JP2018203586A - Production method and apparatus of thallium bromide product - Google Patents

Abstract

To provide a production method that prevents a quartz glass vessel from breaking in production of a thallium bromide product of high purity to be used as a semiconductor for radiation detection.SOLUTION: In a first production step, a thallium bromide raw material is purified and crystallized by a Bridgeman process to produce a thallium bromide intermediate material. The thallium bromide intermediate material is divided to a plurality of pellets which are loaded in a quartz glass vessel to be used in a second production step. In the second production step, the thallium bromide intermediate material is repurified and recrystallized by a zone purification process to produce a thallium bromide product (thallium bromide single crystal). The first production step includes a reduction step and a drying step as pretreatment steps for preventing the quartz glass vessel from breaking.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for producing thallium bromide products, and more particularly to a technique for producing thallium bromide crystals having high purity.

  In various fields, radiation detectors, particularly γ-ray detectors are used. For example, a survey meter that detects radiation from an object and environmental radiation is equipped with a γ-ray detector. Numerous γ-ray detectors are mounted on the nuclear medicine diagnostic apparatus. As such a nuclear medicine diagnostic apparatus, a gamma camera apparatus, a single photon emission tomography imaging apparatus (SPECT (Single Photon Emission Computed Tomography) imaging apparatus), a positron emission tomography imaging apparatus (PET (Positron Emission Tomography) imaging apparatus), etc. Are known.

  A semiconductor radiation detector is a typical γ-ray detector. The semiconductor radiation detector converts electric charges generated by the interaction between radiation and a semiconductor crystal into an electric signal. Among semiconductor crystals, thallium bromide, cadmium telluride, cadmium / zinc / tellurium, gallium arsenide, etc. have a larger linear attenuation coefficient due to the photoelectric effect than other semiconductor crystals, and are thin crystals. Can be obtained. Therefore, if a radiation detector is constructed using these semiconductor crystals, the radiation detector can be reduced in size. In particular, thallium bromide is generally less expensive than other semiconductor crystals such as cadmium telluride, cadmium / zinc / tellurium, and gallium arsenide.

  A semiconductor crystal used for a semiconductor radiation detector is required to have few impurities in the crystal. This is because if there are few impurities, the energy resolution can be increased. For example, Patent Document 1 discloses that an energy resolution of 8% or less can be obtained at 122 keV by configuring a semiconductor radiation detector using a thallium bromide single crystal having a lead concentration of less than 0.1 ppm as an impurity. Is described.

  As a method for obtaining a semiconductor crystal with few impurities, a purification method by a zone purification method is known. In the method disclosed in Non-Patent Document 1, thallium bromide crystals are obtained by performing zone melting slowly once after purification by zone purification for 1 to 300 times for a commercially available thallium bromide powder having a purity of 99.99%. Has been generated. Non-Patent Document 2 describes that band purification is repeated in order to obtain a detector with high energy resolution.

  Conventionally, it has been required to produce a high-purity and relatively large amount of thallium bromide products at the same time. The technology that can be implemented has not yet been realized.

  For example, in order to produce a SPECT imaging device, at least tens of thousands of semiconductor radiation detectors are required, i.e., homogeneous thallium bromide crystals ranging from several hundred grams to 1 kilogram per SPECT imaging device, for example. Need to manufacture. In the zone purification method, in order to process a large amount of thallium bromide of several hundred grams or more in one batch, for example, a quartz glass tube having an inner diameter of about 5 cm needs to be used as a zone purification vessel.

  However, when the present inventors tried using a quartz tube having an inner diameter of 5 cm as a zone refining vessel and purified by 20 times of zone refining using 500 g of commercially available thallium bromide powder having a purity of 99.99% as a raw material, Cracks occurred in the quartz glass tube during purification. The purity of commercially available thallium bromide is specified for metal elements, and is not specified for oxygen and moisture. Commercially available thallium bromide is considered to contain thallium oxide and moisture. In the process of zone purification 20 times, the zone purification vessel was repeatedly heated and cooled, so that the water contained in commercially available thallium bromide, the raw material, reacted with thallium bromide, and thallium oxide and hydroxide. It is considered that they reacted with quartz glass, and thallium oxide originally contained in thallium bromide reacted with quartz glass, resulting in cracks in the quartz glass tube.

  Patent Documents 2 and 3 disclose a method for producing a thallium bromide product. None of the patent literatures and any non-patent literatures describe the execution of the purification crystallization process over two or more times.

Japanese Patent No. 6049166 International Publication WO / 088640 Publication Japanese Unexamined Patent Publication No. 2015-160771

Nuclear Instruments and Methods in Physics Research Section-A, Vol. 428 (1999), pp.372-378. Nuclear Instruments and Methods in Physics Research Section-A, Vol. 579 (2007), pp.153-156.

  The object of the present invention is to produce thallium bromide products with high purity. Alternatively, it is an object of the present invention to produce a high purity and relatively large amount of thallium bromide product at once. Alternatively, an object of the present invention is to prevent breakage of a container containing thallium bromide in the thallium bromide zone purification process.

  The thallium bromide product manufacturing method according to the embodiment includes a first manufacturing step of manufacturing a thallium bromide intermediate material from the thallium bromide raw material by purification and crystallization of the thallium bromide raw material, A second manufacturing step of manufacturing a thallium bromide product from the thallium bromide intermediate material by repurification and recrystallization.

