A mass spectrometer for measuring low isotopic content samples

Abstract

The application discloses a mass spectrometer for measuring a low-isotope-content sample and belongs to the technical field of mass spectrometers. The mass spectrometer comprises a receiving device and a signal processing unit. The receiving device comprises a vacuum cavity, a metal target, a vacuum plastic flash body, a high-voltage electrode plate, a vacuum glass window, a photomultiplier tube and a photomultiplier tube cover. The signal processing unit comprises a high-voltage stabilizer and a pulse amplifier. The application converts ions into secondary electrons through the metal target, provides voltage for the metal target and the high-voltage electrode plate by the high-voltage stabilizer to form a high-intensity electric field, accelerates the secondary electrons to bombard the vacuum plastic flash body to generate an optical signal, receives and converts the optical signal into a pulse signal by the photomultiplier tube through the vacuum glass window, and finally performs shaping, amplification and conversion processing on the pulse signal by the pulse amplifier. The application does not need to rely on imported super-high resistance resistors, realizes the localization of the receiving device of the mass spectrometer, and has the advantages of high signal conversion efficiency, strong anti-interference capability, stable and reliable measurement and the like.

Description

Technical Field

[0001] This invention relates to the field of mass spectrometry, and more particularly to a mass spectrometer for measuring samples with low isotope content. Background Technology

[0002] Mass spectrometry is a core instrument for isotope content analysis, enabling precise measurement of the relative abundance of isotopes in a sample. During measurement, mass spectrometry detects the charge signal generated by the ion beam. However, when the content of the analyte in the sample is low, the generated ion beam is extremely weak, resulting in a very small charge signal, typically reaching the fA level or even lower.

[0003] In traditional mass spectrometer receiving devices, high-impedance amplification technology is typically used to convert this weak current signal into a measurable voltage signal. Specifically, ultra-high resistance resistors with resistances as high as 100 GΩ or even 100 TΩ are required to achieve effective conversion of fA current. However, this technical solution has significant drawbacks in practical applications. First, the high-impedance devices with resistances of 100 GΩ and above that are currently developed domestically have poor temperature drift characteristics and long-term stability, which cannot meet the actual requirements of mass spectrometers for measurement accuracy and stability. Second, ultra-high resistance resistors with excellent performance indicators and resistance values ​​of 100 GΩ and above are currently mainly imported.

[0004] Therefore, how to break free from the dependence on imported ultra-high resistance resistors and design a mass spectrometer receiving device and signal processing unit that can stably measure samples with low isotope content without relying on high-resistance amplification technology has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a mass spectrometer for measuring samples with low isotope content.

[0006] The objective of this invention is achieved through the following technical solution: a mass spectrometer for measuring samples with low isotope content, comprising a receiving device connected to a signal processing unit; The receiving device includes a vacuum chamber, which is connected to a photomultiplier tube cover containing a photomultiplier tube; a metal target, a vacuum plastic scintillator, and a high-voltage electrode plate are sealed inside the vacuum chamber; a vacuum glass window is provided on the side of the vacuum chamber near the photomultiplier tube. The signal processing unit includes a high-voltage stabilizer and a pulse amplifier. The high-voltage stabilizer is electrically connected to a metal target and a high-voltage electrode plate. It provides a negative voltage to the metal target to attract high-energy ions to bombard the metal target and generate secondary electrons. It also provides a voltage to the high-voltage electrode plate to form a preset-intensity electric field between the metal target and the high-voltage electrode plate to accelerate the secondary electrons. After acceleration, high-energy secondary electrons are obtained. The high-energy secondary electrons bombard a vacuum plastic scintillator to generate an optical signal. The optical signal is transmitted to a photomultiplier tube through a vacuum glass window. The photomultiplier tube receives the optical signal and converts it into a pulse signal for output. The pulse amplifier is electrically connected to the output terminal of the photomultiplier tube. It is used to shape, amplify, and convert the pulse signal to complete the isotope measurement of samples with isotope content lower than a preset value.

[0007] Preferably, the high-voltage stabilizer is electrically connected to the metal target and the high-voltage electrode plate via a vacuum connector.

