40Ar-39Ar dating system and method based on accelerator neutron source and nuclide mass spectrometer

Abstract

The invention relates to the technical field of geochronology, in particular to a 40Ar-39Ar dating system based on an accelerator neutron source and a nuclide mass spectrometer, which comprises an accelerator neutron source subsystem, an Ar gas sample preparation subsystem and a nuclide mass spectrometer subsystem, the accelerator neutron source subsystem adopts a D-D accelerator neutron source; the Ar gas sample preparation subsystem comprises an argon gas extraction part, an argon gas purification part and an argon gas collection part; the nuclide mass spectrometer subsystem adopts a nuclide mass spectrometer; according to the method, the accelerator neutron source is used for replacing a traditional large reactor neutron source, meanwhile, the nuclide mass spectrometer is used for replacing a traditional rare gas isotope mass spectrometer, in the method, due to the good monochromaticity of neutrons and no recoil caused by high-energy neutrons, the measurement result is certainly more accurate, and in the instrument system, the measurement result is more accurate. And due to the application of the multiplier neutron source, the method is greatly simplified, and the method has the advantages of accurate measurement result, greatly reduced cost, greatly shortened experimental period and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of geochronology, and in particular to a 40Ar-39Ar dating system and method based on an accelerator neutron source and a nuclear mass spectrometer. Background Art

[0002] The 40Ar-39Ar dating method is an advanced nuclear analysis method that is particularly suitable for high-precision age determination of potassium-containing minerals. The principle is that rock minerals are activated by fast neutrons in a reactor, and a nuclear reaction 39K(n,p)39Ar occurs, which converts 39K in the sample into 39Ar. Considering that 40K / 39K in earth samples is a constant value, a 40Ar and 39Ar isotope dating system is established. All tests are completed by only one argon isotope mass spectrometer, which makes the 40Ar-39Ar dating technology significantly improved in age accuracy compared with other methods. It can reflect more uranium mineralization fluid information at a higher time resolution, and thus more finely characterize the uranium deposits in the The International Geochronological Organization (Earth-Time) also defines 40Ar-39Ar dating technology as one of the two most accurate means of geochronological dating (the other is the ID-TIMSU-Pb method). However, for hydrothermal alteration potassium-containing minerals formed during hydrothermal alteration, the particles are usually relatively small (about 0.1μm). During the neutron activation of fine-grained samples in the reactor, the high-energy neutrons in the irradiation channel of the traditional 235U fission reactor can easily induce nuclear recoil and cause the loss of 39Ar. In addition, many interference reactions are induced, which seriously limits the accurate age determination of extremely fine-grained altered minerals by 40Ar-39Ar dating technology.

[0003] In addition, the use of reactor-activated 40Ar-39Ar dating samples also faces the problem of reactor resource shortage, which is particularly prominent in my country. At present, the samples in my country's 40Ar-39Ar laboratory are basically irradiated in the 49-2 pool reactor of the China Institute of Atomic Energy. However, in recent years, the 49-2 reactor has undertaken heavy scientific research tasks, and irradiation resources are very tight. In addition, the frequency of reactor start-up is relatively low, and the neutron activation cycle of samples is long. These factors have made it difficult to carry out 40Ar-39Ar dating work normally. The normal operation of domestic 40Ar-39Ar laboratories has basically encountered major problems. Even scientists engaged in argon-argon dating in developed countries such as Europe and the United States face similar difficulties as my country.

[0004] The development of China's latest nuclear spectrum mass spectrometer technology (multiple-charged state nuclear mass spectrometer) has provided the possibility for the determination of extremely low amounts of 39Ar in samples activated by DD source. Different from the static test mode of traditional rare gas mass spectrometers (which rely on imports), nuclear mass spectrometers use ultra-strong ionization technology to improve ionization efficiency and beam intensity, greatly improving the measurement sensitivity and accuracy of argon isotopes. In multi-charged state mode, there is no interference from molecular ions or polyatomic ions, which greatly reduces the background level of the instrument and greatly improves the measurement sensitivity. At the same time, it breaks through the technical bottleneck that traditional mass spectrometers can only measure the mass-to-charge ratio (M / q) spectrum, and realizes the determination of nuclide spectrum (ZM / q). Compared with traditional static Ar isotope mass spectrometers, the sensitivity of nuclear mass spectrometers is increased by 100-10000 times, which can achieve ultra-high sensitivity 40Ar-39Ar dating of uranium minerals.

[0005] Therefore, to address the above-mentioned problems such as inaccurate measurement results, high costs and long experimental cycles, a 40Ar-39Ar dating system and method based on an accelerator neutron source and nuclear mass spectrometer can be designed. Summary of the invention

[0006] In order to overcome the problems of inaccurate measurement results, high cost and long experimental cycle.