  According to the above configuration, a thallium bromide product having high purity can be manufactured through at least two purification crystallization processes. By using the thallium bromide product thus manufactured, a small and high performance semiconductor radiation detector can be manufactured. It is desirable to make the purification crystallization method used in the first manufacturing process different from the purification crystallization method used in the second manufacturing process, particularly when the zone purification method is used as the purification crystallization method in the second manufacturing process. In the first manufacturing process, it is desirable to employ a purified crystallization method suitable for the zone purification method. A pre-process for appropriately executing the second manufacturing process may be included in the first manufacturing process. The purification crystallization process may be repeated three or more times.

  In the embodiment, the first manufacturing process includes a reduction process for excluding or reducing thallium oxide contained in the thallium bromide raw material, and the reduction process includes a container used in the second manufacturing process. This corresponds to a pretreatment process for preventing breakage. In an embodiment, the first manufacturing process includes a drying process that excludes or reduces moisture contained in the thallium bromide raw material, and the drying process includes damage to a container used in the second manufacturing process. This corresponds to a pretreatment process for preventing this. By providing the pretreatment process, it is possible to prevent breakage of the container (for example, a quartz glass container) in the second manufacturing process.

  In an embodiment, a processing step of processing the thallium bromide intermediate material is provided between the first manufacturing step and the second manufacturing step, and the processed thallium bromide intermediate material is the second manufacturing step. It is put into a container used in the process. According to this configuration, the thallium bromide intermediate material is processed in accordance with the shape of the container used in the second manufacturing process. However, when the thallium bromide intermediate material manufactured in the first manufacturing process can be placed in the second manufacturing process container as it is, it is not necessary to perform the processing process.

  In the embodiment, in the processing step, a purified portion in the thallium bromide intermediate material is divided into the plurality of small lumps. According to this configuration, it is possible to prevent or reduce the impurities aggregated in the first manufacturing process from being processed in the second manufacturing process. Moreover, if it processes into a several small lump, the thallium bromide intermediate material can be easily thrown into the container for 2nd manufacturing processes.

  In the embodiment, in the first manufacturing step, a thallium bromide polycrystal or a thallium bromide single crystal is manufactured as the thallium bromide intermediate material, and in the second manufacturing step, bromide bromide is used as the thallium bromide product. A thallium single crystal is produced. In an embodiment, the thallium bromide product is used as a semiconductor for radiation detection.

  The thallium bromide product manufacturing apparatus according to the embodiment includes a first manufacturing facility for manufacturing a thallium bromide intermediate material from the thallium bromide raw material by purification and crystallization of the thallium bromide raw material, and the thallium bromide intermediate material. And a second production facility for producing thallium bromide products from the thallium bromide intermediate material by repurification and recrystallization.

  Input of thallium bromide raw material to the first manufacturing facility, extraction of thallium bromide intermediate material from the first manufacturing facility, input of thallium bromide intermediate material to the second manufacturing facility, thallium bromide from the second manufacturing facility The product is taken out manually, for example. They may be automated. After dividing the thallium bromide intermediate material taken out from the first manufacturing facility into a plurality of small lumps, the plurality of small lumps may be input to the second manufacturing facility. The division may be performed manually, but it may be automated. It is also conceivable to apply the above manufacturing method or manufacturing apparatus to semiconductor materials other than thallium bromide.

  According to the present invention, a thallium bromide product with high purity can be produced. Alternatively, according to the present invention, a relatively large amount of thallium bromide product having a high purity can be produced at a time. Alternatively, the object of the present invention is to prevent damage to the container containing thallium bromide in the thallium bromide zone purification process.

It is a flowchart which shows the manufacturing method which concerns on embodiment. It is a figure which shows the installation used at the 1st manufacturing process in 1st Example. It is a flowchart which shows the 1st manufacturing process in 1st Example. It is a flowchart which shows the 1st manufacturing process in 1st Example. It is a figure which shows the installation used at the 2nd manufacturing process in 1st Example. It is a figure which shows the installation used at the 1st manufacturing process in 2nd Example. It is a figure which shows a part of installation shown in FIG. It is a flowchart which shows the 1st manufacturing process in 2nd Example. It is a flowchart which shows the 1st manufacturing process in 2nd Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In order to manufacture a large number of semiconductor radiation detectors with high energy resolution at once, a test for purifying thallium bromide by repeating the band purification over 20 times for a relatively large amount of thallium bromide. Repeatedly. In the process, there was often a problem that the quartz glass tube as the zone purification vessel was broken. It was presumed that the cause was that thallium oxide and water contained in the commercially available thallium bromide powder as a raw material reacted with quartz glass. Therefore, in order to reduce the thallium oxide and moisture in the raw material, the first purification process including the reduction process and the drying process is performed in advance, and then the zone purification method is performed as the second manufacturing process. As a result, it was confirmed that the quartz glass tube was not damaged during the zone refining, and a high-purity thallium bromide single crystal could be produced even when a commercially available thallium bromide powder was used as a raw material. The method for producing a thallium bromide product according to the present embodiment is based on the above knowledge or further developed from the above knowledge.

  The first manufacturing process is a first purification crystallization process, and the second manufacturing process is a second purification crystallization process. From such a viewpoint, it can be said that the manufacturing method according to the present embodiment is a method of manufacturing a high-purity thallium bromide product by repeating the purification crystallization process in two stages.

