System for trace krypton measurement in high purity xenon and method thereof

Abstract

The application discloses a system and method for measuring trace krypton in high-purity xenon, and belongs to the technical field of rare gas purification analysis and mass spectrometry, and solves the problem that a commercial residual gas analyzer cannot directly detect ppt-level krypton impurities in high-purity xenon due to insufficient sensitivity. The application firstly removes impurity gas by an active impurity removal unit, then captures and retains krypton at low temperature by a cold head thermal coupling pre-enrichment unit, and performs primary enrichment of krypton by utilizing the distribution difference of krypton in gas-liquid xenon, and then most of xenon gas is intercepted by condensation or freezing by a cold trap enrichment unit, and secondary enrichment of krypton is performed, so that the signal ratio of krypton to xenon in the sample entering the residual gas analyzer is greatly improved, and the originally undetectable ppt-level trace krypton by the commercial residual gas analyzer can be effectively distinguished and quantitatively measured.

Description

Technical Field

[0001] This invention relates to the field of rare gas purification analysis and mass spectrometry measurement technology, specifically to a system and method for measuring trace krypton in high-purity xenon. Background Technology

[0002] Commercial xenon often contains 10 -9 mol / mol ppb) to 10 -6 Krypton at the mol / mol (ppm) level is crucial for liquid xenon particle detectors using xenon as the target material. Kr-85, a long-lived β-decay nuclide, contributes to the electron recoil background, requiring trace background measurements. Krypton impurities need to be measured to the ppt level or even lower. Meanwhile, with the rapid development of the semiconductor and electronics industry, ultra-high purity electronic gases, as important factors affecting the reliability and yield of electronic devices, have received widespread international attention. Ultra-high purity electronic gases mainly include more than thirty types, such as high-purity xenon (Xe), high-purity krypton (Kr), high-purity ammonia (NH3), high-purity silanes (SiH4), high-purity dichlorosilane (DCS), high-purity trichlorosilane (TCS), high-purity alkane electronic gases (arsine, phosphine, diborane), and high-purity hydrocarbon gases (propylene, acetylene). These are indispensable raw materials for the production of ultra-large-scale integrated circuits, flat panel displays, semiconductor devices, solar cells, and optical fibers, and are mainly used in thin film, etching, doping, vapor deposition, and diffusion processes. The purity requirement for special electronic gases is generally 5N~6N (i.e., 99.999%~99.9999%) or higher, and the concentration of harmful gaseous impurities needs to be controlled below 10%. -9 Level. With the upgrading and replacement of consumer electronics, the requirements for product manufacturing precision are becoming increasingly higher, and the control of product yield and defects is becoming increasingly stringent. The entire electronics industry has increasingly stringent requirements for the purity of electronic gas sources and the prevention of secondary contamination in the delivery system. In the more advanced 28nm and currently leading international 6nm~10nm integrated circuit manufacturing processes, the purity requirements for electronic specialty gases are even higher, with impurity concentration requirements even reaching 10. -12 Level, so krypton impurities also need to be measured in ppt (10 -12 Even lower orders of magnitude.

[0003] However, the direct detection sensitivity of existing commercial residual gas analyzers is typically around 1×10⁻⁶. -6 The mol / mol ratio makes it impossible to directly measure 1×10⁻⁶ mol in high-purity xenon. -12 Krypton on the order of mol / mol. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a system and method for measuring trace krypton in high-purity xenon, which solves the problem that commercial residual gas analyzers cannot directly detect ppt-level krypton impurities in high-purity xenon due to insufficient sensitivity.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: On one hand, a system for measuring trace krypton in high-purity xenon is provided, comprising: an active impurity removal unit, which includes a gas purifier for removing gaseous impurities from xenon; a cold-head thermal coupling pre-enrichment unit, which includes a pre-enricher for enriching krypton in xenon, the pre-enricher including a cold source supply chamber and a cold-head enrichment chamber with thermal contact via a cold guide, the cold-head enrichment chamber having a temperature-controlled heater connected to a host computer inside, one side of the cold-head enrichment chamber being connected to the gas purifier via a feed line with an injection valve, and the other side of the cold-head enrichment chamber being connected to a first vacuum pump via an outlet line; a cold trap enrichment unit, which includes a cold trap connected to the feed line and used for condensing xenon; and a mass spectrometry analysis unit, which includes a residual gas analyzer for measuring krypton concentration, the residual gas analyzer being connected to the cold trap and a second vacuum pump via an inlet pipe.

[0006] In this scheme, an active impurity removal unit first removes impurity gases such as nitrogen and oxygen that interfere with subsequent analysis. Then, a cold-head thermal coupling pre-enrichment unit traps and retains krypton at low temperature, utilizing the difference in krypton distribution in gaseous and liquid xenon for primary enrichment. Subsequently, a cold trap enrichment unit traps most of the xenon gas through condensation or freezing, performing secondary enrichment of krypton. This significantly improves the signal ratio of krypton to xenon in the sample entering the residual gas analyzer. Through the orderly combination of multi-stage enrichment units, this system enables the effective resolution and quantitative measurement of ppt-level trace krypton, which was previously undetectable by commercial residual gas analyzers. This solves the problem that commercial residual gas analyzers or mass spectrometers cannot directly detect ppt-level krypton impurities in high-purity xenon due to insufficient sensitivity and xenon matrix interference.

[0007] Furthermore, the inlet and outlet of the gas purifier are connected to the xenon gas source and the gas purification outlet pipe, respectively. The gas purification outlet pipe is equipped with an inlet valve and is connected to the feed line. By placing the gas purifier upstream of the sample inlet pipe, the xenon gas to be tested must be purified before entering the cold head enrichment chamber. This arrangement ensures that the xenon gas entering the system does not contain light impurities such as moisture, oxygen, and nitrogen, preventing these impurities from condensing in the subsequent cold trap, causing pipe blockage or interfering with the krypton mass spectrometry signal. It also ensures the purity of the xenon liquefaction process during the cold head pre-enrichment step, thereby improving the system's operational stability and measurement accuracy.

