KR20030048218A - METHOD FOR PREPARING CaSO4 BASED THERMOLUMINESCENT POWDER TO IMPROVE CRYSTALLINITY - Google Patents

Abstract

PURPOSE: A method for preparing a CaSO4-based TL (thermoluminescence) powder is provided, to improve the crystallinity of the CaSO4-based TL powder by enabling the noncrystalline powder and the crystalline power to be separated easily. CONSTITUTION: The method comprises the steps of mixing a calcium compound with a TL activator in the presence of sulfuric acid; heating the mixture to obtain a CaSO4-based TL powder; pulverizing the obtained CaSO4-based TL powder; washing the pulverized powder with a solvent; and separating the washed powder according to the size and heating the separated one. Preferably the calcium compound is a hydrate of Ca(NO3)2; the TL activator is an oxide of an activator comprising Dy, Mn, Tm or Sm; and the solvent is distilled water, acetone or ethanol. The pulverized one has a size of 100 micrometers and the heating is carried out at a temperature of 550-750 deg.C for 0.5-2 hours.

Description

METHODS FOR PREPARING CaSO4 BASED THERMOLUMINESCENT POWDER TO IMPROVE CRYSTALLINITY}

The present invention relates to a method for preparing CaSO ₄ series TL powder with improved crystallinity. More specifically, CaSO ₄ series TL powder is prepared and pulverized, washed with a solvent to extract crystalline CaSO ₄ series TL powder, and extracted. The present invention relates to a method for preparing CaSO ₄ series TL crystalline powder, which is composed of a process of separating and drying the CaSO ₄ series TL crystalline powder according to drying and particle size.

In general, personal dose dosimeters used to measure the radiation dose to the human body include TLD (Thermoluminescence Dosimeter) and Film Badge (Film Badge).

TLD is a dosimetry that evaluates dose using the property that the amount of TL emitted as light when heated after exposing radiation (X-ray, γ-ray, β-ray, etc.) to TL material is proportional to the dose of radiation absorbed. Since the TLD is small in size, it is possible to measure a dose in a very small area, can be elementized in an arbitrary size and shape, and has a merit in that a dosimetry range is 10 ^-6 to 10 ³ Gy. As a result, TLD is widely used for the measurement of individual exposure dose, the measurement of environmental radiation dose and the measurement of absorbed dose during diagnosis and treatment of patients. It is also ideal for emergency radioactivity management [M. Oberhofer and A. Scharmann, Applied Thermoluminescence Dosimetry , Adam Hilger Ltd., Bristol 1981; R. Chen and Y. Kirsh, Analysis of Thermally Stimulated Processes , Pregamon Press, Oxford, 1981].

TLD materials include tissue equivalent TL materials (LiF, Li ₂ B ₄ O ₇ and MgB ₄ O ₇ ) and bones (Zeff = 14) whose effective atomic number is similar to air (Zeff = 7.64) or human tissue (Zeff = 7.42). And similar non-tissue equivalent TL materials (CaSO ₄ , CaF _2, etc.). Tissue equivalent TL materials are advantageous for measuring individual exposure doses because their interaction with photons is similar to human tissues, but they have a lower TL sensitivity than non-tissue equivalent TL materials. On the other hand, the non-tissue equivalent TLD has a high TL sensitivity, which is advantageous for measuring weak radiation such as environmental radiation. in need.

ICRP 60 Recommendations [ICRP, 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Pergamon Press, Oxford, New York, 1990] suggest that stochastic effects based on linear non-threshold dose hypotheses ( In order to limit the occurrence of stochastic effects, it is required to keep the dose as low as reasonably achievable (ALARA). In order to maintain the ALARA dose, more accurate and accurate dose assessment is required in the low dose range of 10 ^-7 to 10 ^-4 Gy dose range, and as a dose assessment system or a highly sensitive TL material with higher sensitivity than conventional dosimeters Can be achieved. There is a CaSO ₄ : Dy TL material as a high sensitivity TL material for this purpose. The CaSO ₄ : Dy TL material is prepared by using the prepared CaSO ₄ : Dy TL powder in a capsule or a professionally prepared container, or mixing it with Teflon to form an element, and using the phosphorus compound developed by the inventors as an adhesive. Use it to make an element.