  In the first manufacturing process, after the reduction process using hydrogen bromide, the thallium bromide is used in a stage before the next second manufacturing process is performed by performing a purification crystallization process using a Bridgman method or a distillation method. Inside, the concentration of lead as an impurity is lowered. This makes it possible to manufacture a semiconductor detector having higher energy resolution.

  FIG. 1 is a flowchart showing a method for producing a thallium bromide product according to the embodiment. In S200, the first manufacturing process is performed. A 1st manufacturing process is a manufacturing process according to the Bridgman method in Example 1 mentioned later, and is a manufacturing process according to the distillation method in Example 2 mentioned later. In the first production process, thallium bromide raw material (commercially available thallium bromide powder) is purified and crystallized to produce a thallium bromide intermediate material (polycrystalline or single crystal). The first manufacturing process includes a reduction process and a drying process. Any of these processes can be said to be a pretreatment process for preventing damage to the container as viewed from the second manufacturing process later.

  In S202, the thallium bromide intermediate material manufactured by the first manufacturing process is processed. Specifically, the purified portion (portion other than the impurity aggregation portion) in the thallium bromide intermediate material is divided into a plurality of small blocks. This cutting is performed manually or by a cutting device. By this division, the thallium bromide intermediate material can be introduced into the quartz glass container used in the second manufacturing process. Other processing methods may be employed to appropriately perform the second manufacturing process.

  When the purified portion of the thallium bromide intermediate material (ingot) manufactured in the first manufacturing process can be accommodated in the container for the second manufacturing process as it is, the process of S202 becomes unnecessary. In this case, only the impurity aggregation part exclusion process (purification part cut-out process) may be performed. The thallium bromide intermediate material is relatively soft and the work of dividing it into a plurality of blobs is relatively easy.

  In S204, the second manufacturing process is performed. The second manufacturing process is a manufacturing process according to the zone purification method in the embodiment. In the second production process, a thallium bromide product (thallium bromide single crystal) is produced by repurifying and recrystallizing the thallium bromide intermediate material. The thallium bromide product has a very high purity and is suitable as a semiconductor for semiconductor radiation detectors.

  Hereinafter, Example 1 and Example 2 about the thallium bromide product manufacturing method according to the embodiment will be described. First, Example 1 will be described.

  FIG. 2 is a diagram illustrating an outline of equipment used in the first manufacturing process in the first embodiment. The equipment 1 is for producing a thallium bromide intermediate material by purifying and crystallizing commercially available thallium bromide powder. The thallium bromide intermediate material is a raw material for the next second manufacturing process.

  In FIG. 2, the facility 1 includes an electric furnace 2, a crucible 3, a driving device 4 for moving the crucible 3 up and down while rotating in the electric furnace 2, and a gas cylinder that supplies hydrogen bromide gas into the crucible 3. 5, a trap 6 for collecting a gas containing impurities generated in the crucible 3, a bromine container 10 for supplying bromine gas into the crucible 3, and the like.

  The drive device 4 may be a device that moves the crucible 3 only in the vertical direction. In the electric furnace 2, a plurality of heating coils 21 are disposed along the vertical direction. The heat generation amount of each heating coil 21 is individually adjusted so that the vertical temperature distribution in the electric furnace 2 can be freely set. For this reason, a temperature control device 22, a temperature sensor 23, and a temperature measurement device 24 are provided.

  A commercially available thallium bromide powder as a raw material is enclosed in the crucible 3. The crucible 3 is disposed in the electric furnace 2. The crucible 3 is made of, for example, quartz glass and has an inner diameter of, for example, about 75 mm. The driving device 4 is disposed above the electric furnace 2. The driving device 4 moves the crucible 3 up and down at a predetermined constant speed while rotating the crucible 3 in the electric furnace 2. As the driving device 4, a known configuration can be adopted. The drive device 4 includes, for example, a motor, a transmission, and the like.

  The gas cylinder 5 is filled with hydrogen bromide gas. The gas cylinder 5 is connected to the crucible 3 via a pipe 7a. A pressure gauge 9 is connected to the pipe 7a through a pipe 7b, and a bromine container 10 is connected through a pipe 7e. Further, a pipe 7c extending from the trap 6 described below is connected. A valve 8 a is provided on the pipe 7 a in the vicinity of the gas cylinder 5, and a valve 8 b is provided on the pipe 7 a and in the vicinity of the crucible 3. A valve 8c is provided on the pipe 7b, a valve 8f is provided on the pipe 7e, and a valve 8d is provided on the pipe 7c.

  The trap 6 is a cold trap cooled by a refrigerant such as liquid nitrogen. A vacuum pump 61 is connected to the trap 6 via a pipe 7d. A valve 8e is installed on the pipe 7d.

  Next, the first manufacturing process in the first embodiment will be described with reference to FIGS. 3, 4 and 5. The first production process includes a drying process, a reduction process using hydrogen bromide, and a purification and crystallization process using the Bridgman method.

(Drying process)
In FIG. 3, 6 kg of commercially available thallium bromide powder having a purity of 99.99% as a raw material is filled in the crucible 3 (step S1). The purity of commercially available thallium bromide is specified for metal elements, and is not specified for oxygen and moisture. This commercially available thallium bromide powder having a purity of 99.99% contains a small amount of impurities such as thallium oxide and moisture in addition to thallium bromide. When the concentration of lead contained in this commercially available thallium bromide was analyzed by glow discharge mass spectrometry (GDMS), the concentration was 7.4 ppm.