[0008] Furthermore, a temperature sensor is installed inside the temperature-controlled heater. This sensor allows the heater to sense and report the actual temperature inside the cold head enrichment cavity in real time, forming a closed-loop control circuit with the host computer to achieve precise PID regulation of the cold head enrichment cavity temperature.

[0009] Furthermore, a first pressure sensor is installed on the discharge pipe; a second pressure sensor is installed at the connection between the feed pipe and the cold trap; and a third pressure sensor is installed on the inlet pipe of the residual gas analyzer.

[0010] Furthermore, the first vacuum pump and the second vacuum pump are respectively equipped with a first vacuum valve and a second vacuum valve.

[0011] On the other hand, a method for measuring trace krypton in high-purity xenon is provided, comprising the steps of: S100, Adjust the total effective enrichment response parameter of the system. This makes it greater than the sensitivity of the mass spectrometry analysis unit. The target detection limit of the xenon gas to be tested The ratio; S200. The xenon gas to be tested is passed into a gas purifier for purification to remove gaseous impurities from the xenon gas. S300: The cold head enrichment chamber is cooled to a preset temperature by supplying a cold source to the chamber and the cold finger. The purified xenon gas is introduced into the cold head enrichment chamber through the feed pipe to partially liquefy the xenon gas for krypton enrichment. S400, close the injection valve and turn on the first vacuum pump to extract the gas in the cold head enrichment chamber through the discharge pipeline; S500: Close the discharge pipeline, open the injection valve, and heat the cold head enrichment chamber through the temperature-controlled heater to vaporize the liquefied enriched gas and release it into the cold trap. S600: A portion of the xenon gas in the gas is enriched by condensation in a cold trap, and the gas flowing out of the cold trap is introduced into a residual gas analyzer for analysis to obtain the concentration of krypton in the xenon gas.

[0012] In this scheme, step S300 utilizes the difference in krypton distribution between the gas and liquid phases of xenon at low temperature, causing krypton to preferentially accumulate in the liquid phase xenon in a dissolved state, achieving first-stage enrichment independent of adsorption materials. Step S400, by closing the sample injection valve and then pumping out the sample, cleverly utilizes the saturated vapor pressure of the liquid phase xenon as a self-protection mechanism, effectively removing light impurities such as nitrogen and oxygen while retaining the liquid phase xenon and its dissolved krypton, avoiding the loss of the enriched target. Step S500, through temperature-controlled heating, completely evaporates the liquid phase xenon, releasing the krypton-enriched gaseous sample in a concentrated manner within a narrow time window. Step S600, by condensing most of the xenon gas in a cold trap, further reduces the xenon partial pressure, allowing the krypton / xenon signal ratio entering the residual gas analyzer to be amplified in multiple stages to a range resolvable by commercial mass spectrometers. This method transforms the physical enrichment principle into an operable and reproducible standardized process, achieving a complete closed loop from the original sample to the analytical results.

[0013] Furthermore, adjust the overall effective enriched response parameters of the system. The methods include: S110. Adjust the cold head enrichment factor of the cold head thermal coupling pre-enrichment unit respectively. Cold trap impedance-release matching number of cold trap enrichment cells ; S120, Judgment Is it greater than or equal to? If so, then complete. Adjust accordingly; otherwise, return to S110.

[0014] By introducing the total effective enrichment response parameter Pre-enrichment factor of cold head and cold trap impedance-release matching number The product of these two parameters serves as a quantitative representation of the overall enhancement factor in the krypton concentration detection capability of the residual gas analyzer. This allows for the quantification and optimization of the functional contributions of each of the two enrichment units, while simultaneously forming a unified system-level performance criterion through their product. This parameter transforms the originally qualitative concept of "good enrichment effect" into a calculable and calibrable engineering indicator, providing a unified mathematical basis for the design of system hardware parameters, the selection of operating points, and the quantitative traceability of measurement results.

[0015] Further adjustments The methods include: S111, Calculate the cold head enrichment gas phase retention matching number Its expression is: ; ; in, The gas-liquid distribution ratio, and At the preset temperature Below, the molar concentration of krypton in gaseous xenon and the molar concentration of krypton in liquid xenon; To enrich the gas phase retention matching number in the cold head; To balance the pressure within the cold head enrichment cavity; The volume of the cold head enrichment cavity; Liquid occupancy factor; To achieve the preset temperature Below, the molar volume of liquid xenon; The molar gas constant; The total molar amount of xenon in the cold head enrichment cavity; S112, Judgment Is it less than or equal to the preset threshold? If so, then the calculation is as follows: Otherwise, proceed to step S113; S113, Decrease or or increase Then return to step S111.

[0016] Depend on As can be seen from the expression, in , , and Given, decrease It will decrease ,improve Therefore, the cold head enrichment cavity in this scheme is not aimed at increasing the gas phase retention volume, but rather at "low..." The reverse design was carried out with the goal of "high liquid content and controllable release".

[0017] Further adjustments The methods include: S1101, Calculation Its expression is: ; ; ; ; in, To improve the effective pass rate of Krypton; To limit the release window response factor; The duration for the enriched gas to be released from the cold head enrichment cavity into the cold trap; The cold trap response time constant; The flow resistance between the cold trap outlet and the residual gas analyzer inlet; The flow rate of xenon gas released into the cold trap as enriched gas; This is the impedance-pumping speed matching constant; This is the effective pumping speed of the second vacuum pump; This refers to the partial pressure of xenon gas at the inlet of the residual gas analyzer. This is the total gas volume of all internal interconnected spaces between the cold trap outlet and the residual gas analyzer inlet; S1102, Judgment Is it greater than or equal to? If so, then complete. Adjustments are required; otherwise, proceed to step S1103. S1103, Increase , or Then return to step S1101.