On the other hand, a manufacturing method of CaSO ₄ : Dy TL powder has been reported by Yamashita et al. [T. Yamashita, N. Nada, H. Onishi and S. Kitamura, Health phys. , 1971, 21, 295-300. The manufacturing method by Yamashita is shown by following Reaction Formula 1.

As shown in Scheme 1, CaSO ₄ : Dy TL powder is prepared by dissolving CaSO ₄ · 2H ₂ O and Dy ₂ O ₃ in sulfuric acid solution to prepare a saturated CaSO ₄ aqueous solution, and then evaporate the sulfuric acid solution In addition, CaSO ₄ crystallinity may be obtained during evaporation of the sulfuric acid solution. The diameter of the obtained CaSO ₄ : Dy TL powder is 0.5 to 2.0 mm. The preparation method may use Tm ₂ O ₃ as well as Dy ₂ O ₃ as an activator.

CaSO ₄ : Dy TL powder prepared by the above production method is composed of a mixture of crystalline powder and amorphous powder, the amorphous powder is very fine, is adsorbed on the surface of the crystalline powder. The amorphous powder has a very high low temperature peak in the emission curve, the main peak is very low, which is not suitable for use as a TL material, thereby reducing the TL sensitivity of the CaSO ₄ : Dy TL powder and increasing the fading ratio.

Thus, the inventors of the manufacturing method of trying to solve the above problems, CaSO ₄ Series TL powder, washing the CaSO ₄ Series TL powder as after production and milling solvents to extract the deterministic CaSO ₄ Series TL powder, extract CaSO ₄ series TL powder was isolated by drying and particle size, and then heat treated to prepare CaSO ₄ series TL powder, and it was found that the crystalline powder can be easily extracted to improve crystallinity using the above production method. The invention has been completed.

An object of the present invention is to provide a method for producing CaSO ₄ series TL powder with improved crystallinity.

1 is a schematic diagram of an example of a manufacturing method of CaSO ₄ series TL powder of the present invention,

Figure 2a is a scanning electron microscope (Scanning electron microscope, SEM) photograph showing the CaSO ₄ : Dy TL powder removed by washing the distilled water of the present invention,

Figure 2b is a scanning electron micrograph showing the CaSO ₄ : Dy TL powder after washing with distilled water of the present invention,

3 is a graph showing the emission curve of CaSO ₄ : Dy TL powder of the present invention,

Figure 4 is a graph showing the emission curve of CaSO ₄ : Dy TL powder before and after washing with distilled water in the present invention.

In order to achieve the above object, the present invention provides a method for producing CaSO ₄ series TL powder with improved crystallinity.

Hereinafter, the present invention will be described in more detail.

Mixing the calcium (Ca) compound with the TL activator in the presence of sulfuric acid (step 1),

Heating the obtained mixture to obtain a CaSO ₄ series TL powder (step 2),

Grinding the obtained CaSO ₄ series TL powder (step 3),

Washing the ground CaSO ₄ series TL powder with a solvent (step 4), and

It includes a method for producing a CaSO ₄ series TL powder consisting of the step (step 5) of separating and heat-treating the washed CaSO ₄ series TL powder according to the grain size (grain size).

Step 1 is a mixture of a calcium compound and a TL activator in the presence of sulfuric acid. The calcium compound is an ionic compound of calcium and an anion which exhibits volatility upon heating. Preferably, a hydrate of Ca (NO ₃ ) ₂ is used. The activator uses an oxide of the activator consisting of Dy, Mn, Tm or Sm.

Step 2 is reacted by heating the mixture at 320 ℃ for 6-7 hours and sulfuric acid is evaporated to prepare CaSO ₄ series TL powder. The obtained CaSO ₄ series TL powder is formed on the base wall of the container, and the color thereof shows crystallinity as a transparent color.