  Next, the piping 7a and the crucible 3 are connected (step S2). The crucible 3 is lowered by the driving device 4 and the crucible 3 is placed in the electric furnace 2. At this time, the valves 8a, 8b, 8c, 8d, 8e, and 8f are closed. Subsequently, the temperature in the electric furnace 2 is set to about 120 ° C., the valve 8b, the valve 8d, and the valve 8e are opened, and the vacuum pump 61 is operated to exhaust the gas in the crucible 3 that has been heated. (Step S3). The raw material is dried by going through such steps S1 to S3.

(Reduction process with hydrogen bromide)
The trap 6 is filled with liquid nitrogen LN (step S4). The trap 6 cooled by the liquid nitrogen LN can collect gas containing impurities (hereinafter referred to as “impurity gas”) sucked from the crucible 3 by the vacuum pump 61. Next, the heating coil 21 is energized to raise the temperature in the electric furnace 2 and raise the temperature of the crucible 3 to a predetermined temperature (step S5). Note that the temperature rise width can be appropriately set according to the number of repetitions of steps S5 to S8 described later. This temperature increase range will be described later.

  Next, with the valves 8d and 8e closed, the crucible 3 is filled with the hydrogen bromide gas in the gas cylinder 5 by opening the valves 8a, 8b and 8c via the pipe 7a. (Step S6).

  The inside of the crucible 3 and the pipe 7a is in a state of being depressurized in advance by the vacuum pump 61, and when the valve 8a is opened, the hydrogen bromide that is in the liquid state in the gas cylinder 5 is vaporized and becomes gaseous, It is supplied into the crucible 3 through the pipe 7a. At this time, by monitoring the pressure in the crucible 3 with the pressure gauge 9, the amount of hydrogen bromide gas filled in the crucible 3 can be appropriately adjusted by the regulator of the gas cylinder 5.

  In this way, when the raw material and the hydrogen bromide gas come into contact with each other at a predetermined temperature, the thallium oxide as an impurity contained in the raw material reacts with the hydrogen bromide gas and is reduced. Thereby, impurity gas, for example, water vapor is generated. While maintaining this state, the crucible 3 is left for a predetermined time (for example, 4 to 5 minutes) (step S7).

  Next, the valve 8a is closed, and the valve 8d and the valve 8e are opened with the valve 8b and the valve 8c being opened. In this state, by operating the vacuum pump 61, the gas in the crucible 3, that is, the impurity gas generated in the crucible 3 and the unreacted hydrogen bromide gas are exhausted (step S8). The exhausted gas is collected by the trap 6.

  Steps S5 to S8 are repeated a predetermined number of times set in advance. That is, when the process of step S8 is completed, if the process of S5 to S8 is not repeated a predetermined number of times or more (when the determination in step S9 is NO), the process of S5 to S8 is further executed. On the other hand, if the steps S5 to S8 are repeated a predetermined number of times or more (if the determination in step S9 is YES), the process proceeds to the determination in step S10. The number of repetitions is, for example, 5 times. There is no restriction | limiting in particular about the frequency | count of repetition, For example, what is necessary is just to set suitably in the range of 4-20 times.

  In step S10, it is determined whether or not the crucible 3 has reached a predetermined temperature. 300 ° C. is set as the predetermined temperature. If the crucible 3 is not at a predetermined temperature, that is, 300 ° C. (when the determination at step S10 is NO), the steps S5 to S9 are repeated. On the other hand, if the crucible 3 is at a predetermined temperature, that is, 300 ° C. (when the determination in step S10 is YES), the process proceeds to the next step S11.

  Here, the temperature increase width of the crucible 3 in step S5 will be described. The difference (180 ° C. in this embodiment) between the temperature at the end of the drying process (120 ° C. in this embodiment) and the predetermined temperature (300 ° C. in this embodiment) of the crucible 3 in step S10 is determined as the predetermined temperature in step S9. What is necessary is just to set the temperature (36 degrees C in this embodiment) divided by the number of times (5 times in Embodiment 1) as the temperature increase width. That is, steps S5 to S8 are performed at least five times until the temperature of the crucible 3 reaches 300 ° C. Note that “at least 5 times” is set when the temperature of the crucible 3 in step S10 is less than a predetermined temperature (300 ° C.) after the preset five times of steps S5 to S8 are completed. This means that the execution of steps S5 to S8 is permitted.

  The thallium oxide contained in the thallium bromide raw material is reduced by hydrogen bromide through such steps S5 to S10, and is degassed as an impurity gas.

(Bromine filling process)
The bromine filling process in Example 1 includes steps S11 to S12. First, bromine gas is filled into the crucible 3 (step S11). Specifically, when the valve 8d is closed and the valve 8f is opened, a predetermined amount of bromine gas is filled into the crucible 3 from the bromine container 10. The predetermined amount is determined to be 0.01 to 0.09 mol% bromine with respect to 99.91 to 99.99 mol% thallium bromide, for example. All of the valve 8a, the valve 8b, the valve 8c, the valve 8d, the valve 8e, and the valve 8f are closed, and the crucible 3 is sealed by sealing the pipe 7a in the vicinity of the crucible 3 (step S12). .

