Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Patent
1998-08-17
2000-02-29
Nguyen, Kiet T.
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
H01J 3726
Patent
active
060312270
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a time-of-flight mass spectrometer with a position-sensitive detector which comprises at least one electron multiplier and an anode array for detecting the electrons released in the electron multipliers.
For understanding the processes that take place during light-induced ionization and subsequent dissociation of molecular systems, the reaction products must be identified and energy and pulse of said products must be determined. Photoionized molecules normally dissociate into electrons and ions which must be detected simultaneously. Energy and pulse of such photodissociated fragments can, for instance, be determined by a time-of-flight mass spectrometer, including a position-sensitive detector, with the aid of which the time of flight and the position of impingement of the fragments can be determined. The position-sensitive detectors which are known in the prior art have various disadvantages. Relatively frequent use is made of detectors based on resistive anodes which, however, have very long dead times as a rule, whereby the time resolution of the system is limited. Other detectors consist of a matrix of anodes that are crossed and interconnected in rows and columns, as are, for instance, illustrated in the publication by J. H. D. Eland in Meas. Sci. Technol. 5, 1501-1504 (1994). In these detectors, too, the dead times are long because of the use of delay lines for an indirect position determination from signal travel time measurements and of digital circuits for the time measurement.
It is therefore the object of the present invention to provide a time-of-flight mass spectrometer comprising a position-sensitive detector of improved time and position resolution.
This object is achieved by the subject of patent claim 1. Advantageous embodiments follow from the subclaims.
The detector of the invention consists of at least one electron multiplier and an anode matrix which is arranged behind each electron multiplier and in which anodes are respectively interconnected in lines or columns and each line and each column are connected to a respective output terminal. The electrons which are released in the electron multiplier are detected in position-sensitive fashion by the anodes. The time is measured in a device that is independent of the anode matrix. This device may, for instance, be an analog circuit with the aid of which a time resolution of about 100 ps can be achieved. This is an improvement in time resolution by more than a factor 10 in comparison with the prior art.
The invention will now be explained in more detail with reference to the figures, of which:
FIG. 1 schematically illustrates a first embodiment of the invention;
FIG. 2 is a schematic diagram for explaining the processes that take place during detection;
FIG. 3 schematically illustrates a further embodiment of the invention;
FIG. 4 is a block diagram of the embodiment of FIG. 3; and
FIG. 5 is an example of an anode pattern of an anode matrix.
FIG. 1 shows the basic function of the detector of the invention in a schematic and exemplary manner. In an interaction zone 12 of a time-of-flight mass spectrometer 10 an approximately monochromatic synchrotron radiation SR impinges on the molecules of a molecular beam MB. The synchrotron radiation may, for instance, be emitted by a synchrotron storage ring and guided through a wavelength-selective element, such as a grating or crystal monochromator 1. As a result of the interaction of the synchrotron radiation with the molecules, the latter are ionized and possibly dissociate into individual ions and electrons, of which the ions are to be detected in time- and position-resolved fashion by a detector 20 which is arranged at the end of a drift tube 11.
FIG. 2 schematically illustrates the measuring principle with reference to the dissociation of a CO molecule. On the basis of the positions and times measured for the ions that impinge on the detector 20, energy and pulse of said ions shortly after fragmentation can be determined. The detector 20 consists of two sucessive
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Becker Uwe
Heiser Franz
Max-Planck-Gesellschaft zur Foerderung der Wissenschaften e.V.
Nguyen Kiet T.
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