Patent Description:
Accelerator Mass Spectrometry (AMS) is a high-energy isotope mass spectrometer based on accelerator technology and ion detector technology and is mainly used for the measurement of isotope abundance ratio. By virtue of an accelerator, the current AMS accelerates and measures isotopes sequentially and alternately thereby analyzing the isotopes. Thanks to the use of an accelerator and a detector, AMS is capable of excluding molecular ion background and isobaric ion background, which has greatly improved the analytical sensitivity and, as a result, the isotope abundance sensitivity can reach up to <NUM>×<NUM>-<NUM>. In contrast, the prior-art mass spectrometer (MS) only has an isotope abundance sensitivity of <NUM>×<NUM>-<NUM> due to the interference from molecular ion background and isobaric ion background.

Although the AMS is advantageous in that it has a high sensitivity and requires a less amount of samples, it is more complex in structure than the ordinary MS. Further, as isotopes are injected and measured alternately, the AMS cannot measure the isotopes simultaneously. These have contributed to undesirable measurement accuracy of the AMS, generally around <NUM>%-<NUM>%.

The advantages and disadvantages of AMS and MS are shown in the table below:.

The main reason why AMS cannot be used for measuring isotopes simultaneously lies in that, since the application of accelerator from the <NUM>, it has been the practice that the accelerator can only accelerate a nuclide ion at a time. The accelerator system consists of an ion injector, an accelerator and a high-energy ion analyzer. One of the main components in the injector is an injection magnet which is intended to select one isotope and injects it into the accelerator for acceleration. To allow more than two isotopes to be measured, the mass parameter of the injector must be alternately changed so as to inject and accelerate the isotopes alternately thereby measuring the isotopes alternately.

Due to alternate measurement of isotopes, two major problems occur with the AMS. First, the measurement accuracy is not high enough, generally about <NUM>%-<NUM>%; second, the instrument system of the AMS is more complicated and, as compared with conventional MS, an injection magnet, an alternate injection power supply and a control system in addition to an accelerator are included.

<CIT> discloses a mass spectrometry system based on the general principle of accelerator mass spectrometry (AMS). An ion source generates a beam of ions having a negative charge state. A first mass analyzer transmits only ions having a predetermined mass. The ions are passed through a stripper target comprising helium and/or hydrogen as a stripping gas to change the charge state of said ions from negative to positive charge and to dissociate molecular ions by collisions. A second mass analyzer transmits ions in charge state <NUM>+ having the predetermined mass, which are detected by a detector.

<CIT> discloses a mass spectrum unit of accelerator consists of ion source, beam buncher, RFQ accelerator, electronic stripper, high energy analyzing system and detector. It is featured as connecting said unit and system in sequence; accelerating <NUM>C, <NUM> C and <NUM>C ion separately to be at certain energy for carrying out electronic stripping by RFQ accelerator in order to eliminate disturbance of molecular ion.

<CIT> discloses an acceleration apparatus which reduced backgrounds of accelerator mass spectrometry measurements of <NUM>C and other radionuclides. Backgrounds of AMS measurements are reduced by eliminating unwanted charged particles which undergo charge change during the acceleration process. This reduction is accomplished by a configuration of inclined electric fields throughout the acceleration region.

The present invention provides an accelerator mass spectrometry device for simultaneously measuring isotopes in order to improve the measuring accuracy of mass spectrometry device and simplify its structure, thereby eliminating the drawbacks of the prior art.

To achieve the objective described above, the present invention employs the technical solutions below:
An accelerator mass spectrometry device for simultaneously measuring isotopes, comprising a sputtering negative ion source for generating a plurality of negative stable and unstable isotopic ions, an accelerating tube connected downstream to the sputtering negative ion source for simultaneously accelerating said plurality of isotopic ions; a first electrostatic analyzer connected downstream to the accelerating tube for conducting energy analysis of said plurality of isotopic ions; a magnetic analyzer connected downstream to the first electrostatic analyzer for separating said plurality of isotopic ions; a stable isotope receiver connected downstream to the magnetic analyzer for measuring said negative stable isotopic ions; an electron stripper connected downstream to the magnetic analyzer for converting said negative unstable isotopic ions to positive ions and disintegrating all the molecular ions; a speed selector connected downstream to the electron stripper for excluding the disintegrated molecular fragments and scattered ions; a second electrostatic analyzer connected downstream to the speed selector for excluding neutral particles of zero charge state; a detector connected downstream to the second electrostatic analyzer for measuring said positive ions originating from said conversion by the electron stripper; and a nuclear electronics and data acquisition unit configured to obtain data from the stable isotope receiver and the detector respectively which, after time matching, offers the contents of said plurality of isotopic ions measured simultaneously and an abundance ratio thereof.