[0018] Define cold trap impedance - release matching number This parameter characterizes the overall amplification capability of hardware parameters for the net krypton peak area under given sample volume and mass spectrometry conditions. It incorporates the cold head pre-enrichment factor, post-cold trap selective throughput, xenon flow rate, flow resistance, and finite-time response into a single optimization criterion, serving as the basis for setting valve opening, cold trap xenon ice volume, measurement flow rate, and integration window. The calculations enable the operation of the cold trap to go beyond simple temperature selection, allowing it to operate within a multi-dimensional parameter space of flow rate, flow resistance, and response time, according to... The optimization direction is maximized to systematically determine the matching operating point.

[0019] Furthermore, the formula for calculating the krypton concentration in the xenon gas to be measured is as follows: ;in, The concentration of krypton in the xenon gas to be tested. For response coefficients; The net integral area of ​​the krypton peak measured by the residual gas analyzer. The net integral area of ​​the krypton peak after subtracting the blank from the mass spectrometry measured signal of the residual gas analyzer was established. ), to the target amount (krypton concentration in the xenon gas to be measured) The quantitative conversion relationship between them indicates that the total effective enriched response parameter is directly related to the measurement results. and the overall response coefficient calibrated from the standard sample Instead of any single internal process quantity, the system is calibrated using standard Kr / Xe samples in a single step. This allows all the complex enrichment, transport, and response factors to be packaged into calibrable coefficients, avoiding the tedious procedure of individually calibrating each intermediate physical quantity in each measurement. This enables traceable quantitative analysis from the peak area measured by mass spectrometry to the krypton concentration in the original sample. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system used for measuring trace krypton in high-purity xenon; Figure 2 This is a schematic diagram of the pre-enrichment device; Figure 3 This is a schematic diagram showing how the enrichment factor of the cold head varies with the injection mass and the volume of the enrichment chamber; The components are as follows: 101, Gas purifier; 102, Inlet valve; 103, Sample inlet valve; 104, Pre-enricher; 105, First pressure sensor; 106, First vacuum valve; 107, First vacuum pump; 108, Second pressure sensor; 109, Flow controller; 110, Cold trap; 111, Third pressure sensor; 112, Residual gas analyzer; 113, Second vacuum valve; 114, Second vacuum pump; 201, Cold source supply chamber; 202, Feed pipeline; 203, Temperature-controlled heater; 204, Cold head enrichment chamber; 205, Cold finger; 206, Discharge pipeline. Detailed Implementation

[0021] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0022] Example 1

[0023] refer to Figure 1 This embodiment provides a system for measuring trace krypton in high-purity xenon, applicable to the measurement of krypton impurities at the 10⁻¹² mol / mol (ppt) level in ultra-high-purity xenon gas for electronic etching, liquid xenon dark matter detectors, low-background neutrino detectors, and related high-purity xenon circulation systems. The method is based on cold-head pre-enrichment and multi-stage enrichment techniques. Trace krypton in the xenon sample is enriched in a pre-enrichment chamber and released into krypton-concentrated xenon gas through valve isolation, vacuuming, and temperature control. This gas then enters a post-cold trap 110, where the xenon gas condenses or freezes to further improve the krypton / xenon signal ratio. Finally, a residual gas analyzer 112 or a mass spectrometer is used for quantitative measurement of partial pressure area. This approach avoids reliance on a general-purpose cold trap 110, activated carbon adsorption, or radioactive counting methods, enabling more sensitive and calibrable measurements of extremely low concentrations of krypton impurities in high-purity xenon. Theoretically, it is possible to increase the original krypton concentration to the level of 1×10⁻¹² mol / mol to the range recognizable by mass spectrometers; in practice, the linearity and limiting sensitivity of approximately 1 ppt can be verified by preparing standard samples using the expansion method. A detailed demonstration follows.

[0024] refer to Figure 1 A system for measuring trace krypton in high-purity xenon includes an active impurity removal unit, a cold head thermal coupling pre-enrichment unit, a cold trap enrichment unit, and a mass spectrometry analysis unit.

[0025] An active impurity removal unit is used to remove nitrogen, hydrogen, and oxygen gas impurities. It includes a gas purifier 101. The inlet and outlet of the gas purifier 101 are connected to a xenon gas source and a gas purification outlet pipe, respectively. An inlet valve 102 is provided on the gas purification outlet pipe and is connected to the feed pipe 202.

[0026] The cold-head thermally coupled pre-enrichment unit is used to capture or retain krypton within the pre-enrichment chamber by cooling it to a preset low temperature, while simultaneously reducing the load of xenon and its impurities on subsequent mass spectrometry through valve switching and vacuuming; Reference Figure 2 The cold head thermal coupling pre-enrichment unit includes a pre-enricher 104. The pre-enricher 104 includes a cold source supply chamber 201 and a cold head enrichment chamber 204 that are in thermal contact with each other through a cold finger 205. The cold head enrichment chamber 204 is equipped with a temperature-controlled heater 203 that is connected to a host computer. One side of the cold head enrichment chamber 204 is connected to the gas purifier 101 through a feed pipe 202 equipped with a sample inlet valve 103. The other side of the cold head enrichment chamber 204 is connected to the first vacuum pump 107 through a discharge pipe 206.

[0027] In this embodiment, the pre-enrichment cavity is a metal cavity, preferably with a stainless steel lining structure; the pre-enrichment cavity and the cold end of the cold head are thermally coupled through a copper thermal bridge and an indium sheet, and the temperature of the cold end of the cold head is preferably controlled within the range of 165-190 K. The cold source supply cavity 201 is a liquid nitrogen cavity.

[0028] In this embodiment, a temperature sensor is installed inside the temperature-controlled heater 203, enabling the heater 203 to sense and provide feedback on the actual temperature inside the cold head enrichment cavity 204 in real time. This forms a closed-loop control circuit with the host computer, achieving precise PID regulation of the temperature of the cold head enrichment cavity 204. The temperature-controlled heater 203 is used to control and raise the temperature of the cold head enrichment cavity 204 or pulse-heat it during the release phase, allowing the krypton-enriched sample to be released into the post-cold trap enrichment unit within a narrow time window.

