Method of manufacturing a source core for a radiation source

Abstract

The present application relates to the technical field of radioactive source, in particular to a preparation method of radioactive source core. The preparation method of radioactive source core is to dissolve the metal oxide of nuclide in acid solution, remove acid, and obtain radioactive source solution; then drop the radioactive source solution into the source holder coated with glaze, heat and sinter to obtain the source core. Different from the conventional technology of preparing source core by the method of enamel or tablet pressing, the preparation method of radioactive source core provided by the present application does not involve the preparation step of raw material suspension, and the operation is simpler and safer. At the same time, the source core product prepared by the method has more accurate activity, small error and higher stability.

Description

Technical Field

[0001] This invention relates to the field of radioactive source technology, and specifically to a method for preparing a radioactive source core. Background Technology

[0002] Low-energy photons typically refer to gamma and X-ray photons with energies below 150 keV. Radiation sources that can provide low-energy photons are called low-energy photon sources. These sources are mainly used for online measurement of density and thickness, as well as fluorescence analysis; using nuclides... 241 Am、 238 Low-energy photon sources are mostly fabricated using polypropylene (PPU). A low-energy photon source consists of a source shell and a source core. The source shell provides the necessary mechanical properties to meet the source's safety requirements and prevents environmental pollution caused by the leakage of radioactive nuclides. The source shell is usually made of metal, primarily stainless steel, and is sealed using argon arc (laser) self-fusion welding. The source core is the active material of the source, providing the radioactive nuclides required for photon output.

[0003] There are two main existing methods for fabricating low-energy photon source cores. One is the enamel method, which involves... 241 Am、 238 Metal oxides of nuclides such as Pu are mixed with a glaze, ground with water to form a suspension, which is then dripped into a source holder with a base glaze and sintered in an electric furnace to form a source core; another method is the mixed pressing method, which involves... 241 Am、 238 Metal oxides of nuclides such as Pu are uniformly mixed with aluminum powder and graphite powder, mechanically pressed into blocks, and then sintered in an electric furnace to form source cores. Currently, source cores prepared using the enamel method suffer from poor activity uniformity due to the high specific activity of the nuclides and the suspension nature of the slurry. Furthermore, the grinding process of the slurry leads to higher radiation doses for personnel. On the other hand, source cores prepared using the tablet pressing method are not fully sintered into a metallic body to ensure effective photon output, resulting in poor stability. Prolonged use under vibration can easily lead to core breakage and unstable photon output. Furthermore, damage to the source shell can easily cause the spread of radioactive contamination.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] To address the technical problems existing in the background art, the present invention provides a method for preparing a radioactive source core, as detailed below:

[0006] This invention provides a method for preparing a radioactive source core, comprising the following steps:

[0007] S1. Dissolve the metal oxide of the nuclide in an acidic solution, remove the acid, and obtain the radioactive source liquid;

[0008] S2. Drop the radioactive source material liquid into the source holder coated with surface glaze, and heat and sinter it;

[0009] The heating and sintering process includes: first heating to 520-580℃ and holding at that temperature for 40-60 minutes; then continuing to heat to 720-750℃, stopping the heating, and holding at that temperature for 10-20 minutes.

[0010] Unlike existing conventional methods for preparing radioactive source cores using enamel enamel or pressing techniques, the radioactive source core preparation method provided by this invention uses the metal oxide of a radionuclide as the radioactive source raw material. This is achieved by dissolving the metal oxide in an acidic solution, then removing the acid to obtain a radioactive source solution, which is then dropwise added to a source holder coated with enamel. Notably, the process of obtaining the radioactive source solution does not involve the preparation of a raw material suspension, thus enabling the production of 30 100mCi radioactive cores. 241 Taking the Am low-energy photon source as an example, this invention can reduce raw material grinding time by 30 minutes, raw material suspension settling time by 120 minutes, and slurry dripping time by 30 minutes, totaling 180 minutes, accounting for more than 50% of the total operator time. It can also reduce the operator's hand radiation dose by 0.6 mSv, accounting for more than 30% of the total radiation dose. Furthermore, the method described in this invention uses a method of dripping the radioactive source material into the glazed source holder, which is more precise than existing conventional methods for adding the material, resulting in more accurate source core activity. The error can be controlled within ±5%, far exceeding the ±10% standard of product manufacturers. During mass production of the radioactive source core, the batch activity deviation can be controlled within 3%, far exceeding the 10% standard of product manufacturers. In addition, the method described in this invention uses a specific heating and sintering process to first convert the radioactive metal ions in the radioactive liquid into radioactive metal oxides under heating conditions. Then, during the subsequent heating process, the oxides are fully mixed with the melted glaze, which greatly enhances the coating properties of the glaze, thereby reducing the leaching rate of the source core and making the obtained source core product have higher stability.