(Purification and crystal growth process by Bridgman method)
In the electric furnace 2, a temperature gradient is formed to gradually decrease the temperature from the upper part to the lower part (step S13). This temperature gradient is centered on the melting point of thallium bromide, and in the crucible 3 in the electric furnace 2, a liquid phase of the thallium bromide is formed at the upper part, and a solid phase of the thallium bromide is formed at the lower part. To be set. Specifically, by controlling the amount of heat generated by each heating coil 21, the electric furnace 2 has a range from 500 ° C. to 150 ° C., preferably from 480 ° C. to 150 ° C., from the top to the bottom. A temperature gradient is formed. At that time, the temperature control device 22, the temperature sensor 23, and the temperature measurement device 24 function.

  Next, while the crucible 3 is rotated by the driving device 4, the crucible 3 is lowered from the top to the bottom at a constant speed in the electric furnace 2 (step S14). The descending speed varies depending on the vertical length of the section in which the temperature gradient is formed. For example, when the length is 60 cm, it may be about 2.5 mm / h.

  As the crucible 3 descends in the electric furnace 2, the thallium bromide melted in the upper part of the electric furnace 2 is solidified while gradually lowering the temperature, whereby crystals grow. That is, crystals grow by the Bridgman method. If the contents of the crucible 3 are not completely solidified (if the determination in step S15 is NO), the crucible 3 is further lowered at a constant speed (step S14), while the contents are completely solidified. In the case (when the determination in step S15 is YES), the first manufacturing process ends.

  Since the thallium bromide intermediate material (ingot as thallium bromide crystal) produced in the first production process is a raw material in the next second production process, it does not have to be a single crystal and is polycrystalline. It may be. The diameter of the ingot manufactured in the first manufacturing process is, for example, about 75 mm, and the length of the straight tube portion is, for example, about 130 mm. Due to the segregation effect by the Bridgman method, impurities aggregate at the top of the ingot. In the other part of the ingot, that is, the purified part, the lead concentration as an impurity is reduced as compared with the commercially available thallium bromide powder having a purity of 99.99% used as a raw material. When the lead concentration in the lowermost portion of the straight part of the ingot was analyzed by GDMS, analytical results of 0.6 ppm and 0.9 ppm were obtained for the two ingots, respectively. They are much smaller than the lead concentration of 7.4ppm in the raw materials.

(Processing process)
The purified part other than the upper part (impurity aggregation part) in the ingot manufactured in the first manufacturing process is divided into a plurality of small blocks. The size of each small blob is determined so that the purified portion of the ingot can be put into the container through the opening of the container used in the second manufacturing process described below. In the dividing operation, the operation should be performed so that impurities are not mixed. The ingot manufactured in the first manufacturing process may be deformed by rolling or other methods. In any case, the ingot is processed as necessary to carry out the second manufacturing process. In taking out the ingot from the crucible 3, a known technique such as cutting the crucible 3 is used.

(Purification process by zone purification method)
FIG. 5 shows an installation (band purification apparatus) 200 for performing the band purification method in the second manufacturing process. The container 202 is a quartz glass tube having a cylindrical shape, and has an inner diameter of, for example, 50 mm and a length of, for example, 350 mm. One end (right end in FIG. 5) of the container 202 is sealed, an opening is formed in the other end (left side in FIG. 5) of the container 202, and another quartz glass tube having a thin cylindrical shape in the opening. 222 is connected. The inner diameter of the quartz glass tube 222 is, for example, 10 mm.

  The quartz glass tube 222 serves as an inlet for receiving a raw material (thallium bromide intermediate material) to be processed in the second manufacturing process, and also serves as an inlet for an enclosed gas. The zone purification vessel 202 is inserted into a cylindrical core tube 203 having an inner diameter of 65 mm. The heater 204 is, for example, a heating element that generates heat when energized. The heater 204 is held by the heater moving device 205. The heater moving device 205 has a structure for moving the heater 204 along the axial direction (left and right direction in FIG. 5) of the core tube 203, and also has a function of stopping the heater 204 at an arbitrary position in the axial direction.

  An auxiliary heater 232 is arranged on the upper side of the core tube 203. The auxiliary heater 232 is a heating element that generates heat when energized, for example. The auxiliary heater 232 increases the temperature of the entire core tube 203. In the illustrated configuration example, the auxiliary heater 232 is disposed only in the upper part, but it may be installed so as to cover the entire core tube 203. The heating output per unit area of the auxiliary heater 232 is smaller than that of the heater 204.

Now, thallium bromide (thallium bromide intermediate material) manufactured in the first manufacturing process, specifically, for example, 500 g of thallium bromide 201 is introduced into the container 202 through the quartz glass tube 222. However, out of the 6 kg crystal ingot produced in the crystal growth process by the Bridgeman method, the upper 20 mm where the impurities are segregated is excluded, and a part of the remaining crystal ingot is cut from the lower part. The volume of crystals put into the container 202 is about 66 cm ³ , for example. In that case, in the inside of the horizontally installed container 202, the input is less than half the height of the container 202.

  Next, the upper surface of the core tube 203 is heated by the auxiliary heater 232. The temperature of the upper surface of the container 202 becomes higher than the temperature of the lower surface of the container 202. This avoids the attachment of thallium bromide crystals caused by cooling the thallium bromide gas on the upper surface of the container 202. Further, impurities are prevented from adhering to the surface of thallium bromide 201 at the stage where the zone purification is completed.