[0029] The cold trap enrichment unit is used to reduce the partial pressure of xenon at the mass spectrometer inlet by condensing or freezing xenon, thereby increasing the krypton / xenon signal ratio measured by the mass spectrometer and improving the krypton measurement sensitivity through multi-stage enrichment. It includes a cold trap 110 connected to the feed line 202 and used for condensing xenon gas.

[0030] In this embodiment, the cold trap 110 is sock-shaped or U-shaped and made of stainless steel. The operating temperature of the cold trap 110 is set to allow xenon to condense or freeze within the cold trap 110 while krypton is retained and can be released or permeated. This is preferably achieved through a liquid nitrogen bath, a mechanical cold head, or a combination of both. The cold head pre-enrichment unit operates in a "capture-isolation-extraction-release" sequence: first, a large volume xenon sample is received and krypton is enriched at low temperature; then, the sample inlet valve 103 is closed to isolate the sample end, and the evacuation valve is opened to remove uncaptured xenon and other gaseous impurities from the subsequent measurement pipeline; then, the evacuation valve is closed and the release valve is opened, allowing the sample to enter the post-cold trap 110. After xenon freezing and retention and relative enrichment of krypton, the sample is finally quantitatively determined by the residual gas analyzer 112 or a mass spectrometer based on the partial pressure and integral area during the plateau period.

[0031] The mass spectrometry analysis unit is used to collect and analyze the partial pressures of each component in the gas sample flowing out of the cold trap 110. It includes a residual gas analyzer 112, which is connected to the cold trap 110 and the second vacuum pump 114 through an inlet pipe.

[0032] As a further embodiment, a first pressure sensor 105 is installed on the discharge pipe 206; a second pressure sensor 108 is installed at the connection between the feed pipe 202 and the cold trap 110; and a third pressure sensor 111 is installed on the inlet pipe of the residual gas analyzer 112. The first pressure sensor 105 can monitor the pressure changes in the cold head enrichment chamber 204 during the collection, extraction, and release stages, providing a basis for determining whether the sample injection volume meets the standard, whether the extraction endpoint has been reached, and whether the release process is normal. The second pressure sensor 108 can monitor the pressure of the enriched gas before it enters the cold trap 110, providing a reference for flow control and judging the working status of the cold trap 110. The third pressure sensor 111 can monitor the total pressure at the mass spectrometer inlet in real time, ensuring that it does not exceed the safe operating limit of the residual gas analyzer 112.

[0033] The first vacuum pump 107 and the second vacuum pump 114 are respectively equipped with a first vacuum valve 106 and a second vacuum valve 113. The first vacuum valve 106 and the second vacuum valve 113 enable the pumping operation of the cold head enrichment cavity 204 and the high vacuum maintenance of the mass spectrometry analysis unit to be carried out completely independently without interference.

[0034] The working principle of this embodiment is as follows: First, the active impurity removal unit removes impurity gases such as nitrogen and oxygen that interfere with subsequent analysis. Then, the cold-head thermal coupling pre-enrichment unit traps and retains krypton at low temperature, utilizing the distribution difference of krypton in gaseous and liquid xenon for primary enrichment. Subsequently, the cold trap enrichment unit retains most of the xenon gas through condensation or freezing, performing secondary enrichment of krypton. This significantly improves the signal ratio of krypton to xenon in the sample entering the residual gas analyzer 112. Through the orderly combination of multi-stage enrichment units, this system enables the effective resolution and quantitative measurement of ppt-level trace krypton, which was originally undetectable by the commercial residual gas analyzer 112. This solves the problem that commercial residual gas analyzers 112 or mass spectrometers cannot directly detect ppt-level krypton impurities in high-purity xenon due to insufficient sensitivity and xenon matrix interference.

[0035] Specifically, the system is first evacuated and baked until the system background meets the requirements. Then, a high-purity xenon sample is fed into the cold head enrichment chamber 204 through the feed line 202. The cold head enrichment chamber 204 is maintained at a set temperature by a temperature sensor and a temperature-controlled heater 203, causing krypton to be captured or retained at low temperature. After processing a sufficient volume of xenon sample, the sample inlet valve 103 is closed and the first vacuum valve is opened. The first vacuum pump 107 is used to evacuate any uncaptured xenon gas and light impurities. After evacuation, the first vacuum valve is closed, and the feed valve to the cold trap 110 is opened. The xenon gas enriched after krypton distillation is then controlled by the flow controller 109 before entering the cold trap 110.

[0036] Specifically, the cold trap 110 is maintained at a temperature range that significantly reduces the partial pressure of xenon. This temperature allows most of the xenon to condense or freeze within the cold trap 110, while krypton, under these partial pressure and temperature conditions, has sufficient throughput to be captured almost entirely as a gas by the residual gas analyzer 112. The residual gas analyzer 112 requires operation in a vacuum below 10⁻³ Pa, so a second vacuum pump 114 needs to be connected to the back end, and the second vacuum valve 113 needs to be opened. The residual gas analyzer 112 can also be replaced by a mass spectrometer, used to record the time curves of the krypton characteristic peak and the xenon characteristic peak, integrate the krypton peak area within the selected release window, and subtract the blank run to obtain the net integrated area of ​​the krypton peak. The net integrated area of ​​the krypton peak refers to the area under the krypton peak integrated on the time-signal curve recorded by the residual gas analyzer 112 or the mass spectrometer, then subtracting the background area obtained under the same conditions using a zero-krypton blank sample. The remaining net area comes only from the krypton in the sample and is the direct input for calculating the original krypton concentration.