[0011] In this invention, considering factors such as product performance and production efficiency, the heating rate is preferably 10-20℃ / min, more preferably 15℃ / min.

[0012] The present invention does not particularly limit the specific operation method of acid removal, and conventional acid removal methods in the art (such as constant temperature heating at 50°C) are all acceptable.

[0013] Preferably, the pH value of the radioactive source solution obtained after acid removal treatment in this invention is in the range of 5-7.

[0014] The glaze used in this invention can be a commercially available glaze product from conventional sources in the art.

[0015] As a preferred embodiment of the present invention, the surface glaze comprises SiO2, B2O3, Na2O, K2O, Li2O3, ZnO and NaF, wherein the mass percentage of SiO2 is preferably >45%, the mass percentage of B2O3, K2O or NaF is preferably >10%, the mass percentage of Na2O is preferably >7%, and the mass percentage of Li2O3 or ZnO is preferably >1%.

[0016] More preferably, the mass percentage content of SiO2 is 49%-53%, the mass percentage content of B2O3 is 11%-14%, the mass percentage content of Na2O is 8%-10%, the mass percentage content of K2O is 11%-14%, the mass percentage content of Li2O3 is 1%-2%, the mass percentage content of ZnO is 1%-2%, and the mass percentage content of NaF is 10%-13%.

[0017] In a more specific preferred embodiment provided by the present invention, the composition of the surface glaze is: SiO2 51.18w%, B2O3 12.85w%, Na2O 8.96w%, K2O 12.85%, Li2O3 1.3w%, ZnO 1.3w%, NaF 11.56w.

[0018] The aforementioned preferred glaze formulation exhibits strong coating properties, providing a better sealing effect on the radioactive source nuclides during subsequent heating after the addition of the radioactive source liquid. This results in a lower leaching rate of the source core nuclides, more uniform source core activity, and more stable product properties. Furthermore, based on the excellent stability provided by this glaze formulation, the source core prepared by the method described in this invention is suitable for use in long-term vibration environments and is less prone to breakage.

[0019] In this invention, the weight ratio of the surface glaze to the metal oxide of the nuclide is preferably 1.3-2:1, more preferably 1.5:1. Source cores fabricated with this ratio exhibit a relatively higher photon effective output rate.

[0020] In this invention, the metal oxide of the nuclide is preferably from... 241 AmO2 or 238 PuO2.

[0021] In this invention, the acidic solution is preferably a nitric acid solution with a concentration of 1.5-2.5 mol / L, more preferably 2.0 mol / L.

[0022] In this invention, the source holder is made of alumina ceramic or stainless steel, preferably 316L stainless steel.

[0023] The present invention preferably pre-treats the source holder: the pre-treatment includes placing the source holder in an ethanol solution, ultrasonically cleaning it to remove oil stains from the surface of the source holder, drying it, and then heating it in a high-temperature furnace to a specified temperature to eliminate mechanical stress on the source holder.

[0024] In this invention, the inner bottom of the source holder is preferably coated with a U-shaped ceramic-like base glaze layer, and the base glaze is preferably a cobalt-nickel base glaze.

[0025] In a more specific and preferred embodiment of the present invention, a source holder coated with a U-shaped ceramic-like base glaze layer is obtained using the following method: First, the base glaze is ground with water into a slurry. The slurry is then pipetted into the source holder, where it forms a layer at the bottom under surface tension. Next, the source holder containing the base glaze slurry is heated to 250-350°C at a heating rate of 10-20°C / min and held at that temperature for 10-30 minutes to remove moisture from the slurry. Heating continues at a rate of 10-20°C / min to 800-900°C, causing the base glaze to transform from a granular state to a glassy state. After cooling, a U-shaped ceramic-like base glaze layer is formed on the inner side of the bottom of the source holder.

[0026] Beneficial effects:

[0027] This invention provides a method for preparing a radioactive source core. The method involves dissolving a metal oxide of a nuclide in an acidic solution, removing the acid, and obtaining a radioactive source solution. This solution is then dropped into a source holder coated with a glaze and sintered to obtain the source core. Unlike existing conventional methods for preparing source cores using enamel or pressing techniques, this invention uses a metal oxide of a nuclide as the radioactive source. The radioactive source solution is obtained by dissolving the metal oxide in an acidic solution, removing the acid, and then dropping it into a glaze-coated source holder. The process of obtaining the radioactive source solution does not involve the preparation of a raw material suspension, reducing operator time by approximately 50% and effectively reducing radiation dose to personnel by more than 30%. Furthermore, the method of adding the radioactive source solution dropwise into the glaze-coated source holder is more precise than existing methods, resulting in more accurate source core activity with an error controllable within ±5%. During mass production of radioactive source cores, the batch activity deviation can be controlled within 3%. Furthermore, the method described in this invention, through a specific heating and sintering process, first converts the radionuclide metal ions in the radioactive slurry into radionuclide metal oxides under heating conditions. Then, during subsequent heating, these oxides are thoroughly mixed with the molten glaze, greatly enhancing the glaze's coating properties and thus reducing the leaching rate of the source core, resulting in a more stable source core product. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be described below.

[0029] Figure 1 This is a schematic diagram of the source core structure prepared according to the present invention. In the diagram, 1 is the source support, 2 is the base glaze, 3 is the surface glaze, and 4 is the nuclide metal oxide.

[0030] Figure 2 This is a flowchart of the radioactive source core preparation method provided in Embodiment 1 of the present invention. Detailed Implementation

[0031] This invention provides a method for preparing a radioactive source core. Specifically, after removing oil stains from the source holder, it is placed in a high-temperature furnace for heat treatment; after cooling, the source holder is removed, a quantitative base glaze is cold-coated, and it is sintered in a high-temperature furnace; the source holder with the base glaze is removed, and a quantitative top glaze is cold-coated; the radioactive raw material is dissolved in acid and subjected to acid removal treatment to obtain the required liquid; the quantitative liquid is dripped into the source holder coated with the top glaze and heated to dry; it is placed in a high-temperature furnace for sintering, and after cooling, it is removed, thus completing the preparation of the source core.

[0032] The process involves several steps, including: placing the source holder in an ethanol solution, ultrasonically cleaning to remove surface oil, drying, and then heating it in a high-temperature furnace to a specified temperature to relieve mechanical stress. The base glaze sintering involves cold-coating a measured amount of base glaze into the source holder, placing it in a high-temperature furnace, and sintering it according to a set temperature program. The top glaze cold coating involves grinding the top glaze with water into a slurry, dripping it onto the base-glazed source holder, and then heating and drying it. Radioactive material processing includes... 241 Am、 238 Metal oxides of nuclides such as Pu are dissolved in a measured amount of acidic solution. After dissolution, the solution is subjected to acid removal treatment to obtain a radioactive material solution with the required acidity. The material solution is added dropwise by using a sampler to take a measured amount of the material solution and drop it into a source holder with a cold-coated surface glaze, followed by heating and drying. The source core sintering involves placing the source holder with the material solution in a high-temperature environment and heating it to a specified temperature according to a heating program, causing the surface glaze to melt and encapsulating the radioactive material inside the source holder.

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the term "source core" refers to the active block of a radioactive source, providing the radioactive nuclide required for the source to meet the photon output requirements; "source support" refers to the support for the radioactive material, which can be a metal or a ceramic sheet; "base glaze" is the transition layer between the source support and the top glaze; and "top glaze" is the adhesive for the nuclide metal.

[0035] Example 1

[0036] This embodiment provides a method for preparing a radioactive source core, the specific steps of which are as follows:

[0037] (1) The source material is 316L stainless steel (Baosteel Group Co., Ltd.).

[0038] First, place the source holder in a 95% ethanol solution and ultrasonically clean it for 30 minutes at 0.75Kw to remove oil stains from the surface of the source holder.

[0039] After the source holder is dried, it is placed in a high-temperature furnace and heated to 600°C at a heating rate of 15°C / min, and held at that temperature for 10 minutes to eliminate the mechanical stress of the source holder.

[0040] Remove the source tray from the high-temperature furnace and allow it to cool naturally to room temperature (25°C).

[0041] (2) The base glaze is a cobalt-nickel base glaze with a specification of 300 mesh (Xiangtan Jineng New Materials Co., Ltd.).

[0042] First, the base glaze is ground with water into a slurry. Then, the slurry is pipetted into the source holder. Under the action of surface tension, the slurry forms a 0.1 mm thick layer at the bottom of the source holder.

[0043] The source holder containing the base glaze slurry is heated to 300℃ at a heating rate of 15℃ / min and held at that temperature for 20 minutes to remove moisture from the base glaze slurry. Heating continues at a heating rate of 15℃ / min to 850℃, causing the base glaze to transform from a granular state to a glassy state. After cooling, a U-shaped ceramic-like base glaze layer is formed on the inner side of the bottom of the source holder.

[0044] (3) The surface glaze has a mesh size of 300, and its formula is shown in Table 1 below:

[0045] Table 1

[0046] Weight percentage (w%) 51.18 12.85 8.96 12.85 1.3 1.3 11.56

[0047] First, grind the glaze with water into a slurry. Then, according to the requirement of a weight ratio of glaze to nuclide metal oxide of 1.5:1, use a pipette to draw up the slurry and drop it into the source holder that has been coated with base glaze.

[0048] Place the source tray containing the glaze slurry in a 150℃ forced-air drying oven for 30 minutes to remove the moisture from the glaze slurry.

[0049] (4) 241 Am oxides serve as a source of nuclides.

[0050] First, put 1g 241 AmO2 was dissolved in 10 mL of 2 mol / L nitric acid solution, and then the solution was placed at 50 °C to remove acid until the pH value was 7, thus obtaining the radioactive source solution.

[0051] The radioactive source liquid is drawn up with a pipette and dropped into the source holder containing the glaze. The radioactive source liquid is absorbed by the loose glaze.

[0052] (5) Place the source holder containing the radioactive source solution at 50°C for 30 minutes to dry. Then heat it to 550°C at a heating rate of 15°C / min and hold it at that temperature for 50 minutes to allow the radioactive source solution to dry. 241 Am ions are converted to 241 AmO2; continue heating at a rate of 15℃ / min to 720℃, during this process 241 The AmO2 and the melted glaze are thoroughly mixed; the mixture is kept at the temperature for another 10 minutes (to avoid direct cooling that could cause the glaze to crack), and then cooled in the furnace to obtain the core.

[0053] Example 2

[0054] This embodiment provides a method for preparing a radioactive source core. The specific steps are different from those in Embodiment 1, except for steps (4) and (5):

[0055] (4) 238 The oxide of Pu serves as a source of nuclides.

[0056] First, put 1g 238 PuO2 was dissolved in 10 mL of 2 mol / L nitric acid solution, and then the solution was placed at 50℃ to remove the acid until the pH value was 5-7, thus obtaining the radioactive source solution.

[0057] The radioactive source liquid is drawn up with a pipette and dropped into the source holder containing the glaze. The radioactive source liquid is absorbed by the loose glaze.

[0058] (5) Place the source holder containing the radioactive source solution at 50°C for 30 minutes to dry. Then heat it to 550°C at a heating rate of 15°C / min and hold it at that temperature for 50 minutes to allow the radioactive source solution to dry. 238 Pu ions are converted into 238 PuO2; continue heating at a rate of 15℃ / min to 720℃, during this process 238 The PuO2 and the melted glaze are thoroughly mixed; the mixture is kept at the temperature for another 10 minutes (to avoid direct cooling that could cause the glaze to crack), and then cooled in the furnace to obtain the core.

[0059] Experimental Example

[0060] Three samples (φ10×5mm, nominal activity 30mCi) produced using this invention. 241 Taking the Am low-energy photon source as an example, product performance testing is conducted. Specifically, this includes:

[0061] (1) Detection of effective photon emissivity

[0062] The relative measurement method is used, that is, 30mCi 241 An Am standard source was placed inside the photon emissivity measurement device, and a correction factor was applied to modify the measurement result to the calibrated value of 1.7 × 10⁻⁶. 7 (S -1 ·Sr -1 The standard source was removed and placed into the source to be tested for measurement. The test result was 1.72 × 10⁻⁶. 7 ; 1.78×10 7 ; 1.75×10 7 Conclusion: Deviation < 5%, acceptable.

[0063] (2) Activity test

[0064] The relative measurement method was used. A 30 mCi standard source was placed in the activity meter, and the activity value A was measured. The standard source was then removed, and the test source was placed in the meter for measurement, with the measured activity value recorded as B. The activity of the test source was calculated as 30B / A. The test results were: 30.5; 31.2; 30.8. Conclusion: Deviation < 5%, acceptable.

[0065] (3) Source Core Stability Testing

[0066] The hydrothermal immersion method was used, in which the source core was immersed in 100 mL of still water at 50°C for 4 hours. The radioactivity in the water was then checked to see if it exceeded 0.01% of the total activity. The leaching rate was determined to be: 4 < 10. -6 4.6 < 10 -6 3.9 < 10 -6 Conclusion: The leaching rate is less than 0.01%, which meets the requirements of GB / 4075-2009, and the source core is non-leaching.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing a radioactive source core, the specific steps of which differ from those in Example 1 only in step 4.