[0008] Preferably, the high-voltage stabilizer includes a negative feedback amplifier circuit consisting of an operational amplifier U1, a Zener diode VD1, a transistor Q1, a resistor R3, and a high-voltage module; the Zener diode VD1 is connected to the output pin of the operational amplifier U1 to enhance the voltage drive capability of the output pin of the operational amplifier U1; the emitter of the transistor Q1 is connected to the resistor R3, and the base of the transistor Q1 is connected to the resistor R3, where a Zener diode VD2 is connected for current limiting protection of the output current; the high-voltage module is a linear module, and its output voltage is proportional to the input voltage.

[0009] Preferably, the collector of the transistor Q1 is provided with a resistor R4 for adjusting the operating state of the transistor Q1.

[0010] Preferably, the pulse amplifier includes a non-inverting high-pass filter, the output of which is connected to a non-inverting amplifier, and the output of which is connected to a comparator; the non-inverting high-pass filter is used to amplify and filter the input pulse signal; and the non-inverting amplifier is used to apply a preset bias voltage to the filtered pulse signal.

[0011] Preferably, the photomultiplier tube cover is used to shield the photomultiplier tube from light, thereby reducing interference from ambient light sources.

[0012] The beneficial effects of this invention are: 1) This invention eliminates reliance on imported ultra-high resistance resistors, achieving domestic production of the receiving device: It abandons the high-resistance amplification technology approach and adopts a novel signal conversion link: "a metal target converts ions into secondary electrons—a vacuum plastic scintillator converts electrons into optical signals—a photomultiplier tube amplifies the optical signals and converts them into electrical pulse signals." The photomultiplier tube itself possesses extremely high current gain, enabling direct amplification of weak signals, thus replacing the reliance on ultra-high resistance resistors. This technical solution does not involve any embargoed components, and all core components can be independently designed and manufactured, achieving domestic production of the mass spectrometer receiving device.

[0013] 2) The present invention sets a high-intensity electric field between the metal target and the high-voltage electrode plate to accelerate the low-energy secondary electrons (average about 30eV) ejected from the metal target to thousands or even tens of thousands of electron volts, so that they have enough energy to excite the vacuum plastic scintillator to emit light.

[0014] 3) The raw pulse signal output by the photomultiplier tube is usually small in amplitude, contains high-frequency noise, and has uncertain level offset, making it difficult for the back-end acquisition module to directly identify. The pulse amplifier designed in this invention adopts a three-stage cascaded architecture of "in-phase amplification high-pass filter - in-phase adder - comparator", which together realizes the shaping, amplification and signal conversion of the pulse signal, significantly improving the signal-to-noise ratio and the accuracy of subsequent acquisition.

[0015] 4) Photomultiplier tubes (PMTs) are extremely sensitive to light signals. Stray light from the environment can directly superimpose onto the effective light signal, introducing measurement errors and even causing signal saturation. This invention features a dedicated PMT cover on the outside of the PMT, providing a fully enclosed light-shielding solution that effectively isolates the PMT from all ambient light sources except for the signal light emitted by the vacuum plastic scintillator. This design is simple and inexpensive, yet physically ensures that the PMT only responds to the light signal generated by the vacuum plastic scintillator, significantly improving the purity and repeatability of the measurement results. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the principle of the present invention; Figure 2 This is a three-dimensional structural diagram of the present invention; Figure 3 This is a schematic diagram of a high-voltage stabilizer circuit. Figure 4 This is a schematic diagram of a pulse amplifier circuit. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] See Figures 1-4 The present invention provides a technical solution: a mass spectrometer for measuring samples with low isotope content, including a receiving device, wherein the receiving device is connected to a signal processing unit; The receiving device includes a vacuum chamber, which is connected to a photomultiplier tube cover containing a photomultiplier tube; a metal target, a vacuum plastic scintillator, and a high-voltage electrode plate are sealed inside the vacuum chamber; a vacuum glass window is provided on the side of the vacuum chamber near the photomultiplier tube. The signal processing unit includes a high-voltage stabilizer and a pulse amplifier. The high-voltage stabilizer is electrically connected to a metal target and a high-voltage electrode plate. It provides a negative voltage to the metal target to attract high-energy ions to bombard the metal target and generate secondary electrons. It also provides a voltage to the high-voltage electrode plate to form a preset-intensity electric field between the metal target and the high-voltage electrode plate to accelerate the secondary electrons. After acceleration, high-energy secondary electrons are obtained. The high-energy secondary electrons bombard a vacuum plastic scintillator to generate an optical signal. The optical signal is transmitted to a photomultiplier tube through a vacuum glass window. The photomultiplier tube receives the optical signal and converts it into a pulse signal for output. The pulse amplifier is electrically connected to the output terminal of the photomultiplier tube. It is used to shape, amplify, and convert the pulse signal to complete the isotope measurement of samples with isotope content lower than a preset value.