  A quartz glass tube 222 is connected to the sealed gas supply device. In this state, the sealed gas is supplied into the container 202, and the container 202 is filled with the sealed gas. Thereafter, the glass tube 222 is sealed with a gas burner. The sealed gas in this embodiment is hydrogen bromide gas at about 0.2 atm.

  Thereafter, the heater 204 is scanned in the horizontal direction (left side in the illustrated example) by the heater moving device 205. When the heater 204 is energized, a portion of the thallium bromide 201 in the container 202 facing the heater 204 is heated, and the thallium bromide 201 is partially melted in a band shape. The melting portion moves as the heater 204 moves. The portion that is no longer opposed to the heater 204 is cooled. That part gradually solidifies and crystallizes. When thallium bromide 201 is heated and melted, impurities in thallium bromide 201 are released into the liquid phase, and when thallium bromide 201 is cooled and crystallized (solidifies), the impurities remain in the liquid phase. For this reason, the purity of the crystallized (solidified) portion in the thallium bromide 201 is improved. The moving speed of the heater 204 is, for example, 30 mm / h or more and 60 mm / h or less. For example, when the heater 204 reaches the left end of the container 202, impurities in the thallium bromide 201 are collected on the left end side of the container 202. For this reason, in thallium bromide 201, the purity on the right end side is high and the purity on the left end side is low. The heated heater 204 is scanned 20 times to the left in the horizontal direction at a predetermined speed, and the thallium bromide 201 is repeatedly melted and recrystallized. Such a process improves the purity of thallium bromide.

  Even if the zone refining is repeated, the thallium oxide and moisture contained in the thallium bromide to be treated have been greatly reduced in advance, so that the problem that the quartz glass tube is damaged due to them is unlikely to occur.

(Single crystal growth process by zone melting)
When the required number of zone purification steps have been completed, the heater 204 in the heated state is slowly moved from the right side to the left side, for example, at a low speed of 3 mm / h to 6 mm / h, once in order to single-crystal the thallium bromide 201. Scanned. As a result, the band-shaped melted portion (band melting) of thallium bromide 201 slowly moves from the right side to the left side, and finally a single crystal (ingot) of thallium bromide 201 is generated. Impurities are aggregated on the left side of the ingot, and the portion cut out from the right side is a high purity portion. When the lead concentration was measured by GDMS analysis for a portion corresponding to about 80% of the volume from the right side of the entire ingot, it was confirmed that it was less than 0.1 ppm.

  Next, Example 2 will be described. FIG. 6 is a diagram illustrating equipment used in the first manufacturing process according to the second embodiment. FIG. 7 is a view showing a crucible for distillation included in the facility shown in FIG. 8 and 9 are flowcharts showing the first manufacturing process in the second embodiment. In the second manufacturing process in the second embodiment, the facility shown in FIG. 5 is used, and a plurality of zone purification (purification) and single crystal growth (crystallization) are performed using the facility. This will be specifically described below.

  In FIG. 7, the crucible 120 for distillation includes a holding part 132, a straight pipe part 133, an initial distillation collecting part 134, a main distillation condensing part 136, a crystal growing part 138, and the like. The inner diameter of the crystal growing part 138 is about 75 mm, for example. From the upper end side of the straight pipe part 133, 3 kg of commercially available thallium bromide powder having a purity of 99.99% as a raw material is filled into the holding part 132 (step S101). The concentration of lead contained in this commercially available thallium bromide powder (raw material) was analyzed by GDMS and found to be 7.4 ppm. After completion of the filling of the raw material 140, the distillation crucible 120 is placed in the electric furnace 104 of the crystal growing apparatus 100 as shown in FIG. Specifically, a state is formed in which the distillation crucible 120 is suspended from the lifting device 108 via a stainless steel wire.

(Drying process)
In FIG. 6, a vacuum exhaust pipe 112 is connected to the tip of the straight pipe portion 133, and the inside of the crucible 120 is evacuated by the vacuum exhaust apparatus 110. By leaving it as it is for 1 hour, a component that volatilizes at room temperature is removed (step S102). While continuing to be evacuated to remove moisture, the entire crucible 120 is gradually heated to 120 ° C. (step S103), and then that state is maintained for 1 hour. Thereby, the thallium bromide raw material is dried.

(Reduction process with hydrogen bromide)
A trap (not shown) attached to the vacuum exhaust device 110 is filled with liquid nitrogen. When the trap is cooled with liquid nitrogen, as described later, it becomes possible to collect a gas containing impurities (hereinafter referred to as “impurity gas”) sucked from the crucible 120 by the vacuum exhaust device 110. The heating coil 102 is energized, the temperature in the electric furnace 104 is increased, and the temperature of the crucible 120 is raised to a predetermined temperature. This is due to the setting and control of the heater control unit 106 (step S104). Note that the temperature increase range at this time can be set as appropriate depending on the number of repetitions of steps S104 to S107 described later. This temperature increase range will be described later.

