Method and system for efficiently preparing Te isotope target

Abstract

The invention relates to a method and system for efficiently preparing a Te isotope target, and the method comprises the steps: placing an evaporation crucible containing Te isotope powder in a vacuum evaporation device, and preparing the Te isotope target by adopting an evaporation deposition coating process; measuring the thickness of the Te isotope target prepared after single evaporation; if the target thickness is lower than the range required by the physical experiment, further adding a proper amount of Te isotope powder into the evaporation crucible, and carrying out secondary evaporation deposition; and if the thickness of the target is larger than the range required by the physical experiment, carrying out bombardment sputtering on the over-thick Te isotope target by using a magnetron sputtering device to reduce the thickness of the target. According to the method, the evaporation deposition coating process and the magnetron sputtering process are combined to prepare the Te isotope target, so that the thickness of the Te isotope target can be efficiently and reliably regulated and controlled, the utilization efficiency of an expensive Te isotope material is improved, and the coating uniformity is ensured.

Description

Technical Field

[0001] This invention belongs to the field of isotope target preparation technology, specifically relating to a method and system for efficiently preparing Te isotope targets. Background Technology

[0002] In fundamental nuclear physics research, such as nuclear reactions and nuclear structure, 0.5-5 mg / cm³ is frequently used. 2 Thickness-level isotopic Te targets are used as nuclear reaction targets. Te (tellurium) has eight isotopes in nature, namely... 120 Te、 122 Te、 123 Te、 124 Te、 125 Te、 126 Te、 128 Te, and 130 Te, with abundances of 0.09%, 2.55%, 0.89%, 4.74%, 7.07%, 18.84%, 31.74%, and 34.08% in nature, respectively. Currently, there are no domestic manufacturers specifically producing these isotopes; high-abundance powdered Te isotope materials must be purchased from abroad and then prepared into nuclear reaction targets to meet the needs of related nuclear physics experiments. Each imported concentrated high-abundance (over 99%) Te isotope material is extremely expensive; for example, supplier quotes... 120 Te ~20,000 USD / mg, 123 Te ~5000 USD / mg, 122 Te、 124 Te and 125 Te is priced at $150-$450 / mg. 126 Te、 128 Te, and 130 Te is priced at $35-120 / mg. Therefore, efficient and reliable processes must be employed to prepare this type of nuclear reaction target to ensure the efficient utilization of high-abundance Te isotope materials and avoid material waste. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the prior art by providing a method and system for efficiently preparing Te isotope targets. This method improves the uniformity of Te target coatings through reasonable design and combines evaporation deposition coating process with magnetron sputtering process to effectively control the thickness of Te targets.

[0004] To achieve the above objectives, in one aspect, a specific embodiment of the present invention provides a method for efficiently preparing a Te isotope target, comprising:

[0005] An evaporation crucible containing Te isotope powder was placed in a vacuum evaporation deposition apparatus, and a Te isotope target was prepared by evaporation deposition deposition process.

[0006] The thickness of the Te isotope target prepared after a single vapor deposition was measured.

[0007] If the target thickness is lower than the range required by the physical experiment, an appropriate amount of Te isotope powder is added to the evaporation crucible for secondary evaporation deposition; if the target thickness is greater than the range required by the physical experiment, a magnetron sputtering device is used to bombard the excessively thick Te isotope target to reduce the target thickness.

[0008] Furthermore, in a specific embodiment, the method for efficiently preparing Te isotope targets as described above, wherein the distance between the evaporation source and the target substrate in the evaporation deposition coating process is 2.4–2.8 cm, and the evaporation current is 60–70 A.

[0009] Furthermore, the target substrate material for the evaporation deposition coating process is graphite.

[0010] Furthermore, in a specific embodiment, the method for efficiently preparing a Te isotope target as described above, wherein the specific method for bombarding and sputtering an excessively thick Te isotope target using a magnetron sputtering device is as follows: the excessively thick Te isotope target is embedded as part of the magnetron sputtering target within the magnetron sputtering body target, and then the Ar generated by magnetron sputtering is used... + Ions bombard and sputter the embedded target.