[0019] In this embodiment, as Figure 1 As shown. The receiving device includes a metal target, a vacuum plastic scintillator, a high-voltage electrode plate, a vacuum glass window, a vacuum chamber, a vacuum connector, a photomultiplier tube, and a photomultiplier tube cover; the vacuum chamber and vacuum glass window seal the metal target, vacuum plastic scintillator, and high-voltage electrode plate under vacuum conditions; the photomultiplier tube is shielded from light by the photomultiplier tube cover; the signal processing unit includes a high-voltage stabilizer and a pulse amplifier; the high-voltage stabilizer supplies power to the metal target and high-voltage electrode plate through the vacuum connector; the pulse signal output by the photomultiplier tube is processed by the pulse amplifier.

[0020] 3D image Figure 2As shown. Working principle: To attract high-energy ions to bombard the metal target in a vacuum environment, a negative voltage is applied to the metal target; the secondary electrons ejected from the metal target have low energy, averaging only 30 eV; to ensure that the secondary electrons have sufficient energy to make the vacuum plastic scintillator emit light, the energy of the secondary electrons needs to be increased to several thousand or even ten thousand electron volts; to increase the energy of the secondary electrons, a high-voltage electrode plate is added behind the vacuum plastic scintillator to ensure a high-intensity electric field between the metal target and the high-voltage electrode plate; to transmit the light signal converted by the high-energy secondary electrons through the vacuum plastic scintillator, a vacuum glass window is designed in the structure; to convert the light signal into an electrical signal, a photomultiplier tube is used to output the pulse signal; to reduce the interference of other light sources on the photomultiplier tube, a photomultiplier tube cover is designed to shield it from light; to allow the pulse signal to be acquired by the back-end acquisition module, a pulse amplifier is used for shaping, amplification, and conversion.

[0021] In some embodiments, the high-voltage stabilizer is electrically connected to the metal target and the high-voltage electrode plate via a vacuum connector.

[0022] In some embodiments, the high-voltage stabilizer includes a negative feedback amplifier circuit consisting of an operational amplifier U1, a Zener diode VD1, a transistor Q1, a resistor R3, and a high-voltage module; the Zener diode VD1 is connected to the output pin of the operational amplifier U1 to enhance the voltage drive capability of the output pin of the operational amplifier U1; the emitter of the transistor Q1 is connected to the resistor R3, and a Zener diode VD2 is connected between the base of the transistor Q1 and the resistor R3 to provide current limiting protection for the output current; the high-voltage module is a linear module, and its output voltage is proportional to the input voltage.

[0023] In this embodiment, the circuit principle of the high-voltage stabilizer is as follows: Figure 3 As shown. To form a negative feedback amplifier circuit with operational amplifier U1, Zener diode VD1, transistor Q1, resistor R3, and high-voltage module, a linear module is selected (i.e., the larger the input voltage, the larger the output voltage). Pins 2 and 3 of operational amplifier U1 are equal; since pin 3 is 0V, pin 2 is also 0V. The current flowing through R1 is I = Uo / R1, therefore the high-voltage output U = I × R2 = R2 / R1 × Uo. To improve the driving voltage capability of pin 1 of U1, a Zener diode VD1 is connected after pin 1 of U1. To adjust the operating state of Q1, a resistor R4 is connected to pin 3 of Q1. To limit the output current of transistor Q1, a resistor R3 is connected to pin 2 of transistor Q1, and a Zener diode VD2 is connected between pin 1 of Q1 and resistor R3. Assuming the output current of Q1 is I1, if I1 × R3 > the Zener voltage value of VD2, the circuit will activate protection.