  Using a gas cylinder (not shown) connected to the vacuum exhaust pipe 112, the crucible 120 is filled with hydrogen bromide gas (step S105). Thus, when the raw material 140 and the hydrogen bromide gas come into contact with each other at a predetermined temperature, the thallium oxide contained in the raw material 140 reacts with the hydrogen bromide gas and is reduced, and an impurity gas such as water vapor is generated. The While maintaining this state, the crucible 120 is left for a predetermined time (for example, 4 to 5 minutes) (step S106).

  Next, by operating the vacuum exhaust device 110, the gas in the crucible 120, that is, the impurity gas generated in the crucible 120 and the unreacted hydrogen bromide gas are exhausted (step S107). This exhausted gas is collected in a trap.

  Such steps S104 to S107 are repeated a predetermined number of times. That is, after the process of step S107 is completed, if the process of S104 to S107 is not repeated a predetermined number of times or more (if the determination in step S108 is NO), the process of S104 to S107 is further executed. On the other hand, if the steps S104 to S107 are repeated a predetermined number of times or more (if the determination in step S108 is YES), the process proceeds to the next determination in step S109. Although the number of repetitions is set to 5, the number of repetitions is not particularly limited, and may be set as appropriate within a range of 5 to 20 times, for example.

  Next, in step S109, it is determined whether or not the crucible 120 has reached a predetermined temperature. 300 ° C. is set as the predetermined temperature. If the crucible 120 is not at the predetermined temperature, that is, 300 ° C. (when the determination in step S109 is NO), the steps S104 to S108 are repeated. On the other hand, if crucible 120 is at a predetermined temperature, that is, 300 ° C. (when the determination in step S109 is YES), the process proceeds to the next step S110.

  The temperature increase width of the crucible 120 in step S104 will be described. The difference (180 ° C. in this embodiment) between the temperature at the end of the drying process (120 ° C. in this embodiment) and the predetermined temperature of the crucible 120 in step S109 (300 ° C. in this embodiment) is determined by the predetermined temperature in step S108. The temperature (36 ° C. in this embodiment) divided by the number of times (5 in this embodiment) may be set as the temperature increase range. That is, in Example 2, the processes of steps S104 to S107 are executed at least five times until the temperature of the crucible 120 reaches 300 ° C.

  The thallium oxide contained in the thallium bromide raw material is reduced by hydrogen bromide through such steps S104 to S109 and degassed as an impurity gas.

(Purification and crystal growth process by distillation method)
Next, the vicinity of the tip of the crucible 120 is sealed using a burner (step S110). Then, the process proceeds to an initial distillation recovery process for removing the initial distillation containing a large amount of impurities that are easily evaporated. First, in FIG. 5, the temperatures of the crystal growing unit 138, the holding unit 132, and the main distillation condensing unit 136 are set to be equal to or higher than the temperature of the initial distillation collecting unit 134. Specifically, the heater control unit 106 is set so that the crystal growing unit 138, the holding unit 132, and the main distillation condensing unit 136 are 600 ° C., and the initial distillation collecting unit 134 is 480 ° C., and this temperature state is maintained for 30 minutes. Hold (step S111).

  Due to the temperature gradient generated by lowering the initial distillation collecting unit 134 at a temperature lower than that of the crystal growing unit 138, the holding unit 132, and the main distillation condensing unit 136, the component 140 and the thallium bromide contained in the raw material 140 are easily evaporated. Then, it goes to the initial distillation collecting unit 134 and is condensed in the initial distillation collecting unit 134 to become a liquid or a solid.

  After the initial distillation recovery step, the process shifts to a main distillation recovery step in which the main distillation with less impurities is led to the crystal growth unit 138. First, the temperature of the crystal growing unit 138 and the main distillation condensing unit 136 is lowered to the vicinity of the melting point of the raw material 140. Specifically, the heater control unit 106 is set so that the crystal growth unit 138 and the main distillation condensing unit 136 are 480 ° C., the holding unit 132 is 600 ° C., and the initial distillation collecting unit 134 is 300 ° C. Hold for 5 hours (step S113).

  In step S113, before the steam generated from the raw material reaches the initial distillation recovery unit 134, the steam condenses into a liquid at the tube 135 at the latest in the main distillation condensing unit 136, and the inside of the main condensing unit 136 of the crucible 120 Adhere to the side tube wall. The adhering condensed liquid travels down the wall surface projecting downward in the main distillation condensing unit 136 and moves to the center, finally falls as a droplet, and is guided to the crystal growing unit 138 through the tube unit 137. . As a result, the main tail having the least amount of impurities is recovered by the crystal growth unit 138.

  If collection of the main distillation is continued, impurities that are difficult to evaporate accumulate in the raw material 140 of the holding unit 132, so that the purity of the main distillation decreases as the amount of main collection increases. Become. For this reason, the heater control unit 106 is set so that the temperature of the holding unit 132 is reduced to a temperature at which evaporation hardly occurs, specifically, 480 ° C. with the raw material 140 remaining in the holding unit 132 to some extent. The collection of the distillate is terminated (step S114).

  Next, the crucible 120 is raised using the lifting device 108 shown in FIG. 6 (step S115). The initial distillation collecting unit 134 goes out of the electric furnace 104 and decreases to near room temperature, and the main distillation condensing unit 136 and the holding unit 132 reach 300 ° C. in the electric furnace 104. Therefore, the raw material remaining in these parts is solidified below the melting point, and there is no possibility of moving to other parts.