Step 3 is washed with distilled water to remove sulfuric acid present in the CaSO ₄ series TL powder obtained, dried and milled. The drying is a degree to dry completely by applying a weak heat, using acetone can shorten the drying time. In addition, the size of the pulverized powder is to maintain the size of about 100 ㎛ or less.

Step 4 removes the amorphous CaSO ₄ series TL powder present in the CaSO ₄ series TL powder using the pulverized CaSO ₄ series TL powder.

The pulverized CaSO ₄ series TL powder exists in a state where the amorphous powder and the crystalline powder are mixed, and the amorphous powder surrounds the surface of the crystalline powder, which causes a decrease in TL sensitivity due to crystallinity. . Thus, the amorphous powder is removed using a solvent. When the CaSO ₄ series TL powder and the solvent are mixed, the low specific gravity amorphous powder floats on the upper layer of the solvent and the remaining crystalline powder sinks. At this time, the amorphous powder is removed by removing the upper layer of the solvent including the amorphous powder. It can be easily removed.

As shown in FIG. 2 , it can be seen that CaSO ₄ series TL powders removed during distilled water washing contained almost no crystals, and CaSO ₄ series TL powders obtained after distilled water washing contained most of the crystallinity. Can be. From the above results, it can be seen that the amorphous powder in the CaSO ₄ series TL powder can be removed by washing to obtain a crystalline powder.

The solvent may be a solvent which does not dissolve the TL powder as a solvent that can be commonly used, preferably distilled water, acetone or ethanol. The solvent washing step is repeated several times to remove the amorphous powder in the CaSO ₄ series TL powder, the washing step is preferably washed up to three times, it may vary depending on the amount of solvent used. The amount of solvent in one wash is preferably 12 g of 150 to 200 ml / TL powder.

The amorphous powder removed is 12-17% by weight relative to the total CaSO ₄ series TL powder.

Step 5 separates and heat-treats the washed CaSO ₄ series TL powder according to the diameter.

CaSO ₄ series TL powder prepared by the production method of the present invention can be further washed by the solvent to further improve the crystallinity of CaSO ₄ series TL powder, thereby further improving the TL sensitivity of the powder.

As shown in FIG. 3 , the CaSO ₄ series TL powder removed by distilled water shows a typical TL curve of amorphous CaSO ₄ series TL powder, and the low temperature peak appearing near 120 ° C. is very strong and appears around 210 ° C. High temperature peaks appear very low. On the other hand, CaSO ₄ series TL powder after washing with distilled water shows a typical TL curve of crystalline CaSO ₄ series TL powder.

In addition, through the production method of the present invention, it is possible to easily remove the amorphous powder present in the CaSO ₄ series TL powder, thereby improving the crystallinity is showing a better TL sensitivity. Specifically, as shown in FIG. 4 , the sensitivity of the CaSO ₄ : Dy TL crystalline powder prepared by the present method is increased by about 1.1 times or more compared to the sensitivity of the CaSO ₄ : Dy TL powder which is not subjected to the solvent washing step. Able to know. If CaSO ₄ : Dy TL crystalline powder is used, the sensitivity of the TL device can be further improved.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Example 1 CaSO ₄ Manufacturing Method of Series TL Powder 1

0.0373 g of Dy ₂ O ₃ was dissolved in 10 ml of dilute sulfuric acid aqueous solution, then poured into a flask, either concentrated sulfuric acid, and 23.625 g of Ca (NO ₃ ) ₂ .4H ₂ O was added. The flask was heated at 320 ° C. to distill the concentrated sulfuric acid. Distillation of the concentrated sulfuric acid formed CaSO ₄ : Dy crystallinity on the inner wall of the flask. The crystallization formed was separated, washed three times with distilled water, and then ground and dried at 200 ° C. for 30 minutes. The crystallinity of 63 μm or more and the crystallinity of 63 μm or less were separated using a 230 mesh (63 μm) sieve, and then heat-treated at 650 ° C. for 1 hour. The CaSO ₄ : Dy TL powder prepared was about 12 g.

Example 2 CaSO ₄ Manufacturing Method of Series TL Powder 2

A CaSO ₄ : Dy TL powder was washed three times with ethanol, and the same method as in Example 1 was performed.

