pieces / cm ² . The curves C to F show that the sample B is further 500 ° C., 700 ° C., 9 ° C.
It is a curve of the sample which heat-processed at 00 degreeC and 1150 degreeC. After irradiating each sample with 10 Gy of X-ray, which is the radiation to be measured, the temperature was raised and the thermoluminescence intensity was measured. With reference to FIG. 1, it can be seen that the thermoluminescence intensity increases as the heat treatment temperature rises, and the thermoluminescence intensity becomes maximum by the heat treatment at 900 ° C. The thermoluminescence intensity is represented by the difference between the flat portion and the peak portion of each curve. The thermoluminescence intensity of the diamond sample (E curve) heat-treated at 900 ° C. is almost 100 times higher than that of the untreated crystal (A curve). The heat treatment temperature at which the thermoluminescence intensity starts to increase is around 600 ° C., and this temperature is NV.
Matches the temperature at which the center begins to form. Thus N
It has been clarified that the thermoluminescence intensity is improved and a highly sensitive radiation dosimeter can be provided by forming the V center in the diamond crystal.

Next, the reason why the absorption coefficient of the emission center is set to 8 cm ^-1 or more and 25 cm ^-1 or less will be described below. Figure 2
[Fig. 4] is a correlation diagram showing an optical absorption spectrum of NV center. Referring to FIG. 2, the NV center is in the visible range 5
The diamond, which has an absorption band at a wavelength of 80 nm and thus contains NV centers, exhibits a red color. The amount of NV centers produced is proportional to the absorption coefficient at this wavelength of 580 nm. FIG. 3 is a correlation diagram showing the relationship between the absorption coefficient at 580 nm and the thermoluminescence intensity, which is an index of the amount of NV centers produced. The diamond sample used for this measurement was irradiated with 10 Gy of X-ray in advance and then kept at 225 ° C. to measure the thermoluminescence intensity. Referring to FIG.
The thermoluminescence intensity increases linearly until the NV center has an absorption coefficient of about 10 cm ^-1, and then saturates. At 20 cm ^-1 or more, on the contrary, the thermoluminescence intensity gradually decreases. Therefore, in order to obtain a highly sensitive thermoluminescence dosimeter, the absorption coefficient of the NV center is 8 cm.
^-1 or more and 25 cm ^-1 or less is desirable. In addition, as shown in FIG. 1, the thermoluminescence of the diamond including the NV center appears in the range of 150 ° C. or higher and 320 ° C. or lower. Therefore, if the correspondence relationship between the radiation dose and the thermoluminescence intensity is obtained as a calibration curve in advance, it is possible to determine the radiation dose exposed by measuring the thermoluminescence intensity by holding the diamond in the above temperature range after irradiation of the radiation. it can.

Diamond thermolumines according to claims 3 to 5
In the manufacturing method of the luminescence dosimeter, Ib type nitrogen is added at 30 p
1 to 4M for diamond containing pm or more and 200ppm or less
Electron beam with energy of eV is 0.4 × 10¹⁸Pieces / cm²
1.3 x 10 or more¹⁸Pieces / cm ²It is irradiated with the following dose
Therefore, vacancies are generated in the diamond crystal. Well
Also, the temperature of diamond is above 600 ℃ and below 1400 ℃
Since it is heat-treated under the conditions, the above-mentioned vacancies are present in the crystal.
The NV center, which is a complex defect, diffuses and bonds with nitrogen to form
Is made. This improves the thermoluminescence intensity
A highly sensitive radiation dosimeter can be easily manufactured. Note that N
The concentration of V center is the concentration of Ib-type nitrogen, the irradiation of electron beam
Optimum depending on the amount and heat treatment temperature
The value is determined as follows.

First, the optimum value of nitrogen concentration will be examined. FIG. 4 is a correlation diagram showing the relationship between the Ib type nitrogen concentration and the amount of NV centers produced. Here, the normal high-pressure synthetic diamond contains nitrogen at about 120 ppm.
In order to obtain a diamond crystal having a higher nitrogen concentration, a nitride such as iron nitride or silicon nitride was added to a metal solvent for synthesis. On the other hand, in order to obtain a diamond crystal with a low nitrogen concentration, Al, T
Nitrogen was removed by adding elements such as i and Zi that form refractory nitrides. 2Me was added to the sample prepared in this way.
Irradiation dose of electron beam of V energy 1 × 10 ¹⁸ / cm ²
And then heat treated at 900 ° C. The NV center concentration was evaluated by the absorption coefficient at a wavelength of 580 nm.
Referring to FIG. 4, the absorption coefficient of the NV center is directly proportional to the nitrogen concentration when the nitrogen concentration is about 30 ppm or less, and is 30 pp.
Above m, it is constant at about 18 cm ^-1 . Here, the nitrogen concentration in the diamond crystal is not uniform and has a shade.
Therefore, in order to generate a uniform NV center, conditions that do not depend on the nitrogen concentration are desired. Therefore, the nitrogen concentration needs to be 30 ppm or more. On the other hand, 200p
A crystal containing nitrogen impurities of pm or more has too many impurities, so that the internal strain in the crystal increases and the quality of the crystal deteriorates. Therefore, the nitrogen concentration needs to be 200 ppm or less.