[0024] In some embodiments, the collector of the transistor Q1 is provided with a resistor R4 for adjusting the operating state of the transistor Q1.

[0025] In some embodiments, the pulse amplifier includes a non-inverting high-pass filter, the output of which is connected to a non-inverting amplifier, and the output of which is connected to a comparator; the non-inverting high-pass filter is used to amplify and filter the input pulse signal; and the non-inverting amplifier is used to apply a preset bias voltage to the filtered pulse signal.

[0026] In this embodiment, the circuit principle of the pulse amplifier is as follows: Figure 4 As shown. To amplify and filter the pulse signal Vpluse, a non-inverting high-pass filter composed of capacitor C1, resistors R1, R2, R3, and operational amplifier D1 was designed; to apply a bias voltage to the pulse signal, a non-inverting amplifier composed of capacitor C2, resistors R4, R5, R7, R8, and operational amplifier D2 was designed; to convert the pulse signal into a frequency signal Vf, a comparator composed of resistors R6 and D3 was designed, with resistor R6 used to set the comparator's threshold.

[0027] In some embodiments, the photomultiplier tube cover is used to shield the photomultiplier tube from light, thereby reducing interference from ambient light sources.

[0028] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A mass spectrometer for measuring samples with low isotopic content, characterized in that: Includes a receiving device, which is connected to a signal processing unit; The receiving device includes a vacuum chamber, which is connected to a photomultiplier tube cover containing a photomultiplier tube; a metal target, a vacuum plastic scintillator, and a high-voltage electrode plate are sealed inside the vacuum chamber; a vacuum glass window is provided on the side of the vacuum chamber near the photomultiplier tube. The signal processing unit includes a high-voltage stabilizer and a pulse amplifier. The high-voltage stabilizer is electrically connected to a metal target and a high-voltage electrode plate. It provides a negative voltage to the metal target to attract high-energy ions to bombard the metal target and generate secondary electrons. It also provides a voltage to the high-voltage electrode plate to form a preset-intensity electric field between the metal target and the high-voltage electrode plate to accelerate the secondary electrons. After acceleration, high-energy secondary electrons are obtained. The high-energy secondary electrons bombard a vacuum plastic scintillator to generate an optical signal. The optical signal is transmitted to a photomultiplier tube through a vacuum glass window. The photomultiplier tube receives the optical signal and converts it into a pulse signal for output. The pulse amplifier is electrically connected to the output terminal of the photomultiplier tube. It is used to shape, amplify, and convert the pulse signal to complete the isotope measurement of samples with isotope content lower than a preset value.

2. The mass spectrometer for measuring samples with low isotopic content according to claim 1, characterized in that: The high-voltage stabilizer is electrically connected to the metal target and the high-voltage electrode plate via a vacuum connector.

3. The mass spectrometer for measuring samples with low isotopic content according to claim 1, characterized in that: The high-voltage stabilizer includes a negative feedback amplifier circuit consisting of an operational amplifier U1, a Zener diode VD1, a transistor Q1, a resistor R3, and a high-voltage module. The Zener diode VD1 is connected to the output pin of the operational amplifier U1 to enhance the voltage drive capability of the output pin. The emitter of the transistor Q1 is connected to the resistor R3, and the base of the transistor Q1 is connected to the resistor R3, where a Zener diode VD2 is used for current limiting protection of the output current. The high-voltage module is a linear module, and its output voltage is proportional to the input voltage.

4. The mass spectrometer for measuring samples with low isotope content according to claim 3, characterized in that: The collector of the transistor Q1 is equipped with a resistor R4 to adjust the operating state of the transistor Q1.

5. The mass spectrometer for measuring samples with low isotopic content according to claim 1, characterized in that: The pulse amplifier includes a non-inverting high-pass filter, the output of which is connected to a non-inverting amplifier, and the output of which is connected to a comparator. The non-inverting high-pass filter is used to amplify and filter the input pulse signal. The non-inverting amplifier is used to apply a preset bias voltage to the filtered pulse signal.

6. The mass spectrometer for measuring samples with low isotopic content according to any one of claims 1-5, characterized in that: The photomultiplier tube cover is used to shield the photomultiplier tube from light, thereby reducing interference from ambient light sources.

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