[0011] Furthermore, in the magnetron sputtering process, the Ar flow rate, Ar pressure in the vacuum chamber, and sputtering power parameters are fixed in advance, and the relationship between sputtering time and target thickness reduction is calibrated. Then, by controlling the sputtering time, the amount of target thickness reduction that needs to be controlled is indirectly controlled.

[0012] Furthermore, the magnetron sputtering target is made of spectrally pure graphite.

[0013] Furthermore, the Ar flow rate of magnetron sputtering is 2 sccm, the Ar pressure in the vacuum chamber is 0.5 Pa, and the sputtering power supply is 120 W.

[0014] On the other hand, a specific embodiment of the present invention further provides a system for efficiently preparing Te isotope targets to implement the above method, including a vacuum evaporation device and a magnetron sputtering device. The vacuum evaporation device uses an evaporation deposition coating process to prepare Te isotope targets, and the magnetron sputtering device bombards and sputters excessively thick Te isotope targets to reduce the target thickness. An evaporation crucible is provided in the evaporation deposition chamber of the vacuum evaporation device. The evaporation crucible has an inverted frustum-shaped structure, with the diameter of the top opening larger than the diameter of the bottom sealing. Electrodes are provided on both sides of the crucible wall, and a cover with vent holes is provided on the top opening.

[0015] Furthermore, in a specific embodiment, the evaporation crucible is made of high-purity tantalum.

[0016] Furthermore, in a specific embodiment, the cover has multiple air holes, which are evenly distributed on the cover.

[0017] Furthermore, in a specific embodiment, the bottom sealing diameter of the evaporation crucible is 0.8–0.9 mm, and the top opening diameter is 14–16 mm.

[0018] Furthermore, in a specific embodiment, when bombarding an excessively thick Te isotope target with a magnetron sputtering device to reduce the target thickness, the excessively thick Te isotope target is embedded as part of the magnetron sputtering target in the magnetron sputtering body target. The magnetron sputtering body target is a graphite target with a groove adapted to the Te isotope target. The Te isotope target is embedded in the groove, and its surface is pressed by a graphite ring.

[0019] The beneficial effects of this invention are as follows: This invention combines evaporation deposition coating process with magnetron sputtering process to prepare Te isotope targets, which can efficiently and reliably control the thickness of Te isotope targets; through the design of the evaporation crucible structure, the utilization efficiency of expensive Te isotope materials is improved and the coating uniformity is guaranteed. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of a method for efficiently preparing Te isotope targets in a specific embodiment of the present invention;

[0022] Figure 2 This is a front view of the evaporation crucible in a specific embodiment of the present invention;

[0023] Figure 3 This is a top view of the evaporation crucible in a specific embodiment of the present invention;

[0024] Figure 4 This is a perspective view of the evaporation crucible in a specific embodiment of the present invention;

[0025] Figure 5 These are SEM images of Te targets deposited with different evaporation currents in a specific embodiment of the present invention;

[0026] Figure 6This is a schematic diagram of a magnetron sputtering embedded isotope Te target in a specific embodiment of the present invention;

[0027] Figure 7 This is a schematic diagram illustrating the relationship between sputtering time and thickness reduction in a specific embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0030] The terms “comprising”, “including”, etc., as used herein indicate the presence of the steps, features, operations, or components, but do not preclude the addition of one or more other steps, features, operations, or components.

[0031] like Figure 1 As shown, this invention provides a method for efficiently preparing Te isotope targets, comprising:

[0032] An evaporation crucible containing Te isotope powder was placed in a vacuum evaporation deposition apparatus, and a Te isotope target was prepared by evaporation deposition deposition process.

[0033] The thickness of the Te isotope target obtained after a single evaporation deposition is measured. There are usually three results after a single evaporation deposition: the target thickness is exactly within the range required by the physical experiment, the target thickness is less than the range required by the physical experiment, and the target thickness is greater than the range required by the experiment.