The stable isotope receiver may be a Faraday cup.

The measurement signal of the stable isotope receiver may be delayed by a delay line and then transmitted to the nuclear electronics and data acquisition unit such that it arrives simultaneously with the measurement signal of the detector.

The accelerator mass spectrometry device for simultaneously measuring isotopes may further comprise an automatic control system for controlling the operation of each system, isotope measurement, data acquisition and operation, sample replacement as well as vacuum environment.

The advantageous effects of the present invention are as follows:
By virtue of the accelerator mass spectrometry device for simultaneously measuring isotopes according to the present invention, a plurality of isotopic negative ions originating from an ion source are directly admitted into the accelerating tube without passing through the conventional electric and magnetic analyzers so that a plurality of isotopic negative ions are accelerated simultaneously. The plurality of accelerated isotopic negative ions is separated by the isotope mass resolution system. Stable isotopic negative ions are measured by the stable isotope receiver and unstable isotope negative ions are converted to positive ions and then measured by the detector. The isotope signals measured separately are time-matched and then transmitted to the nuclear electronics and data acquisition unit for data operations. The present invention is advantageous in that it is simple in structure and can be convenient to operate and maintain, which make it easy to popularize it in the market and promote its application. Moreover, it is featured with greater measurement accuracy than the conventional AMS, which contributes to more accurate measurement results.

Below is a detailed description of the present invention in connection with the accompanying drawings and the preferred embodiments.

<FIG> is a schematic diagram of a conventional AMS. As shown in <FIG>, two isotopes respectively having a mass number of M and M-<NUM> are separated from a sputtering negative ion source <NUM>. AMS is unable to measure the two isotopes simultaneously at rear end of a high-energy magnetic analyzer or electrostatic analyzer; instead, an electrostatic and magnetic analyzer <NUM> can only select one of the isotopes to be accelerated by a tandem accelerator <NUM>. The accelerated isotope passes through a high-energy magnetic analyzer <NUM> and a high-energy electrostatic analyzer <NUM> and arrives at a detector <NUM>. By varying the mass parameter of the injector alternately so as to inject and accelerate the isotopes alternately, the isotopes can be measured alternately.

The accelerator mass spectrometry device of the present invention that has the function of measuring isotopes at the same time is referred to as ST-AMS. ST-AMS mainly serves to solve two technical problems, one of which is accelerating isotopes simultaneously and the other is measuring the isotopes simultaneously.

<FIG> is a simplified schematic diagram of the ST-AMS according to the present invention. As shown in <FIG>, negative ions originating from the sputtering negative ion source <NUM> are directly admitted into an accelerating tube <NUM> (comprising a pre-accelerating tube and a main accelerating tube) and, therefore, the individual isotopic negative ions contained in the negative ions, for example, in the case of carbon isotopes, respectively <NUM>C, <NUM>C and <NUM>C negative ions, are all admitted into the accelerator tube to be accelerated. After the negative ions pass through the accelerator, their masses are resolved directly using an electric and magnetic analyzer <NUM>. For example, when carbon isotopes are analyzed using this analyzer, <NUM>C, <NUM>C and <NUM>C negative ions among carbon isotopes are separated. <NUM>C and <NUM>C are stable isotopes and can form negative ion beams capable of being measured directly, <NUM>C and <NUM>C negative ions are hence capable of being measured simultaneously using a stable isotope receiver <NUM> (such as a Faraday cup). In contrast, unstable isotopes, for example, <NUM>C negative ions, are extremely low in abundance (<NUM>C/<NUM>C in the range of <NUM>-<NUM> to <NUM>-<NUM>) so that they cannot form a measurable beam with a maximum of <NUM> counts per second. Thus, on one hand, a heavy-particle detector is used to record the number of atoms of <NUM>C ions and the stable isotope receiver <NUM> cannot be used. On the other hand, as other isotopic molecular ions, such as <NUM>CH, <NUM>CH<NUM> and <NUM>Li<NUM> negative ions, are present in <NUM>C negative ions, all the molecular ions are disintegrated through an electron stripper <NUM> by means of a stripper technique in the AMS analysis method and the disintegrated molecular fragments and scattered ions are excluded through a speed selector <NUM> and an electrostatic analyzer <NUM>, simply allowing <NUM>C+ ions to enter a heavy ion detector <NUM> and to be recorded. The speed selector <NUM> is mainly used to exclude the disintegrated molecular fragments and scattered ions and the electrostatic analyzer <NUM> is mainly used to exclude neutral particles of zero charge state. Since the point of time when <NUM>C+ ion arrives at the detector is later than the point of time when <NUM>C and <NUM>C ion beam streams arrive at the stable isotope receiver <NUM>, the present invention employs a dedicated delay line to delay the signals of the stable isotope receiver such that the signals arrive at the receiver simultaneously with the signals of the detector. In this way, <NUM>C+ ions, <NUM>C and <NUM>C negative ions can be measured simultaneously thereby enabling more isotopes to be received simultaneously.