Next, the optimum value of the electron beam irradiation amount will be examined. The electron beam irradiation energy required to generate vacancies is 1 to 4 MeV. This is because vacancies are not formed below this range, and above this range, the diamond crystal itself is severely damaged. Further, the amount of vacancies produced is proportional to the amount of electron beam irradiation, and as a result, the amount of NV center produced is also proportional to the amount of irradiation. FIG. 5 is a correlation diagram showing the relationship between the electron beam irradiation amount and the NV center generation amount. The Ib type nitrogen concentration was 120 ppm in all the samples, and after the electron beam irradiation, heat treatment was performed at 900 ° C. The amount of NV centers produced was evaluated by the absorption coefficient at a wavelength of 580 nm. Referring to FIG. 5, in order to obtain the optimum absorption coefficient of the NV center of 8 cm ⁻¹ or more and 25 cm ⁻¹ or less, the electron beam irradiation amount is 0.4 × 10 ¹⁸ or more and 1.3 × 10 ¹⁸ or more.
It is necessary to set the number to less than or equal to pieces / cm ² .

Further, the optimum value of the heat treatment temperature will be examined. As shown in FIG. 1, the thermoluminescence intensity is 6
The temperature starts to increase from 00 ° C, reaches a maximum at 900 ° C, and decreases at higher temperatures. And at 1400 ° C or higher, N
The V Center disappears. This is because the diffusion of nitrogen impurities starts and combines with the NV center to convert it into another color center. Therefore, the heat treatment temperature is suitably 600 ° C. or higher and 1400 ° C. or lower, preferably 900 ° C.

The above-mentioned Ib type diamond is synthesized under thermodynamically stable ultrahigh pressure and high temperature conditions, but the present invention is not limited to this, and I synthesized by gas phase synthesis.
Thermoluminescence is similarly observed in b-type diamond. In the gas phase synthesis method, raw material gases (methane, hydrogen, C
By mixing 1 to 6% of nitrogen gas into (O ₂ etc.), polycrystalline or single crystal diamond containing 30 to 200 ppm of Ib type nitrogen is synthesized. Vapor-phase synthetic diamond has the advantage that it has a higher degree of freedom in shape than ultra-high pressure synthetic diamond, and therefore a dosimeter in the form of a film can be obtained.

[0017]

【Example】

(Example 1) Single crystal Ib type diamond produced by the ultra-high pressure synthesis method had an energy of 2 MeV and an irradiation dose of 0.2 × 10 ^18.
The electron beam irradiation was carried out at ˜2 × 10 ¹⁸ pieces / cm ² . Then, heat treatment was performed at 900 ° C. to generate NV centers in the crystal. These crystals were irradiated with 10 Gy of X-ray and then held at 225 ° C. to measure thermoluminescence intensity. The thermoluminescence intensity was measured by using a photomultiplier (IP-28 type manufactured by Hamamatsu Photonics KK), and the output voltage was measured by a digital voltmeter. The results are shown in Table 1 below.

[0018]

[Table 1]

It can be seen from Table 1 above that Comparative Example A, which has a small electron beam irradiation amount, also has a small absorption coefficient at the NV center, and as a result, the thermoluminescence intensity is also small. Also,
It can be seen that in Comparative Example E where the electron beam irradiation amount is too large, the absorption coefficient of the NV center becomes too large, and as a result, the thermoluminescence intensity becomes small. On the other hand, Examples B, C and D in which the electron beam dose is within the optimum range
Then, the absorption coefficient of the NV center is also within the optimum range,
As a result, it can be seen that the thermoluminescence intensity is also higher than that of the comparative example.

(Embodiment 2) First, NV concentration was changed by changing the Ib type nitrogen concentration and the electron beam irradiation amount (energy 2 MeV).
The production amount of the center was examined. The results are shown in Table 2 below.

[0021]

[Table 2]

Referring to Table 2 above, in Comparative Example F having a low concentration of Ib-type nitrogen, the absorption coefficient of the NV center is smaller than that in Examples G and H having the same electron beam dose and a high concentration of Ib-type nitrogen. I understand. Further, it can be seen that Comparative Example J, which has a smaller electron beam dose than the others, has a smaller absorption coefficient at the NV center than Examples G, H, and I.

