Detector and slit configuration in an isotope ratio mass spectrometer

Patent metadata

Field	Value
Publication number	US-9768003-B2
Application number	US-201615235566-A
Country	US
Kind code	B2
Filing date	Aug 12, 2016
Priority date	Aug 14, 2015
Publication date	Sep 19, 2017
Grant date	Sep 19, 2017

Abstract

A method of configuring a Faraday detector in a mass spectrometer is described. The mass spectrometer defines a central ion beam axis, and the Faraday detector is moveable relative to the central ion beam axis. The Faraday detector includes a detector arrangement having a detector surface, and a Faraday slit defining an entrance for ions into the detector arrangement. The Faraday detector has an axis of elongation which extends through the Faraday slit. A width of the Faraday slit is chosen, and the angle between the axis of elongation of the Faraday detector and the central ion beam axis is adjusted such that ions striking the detector surface do not generate secondary electrons.

First claim

The invention claimed is:

1. A method of configuring a Faraday detector in a mass spectrometer, wherein the mass spectrometer defines a central ion beam axis I, and further wherein the Faraday detector is moveable relative to the central ion beam axis I and includes a detector arrangement having a detector surface, and a Faraday slit defining an entrance for ions into the detector arrangement, the Faraday detector having an axis of elongation A which extends through the Faraday slit; the method comprising the steps of:
(a) selecting a width of the Faraday slit; and
(b) adjusting an angle α of the Faraday detector, where α represents the angle between the axis of elongation, A, of the Faraday detector, and the central ion beam axis I so as to prevent admittance of incident ions into the detector cup of the Faraday detector, outside of a maximum admittance angle γ defined between the axis of elongation A of the Faraday detector and a direction of incidence, B, of ions, at the Faraday detector,
where α and/or γ is selected according to the criterion that ions entering the detector arrangement should strike the detector surface at a location which prevents secondary electrons generated thereby from exiting the Faraday detector via the Faraday slit.

2. The method of claim 1 , when the step (b) of adjusting the angle α of the Faraday detector is carried out iteratively.

3. The method of claim 1 , wherein the Faraday detector is moveable within the mass spectrometer in a direction having at least a component in a direction across a beam of the incident ion, the method further comprising:
carrying out the step (b) at a plurality of different positions across the incident ion beam; and
identifying a single compromise angle α between the axes A and I for each of the plurality of different positions across the incident ion beam, which results in a maximum admittance angle γ based upon the said criterion.

4. The method of claim 1 , wherein the Faraday detector is moveable within the mass spectrometer in a first, translational direction having at least a component in a direction across the incident ion beam, and in a second, rotational direction about an axis that permits change of the angle α, the method further comprising carrying out the step (b) of adjusting the angle α by rotating the Faraday detector in the second rotational direction as the Faraday detector is moved in the first translational direction.

5. The method of claim 4 , wherein the Faraday detector orientation relative to the central ion beam axis is fixed so that the angle α remains constant, as the Faraday detector moves in the first translational direction, when the Faraday detector is located in a first range of positions along the first translational direction, and wherein the Faraday detector orientation relative to central ion beam axis I is varied by rotation in the second, rotational direction so that the angle α varies, as the Faraday detector moves in the first translational direction, when the Faraday detector is located in a second, different range of positions along the first translational direction.

6. The method of claim 4 , further comprising:
controlling the movement of the Faraday detector in each of the first translational and second rotational directions so as to maintain the maximum admittance angle γ as the Faraday detector moves.

7. The method of claim 1 , further comprising moving the Faraday detector within the focal plane of an incident ion beam.

8. The method of claim 1 , wherein the Faraday detector is one of a plurality of Faraday detectors within a multiple collector of a mass spectrometer, each Faraday detector being spaced from one another in a direction perpendicular to the central ion beam axis I, the method further comprising separately carrying out the step (b) in respect of each of the plurality of moveable Faraday detectors, so as independently to identify a maximum admittance angle γ in respect of each such Faraday detector.

9. A multiple collector for a mass spectrometer, the multiple collector comprising a plurality of moveable collectors, at least some of which include a Faraday detector, the mass spectrometer defining a central ion beam axis I, and the Faraday detector having a Faraday slit, the multiple collector being under the control of a controller configured with a computer programme which, when executed, carries out the method of claim 1 so as to configure the Faraday detector.

10. A multiple collector for an isotope ratio mass spectrometer, the mass spectrometer defining a central ion beam axis upon which the multiple collector is positioned, the mass spectrometer being arranged to transport ions in an ion beam from an ion source towards the multiple collector; the multiple collector comprising:
at least one moveable collector including a Faraday detector, the Faraday detector defining a longitudinal axis A, a Faraday slit configured to face the incident ion beam, and through which the longitudinal axis A passes, and a detector arrangement for detecting ions that pass through the Faraday slit;
a guide upon which the moveable collector is arranged to move, the guide extending in a first translational direction which has a component orthogonal to the central ion beam axis I;
a rotational connector for connecting the moveable collector with the guide, the connector defining a rotational axis perpendicular to the first, translational direction; and
a controller configured to control both movement of the moveable collector along the guide, and also the rotation of the moveable collector about the rotational connector, so as to constrain an admittance angle γ, defined as the angle between the direction of travel of ions in the ion beam that pass through the Faraday slit, and the longitudinal axis A of the Faraday detector, to be no greater than a predetermined maximum admittance angle γ max as the moveable collector moves to different positions along the guide.

11. The multiple collector of claim 10 , comprising a plurality of moveable collectors, the movement of each of which is controlled by the controller so as, independently, to constrain the admittance angle γ to be no greater than a predetermined maximum admittance angle γ max for each of the plurality of moveable collectors.

12. The multiple collector of claim 11 , wherein each of the plurality of moveable collectors is independently mounted upon a common guide.

13. A multiple collector for an isotope ratio mass spectrometer, the multiple collector comprising a plurality of collectors each of which includes a detector having a detector body containing a detector arrangement, and a detector front face having first and second opposed surfaces in a direction into the detector body, the detector front defining an entrance slit; characterized in that the entrance slit has an opening which is smaller on a first, front surface of the detector face, than on a second, opposed rear surface of the detector face.

14. The multiple collector of claim 13 , wherein the dimensions of the opening increase at a substantially constant rate, between the first, front surface of the detector face, and the second, opposed rear surface of the detector face.

15. The multiple collector of claim 13 , wherein the detector is a Faraday detector.

16. The multiple collector of claim 13 , wherein the detector is a compact discrete dynode (CDD) dynode.

Assignees

• Thermo Fisher Scient (Bremen) Gmbh

Inventors

• Deerberg Michael
• Krummen Michael
• Seedorf Ronald
• Seedorf Silke

Classifications

• H01J49/025 Primary

  Detectors specially adapted to particle spectrometers (data acquisition H01J49/0036; detectors per se G01T, e.g. G01T1/28, G01T1/29) · CPC title

• G01N27/626

  using heat to ionise a gas · CPC title

• G01N27/62

  by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode · CPC title