[0007] The technical solution of the present invention is: a 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer, comprising an accelerator neutron source subsystem, an Ar gas sample preparation subsystem and a nuclear mass spectrometer subsystem;

[0008] The accelerator neutron source subsystem adopts the DD accelerator neutron source. The accelerator neutron source subsystem includes: ion source, high voltage electrode, accelerator, ground electrode, triple magnetic quadrupole lens, rotating target and sample irradiation rack. The ion source is used to generate D+ ion beam. The high voltage electrode includes high voltage power supply and high voltage stand. The accelerator is used to accelerate the energy of D+ ions. The ground electrode is used to provide a good zero potential. The triple magnetic quadrupole lens is used for focusing and transmitting the D+ ion beam. The rotating target and sample irradiation rack are used to place lithium deuteride target and irradiate samples to realize D+D reaction to produce neutrons, as well as neutron irradiation of geological samples to realize 39K(n,p)39Ar nuclear reaction.

[0009] The Ar gas sample preparation subsystem includes an argon extraction component, an argon purification component and an argon collection component. The argon extraction component heats the sample to a high temperature to melt, thereby realizing efficient extraction of argon isotopes in the sample. The argon purification component removes active gases such as nitrogen, oxygen, and carbon dioxide released by the sample, thereby realizing efficient purification of argon isotopes in the sample. After the sample gas is fully purified, the argon collection component enriches the argon in an activated carbon cold trap at liquid nitrogen temperature, seals the cold finger with an all-metal valve, and finally sends it to the inlet of the nuclear mass spectrometer to measure the argon isotopes.

[0010] The nuclear mass spectrometer subsystem adopts a nuclear mass spectrometer analyzer, which includes an injector, an ECR ion source, an accelerator, a magnetic analyzer, a Faraday cup, an energy absorption membrane and a detector. The injector is connected to the sampler of the argon collection component to send the argon gas to the ECR ion source for ionization. The ECR ion source is used to generate Ar gas ions with multiple charge states. The accelerator is used to increase the energy of the Ar ions. The magnetic analyzer is used to separate ions of various M / q. The Faraday cup is used to measure the size of each different M / q ion beam separated by the magnetic analyzer. The energy absorption membrane is used to separate 39Ar and 39K ions. The detector is used to measure the energy spectrum of the ions entering the detection and record the counting rate and total count of the ions.

[0011] Preferably, the ion source in the accelerator neutron source adopts an electron cyclotron resonance ion source with a frequency of 2.45 GHz.

[0012] Preferably, the high voltage power supply in the accelerator neutron source is 300 kV, and the accelerator in the accelerator neutron source accelerates the energy of D+ ions to 300 keV.

[0013] Preferably, the argon extraction component adopts a double vacuum heating furnace, which includes a sample tray, a stainless steel furnace body, a heat shield, a heating element, a tantalum crucible and a vacuum pump group. The heating element is made of tantalum sheet material, and the tantalum crucible is made of ultra-pure tantalum rods.

[0014] Preferably, the ECR ion source in the nuclear mass spectrometer subsystem is an electron cyclotron resonance ionization ion source.

[0015] Preferably, the acceleration voltage of the accelerator in the nuclear mass spectrometer subsystem is selected in the range of 0 to 800 kV, and the accelerator terminal voltage is in the range of 0 to 1000 kV, wherein 0 kV means removing the accelerator.

[0016] Preferably, the DD accelerator neutron source is a device based on a particle accelerator to generate neutrons, which can accelerate D ions to an energy range of 50keV to 800keV. The ion source of the nuclear mass spectrometer can extract ions in the ≥2+ state. The nuclear mass spectrometer is an analyzer with the function of excluding separated ions and isobaric ions.

[0017] A 40Ar-39Ar dating method based on an accelerator neutron source and a nuclear mass spectrometer is provided, wherein the method is based on any one of the above-mentioned 40Ar-39Ar dating systems based on an accelerator neutron source and a nuclear mass spectrometer.

[0018] The beneficial effects of the present invention are as follows: the accelerator neutron source replaces the traditional large reactor neutron source, and the nuclear mass spectrometer replaces the traditional rare gas isotope mass spectrometer. In terms of method, due to the good monochromaticity of neutrons and the absence of recoil caused by high-energy neutrons, the measurement results will be more accurate. In terms of instrument system, due to the application of multiplier neutron source, it will also be greatly simplified, with the advantages of accurate measurement results, greatly reduced costs and greatly shortened experimental cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic diagram of the framework of the 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer of the present invention;

[0020] Figure 2 Shown is a schematic diagram of the structure of the nuclear mass spectrometer subsystem in the 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0022] See also Figure 1-Figure 2 , the present invention provides an embodiment: a 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer, comprising an accelerator neutron source subsystem, an Ar gas sample preparation subsystem and a nuclear mass spectrometer subsystem;