[0037] The beneficial effects of this scheme are as follows: the effective identification limit of the residual gas analyzer 112 is about 1×10-6 mol / mol, and when the total enrichment factor of the cold head thermal coupling pre-enrichment unit and the cold trap enrichment unit reaches 1×105-1×106, the measurement limit of krypton concentration in the original xenon sample reaches the order of 1×10-11~1×10-12 mol / mol; verified by krypton xenon standard samples prepared by the expansion method, this system still maintains linear response and resolvable measurement at the order of about 1 ppt (1×10-12 mol / mol).

[0038] Example 2

[0039] This embodiment further defines Embodiment 1 and aims to provide a method for using a system for measuring trace krypton in high-purity xenon. It does not rely on a radioactive counter to measure krypton-85 activity, but rather estimates or constrains the krypton-85 content in xenon through cold head pre-enrichment, cold trap enrichment, and mass spectrometry partial pressure quantification of natural krypton in high-purity xenon. Other parts not mentioned refer to Embodiment 1 or the prior art.

[0040] A method of using a system for measuring trace krypton in high-purity xenon, comprising the steps of: S100, Adjust the total effective enrichment response parameter of the system. This makes it greater than the sensitivity of the mass spectrometry analysis unit. The target detection limit of the xenon gas to be tested The ratio; S200. The xenon gas to be tested is passed into the gas purifier 101 for purification to remove gaseous impurities from the xenon gas.

[0041] S300, the cold head enrichment chamber 204 is cooled to a preset temperature by the cold source supply chamber 201 and the cold finger 205, and the purified xenon gas is introduced into the cold head enrichment chamber 204 through the feed pipe 202 to partially liquefy the xenon gas for krypton enrichment.

[0042] S400, close the injection valve 103, turn on the first vacuum pump 107, and pump out the gas in the cold head enrichment chamber 204 through the discharge pipeline 206.

[0043] S500: Close the discharge pipe 206 passage, open the injection valve 103, and heat the cold head enrichment chamber 204 through the temperature control heater 203 to vaporize the liquefied enrichment gas and release it into the cold trap 110.

[0044] S600: A portion of the xenon gas in the gas is condensed and enriched using a cold trap 110, and the gas flowing out of the cold trap 110 is introduced into a residual gas analyzer 112 for analysis to obtain the concentration of krypton in the xenon gas.

[0045] As a further embodiment, the total effective enrichment response parameter of the system is adjusted. The methods include: S110. Adjust the cold head enrichment factor of the cold head thermal coupling pre-enrichment unit respectively. Cold trap impedance-release matching number of cold trap enrichment cells ; S120, Judgment Is it greater than or equal to? If so, then complete. Adjust accordingly; otherwise, return to S110.

[0046] Adjustment The method is as follows: S111, Calculate the cold head enrichment gas phase retention matching number Its expression is: ; ; Among them, among them, The gas-liquid distribution ratio, and At the preset temperature Below, the molar concentration of krypton in gaseous xenon and the molar concentration of krypton in liquid xenon; The gas phase retention matching number for cold head enrichment is used to quantify the dilution effect of the amount of xenon retained in the gas phase after gas-liquid two-phase equilibrium on the enrichment effect. The equilibrium pressure within the cold head enrichment cavity 204 is approximately equal to the preset temperature after the extraction is completed in step S300. The saturated vapor pressure of xenon; The volume of the cold head enrichment cavity 204 is the total volume inside the cold head enrichment cavity 204 that can be occupied by gas and liquid. The liquid occupancy factor indicates the liquid occupancy at a preset temperature. and balancing pressure The equivalent relationship between the volume occupied by one mole of gaseous xenon and the volume occupied by one mole of liquid xenon is used to correct the influence of the volume occupied by liquid xenon on the effective gas phase space. To achieve the preset temperature Below, the molar volume of liquid xenon; The molar gas constant; The total molar amount of xenon in the cold head enrichment cavity 204.

[0047] S112, Judgment Is it less than or equal to the preset threshold? If so, then the calculation is as follows: Otherwise, proceed to step S113; S113, Decrease or or increase Then return to step S111.

[0048] Adjustment The methods include: S1101, Calculation Its expression is: ; ; ; ; in, The effective krypton throughput represents the proportion (dimensionless, ranging from 0 to 1) of krypton atoms that ultimately reach the residual gas analyzer from the krypton atoms entering the cold trap. This value is determined by measuring standard krypton-xenon samples at different xenon flow rates. and xenon ice volume The fitting model in this embodiment can be determined by scanning measurement under certain conditions and then fitting the model. ,in , , , All of these are fitting parameters.

[0049] To limit the release window response factor; The duration for the enriched gas to be released from the cold head enrichment cavity 204 into the cold trap; The cold trap response time constant; The flow resistance between the cold trap outlet and the residual gas analyzer inlet; The flow rate of xenon gas released into the cold trap as enriched gas; This is the impedance-pumping speed matching constant; This is the effective pumping speed of the second vacuum pump; This refers to the partial pressure of xenon gas at the inlet of the residual gas analyzer. This refers to the total gas volume of all internal interconnected spaces between the cold trap outlet and the residual gas analyzer inlet.

[0050] S1102, Judgment Is it greater than or equal to? If so, then complete. Adjustments are required; otherwise, proceed to step S1103. S1103, Increase , or Then return to step S1101.

[0051] As a further embodiment, the formula for calculating the krypton concentration in the xenon gas to be measured is as follows: ; in, The concentration of krypton in the xenon gas to be tested. For response coefficients; The net integral area of ​​the krypton peak as measured by the residual gas analyzer.

[0052] To better understand the calculation expression, this embodiment provides a detailed derivation process: The core function of the cold head enrichment cavity 204 is to utilize the difference in the distribution of krypton in the gas-liquid two-phase xenon to give the gas phase sample that subsequently enters the cold trap and mass spectrometer end a higher krypton / xenon ratio; the post-cold trap is mainly used to reduce the partial pressure of xenon so that the mass spectrometer response to the krypton characteristic peak is not overwhelmed by a large amount of xenon matrix.