(Crystal growth)
Subsequently, the heater control unit 106 is set so that the space below the crystal growth unit 138 generated by raising the crucible 120 is 370 ° C. and the crystal growth unit 138 is 480 ° C. (step S116). Using this temperature difference, crystal growth is started in the crystal growth unit 138. In order to shift to the crystal growth step, the crucible 120 is lowered using the lifting device 108, and the liquid main stream is cooled from the lower side of the crucible 120 and solidified (step S117). The descending speed of the crucible 120 at this time may be about 2.5 mm / h, for example.

  After the main distillation is completely solidified, the grown crystal (ingot) is taken out from the crucible 120 (step S118). Since the crystal is used as a raw material for zone purification, it does not have to be a single crystal and may be a polycrystal. The diameter of the ingot is about 75 mm, for example, and the length of the straight tube portion included in the ingot is about 45 mm, for example. Since ingots are grown through purification by a distillation method, the concentration of lead as an impurity is particularly reduced due to the effect of distillation, compared to commercially available thallium bromide powder having a purity of 99.99% used as a raw material. When the lead concentration of the ingot was analyzed by GDMS, it was less than 0.2 ppm at the bottom of the straight tube portion and 0.5 ppm at a position 20 mm from the bottom of the straight tube portion. Those values are significantly smaller than the lead concentration of 7.4 ppm in the raw material.

(Ingot processing)
After the first manufacturing process is completed, an ingot as a thallium bromide intermediate material is processed as necessary. For example, the ingot is divided into a plurality of small blobs. This is a process for charging the ingot into the container in the following second manufacturing process.

(Repurification and recrystallization)
For example, 500 g of the ingot as the thallium bromide intermediate material is put into the container of the zone purification apparatus shown in FIG. Then, as in Example 1, after 20 purifications by zone purification, the zone is melted only once at a slow rate so that a single crystal is grown.

  Also in Example 2, since the drying process and the reduction process are included in the first manufacturing process, that is, prior to the second manufacturing process, the thallium oxide as an impurity contained in the thallium bromide intermediate material and Since the moisture is greatly reduced, it is possible to avoid the problem that the zone refining vessel is damaged by those impurities. In particular, in the final thallium bromide single crystal (ingot) obtained, the lead concentration is greatly reduced, so if a semiconductor radiation detector is constructed using it, the energy resolution will be improved. Is possible.

  In both Example 1 and Example 2, the first manufacturing process and the second manufacturing process are performed in combination. In other words, the purification crystallization process is repeated twice. In the second manufacturing process, a zone purification method is used, and it is easy to increase the purity by increasing the number of zone purification. Therefore, a thallium bromide product with high purity can be manufactured. Moreover, since the drying process and the reduction process are included in the first manufacturing process, it is possible to avoid the problem of container breakage in the second manufacturing process. It is possible to produce a relatively large amount of thallium bromide product in a single production process using a large container. This has the advantage that a large number of semiconductor radiation detectors can be manufactured in a batch. In addition, you may make it apply the manufacturing method which concerns on the said embodiment with respect to another semiconductor material.

S200 1st manufacturing process, S202 processing process, S204 2nd manufacturing process.

Claims (9)

A first production process for producing a thallium bromide intermediate material from the thallium bromide raw material by purification and crystallization of the thallium bromide raw material;
A second manufacturing step of manufacturing a thallium bromide product from the thallium bromide intermediate material by repurification and recrystallization of the thallium bromide intermediate material;
A method for producing a thallium bromide product, comprising: In the manufacturing method of Claim 1,
The second manufacturing process is a process according to a zone purification method,
In the second manufacturing process, zone purification is performed a plurality of times.
A method for producing a thallium bromide product. In the manufacturing method of Claim 1,
The first manufacturing step includes a reduction step of excluding or reducing thallium oxide contained in the thallium bromide raw material,
The reduction step corresponds to a pretreatment step for preventing breakage of the container used in the second manufacturing step.
A method for producing a thallium bromide product. In the manufacturing method of Claim 1,
The first manufacturing process includes a drying process for excluding or reducing moisture contained in the thallium bromide raw material,
The drying step corresponds to a pretreatment step for preventing breakage of the container used in the second manufacturing step.
A method for producing a thallium bromide product. In the manufacturing method of Claim 1,
A processing step for processing the thallium bromide intermediate material is provided between the first manufacturing step and the second manufacturing step,
The processed thallium bromide intermediate material is put into a container used in the second manufacturing step,
A method for producing a thallium bromide product. In the manufacturing method of Claim 5,
In the processing step, the purified portion in the thallium bromide intermediate material is divided into a plurality of small lumps,
A method for producing a thallium bromide product. In the manufacturing method of Claim 1,
In the first production step, as the thallium bromide intermediate material, a thallium bromide polycrystal or a thallium bromide single crystal is produced,
In the second production step, a thallium bromide single crystal is produced as the thallium bromide product.
A method for producing a thallium bromide product. In the manufacturing method of Claim 1,
The thallium bromide product is used as a semiconductor for radiation detection.
A method for producing a thallium bromide product. A first production facility for producing a thallium bromide intermediate material from the thallium bromide raw material by purification and crystallization of the thallium bromide raw material;
A second production facility for producing a thallium bromide product from the thallium bromide intermediate material by repurification and recrystallization of the thallium bromide intermediate material;
An apparatus for producing thallium bromide products, comprising: