A method for preparing an ultrathin 4π fission source based on graphene substrate material
By using graphene-toughened carbon films and vacuum self-transfer technology, fissile material is transferred to a graphene substrate with a thickness of nanometers, solving the problems of self-absorption and strength of traditional fissile source substrate materials. This results in the preparation of an efficient and stable ultrathin 4π fissile source, suitable for fissile physics experiments and detector calibration.
Patent Information
- Application Number
- CN202610002568.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-04
- Publication Date
- 2026-05-26
AI Technical Summary
Traditional fission source substrates exhibit significant self-absorption effects, affecting the accuracy of energy measurements. Furthermore, existing materials have poor strength, making it difficult to fabricate high-quality, ultrathin 4π fission sources.
Using graphene-toughened carbon film as substrate material, graphene is grown by chemical vapor deposition and combined with solution drying and vacuum self-transfer technology to transfer fissile material onto a graphene substrate with a thickness of nanometers, thus preparing an ultrathin 4π fission source.
The 4π direction emission of fission fragments was achieved with minimal energy loss and negligible self-absorption effect, resulting in the fabrication of a high-strength, stable, ultrathin 4π fission source suitable for fission physics experiments and detector calibration.
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Figure CN122091297A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fission source preparation, specifically relating to a method for preparing an ultrathin 4π fission source based on a graphene substrate material. Background Technology
[0002] A 4π fission source is a radioactive source that emits fission fragments in a 4π direction, and it has wide applications in fundamental research on fission physics and the use of nuclear technology. However, low-energy fission fragments have poor penetrating power. The resistance of the fission source substrate material to the fission fragments softens the energy spectrum of the fission fragments, affecting the accuracy of energy measurements. This necessitates that the substrate material be thin enough so that the fission fragments penetrating the substrate material do not lose too much energy.
[0003] When conducting fission physics experiments using a double-grid ionization chamber or fission chamber, the fission source is typically used as an electrode of the detector. This requires the substrate of the fission source to be a conductive material to prevent charge accumulation on the substrate, which could affect experimental measurements. Common substrate materials for radioactive sources, such as Mylar films, polyimide films, and silicon nitride films, are insulating media. Depositing metal films on these materials can increase the self-absorption of the substrate material, affecting measurements. For metal foil materials, such as nickel and gold, their high atomic density provides strong resistance to fission fragments. Traditional carbon films are good lightweight conductive materials, but their loose structure and poor strength make them less effective.
[0004] A crucial step in the preparation of 4π fission sources is the transfer of fissile nuclides onto a substrate with extremely low self-absorption. The quality of the fission source preparation is a significant factor affecting the quality of experimental data. Due to the extremely high ionization capacity of fission fragments, not only will the substrate material of the fission source cause severe energy loss, but even the self-absorption of the fissile material itself can cause distortion of the fission energy spectrum. Therefore, it is also necessary to control the thickness of the fissile material itself during the fission source preparation process. Summary of the Invention
[0005] To address the significant self-absorption effect of the substrate material in traditional fission sources, the present invention aims to provide a method for preparing an ultrathin 4π fission source based on a graphene substrate. This method transfers fission nuclides onto a nanometer-thick graphene substrate, enabling the fission products released from the fission source to be emitted in the 4π direction. Furthermore, the average energy loss of the fission fragments penetrating the substrate material is much less than their own kinetic energy, resulting in a high-quality fission source with low energy loss and minimal self-absorption. This method achieves efficient and stable preparation of an ultrathin 4π fission source, providing a relatively "perfect" fission source for fission physics experiments or related detector calibration.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention discloses a method for preparing an ultrathin 4π fission source based on a graphene substrate material. The method involves preparing a graphene-toughened carbon film, growing graphene of a predetermined thickness using the graphene-toughened carbon film, and transferring the graphene substrate material to obtain the fission source substrate material. The fission material is transferred onto the graphene substrate by a combination of solution drying method and vacuum self-transfer technology, thereby obtaining an ultrathin fission source capable of emitting fission fragments in the 4π direction.
[0007] Furthermore, the method includes the following steps:
[0008] S1. Graphene of a predetermined thickness is grown using chemical vapor deposition (CVD) process;
[0009] S2. Use an etching solution to etch the graphene metal substrate to obtain a carbon nanotube in-situ toughened graphene film floating on the surface of the etching solution, namely a graphene toughened carbon film.
[0010] S3. Fabricate a metal substrate with a central hole, and transfer the in-situ toughened graphene film of carbon nanotubes on the liquid surface onto the metal substrate as a substrate for the self-transfer source.
[0011] S4. Prepare the mother material liner;
[0012] S5. Dissolve the fissile material in a specific solution, drop it onto the parent source substrate, and dry it to form a surface source, which serves as the parent source for vacuum self-migration.
[0013] S6. Place the substrate of the self-transfer source close to the parent source, put it in a vacuum chamber, and operate according to the preset experimental conditions to prepare a material capable of transferring to the parent source using the self-transfer properties of fissile material.
[0014] An ultrathin fission source that emits fission fragments in the 4π direction.
[0015] Furthermore, step S1 includes the following sub-steps:
[0016] S11. Prepare a surfactant aqueous solution of a preset concentration, disperse the toner in the aqueous solution, and shake the aqueous solution to obtain a toner dispersion solution.
[0017] S12. Load the carbon powder dispersion solution evenly onto the metal foil according to the preset loading amount;
[0018] S13. Place the metal foil with carbon powder dispersion solution on its surface into a chemical vapor deposition atmosphere furnace. Under preset conditions, thermally reduce the metal foil with carbon powder dispersion solution on its surface in an H2 atmosphere. Introduce CH4 into the atmosphere furnace and perform chemical vapor deposition under preset gas ratios of CH4 and H2. Remove the metal foil with a graphene film grown on its surface.
[0019] Furthermore, the etching solution in step S2 includes an etching solution of (NH4)2S2O3:BtOH:deionized water prepared using a preset mass-volume ratio.
[0020] Furthermore, in step S2, the metal foil on which the graphene film is grown is placed flat on the surface of the etching solution. The metal foil is completely etched and dissolved to obtain a carbon nanotube in-situ toughened graphene film floating on the surface of the etching solution, namely a graphene toughened carbon film.
[0021] Furthermore, in step S4, a flat stainless steel disc is used as the source substrate, and the edge of the stainless steel disc is coated with a hydrophobic substance to prevent the radioactive source solution from overflowing from the source substrate in subsequent steps.
[0022] Furthermore, the specific solution in step S5 includes an HNO3 solution.
[0023] Furthermore, the preset experimental conditions in step S6 include using an initial source with appropriate surface emissivity, performing a self-transfer operation in a vacuum environment, wherein the vacuum level of the vacuum environment is not higher than 1000 Pa, preferably not higher than 10 Pa. The self-transfer distance is not greater than 10 mm, preferably not greater than 1 mm. The self-transfer time is determined according to the fission source activity, typically ranging from several days to several weeks.
[0024] Furthermore, in step S6, the substrates of the parent source and the self-transfer source are brought close together while maintaining a preset distance. The parent source and the substrates of the self-transfer source are placed in the transfer vacuum chamber, and a vacuum pump is used to evacuate the air. During evacuation, a filter is used to filter the radioactive material. The vacuum level should be lower than the preset pressure during the transfer of fission material. The fission material in the parent source has self-transfer characteristics under low vacuum conditions and will transfer to the surface of the substrate of the self-transfer source to form an ultrathin 4π fission source.
[0025] Furthermore, the method also includes the following steps:
[0026] S7. The performance of the self-transfer source prepared by the ultrathin fission source capable of emitting fission fragments in the 4π direction was tested. By comparing the effects of different preset experimental conditions on the performance of the self-transfer source, the preset experimental conditions for the preparation of the self-transfer source were optimized.
[0027] Furthermore, the fissile material in step S5 includes Cf-252.
[0028] The beneficial technical effects of this invention are as follows: This invention discloses a method for preparing an ultrathin 4π fission source based on a graphene substrate. Using nano-thin graphene material as a substrate, and combining solution drying and vacuum self-transfer techniques, the ultrathin 4π fission source is prepared. The graphene substrate has good uniformity and high strength, and is not easily damaged in a gas flow environment, which is crucial for the long-term stable operation of the experiment. The fission source is prepared on the substrate, and the thickness of the substrate is sufficient to ensure that the average energy loss of the fission fragments penetrating the substrate is much less than their own kinetic energy. Preferably, the thickness of the substrate is on the nanometer scale, for example, from tens to hundreds of nanometers.
[0029] By systematically comparing the effects of different source preparation conditions on the performance of self-transfer sources, this invention provides optimized preparation conditions for self-transfer sources: using an initial source with appropriate surface emissivity, performing self-transfer operations in a vacuum environment, wherein the vacuum level of the vacuum environment is not higher than 1000 Pa, preferably not higher than 10 Pa. The self-transfer distance is not greater than 10 mm, preferably not greater than 1 mm. The self-transfer time is determined according to the fission source activity, typically ranging from several days to several weeks.
[0030] Based on the nano-thin graphene substrate and optimized self-transfer source conditions, the prepared ultrathin 4π fission source has a thickness close to "infinitely thin", the self-absorption effect is negligible, and the light and heavy fragment peaks of the fission fragment energy spectrum are significantly distinguished, making it very suitable for basic fission experimental research. Attached Figure Description
[0031] Figure 1 This is a schematic diagram of the self-transfer fission source preparation device used in step S6 of a method for preparing an ultrathin 4π fission source based on a graphene substrate material, as shown in Embodiment 1 of the present invention.
[0032] Figure 2 The fission fragment energy spectrum of a Cf-252 spontaneous fission source prepared using the ultrathin 4π fission source preparation method based on graphene substrate material shown in Embodiment 1 of this invention is shown, wherein N L Indicates the peak height of light fission fragments, N H N represents the height of the heavy fission fragment peak. V Indicates the altitude of the valley area;
[0033] Wherein: 1-parent material, 2-graphene substrate, 3-transfer vacuum chamber, 4-filter,
[0034] 5-Screw valve, 6-Screw valve, 7-Filter, 8-Vacuum pump, 9-Vacuum gauge, 10-Fume hood. Detailed Implementation
[0035] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.
[0036] Example 1
[0037] This invention provides a method for preparing an ultrathin 4π fission source based on a graphene substrate. The method involves preparing a graphene-toughened carbon film, growing graphene with a thickness of less than 100 nm using the graphene-toughened carbon film, and transferring the graphene substrate to obtain the fission source substrate. The fission material is then transferred onto the graphene substrate using a combination of solution drying and vacuum self-transfer technology, thereby preparing an ultrathin fission source capable of emitting fission fragments in the 4π direction.
[0038] The graphene-reinforced carbon film differs from traditional thin pure carbon support films, which are typically a few micrometers thick, exhibit strong self-absorption of fission fragments, and are lightweight, brittle, and easily damaged. The graphene-reinforced carbon film prepared in this embodiment can be as thin as tens of nanometers and possesses higher strength, making it less prone to damage in a continuously flowing gas environment.
[0039] Cf-252 has a moderate half-life and is one of the most commonly used spontaneous fission radioactive sources. Its fission fragment energy spectrum can be used as a standard energy spectrum for studying the energy response of nuclear radiation detectors. In this embodiment of the invention, an ultrathin graphene substrate based on nanomaterials is used to prepare...
[0040] Taking the 4π Cf-252 fission source as an example, in fact, there is no limitation on the type of radioactive source.
[0041] This invention provides a method for preparing an ultrathin 4π fission source based on a graphene substrate, comprising the following steps:
[0042] S1. Graphene is grown using chemical vapor deposition (CVD) process, and the thickness of the grown graphene is less than 100 nm.
[0043] Step S1 includes the following sub-steps:
[0044] S11. Preparation of carbon film loading: Prepare an aqueous solution of surfactant with a concentration of 0.5 g / L, disperse carbon powder in the solution, and subject the prepared solution to ultrasonic vibration with an ultrasonic power of 100-120 W and an ultrasonic time of 30-60 min to obtain a carbon powder dispersion solution.
[0045] S12. The carbon powder dispersion solution obtained in step S11 is uniformly loaded onto a nickel metal foil, with the loading amount of the solution on the metal foil being 10-20 μg / cm³. 2 ;
[0046] S13. Graphene is grown using chemical vapor deposition (CVD). The nickel foil with a carbon powder dispersion solution on its surface, obtained in step S12, is placed in a CVD atmosphere furnace. The atmosphere furnace is evacuated to 0.1 MPa, and H2 is continuously introduced into the furnace. The isothermal zone of the atmosphere furnace is heated to 1200-1300°C, and the nickel foil with the carbon powder dispersion solution on its surface is placed in the isothermal zone for thermal reduction for 10-30 min in the H2 atmosphere. While maintaining the isothermal zone of the atmosphere furnace at a temperature of 900-1070°C, CH4 is introduced into the atmosphere furnace, and CVD growth is performed for 5-30 min under the condition that the CH4:H2 gas ratio in the isothermal zone is maintained at 30:1-100:1. After CVD, the introduction of CH4 and H2 into the furnace is stopped, and the nickel foil is removed from the isothermal zone until it cools to room temperature. Then, an inert gas is introduced into the furnace, and the metal foil with a carbon nanotube / graphene film grown on its surface is removed.
[0047] S2. Use an etching solution to etch the graphene metal substrate to obtain a graphene film floating on the liquid surface.
[0048] Continuing from the previous example, an etching solution of (NH4)2S2O3:BtOH:deionized water was prepared according to a certain mass-volume ratio to etch the metal foil substrate. The metal foil with carbon nanotube / graphene films grown on its surface was placed flat on the surface of the etching solution. The metal foil was completely etched and dissolved, resulting in an in-situ toughened graphene film with carbon nanotubes floating on the surface of the etching solution.
[0049] S3. Transfer of graphene film: A metal substrate with a central hole is fabricated using an electrochemical etching process, and the graphene film on the liquid surface is transferred onto the metal substrate as a substrate for the self-transfer source.
[0050] Continuing from the previous example, a stainless steel substrate was fabricated using an electrochemical etching process, with a central pore diameter of 1 cm. The in-situ toughened graphene film with carbon nanotubes on the liquid surface in step S2 was transferred to the metal substrate as a substrate for the self-transfer source. The graphene adhered well to the stainless steel substrate, with a thickness of 80 nm and a non-uniformity of less than 5%.
[0051] S4. Preparation of the source substrate material: A flat stainless steel disc is used as the source substrate. The edges of the stainless steel disc are coated with a hydrophobic substance such as petroleum jelly to prevent the radioactive source solution from overflowing from the source substrate in subsequent steps.
[0052] Because the stainless steel disc is very smooth, the solution is prone to overflow when a radioactive fission material solution is titrated onto it in subsequent steps. Therefore, it is necessary to apply a hydrophobic material to the edge of the stainless steel disc beforehand.
[0053] S5. Preparation of the source material: Dissolve the fission material in a specific solution, titrate it onto the source material substrate with a dropper, and dry it in a fume hood using an infrared lamp to form a surface source.