[0034] If the target thickness is lower than the range required by the physical experiment, an appropriate amount of Te isotope powder is added to the evaporation crucible for secondary evaporation deposition.

[0035] If the target thickness exceeds the range required by the physical experiment, a magnetron sputtering device is used to bombard and sputter the excessively thick Te isotope target to reduce the target thickness.

[0036] This invention combines evaporation deposition with magnetron sputtering. Evaporation deposition is used to prepare Te isotope targets, while magnetron sputtering is used to control the thickness of the Te isotope targets. The system for preparing Te isotope targets according to this invention should include a vacuum evaporation apparatus and a magnetron sputtering apparatus.

[0037] Because Te isotopes are extremely expensive, they must be used efficiently, and losses during the evaporation deposition coating process must be minimized. Tellurium (Te) has a low melting point (~449°C) but a high vapor pressure and is prone to sublimation, requiring precise temperature control during preparation to avoid violent boiling that could lead to splashing. Nuclear physics experiments demand uniform target film thickness and a smooth surface, which places demands on the geometric design of the evaporation source and the control of evaporation process parameters.

[0038] The evaporation deposition coating process is completed within a vacuum evaporation apparatus, which includes a vacuum system and an evaporation deposition chamber. The vacuum system evaporates the base vacuum of the evaporation deposition chamber to below ~3×10⁻⁶. -4 Pa is used to eliminate oxygen and water vapor, preventing Te oxidation and film fouling. An evaporation source and target liner are set in the evaporation deposition chamber. The evaporation source is an evaporation crucible containing Te isotope powder, and the target liner is a graphite substrate. The evaporation crucible containing Te isotope powder and the prepared substrate are installed in the correct positions in the evaporation deposition chamber.

[0039] The source-substrate distance and the magnitude of the evaporation current are crucial to the formation quality of the coating surface. To improve material deposition efficiency and surface quality, in some specific embodiments, the distance h from the evaporation source to the target substrate is 2.4–2.8 cm, such as 2.4 cm, 2.5 cm, 2.6 cm, 2.7 cm, and 2.8 cm, and the evaporation current I is 60–70 A. If the current is too small, the isotope Te will not evaporate or the deposition rate will be very low; if the current is too large, the isotope Te deposition rate will increase, which can easily lead to the formation of "droplets" or localized defects on the coating surface. Figure 5 The images shown are SEM images of the deposited Te target films at evaporation currents of 65 A and 80 A, respectively. Figure 5 It can be seen from this that when the evaporation current is 65 A ( Figure 5 The SEM image on the left shows a smooth surface with almost no macroscopic droplets; when the evaporation current is 80 A ( Figure 5 (SEM image on the right) shows a large number of macroscopic droplets on the surface. Therefore, the preferred evaporation current I in this invention is 60~70A, which can form a smooth, high-quality Te coating.

[0040] In some specific embodiments, to efficiently prepare uniform Te isotope targets, designs such as Figures 2-4 The inverted frustum-shaped evaporation crucible shown was fabricated using electron beam welding technology. See [link / reference]. Figure 1 The diameter of the top opening 1 of the evaporation crucible is larger than the diameter of the bottom seal 2, and electrodes 3 are fixedly connected to both sides of the crucible wall. See Figure 2 , Figure 3The top opening is provided with a cover 4 with vents 5. The cover 4 has a certain height at the bottom edge, and the diameter is slightly smaller than the diameter of the top opening 1, so it can be directly fastened to the top opening. The bottom sealing diameter of the inverted cone-shaped evaporation crucible designed in this invention is very small (usually less than 1 mm), and the top opening diameter is more than ten times the bottom sealing diameter. There are multiple vents on the cover, and the multiple vents are evenly distributed on the cover. The design of this evaporation crucible structure has the following characteristics: (1) It can make a small amount (mg level) of precious Te isotope powder material always automatically slide to the bottom, so as to improve the utilization efficiency of Te isotope powder; (2) The large opening at the top can make the vapor relatively dispersed during evaporation, so as to ensure the uniformity of coating; (3) A multi-hole cover is added to the top, which can prevent the isotope material from vibrating and popping out of the crucible due to uneven instantaneous heating during evaporation, and can also improve the uniformity of coating.