[0053] After the cold head enrichment chamber 204 is cooled, the xenon sample entering the chamber undergoes a gas-liquid two-phase partitioning. The molar concentration of krypton in the gaseous xenon phase is typically higher than its molar concentration in the liquid xenon phase. If, after equilibrium, the gas phase is primarily released or a portion of the gas phase is preferentially released, the Kr / Xe ratio in the released gas is higher than that of the original xenon sample. The essence of this process is not to increase the number of krypton atoms, but to utilize the difference in gas-liquid partitioning to enrich the krypton relative in the releasable gas phase.

[0054] Let the krypton concentration in the original xenon sample (xenon gas to be tested) be... The total molar amount of xenon entering the cold head enrichment cavity 204 is After equilibrium, the molar amount of xenon in the gas phase is The molar amount of liquid-phase xenon is e Then we have: ; Define the gas-liquid partition ratio of krypton for: ; We obtain this from the krypton conservation principle: ; The first enrichment multiple of the cold head enrichment cavity 204 can be obtained. : ; Therefore, in At a given time, the enrichment effect of the cold head enrichment cavity 204 is determined by the molar amount of xenon retained in the gas phase. Decide. The smaller the value, the closer the krypton concentration in the released gas is to... When the amount of gas phase retention approaches zero, Approaching .

[0055] Existing simplified estimates often use the volume of the cold head enrichment cavity 204. All volumes are considered as gas phase. However, within the cold head enrichment cavity 204, xenon liquefaction will occupy a portion of the volume, so the actual gas phase volume should be... Therefore, this embodiment performs liquid level correction on the cold head enrichment cavity 204.

[0056] Let the molar volume of liquid xenon be The liquid phase occupies a volume of for: ; From the ideal gas approximation and the equilibrium gas phase volume relationship, we can obtain: ; After simplification, the equilibrium gas phase xenon molar amount is obtained after considering the volume occupied by liquid xenon: ; make Then it can be written as: This formula indicates that, at a given temperature and pressure, the effective volume of the cold head enrichment cavity 204 is... The smaller the value, the less xenon remains in the equilibrium gas phase, and the stronger the krypton enrichment effect of the subsequently released gas. However, It cannot be reduced indefinitely; it must meet the engineering constraints of liquid xenon volume, safe gas phase volume, and release channel.

[0057] To make this low-temperature enrichment principle a designable, optimizable, and protection-limitable engineering method, this embodiment defines the cold-head enrichment gas phase retention matching number. : Substitute liquid volume after correction We can obtain: ; Therefore, the enrichment factor of the cold head can be reduced to: in, This represents the enrichment factor of the cold head after considering the volume occupied by liquid xenon. This expression provides clear engineering design guidelines: The smaller the value, the closer the Kr / Xe enrichment factor of the gas released from the cold head enrichment cavity 204 is to the desired value. ; The larger the xenon concentration, the more gaseous xenon will remain, which will dilute the krypton enrichment effect.

[0058] Depend on As can be seen from the expression, in , , and Given, decrease It will decrease ,improve Therefore, the cold head enrichment cavity 204 in this scheme is not aimed at increasing the gas phase retention volume, but rather at "low..." The reverse design was carried out with the goal of "high liquid content and controllable release".

[0059] refer to Figure 3 , Figure 3 This is a schematic diagram showing how the enrichment factor of the cold head varies with the injection mass and the volume of the enrichment chamber. Figure 3 Note: Without causing liquid overfilling, blockage, or uncontrolled release, a smaller volume of the cold head enrichment cavity 204 can reduce the gas phase retention matching number. This makes the enrichment factor closer to the upper limit defined by the gas-liquid partition ratio β. The parameters in the figure are only examples and do not constitute a limitation on the scope of protection.

[0060] Subsequently, after the cold head enrichment chamber 204 increases the Kr / Xe ratio in the released gas, the cold trap further reduces the xenon partial pressure at the mass spectrometer inlet by condensing or freezing xenon, and converts the krypton signal into a partial pressure peak or plateau measurable by the residual gas analyzer. The cold trap is not just a cryogenic container; its effective response depends on the impedance from the cold trap to the mass spectrometer inlet, the effective pump rate on the mass spectrometer side, the cold trap geometry, the xenon ice morphology, and the integration window.

[0061] Under constant cold trap temperature and flow rate, the krypton equilibrium partial pressure at the mass spectrometer end... The expression is: ; in, The effective passage factor for krypton released from the cold trap and reaching the residual gas analyzer; This is the effective pumping speed of the second vacuum pump, i.e., the effective pumping speed on the mass spectrometer side. The flow rate of xenon gas released into the cold trap is used to enrich the gas. If the impedance from the cold trap to the inlet of the residual gas analyzer is Z1, and S is adjusted via a valve... RGA If Z1≈χ, then: ; Cold trap response time Approximately: ; Regarding the release window duration (The plateau of the time during which the enriched gas is released from the cold head enrichment cavity 204 into the cold trap) When the system is not fully established, a finite release window response factor needs to be introduced. : ; Therefore, larger cold trap parameters are not always better: increasing Z1 can improve the equilibrium partial pressure, but it also increases... ;improve It can increase the krypton flux, but excessive flow will change the form of xenon ice and reduce its efficiency. .

[0062] To distinguish cold traps from ordinary cold traps as optimizable and calibrable engineering units, this embodiment defines "cold trap impedance-release matching number". : in, To consider the effective krypton throughput after taking into account cold trap geometry, xenon ice morphology, and high flow entrainment losses. The larger the value, the stronger the effective krypton response achievable per unit residual xenon load. This parameter simultaneously constrains cold trap geometry, flow rate, impedance, pumping speed, and release window, unlike traditional methods that rely solely on cold trap temperature or a single flow rate for adjustment.

[0063] Introducing the cold head enrichment cavity Λ KZ After the cold head enrichment cavity is filled, the krypton peak integral area after deducting the blank area can be written as: Therefore, the total effective enriched response parameters in this embodiment for .