[0069] First, put 1g 241 AmO2 was dissolved in 10 mL of 2 mol / L nitric acid solution, and then the solution was placed at 50 °C to remove acid until the pH value was 3.5, thus obtaining the radioactive source solution.

[0070] The radioactive source liquid is drawn up with a pipette and dropped into the source holder containing the glaze. The radioactive source liquid is absorbed by the loose glaze.

[0071] After the liquid material is added, the residual acidic solution reacts chemically with the alkaline metal oxides in the glaze, causing bubbles to overflow and affecting the glaze quality after sintering.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing a radioactive source core, the specific steps of which differ from those in Example 1 only in step 3.

[0074] (3) The surface glaze is 300 mesh, and its formula is shown in Table 1.

[0075] First, grind the glaze with water into a slurry. Then, according to the requirement of a 1:1 weight ratio of glaze to nuclide metal oxide, use a pipette to draw up the slurry and drop it into the source holder that has been coated with base glaze.

[0076] Place the source tray containing the glaze slurry in a 150℃ forced-air drying oven for 30 minutes to remove the moisture from the glaze slurry.

[0077] After sintering, the surface glaze layer cracked, failing to form a stable source core and not meeting the requirements for source core preparation.

[0078] Comparative Example 3

[0079] This comparative example provides a method for preparing a radioactive source core. The specific steps are different from those in Example 1, except for step 5.

[0080] The source holder containing the radioactive source solution was dried at 50°C for 30 minutes. Then, it was heated to 550°C at a heating rate of 15°C / min and held at that temperature for 10 minutes to allow the radioactive source solution to evaporate. 241 Am ions are converted to 241 AmO2; continue heating at a rate of 15℃ / min to 720℃, during this process 241 The AmO2 and the melted glaze are thoroughly mixed; the mixture is kept at the temperature for another 10 minutes (to avoid direct cooling that could cause the glaze to crack), and then cooled in the furnace to obtain the core.

[0081] Making the source core 241 Am ions were not fully transformed. 241 AmO2, radioactive material leaching rate of the source core >10 -4 It does not meet the requirement that the source core cannot be leached.

[0082] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a radioactive source core, characterized in that, The steps include the following: S1. Dissolve the metal oxide of the nuclide in an acidic solution, remove the acid, and obtain the radioactive source liquid; S2. Drop the radioactive source material liquid into the source holder coated with surface glaze, and heat and sinter it; The heating and sintering process includes: first heating to 520-580℃ and holding at that temperature for 60 minutes; Continue heating to 720-750℃, then stop heating and keep warm for 10-20 minutes.

2. The method for preparing the radioactive source core according to claim 1, characterized in that, The heating rate is 10-20℃ / min.

3. The method for preparing the radioactive source core according to claim 1, characterized in that, The pH value of the radioactive source solution is 5-7.

4. The method for preparing the radioactive source core according to claim 1, characterized in that, The surface glaze is composed of SiO2, B2O3, Na2O, K2O, Li2O3, ZnO and NaF, wherein the mass percentage of SiO2 is >45%, the mass percentage of B2O3, K2O or NaF is >10%, the mass percentage of Na2O is >7%, and the mass percentage of Li2O3 or ZnO is >1%.

5. The method for preparing the radioactive source core according to claim 4, characterized in that, The mass percentages of SiO2, B2O3, Na2O, K2O, Li2O3, ZnO, and NaF are 49%-53%, 11%-14%, 8%-10%, 11%-14%, 1%-2%, 1%-2%, and 10%-13%, respectively.

6. The method for preparing the radioactive source core according to any one of claims 1-5, characterized in that, The weight ratio of the glaze to the metal oxide of the nuclide is 1.3-2:

1.

7. The method for preparing the radioactive source core according to claim 1, characterized in that, The metal oxide of the nuclide is selected from 241 AmO2 or 238 PuO2.

8. The method for preparing the radioactive source core according to claim 1 or 7, characterized in that, The acidic solution is a 1.5-2.5 mol / L nitric acid solution.

9. The method for preparing the radioactive source core according to claim 1, characterized in that, The source holder is made of alumina ceramic or stainless steel.

10. The method for preparing the source core of the radioactive source according to claim 1 or 9, characterized in that, The bottom inner side of the source holder is coated with a U-shaped ceramic-like base glaze layer, which is a cobalt-nickel base glaze.

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