[0041] In some specific embodiments, the evaporation crucible is made of 0.3 mm thick high-purity Ta (99.99%), the bottom sealing diameter of the inverted frustum-shaped crucible is 0.84 mm, the top opening diameter is 15 mm, the size of the two side electrodes is 15 mm × 6 mm, the top perforated cover has a diameter of 14.5 mm, and 19 small holes with a diameter of 2 mm are drilled on it to form steam outlet holes.

[0042] By precisely controlling the evaporation current applied to the electrodes on both sides of the crucible wall, Te is sublimated / evaporated at a stable and moderate rate and deposited on the graphite substrate. After a single evaporation is completed, the system is cooled to room temperature under vacuum, and then the thickness of the Te isotope target is measured.

[0043] When preparing Te isotope targets by evaporation deposition using the above method, three results usually occur in a single evaporation deposition: (1) The target thickness is exactly within the range required by the physical experiment. This is the most ideal situation. The prepared Te isotope target can be directly delivered for experimental use. (2) The target thickness is lower than the range required by the physical experiment. This situation is also relatively easy to handle. Just add a small amount of appropriate isotope material to the evaporation crucible for secondary evaporation deposition to increase the target thickness to the range required by the experiment before delivery. (3) The target thickness is greater than the range required by the experiment. This is the worst situation. Because isotope materials are expensive and scarce, the thickened target cannot be discarded and remade directly. This would waste money and lead to a shortage of target materials. Therefore, measures can only be taken to reduce the target thickness.

[0044] This invention employs magnetron sputtering technology to control the thickness of excessively thick Te isotope targets. Specifically, it uses a magnetron sputtering device to bombard and sputter the excessively thick Te isotope target, reducing its thickness. In particular, it reverses the magnetron sputtering principle by embedding the thickened Te isotope target as part of the magnetron sputtering target within the main magnetron sputtering target. Then, it utilizes the Ar generated by magnetron sputtering... + Ions bombard the embedded target with sputtering to reduce the target thickness.

[0045] The basic principle of magnetron sputtering is to fill the vacuum chamber of the magnetron sputtering apparatus with a small amount of inert gas (such as argon) and apply a high voltage between the cathode (magnetron sputtering target) and the anode (substrate stage). The gas molecules are ionized, producing positively charged Ar atoms. + Ions. Ar + Ions, accelerated by an electric field, bombard the surface of a cathode magnetron sputtering target at high speed, sputtering target atoms or molecules through momentum transfer. This invention embeds a thickened Te isotope target as part of the magnetron sputtering target within the magnetron sputtering body target, and Ar... + When ions bombard the surface of a magnetron sputtering target at high speed, the coating on the Te isotope target surface becomes thinner, thereby achieving control over the target thickness.

[0046] This process requires pre-fixing parameters such as Ar flow rate, Ar pressure in the vacuum chamber, and sputtering power supply for magnetron sputtering, calibrating the relationship between sputtering time and target thickness reduction, and then indirectly controlling the amount of target thickness reduction by controlling the sputtering time.

[0047] Figure 6 This is a schematic diagram of embedding a Te isotope target in magnetron sputtering. An excessively thick Te isotope target is embedded as part of the magnetron sputtering target in the magnetron sputtering body target. The magnetron sputtering body target is a graphite target with a groove adapted to the Te isotope target. The Te isotope target is embedded in the groove and its surface is pressed by a graphite ring.

[0048] The magnetron sputtering target body material is spectrally pure graphite (99.99%). The reasons for choosing graphite are: (1) high-purity graphite is inexpensive and easy to process; (2) graphite has a small atomic number and is mostly used as a substrate material for isotope nuclear reaction targets, with little interference to the host nuclear reaction; (3) the sputtering rate of graphite is much lower than that of Te material, and the contamination of the isotope Te target is small during the process of sputtering to reduce the thickness of the isotope Te target.