[0064] The optimization goal of the device is to enrich the cold head cavity Π without exceeding the xenon load of the mass spectrometer, without excessively prolonging the response time, and without causing cold trap blockage. total Maximize the enrichment cavity of the cold head.

[0065] Based on the above model, this embodiment proposes a collaborative design criterion for the cold head enrichment cavity and the cold trap, as shown in Table 1.

[0066] Table 1 – Co-design Criteria for Cold Head Enrichment Cavities and Cold Trap As a further aspect of this embodiment, this embodiment also provides a design method for a system for measuring trace krypton in high-purity xenon, including the following steps: S1. Based on the direct sensitivity of the mass spectrometry analysis unit and target detection limit The ratio of the two values ​​determines the required total effective enriched response parameters. The minimum value, and according to Minimum value setting The preset threshold, and the cold trap impedance-release matching number ; S2, according to The effective volume of the pre-enriched cavity is solved by simultaneously solving the preset thresholds. and injection xenon amount The feasible range of values ​​is determined so that the pre-enrichment cavity can meet the safety containment constraints of liquid xenon. It does not exceed the preset threshold; S3, in Under the constraints, such that It reaches its maximum under its constraints.

[0067] Cold trap impedance - release matching number The constraints include: First, the total pressure at the inlet of the residual gas analyzer must be less than the upper limit allowed for normal operation; second, the xenon characteristic signal acquired by the mass spectrometer must not enter the saturation region to ensure that the krypton signal is detected within the linear range; third, the response time constant of the cold trap should be less than or not significantly greater than the measurement integration window duration to avoid excessively wide release peaks due to response lag, thereby causing deviations in peak area integration; fourth, the effective krypton throughput must not be lower than the preset minimum acceptable threshold to prevent significant krypton loss due to excessive flow rates or the formation of excessive xenon ice. Each of these thresholds can be determined through standard sample experiments based on the specific instrument model used and the target sensitivity to be achieved.

[0068] S4. Overall response coefficient of the calibration system using standard krypton-xenon samples with known krypton concentrations. Calculate the krypton concentration in the xenon gas to be tested. .

[0069] As a specific implementation method of this embodiment, firstly, a blank xenon sample with near-zero krypton content is used, and blank curves I of krypton characteristic signal changing over time are acquired and recorded by RGA. Kr,blank (t), and the standard deviation σ of the blank signal. blank Subsequently, measurements were performed using at least two standard krypton-xenon samples with known krypton concentrations under a series of different conditions, including: xenon flow rate into the cold trap, flow resistance between the cold trap outlet and the mass spectrometer inlet, cold trap trap temperature, and the amount of xenon ice formed within the cold trap. For each measurement, the net integrated area of ​​the krypton peak after subtracting the blank and the cold trap response time constant were recorded. Based on these measurement data, the effective throughput of krypton in the cold trap and the cold trap impedance-release matching number were calculated, thus establishing a measurement worksheet or calibration curve indexed by relevant operating parameters. When performing formal measurements on unknown samples, the system operating parameters were set within a pre-selected cold trap impedance-release matching number working interval. The measured signal was integrated using the same integration time window as in the calibration process to obtain the net peak area of ​​krypton, and then the original krypton concentration in the unknown sample was calculated based on the calibration relationship.

[0070] In summary, the beneficial effects of this plan are as follows: 1. This solution effectively solves the problem of insufficient direct sensitivity in commercial residual gas analyzers, which prevents the measurement of ppt-level krypton impurities in high-purity xenon, through a multi-stage, orderly integration of active impurity removal, cold-head thermal coupling pre-enrichment, cold trap enrichment, and mass spectrometry analysis. This technical solution does not rely on radioactive counting or traditional adsorption enrichment methods. Instead, it utilizes the difference in krypton distribution between the gaseous and liquid phases of xenon at low temperatures. First, krypton is efficiently captured and retained in the liquid phase xenon within the cold-head enrichment chamber 204, achieving primary enrichment. Then, combined with the selective condensation or freezing of xenon by the post-cold trap, the partial pressure of xenon entering the mass spectrometer is significantly reduced while allowing krypton to pass through effectively. This elevates the krypton-to-xenon signal ratio to a level clearly distinguishable by commercial instruments. Through the synergistic effect of these two enrichment stages, the system's krypton detection limit can reach 10-1. -12 With a mol / mol scale, the ppt-level krypton peaks that would otherwise be submerged in the xenon matrix can be reliably measured, meeting the stringent detection requirements for trace krypton impurities in ultra-high purity xenon in advanced semiconductor processes, liquid xenon dark matter detectors, and other applications.

[0071] 2. In this scheme, after the sample to be tested enters the cold head enrichment chamber 204 and undergoes low-temperature liquefaction enrichment, the pumping operation is initiated with the injection valve closed. Utilizing the saturated vapor pressure of liquid xenon at a specific temperature as an internal barrier, residual xenon and light impurities such as nitrogen and oxygen in the gas phase are effectively removed, while the dissolved and enriched krypton liquid xenon is firmly retained within the chamber. This avoids the loss of the enriched target that may occur during conventional pumping, ensuring enrichment efficiency and measurement reproducibility. Subsequently, precise temperature control heating rapidly evaporates the liquid xenon, and the enriched krypton is released in a concentrated manner within a time window and sent to the cold trap and mass spectrometry analysis unit. This creates conditions for obtaining high signal-to-noise ratio krypton characteristic peaks and performing accurate integral quantification.

[0072] 3. This scheme does not rely solely on experimental experience for condition exploration. Instead, it defines a series of calculable engineering indicators, such as the cold head enrichment factor, the cold head enrichment gas-phase retention matching number, the cold trap impedance-release matching number, and the total effective enrichment response parameters, incorporating the main physical factors of the enrichment process into a unified mathematical description. This quantitative model provides clear optimization criteria for the selection of key hardware parameters and operating points of the system. For example, the appropriate volume and injection volume of the cold head enrichment cavity 204 can be deduced from the target detection limit, and the flow rate and flow resistance can be matched within the constraint of not exceeding the cold trap response time constant. The system design can precisely coordinate towards reducing gas-phase xenon retention, increasing the liquid ratio, and maximizing the effective krypton response, significantly enhancing the designability and reproducibility of the technical solution.