Below is a description of an embodiment of the present invention with reference to a specific structure of the ST-AMS by taking the analysis on <NUM>C, <NUM>C and <NUM>C for example.

<FIG> is a specific structure of the ST-AMS of the present invention, which comprises five parts, respectively:.

The sputtering negative ion source <NUM> is connected to the accelerating tube <NUM> for simultaneously accelerating a plurality of isotopic ions. The accelerating tube <NUM> consists of a pre-accelerating section and a main accelerating section and a lens is disposed in the middle thereof, and the output end of the accelerating tube <NUM> is connected with an isotopic mass resolution system. The first electrostatic analyzer <NUM> of the isotope mass resolution system conducts energy analysis of a plurality of isotopic ions. The magnetic analyzer <NUM> separates a plurality of isotopic ions. The stable isotope receiver <NUM> of the charge conversion analysis and multi-receiving measurement system measures stable isotopic negative ions (such as <NUM>C beam stream a, <NUM>C beam stream b); the electron stripper <NUM> converts unstable isotope negative ion (such as <NUM>C) into a positive ion and disintegrates all molecular ions. The detector <NUM> of the ion detection system measures isotopic positive ions (such as <NUM>C beam stream c) converted by the electron stripper <NUM>. The nuclear electronics and data acquisition unit acquires the data measured by the stable isotope receiver <NUM> and the detector <NUM> which, after time matching, offers the contents of multiple isotopes measured simultaneously and abundance ratio thereof. In the present invention, the measurement signals of the stable isotope receiver <NUM> (a Faraday cup) are delayed by a delay line before transmitted to the nuclear electronics and data acquisition unit such that these signals arrive at the receiver simultaneously with the measurement signals of the detector <NUM>.

Below is a description of the measurement steps of the ST-AMS by taking the measurement of carbon isotopes <NUM>C, <NUM>C and <NUM>C contained in atmospheric particulates for example.

In addition to being useful for the measurement of carbon <NUM>C, <NUM>C and <NUM>C isotopes, the present invention is also applicable to simultaneous measurement of nuclides such as <NUM>H, <NUM>Be, <NUM>Al and their isotopes in a way similar to that described in the above embodiment and those of ordinary skill in the art may tailor the design to the specific situations.

The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described within the scope of the invention as defined by the appended claims.

Claim 1:
An accelerator mass spectrometry device for simultaneously measuring isotopes, comprising:
a sputtering negative ion source (<NUM>) for generating a plurality of negative stable and unstable isotopic ions;
an accelerating tube (<NUM>) connected downstream to the sputtering negative ion source (<NUM>) for simultaneously accelerating said plurality of isotopic ions;
a first electrostatic analyzer (<NUM>) connected downstream to the accelerating tube (<NUM>) for conducting energy analysis of said plurality of isotopic ions;
a magnetic analyzer (<NUM>) connected downstream to the first electrostatic analyzer (<NUM>) for separating said plurality of isotopic ions;
a stable isotope receiver (<NUM>) connected downstream to the magnetic analyzer (<NUM>) for measuring said negative stable isotopic ions;
an electron stripper (<NUM>) connected downstream to the magnetic analyzer (<NUM>) for converting said negative unstable isotopic ions to positive ions and disintegrating all the molecular ions;
a speed selector (<NUM>) connected downstream to the electron stripper (<NUM>) for excluding the disintegrated molecular fragments and scattered ions;
a second electrostatic analyzer (<NUM>) connected downstream to the speed selector (<NUM>) for excluding neutral particles of zero charge state;
a detector (<NUM>) connected downstream to the second electrostatic analyzer (<NUM>) for measuring said positive ions originating from said conversion by the electron stripper (<NUM>); and
a nuclear electronics and data acquisition unit configured to obtain data from the stable isotope receiver (<NUM>) and the detector (<NUM>) respectively which, after time matching, offers the contents of said plurality of isotopic ions measured simultaneously and an abundance ratio thereof.