[0049] Figure 7 This describes the relationship between sputtering time and the reduction in Te target thickness in a specific implementation of a magnetron sputtering process (RF sputtering power of 120 W, Ar flow rate of 2 sccm, and Ar pressure in the vacuum chamber of 0.5 Pa). From... Figure 7As can be seen, under the condition of fixed sputtering parameters, the sputtering time and the thickness reduction are approximately linearly related. By controlling the sputtering time, the amount of thickness reduction that needs to be adjusted can be easily controlled.

[0050] Example

[0051] This embodiment provides a method for efficiently preparing a Te-124 isotope target, including evaporation deposition coating and magnetron sputtering thickness control.

[0052] First, an evaporation crucible containing Te-124 isotope powder was placed in a vacuum evaporation deposition apparatus to prepare a Te isotope target using an evaporation deposition process. In this embodiment, the evaporation crucible was made of 0.3 mm thick high-purity Ta material, with a bottom sealing diameter of 0.84 mm, a top opening diameter of 15 mm, side electrode dimensions of 15 mm × 6 mm, and a top porous cap with a diameter of 14.5 mm. Nineteen small holes with a diameter of 2 mm were drilled on the cap to form vapor vents. The substrate used for the evaporation deposition process was a C substrate with a thickness of 10 μm and a diameter of 20 mm. The evaporation source-substrate distance h was 2.5 cm, and the evaporation current was 65 A. By precisely controlling the evaporation current applied to the electrodes on both sides of the crucible wall, Te was sublimated / evaporated at a stable and moderate rate, depositing a film on the graphite substrate. After a single evaporation deposition, the system was cooled to room temperature under vacuum, and then the thickness of the prepared Te-124 isotope target was measured.

[0053] After evaporation deposition, the thickness of the Te-124 isotope target prepared by a single evaporation deposition was measured. In this embodiment, the thickness of the Te-124 isotope target prepared by the first evaporation deposition was 1.38 mg / cm. 2 This exceeds the 1.0-1.2 mg / cm³ requirement for physical experiments. 2 According to the design method of this invention, a magnetron sputtering device is needed to bombard and sputter an excessively thick Te isotope target to reduce the target thickness. Specifically, a trace amount of inert gas (such as argon) is filled into the vacuum chamber of the magnetron sputtering device, and a high voltage is applied between the cathode (magnetron sputtering target) and the anode (substrate stage). The gas molecules are ionized, generating positively charged Ar... + Ions. Ar + Ions are accelerated by an electric field and bombard the surface of the cathode magnetron sputtering target at high speed, sputtering out the target atoms or molecules through momentum transfer.

[0054] In this embodiment, a thickened Te-124 isotope target is embedded in the magnetron sputtering body target as part of the magnetron sputtering target. The magnetron sputtering body target is a graphite target with grooves adapted to the Te isotope target. The Te isotope target is embedded in the grooves, and its surface is pressed together by a graphite ring.

[0055] Under fixed controlled sputtering process parameters, the relationship between calibrated sputtering time and the thickness reduction of the Te-124 isotope target was investigated. The linear relationship determined in this embodiment is y = 2.99x + 1.45, where x is the sputtering time (minutes) and y is the thickness reduction (μg / cm²). 2 ).

[0056] The magnetron sputtering target, embedded with a Te-124 isotope target, was placed in the vacuum chamber of the magnetron sputtering apparatus. Argon gas was introduced into the vacuum chamber, and the parameters of the magnetron sputtering process were set as follows: RF sputtering power of 120 W, Ar flow rate of 2 sccm, and Ar pressure in the vacuum chamber of 0.5 Pa. Based on the pre-calibrated relationship between sputtering time and thickness reduction, magnetron sputtering was performed for 73 minutes, reducing the thickness of the Te-124 isotope target to 1.16 mg / cm. 2 This meets the requirements of physical experiments.

[0057] The above process method was successfully used to prepare 124 The Te / C target and the Te-124 isotope target thickness are 1.16 mg / cm². 2 With a diameter of 15 mm, the Te-124 material utilization rate reaches 62.6%, and the uniformity is 92.3%.