Claims

1. A system for measuring trace amounts of krypton in high-purity xenon, characterized in that, include: An active impurity removal unit includes a gas purifier (101) for removing gaseous impurities from xenon gas. The cold head thermal coupling pre-enrichment unit includes a pre-enricher (104) for enriching xenon with krypton. The pre-enricher (104) includes a cold source supply chamber (201) and a cold head enrichment chamber (204) that are in thermal contact with a cold finger (205). The cold head enrichment chamber (204) is provided with a temperature-controlled heater (203) connected to a host computer. One side of the cold head enrichment chamber (204) is connected to the gas purifier (101) through a feed pipe (202) equipped with a sample inlet valve (103). The other side of the cold head enrichment chamber (204) is connected to a first vacuum pump (107) through a discharge pipe (206). The cold trap enrichment unit includes a cold trap (110) connected to the feed line (202) and used for condensing xenon gas. The mass spectrometry analysis unit includes a residual gas analyzer (112) for measuring krypton concentration, which is connected to the cold trap (110) and the second vacuum pump (114) via an inlet pipe.

2. The system for measuring trace krypton in high-purity xenon according to claim 1, characterized in that, The gas purifier (101) has an inlet and an outlet connected to a xenon gas source and a gas purification outlet pipe, respectively. The gas purification outlet pipe is equipped with an inlet valve (102) and is connected to the feed pipe (202).

3. The system for measuring trace krypton in high-purity xenon according to claim 1, characterized in that, A temperature sensor is installed inside the temperature-controlled heater (203).

4. The system for measuring trace krypton in high-purity xenon according to claim 1, characterized in that, A first pressure sensor (105) is installed on the discharge pipe (206); a second pressure sensor (108) is installed at the connection between the feed pipe (202) and the cold trap (110); and a third pressure sensor (111) is installed on the inlet pipe of the residual gas analyzer (112).

5. The system for measuring trace krypton in high-purity xenon according to claim 1, characterized in that, The first vacuum pump (107) and the second vacuum pump (114) are respectively equipped with a first vacuum valve (106) and a second vacuum valve (113).

6. The method of using the system for measuring trace krypton in high-purity xenon according to any one of claims 1 to 5, characterized in that, Including the following steps: S100, Adjust the total effective enrichment response parameter of the system. This makes it greater than the sensitivity of the mass spectrometry analysis unit. The target detection limit of the xenon gas to be tested The ratio; S200. The xenon gas to be tested is passed into the gas purifier (101) for purification to remove gaseous impurities from the xenon gas. S300, the cold head enrichment chamber (204) is cooled to a preset temperature by the cold source supply chamber (201) and the cold finger (205), and the purified xenon gas is introduced into the cold head enrichment chamber (204) through the feed pipe (202) to partially liquefy the xenon gas for krypton enrichment. S400, close the injection valve (103), turn on the first vacuum pump (107), and pump out the gas in the cold head enrichment chamber (204) through the discharge pipeline (206); S500, close the discharge pipeline (206) passage, open the injection valve (103), heat the cold head enrichment chamber (204) through the temperature control heating (203), vaporize the liquefied enrichment gas and release it into the cold trap (110); S600. A portion of the xenon gas in the gas is condensed and enriched using a cold trap (110), and the gas flowing out of the cold trap (110) is introduced into the residual gas analyzer (112) for analysis to obtain the concentration of krypton in the xenon gas.

7. The method according to claim 6, characterized in that, Adjusting the total effective enrichment response parameters of the system The methods include: S110. Adjust the cold head enrichment factor of the cold head thermal coupling pre-enrichment unit respectively. Cold trap impedance-release matching number of cold trap enrichment cells ; S120, Judgment Is it greater than or equal to? If so, then complete. Adjust accordingly; otherwise, return to S110.

8. The method according to claim 7, characterized in that, Adjustment The methods include: S111, Calculate the cold head enrichment gas phase retention matching number Its expression is: ； ； in, The gas-liquid distribution ratio, and At the preset temperature Below, the molar concentration of krypton in gaseous xenon and the molar concentration of krypton in liquid xenon; To enrich the gas phase retention matching number in the cold head; To balance the pressure within the cold head enrichment cavity; The volume of the cold head enrichment cavity; Liquid occupancy factor; To achieve the preset temperature Below, the molar volume of liquid xenon; The molar gas constant; The total molar amount of xenon in the cold head enrichment cavity; S112, Judgment Is it less than or equal to the preset threshold? If so, then the calculation is as follows: Otherwise, proceed to step S113; S113, Decrease or or increase Then return to step S111.

9. The method according to claim 7, characterized in that, Adjustment The methods include: S1101, Calculation Its expression is: ； ； ； ； in, To improve the effective pass rate of Krypton; To limit the release window response factor; The duration for the enriched gas to be released from the cold head enrichment cavity into the cold trap; The cold trap response time constant; The flow resistance between the cold trap outlet and the residual gas analyzer inlet; The flow rate of xenon gas released into the cold trap as enriched gas; This is the impedance-pumping speed matching constant; This is the effective pumping speed of the second vacuum pump; This refers to the partial pressure of xenon gas at the inlet of the residual gas analyzer. This is the total gas volume of all internal interconnected spaces between the cold trap outlet and the residual gas analyzer inlet; S1102, Judgment Is it greater than or equal to? If so, then complete. Adjustments are required; otherwise, proceed to step S1103. S1103, Increase , or Then return to step S1101.

10. The method according to claim 7, characterized in that, The expression for calculating the krypton concentration in the xenon gas to be tested is as follows: ;in, The concentration of krypton in the xenon gas to be tested. For response coefficients; The net integral area of ​​the krypton peak as measured by the residual gas analyzer.

Images