Next, the amount of NV centers produced was examined by changing the heat treatment temperature. The results are shown in Table 3 below.

[0024]

[Table 3]

Referring to Table 3 above, the heat treatment temperature is 500
In Comparative Example K, which has a temperature of ° C, the absorption coefficient of the NV center is zero, and it can be seen that the NV center is not generated.
Further, in Comparative Example N in which the heat treatment temperature is 1400 ° C., NV
It can be seen that the absorption coefficient of the center is smaller than that of Examples L and M.

(Example 3) Methane 2 was used as a source gas.
%, Hydrogen 96%, and nitrogen gas 2% were used to produce an Ib-type diamond polycrystalline thin film by the plasma CVD method. At this time, the substrate temperature was 850 ° C. and the microwave power was 350W. The Ib type nitrogen concentration was 50 ppm. This diamond thin film was subjected to electron beam irradiation (1 × 10 ¹⁸ pieces / cm ² ) and heat treatment (900 ° C.) to prepare an NV center. The absorption coefficient of the NV center was 17 cm ^-1 . This was irradiated with 10 Gy of X-ray and then heated, and the heating temperature and thermoluminescence intensity were measured. The measuring method is the same as in Example 1. Figure 6
FIG. 4 is a correlation diagram (glow curve) showing the relationship between temperature and thermoluminescence intensity in this measurement result. Referring to FIG. 6, it can be seen that the glow curve of the diamond thin film produced by this vapor phase synthesis method shows the same glow curve as the ultrahigh pressure diamond shown in FIG. Therefore, it is understood that the present invention can be applied to the diamond thin film produced by the vapor phase synthesis method.

Example 4 Using the sample B in Example 1, the linearity between the X-ray irradiation dose and the thermoluminescence intensity was examined. The heating temperature of sample B is 225 ° C., and the method for measuring the thermoluminescence intensity is the same as in Example 1. Figure 7
[Fig. 4] is a correlation diagram showing the relationship between the X-ray radiation dose and thermoluminescence intensity in Example 4. With reference to FIG. 7, it can be seen that the X-ray radiation dose is in a proportional relationship up to 10 Gy and has favorable characteristics as a radiation dosimeter.

[Brief description of drawings]

FIG. 1 is a correlation diagram (glow curve) showing the temperature dependence of thermoluminescence intensity.

FIG. 2 is a correlation diagram showing an optical absorption spectrum of NV center.

FIG. 3 is a correlation diagram showing the relationship between the absorption coefficient of the NV center at a wavelength of 580 nm and the thermoluminescence intensity.

FIG. 4 is a correlation diagram showing a relationship between an Ib type nitrogen concentration and an NV center production amount.

FIG. 5 is a correlation diagram showing a relationship between an electron beam irradiation amount and an NV center generation amount.

FIG. 6 is a correlation diagram (glow curve) showing the relationship between temperature and thermoluminescence intensity in polycrystalline Ib type diamond produced by a vapor phase synthesis method.

FIG. 7 is a correlation diagram showing the relationship between the X-ray irradiation amount and the thermoluminescence intensity.

Claims (5)

[Claims] 1. A crystal having diamond having an emission center accompanied by absorption and emission of light, wherein the absorption center of said emission center at a wavelength of 580 nm is 8.
cm ^-1 more than 25cm ^-1 or less, diamond thermoluminescence dosimeter. 2. The diamond thermoluminescence dosimeter produces a thermoluminescence by irradiating the diamond with a radiation to be measured and then heating the diamond to a temperature of 150 ° C. or higher and 320 ° C. or lower to generate the thermoluminescence of the thermoluminescence. The diamond thermoluminescence dosimeter according to claim 1, wherein the exposure dose of the radiation is measured from the intensity. 3. Ib type nitrogen is 30 ppm or more and 200 pp
0.4 × 10 ¹⁸ electron beams / cm ² or more and 1.3 × 10 electron beams having an energy of 1 to 4 MeV are added to a diamond containing m or less.
^A method for manufacturing a diamond thermoluminescence dosimeter, comprising: a step of irradiating with a dose of ¹⁸ pieces / cm ² or less; and a step of heat-treating the diamond under a temperature condition of 600 ° C. or more and 1400 ° C. or less. 4. The method for manufacturing a diamond thermoluminescence dosimeter according to claim 3, wherein the diamond includes single crystal diamond synthesized under thermodynamically stable high temperature and high pressure conditions. 5. The method for manufacturing a diamond thermoluminescence dosimeter according to claim 3, wherein the diamond includes a diamond thin film formed by a vapor phase synthesis method.