Example 3 CaSO ₄ Manufacturing Method of Series TL Powder 3

The same method as in Example 1 was performed except that the prepared CaSO ₄ : Dy TL powder was washed three times with acetone.

Experimental Example 1 Surface Measurement

In order to confirm the crystallinity of the powder washed out with distilled water and the remaining powder was measured using SEM (Hitachi X-650). The results are shown in Fig.

Figure 2a is a SEM photograph showing the powder washed out with distilled water, Figure 2b is a SEM photograph showing the powder after washing. As shown in FIG. 2 , the powder of (a) has almost no crystals, and the powder of (b) shows that crystals are formed. For this reason, it can be seen that the amorphous powder and the crystalline powder can be separated by distilled water.

Experimental Example 2 Comparison of Sensitivity between Amorphous Powder and Crystalline Powder

In order to compare the sensitivity of the amorphous powder and the crystalline powder separated by the distilled water, the TLD reading apparatus after irradiating the amorphous powder and the crystalline powder separated in Example 1 with ¹³⁷ Cs γ ray owned by the Korea Atomic Energy Research Institute (Teledyne system 310, USA) was used to measure the TL curve and analyze the TL sensitivity to radiation. The results are shown in Fig.

As shown in FIG. 3 , the light emission curve of the amorphous powder has a very high low temperature peak, unlike the light emission curve of the crystalline powder, and the main peak is very low, which is not suitable for use as a TL material.

Experimental Example 3 TL Sensitivity Measurement

In order to compare the sensitivity of the CaSO ₄ : Dy TL powder extracted with distilled water and the crystalline powder of CaSO ₄ : Dy TL powder not subjected to the extraction method of the present invention, each CaSO ₄ : 63-100 μm in diameter: Dy TL powder was irradiated with ¹³⁷ Cs γ-rays owned by the Korea Atomic Energy Research Institute, and then luminescence curves were measured using a TLD reader (Teledyne system 310, USA) and analyzed for TL sensitivity to radiation. The results are shown in Fig.

As shown in Figure 4 , compared to the TL sensitivity of the CaSO ₄ : Dy TL powder without a conventional extraction method, it can be seen that the TL sensitivity of the CaSO ₄ : Dy TL powder of the present invention is improved by 1.1 times or more. The fall of TL sensitivity by qualitative powder can be prevented.

As described above, the present invention using a solvent CaSO ₄ series to easily remove the non-crystalline powder in the TL powder crystalline CaSO ₄ sequence obtained TL powder I to prepare a CaSO ₄ Series TL powder has an optimum TL sensitivity Can be.

Claims (8)

Mixing the calcium compound with the TL activator in the presence of sulfuric acid (step 1), Heating the obtained mixture to obtain a CaSO ₄ series TL powder (step 2), Grinding the obtained CaSO ₄ series TL powder (step 3), Washing the ground CaSO ₄ series TL powder with a solvent (step 4), and Separating and heat-treating the washed CaSO ₄ series TL powder according to the particle size (step 5), characterized in that the manufacturing method of CaSO ₄ series TL powder. The method according to claim 1, wherein the calcium compound of step 1 is a hydrate of Ca (NO ₃ ) ₂ . The method of claim 1, wherein the TL activator of step 1 is an oxide of the activator consisting of Dy, Mn, Tm or Sm. The method of claim 1, wherein the pulverized CaSO ₄ series TL powder of step 3 is characterized in that less than 100 ㎛. The method of claim 1, wherein the washing of step 4 comprises mixing the CaSO ₄ series TL powder with the solvent and then removing the upper layer of the solvent including the amorphous powder. The method of claim 1, wherein the solvent of step 4 is distilled water, acetone or ethanol. The method according to claim 1, wherein the washing in Step 4 is performed one to three times, and the amount of the solvent is added in an amount of 150 to 200 ml per 12 g of CaSO ₄ series TL powder. The method according to claim 1, wherein the heat treatment of step 5 is performed at 550 to 750 ° C for 30 minutes to 2 hours.