[0023] The accelerator neutron source subsystem adopts the DD accelerator neutron source. The accelerator neutron source subsystem includes: ion source, high voltage electrode, accelerator, ground electrode, triple magnetic quadrupole lens, rotating target and sample irradiation rack. The ion source is used to generate D+ ion beam. The high voltage electrode includes high voltage power supply and high voltage stand. The accelerator is used to accelerate the energy of D+ ions. The ground electrode is used to provide a good zero potential. The triple magnetic quadrupole lens is used for focusing and transmitting the D+ ion beam. The rotating target and sample irradiation rack are used to place lithium deuteride target and irradiate samples to realize D+D reaction to produce neutrons, as well as neutron irradiation of geological samples to realize 39K(n,p)39Ar nuclear reaction.

[0024] The Ar gas sample preparation subsystem includes an argon extraction component, an argon purification component and an argon collection component. The argon extraction component heats the sample to a high temperature to melt, thereby realizing efficient extraction of argon isotopes in the sample. The argon purification component removes active gases such as nitrogen, oxygen, and carbon dioxide released by the sample, thereby realizing efficient purification of argon isotopes in the sample. After the sample gas is fully purified, the argon collection component enriches the argon in an activated carbon cold trap at liquid nitrogen temperature, seals the cold finger with an all-metal valve, and finally sends it to the inlet of the nuclear mass spectrometer to measure the argon isotopes.

[0025] The nuclear mass spectrometer subsystem adopts a nuclear mass spectrometer analyzer. The nuclear mass spectrometer subsystem includes an injector, an ECR ion source, an accelerator, a magnetic analyzer, a Faraday cup, an energy absorption membrane and a detector. The injector is connected to the sampler of the argon collection component to send the argon gas to the ECR ion source for ionization. The ECR ion source is used to generate multi-charged Ar gas ions. The accelerator is used to increase the energy of the Ar ions. The magnetic analyzer is used to separate various ions of different M / q, such as distinguishing 40Ar 9+ 、40Ar 10+ 、39Ar 9+ 、39Ar 10+ Etc., because their M / q values ​​are different, the Faraday cup is used to measure the size of each different M / q ion beam separated by the magnetic analyzer, the energy absorption membrane is used to separate 39Ar and 39K ions, and eliminate the interference of 39K ions on 39Ar, because 39Ar and 39K have the same M / q and the same energy, and the detector cannot distinguish between the two. With the energy absorption membrane, when 39Ar and 39K ions pass through the absorption membrane, their energies are different, because the energy lost by the two in the membrane is different. The detector is used to measure the energy spectrum of the ions entering the detection, and record the counting rate and total count of the ions. Since the energies of 39Ar and 39K ions are different after passing through the energy absorption membrane, the detector can distinguish between the two by measuring the difference in energy, thereby eliminating the interference of 39K.

[0026] Preferably, the ion source in the accelerator neutron source adopts an electron cyclotron resonance ion source with a frequency of 2.45 GHz.

[0027] Preferably, the high voltage power supply in the accelerator neutron source is 300 kV, and the accelerator in the accelerator neutron source accelerates the energy of D+ ions to 300 keV.

[0028] Preferably, the argon extraction component adopts a double vacuum heating furnace, which includes a sample tray, a stainless steel furnace body, a heat shield, a heating element, a tantalum crucible and a vacuum pump group. The heating element is made of tantalum sheet material. The furnace heating temperature is above 1800°C to ensure that the sample argon isotope in the sample is completely extracted. The tantalum crucible is made of ultra-pure tantalum rods to ensure that the sample heating process has an extremely low argon background.

[0029] Preferably, the ECR ion source in the nuclear mass spectrometer subsystem is an electron cyclotron resonance ionization ion source.

[0030] Preferably, the acceleration voltage of the accelerator in the nuclear mass spectrometer subsystem is selected in the range of 0 to 800 kV, and the accelerator terminal voltage is in the range of 0 to 1000 kV, wherein 0 kV means removing the accelerator.

[0031] Preferably, the DD accelerator neutron source is a device based on a particle accelerator to generate neutrons, which can accelerate D ions to an energy range of 50keV to 800keV. The ion source of the nuclear mass spectrometer can extract ions in the ≥2+ state. The nuclear mass spectrometer is an analyzer with the function of excluding separated ions and isobaric ions.

[0032] A 40Ar-39Ar dating method based on an accelerator neutron source and a nuclear mass spectrometer is provided, wherein the method is based on any one of the above-mentioned 40Ar-39Ar dating systems based on an accelerator neutron source and a nuclear mass spectrometer.