[0054] Continuing the previous example, Cf-252 was dissolved in a 2 mol / L HNO3 solution and titrated onto a source substrate using a dropper. The Cf-252 radioactive solution rapidly spread under the action of a surfactant. The liquid components were dried using an infrared lamp inside a fume hood, forming a surface source the size of a circular spot of solution, which served as a vacuum self-migration source.
[0055] S6. Preparation of self-transfer fission source: The graphene substrate is placed close to the parent source, and the two are placed in a vacuum chamber. The operation is carried out according to the preset experimental conditions (initial source emissivity of about 5000 cps, vacuum degree <10 Pa, self-transfer distance 1 mm, transfer time >5 days) to prepare a high-performance self-transfer fission source by utilizing the self-transfer characteristics of fissionable material.
[0056] The preset experimental conditions include using an initial source with appropriate surface emissivity, performing a self-transfer operation in a vacuum environment, wherein the vacuum level is not higher than 1000 Pa, preferably not higher than 10 Pa. The self-transfer distance is not greater than 10 mm, preferably not greater than 1 mm. The self-transfer time is determined according to the fission source activity, typically ranging from several days to several weeks.
[0057] Continuing from the previous example, such as Figure 1 As shown, the Cf-252 source 1 prepared in step S5 and the self-transfer source substrate 2 of the ultrathin graphene material in step S3 are placed close together, with a distance of 1 mm between them. The source 1 and the graphene substrate 2 are placed in the transfer vacuum chamber 3. The vacuum pump 8 is turned on, and the rotary valves 5 and 6 are opened to begin evacuation. During evacuation, the radioactive material is filtered using filters 4 and 7. The exhaust gas from the vacuum pump 8 is connected to the fume hood 10. The vacuum level of the transfer vacuum chamber 3 is monitored by the vacuum gauge 9. The vacuum level should be less than 10 Pa during the transfer of fission material. The transfer process lasts for more than 5 days, during which the transfer vacuum chamber 3 needs continuous evacuation. The Cf-252 fission material in the source 1 exhibits self-transfer characteristics under low vacuum conditions and will transfer to the surface of the graphene substrate 2, forming an ultrathin 4π Cf-252 fission source.
[0058] S7. Conduct self-transfer source performance tests, and optimize the self-transfer source preparation conditions by comparing the effects of different source preparation conditions on the performance of the self-transfer source.
[0059] The prepared fission source was subjected to performance testing. Its energy spectrum and activity were measured using a charged particle detector. Meanwhile, the impurity elements of the fission source could be analyzed by alpha and gamma spectra.
[0060] The fission fragment energy spectrum of a fabricated Cf-252 fission source was measured using a gold-silicon surface-barrier semiconductor detector. A typical measurement result for a Cf-252 self-transfer source is shown below. Figure 2 As shown, the average energy loss of fission fragments penetrating the graphene substrate is less than 1.5 MeV. Figure 2 N L Indicates the peak height of light fission fragments, N H N represents the height of the heavy fission fragment peak. V The height of the valley region is typically described by the ratio of the peak region height to the valley region height, indicating the performance of the fission source. A larger ratio indicates a thinner fission source. L / N V =2.92, N H / N V =2.20, which indicates that the prepared Cf-252 fission source satisfies the "infinitely thin" characteristic.
[0061] As can be seen from the above embodiments, the method for preparing an ultrathin 4π fission source based on a graphene substrate disclosed in this invention solves the problem of significant self-absorption effect in traditional fission source substrates, and achieves an efficient and stable preparation process for an ultrathin 4π fission source. Self-transfer source performance tests were conducted, and the effects of different source preparation conditions on the self-transfer source performance were compared to optimize the self-transfer source preparation conditions.
[0062] The method described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.
Claims
1. A method for preparing an ultrathin 4π fission source based on a graphene substrate, characterized in that: The method involves preparing a graphene-toughened carbon film, growing graphene of a predetermined thickness on the graphene-toughened carbon film, and transferring it to obtain a substrate material for the fission source. The fission material is then transferred onto the graphene substrate using a combination of solution drying and vacuum self-transfer technology, resulting in an ultrathin fission source capable of emitting fission fragments in the 4π direction.
2. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 1, characterized in that: The method includes the following steps: S1. Graphene of a predetermined thickness is grown using chemical vapor deposition (CVD) process; S2. Use an etching solution to etch the graphene metal substrate to obtain a carbon nanotube in-situ toughened graphene film floating on the surface of the etching solution, namely a graphene toughened carbon film. S3. Fabricate a metal substrate with a central hole, and transfer the in-situ toughened graphene film of carbon nanotubes on the liquid surface onto the metal substrate as a substrate for the self-transfer source. S4. Prepare the mother material substrate; S5. Dissolve the fissile material in a specific solution, drop it onto the parent source substrate, and dry it to form a surface source, which serves as the parent source for vacuum self-migration. S6. Place the substrate of the self-transfer source close to the parent source and put it in a vacuum chamber. Operate according to the preset experimental conditions to prepare an ultrathin fission source that can emit fission fragments in the 4π direction by utilizing the self-transfer characteristics of fission material.
3. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: Step S1 includes the following sub-steps: S11. Prepare a surfactant aqueous solution of a preset concentration, disperse the toner in the aqueous solution, and shake the aqueous solution to obtain a toner dispersion solution. S12. Load the carbon powder dispersion solution evenly onto the metal foil according to the preset loading amount; S13. Place the metal foil with carbon powder dispersion solution on its surface into a chemical vapor deposition atmosphere furnace. Under preset conditions, thermally reduce the metal foil with carbon powder dispersion solution on its surface in an H2 atmosphere. Introduce CH4 into the atmosphere furnace and perform chemical vapor deposition under preset gas ratios of CH4 and H2. Remove the metal foil with a graphene film grown on its surface.
4. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: The etching solution in step S2 includes a (NH4)2S2O3:BtOH:deionized water etching solution prepared using a preset mass-volume ratio.
5. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: In step S2, the metal foil on which the graphene film is grown is placed flat on the surface of the etching solution. The metal foil is completely etched and dissolved to obtain a carbon nanotube in-situ toughened graphene film floating on the surface of the etching solution, namely a graphene toughened carbon film.
6. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: In step S4, a flat stainless steel disc is used as the mother source substrate. The edges of the stainless steel disc are coated with a hydrophobic substance to prevent the radioactive source solution from overflowing from the mother source substrate in subsequent steps.
7. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: The specific solution in step S5 includes an HNO3 solution.
8. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that: The preset experimental conditions in step S6 include using an initial source and performing a self-transfer operation in a vacuum environment. The vacuum degree of the vacuum environment is not higher than 1000 Pa, preferably not higher than 10 Pa. The self-transfer distance is not greater than 10 mm, preferably not greater than 1 mm. The self-transfer time is determined according to the fission source activity, usually from several days to several weeks.
9. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 8, characterized in that: In step S6, the substrates of the parent source and the self-transfer source are brought close together, maintaining a preset distance between them. The parent source and the substrates of the self-transfer source are placed in the transfer vacuum chamber, and a vacuum pump is used to evacuate the air. During evacuation, a filter is used to filter the radioactive material. The vacuum level should be lower than the preset pressure during the transfer of fission material. The fission material in the parent source has self-transfer characteristics under low vacuum conditions and will transfer to the surface of the substrate of the self-transfer source to form an ultrathin 4π fission source.
10. The method for preparing an ultrathin 4π fission source based on a graphene substrate according to claim 2, characterized in that, The method further includes the following steps: S7. The performance of the self-transfer source prepared by the ultrathin fission source capable of emitting fission fragments in the 4π direction was tested. By comparing the effects of different preset experimental conditions on the performance of the self-transfer source, the preset experimental conditions for the preparation of the self-transfer source were optimized.