[0058] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. Thus, the invention also intends to include such variations and adaptations if they fall within the scope of the claims and their equivalents.

[0059] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of protection of the present invention should be defined by the claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A method for efficiently preparing Te isotope targets, characterized in that, include: An evaporation crucible containing Te isotope powder was placed in a vacuum evaporation deposition apparatus, and a Te isotope target was prepared by evaporation deposition deposition process. The thickness of the Te isotope target prepared after a single vapor deposition was measured. If the target thickness is lower than the range required by the physical experiment, an appropriate amount of Te isotope powder is added to the evaporation crucible for secondary evaporation deposition; if the target thickness is greater than the range required by the physical experiment, a magnetron sputtering device is used to bombard the excessively thick Te isotope target to reduce the target thickness.

2. The method for efficiently preparing Te isotope targets as described in claim 1, characterized in that, The distance between the evaporation source and the target substrate in the evaporation deposition coating process is 2.4 to 2.8 cm, and the evaporation current is 60 to 70 A.

3. The method for efficiently preparing Te isotope targets as described in claim 1, characterized in that, The target substrate material for the evaporation deposition coating process is graphite.

4. The method for efficiently preparing Te isotope targets as described in claim 1, characterized in that, The specific method for bombarding and sputtering an excessively thick Te isotope target using a magnetron sputtering device is as follows: the excessively thick Te isotope target is embedded as part of the magnetron sputtering target within the magnetron sputtering body target, and then the Ar generated by magnetron sputtering is used... + Ions bombard and sputter the embedded target.

5. The method for efficiently preparing Te isotope targets as described in claim 4, characterized in that, In the magnetron sputtering process, the Ar flow rate, Ar pressure in the vacuum chamber, and sputtering power parameters are fixed in advance. The relationship between sputtering time and target thickness reduction is calibrated. Then, by controlling the sputtering time, the amount of target thickness reduction that needs to be controlled is indirectly controlled.

6. The method for efficiently preparing Te isotope targets as described in claim 4, characterized in that, The magnetron sputtering target is made of spectrally pure graphite.

7. The method for efficiently preparing Te isotope targets as described in claim 5, characterized in that, The Ar flow rate for magnetron sputtering is 2 sccm, the Ar pressure in the vacuum chamber is 0.5 Pa, and the sputtering power supply is 120 W.

8. A system for efficiently preparing a Te isotope target using the method described in any one of claims 1-7, characterized in that, The device includes a vacuum evaporation deposition apparatus and a magnetron sputtering apparatus. The vacuum evaporation deposition apparatus uses an evaporation deposition coating process to prepare a Te isotope target. The magnetron sputtering apparatus bombards and sputters an excessively thick Te isotope target to reduce the target thickness. An evaporation crucible is set in the evaporation deposition chamber of the vacuum evaporation deposition apparatus. The evaporation crucible has an inverted frustum-shaped structure with a top opening diameter larger than the bottom sealing diameter. Electrodes are provided on both sides of the crucible wall, and a cover with vent holes is provided on the top opening.

9. The system for efficiently preparing Te isotope targets as described in claim 8, characterized in that, The evaporation crucible is made of high-purity tantalum.

10. The system for efficiently preparing Te isotope targets as described in claim 8, characterized in that, The cover has multiple air holes, which are evenly distributed on the cover.

11. The system for efficiently preparing Te isotope targets as described in claim 8, characterized in that, The bottom sealing diameter of the evaporation crucible is 0.8-0.9 mm, and the top opening diameter is 14-16 mm.

12. The system for efficiently preparing Te isotope targets as described in claim 8, characterized in that, When bombarding an excessively thick Te isotope target with a magnetron sputtering device to reduce the target thickness, the excessively thick Te isotope target is embedded as part of the magnetron sputtering target in the magnetron sputtering body target. The magnetron sputtering body target is a graphite target with a groove adapted to the Te isotope target. The Te isotope target is embedded in the groove and its surface is pressed by a graphite ring.

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