[0033] Through the above steps, the traditional large reactor neutron source is replaced by an accelerator neutron source, and the traditional rare gas isotope mass spectrometer is replaced by a nuclear mass spectrometer. In terms of method, the measurement results will be more accurate due to the good monochromaticity of neutrons and the absence of recoil caused by high-energy neutrons. In terms of instrument system, the application of multiplier neutron source will also be greatly simplified, with the advantages of accurate measurement results, greatly reduced costs and greatly shortened experimental cycles, so as to solve the problems of inaccurate measurement results, high costs and long experimental cycles.

[0034] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of those skilled in the art without departing from the spirit of the present invention.

Claims

1. A 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer, comprising an accelerator neutron source subsystem, an Ar gas sample preparation subsystem and a nuclear mass spectrometer subsystem; characterized in that: The accelerator neutron source subsystem adopts the DD accelerator neutron source. The accelerator neutron source subsystem includes: ion source, high voltage electrode, accelerator, ground electrode, triple magnetic quadrupole lens, rotating target and sample irradiation rack. The ion source is used to generate D+ ion beam. The high voltage electrode includes high voltage power supply and high voltage stand. The accelerator is used to accelerate the energy of D+ ions. The ground electrode is used to provide a good zero potential. The triple magnetic quadrupole lens is used for focusing and transmitting the D+ ion beam. The rotating target and sample irradiation rack are used to place lithium deuteride target and irradiate samples to realize D+D reaction to produce neutrons, as well as neutron irradiation of geological samples to realize 39K(n,p)39Ar nuclear reaction. The Ar gas sample preparation subsystem includes an argon extraction component, an argon purification component and an argon collection component. The argon extraction component heats the sample to a high temperature to melt, thereby realizing efficient extraction of argon isotopes in the sample. The argon purification component removes active gases such as nitrogen, oxygen, and carbon dioxide released by the sample, thereby realizing efficient purification of argon isotopes in the sample. After the sample gas is fully purified, the argon collection component enriches the argon in an activated carbon cold trap at liquid nitrogen temperature, seals the cold finger with an all-metal valve, and finally sends it to the inlet of the nuclear mass spectrometer to measure the argon isotopes. The nuclear mass spectrometer subsystem adopts a nuclear mass spectrometer analyzer, which includes an injector, an ECR ion source, an accelerator, a magnetic analyzer, a Faraday cup, an energy absorption membrane and a detector. The injector is connected to the sampler of the argon collection component to send the argon gas to the ECR ion source for ionization. The ECR ion source is used to generate Ar gas ions with multiple charge states. The accelerator is used to increase the energy of the Ar ions. The magnetic analyzer is used to separate ions of various M / q. The Faraday cup is used to measure the size of each different M / q ion beam separated by the magnetic analyzer. The energy absorption membrane is used to separate 39Ar and 39K ions. The detector is used to measure the energy spectrum of the ions entering the detection and record the counting rate and total count of the ions.

2. The 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer according to claim 1, characterized in that: The ion source in the accelerator neutron source adopts an electron cyclotron resonance ion source with a frequency of 2.45 GHz.

3. The 40Ar-39Ar dating system based on accelerator neutron source and nuclear mass spectrometer according to claim 1, characterized in that: The high voltage power supply in the accelerator neutron source adopts 300kV, and the accelerator in the accelerator neutron source accelerates the energy of D+ ions to 300keV.

4. The 40Ar-39Ar dating system based on accelerator neutron source and nuclear mass spectrometer according to claim 1, characterized in that: The argon extraction component adopts a double vacuum heating furnace, which includes a sample tray, a stainless steel furnace body, a heat shield, a heating element, a tantalum crucible and a vacuum pump group. The heating element is made of tantalum sheet material, and the tantalum crucible is made of ultra-pure tantalum rods.

5. The 40Ar-39Ar dating system based on accelerator neutron source and nuclear mass spectrometer according to claim 1, characterized in that: The ECR ion source in the nuclear mass spectrometer subsystem is an electron cyclotron resonance ionization ion source.

6. The 40Ar-39Ar dating system based on accelerator neutron source and nuclear mass spectrometer according to claim 1, characterized in that: The acceleration voltage selection range of the accelerator in the nuclear mass spectrometer subsystem is 0-800kV, and the accelerator terminal voltage ranges from 0 to 1000kV, where 0kV means removing the accelerator.

7. The 40Ar-39Ar dating system based on accelerator neutron source and nuclear mass spectrometer according to claim 1, characterized in that: The DD accelerator neutron source is a device based on a particle accelerator to generate neutrons, which can accelerate D ions to an energy range of 50keV to 800keV. The ion source of the nuclear mass spectrometer can extract ions in the ≥2+ state. The nuclear mass spectrometer is an analyzer with the function of excluding separated ions and isobaric ions.

8. A 40Ar-39Ar dating method based on an accelerator neutron source and a nuclear mass spectrometer, characterized in that: The method is based on the 40Ar-39Ar dating system based on an accelerator neutron source and a nuclear mass spectrometer as described in any one of claims 1 to 7.

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