DE1026880B - Secondary electron multiplier and its use in a mass spectrometer - Google Patents

Description

GERMAN

The invention relates to a secondary electron multiplier with a series of secondary electrons emitting plates and a control electrode for controlling the flow of electrons between two plates of the series.

It is known to arrange a control electrode in a secondary electron multiplier to the Flow of secondary electrons between two successive plates of the multiplier steer. Such an arrangement is useful in various cases, for example when the multiplier is used as a signal amplifier and the signal to be amplified is applied to the control electrode will. Another useful application of such a control electrode is given in cases in which is the multiplier at the output of a mass spectrometer, which is based on the time-of-flight measurement works, is used. Here it is by acting on the potential of the control electrode possible to indicate the presence of a certain proportion of masses in an ion mixture.

However, the earlier designs using such control electrodes have disadvantages. if the flow of electrons through the multiplier is to be interrupted, the control grid is using fed at such a voltage that the electrons from the plate upstream of the control electrode be thrown back onto this plate. This can cause an accumulation of negative charges on this Plate and create a space charge between the plate and the control electrode, thereby causing energy losses and distortions occur.

According to the invention, the disadvantages are completely eliminated in that the control electrode so before an auxiliary electrode is arranged that the electrons at a certain size of the to the control electrode Applied voltage can enforce this control electrode, in order to then from the auxiliary electrode to be caught so that the flow of electrons through the multiplier is stopped, while with a different magnitude of the voltage applied to the control electrode, the electrons die Control electrode does not enforce and thus its normal route through the secondary electron multiplier can continue.

With such an arrangement, the plate adjoining the control grid must not have any secondary electrons send out. The display device can work with the last plate as well as with the one adjacent to the grid Plate to be connected.

Details of the invention are explained in the drawings.

In Fig. 1, the secondary electron multiplier consists of a set of plates 16, 20, 22, 24, 26.

and its use in a mass spectrometer

Applicant:

Bendix Aviation Corporation, New York, N.Y. (V. St. A.)

Representative: Dr.-Ing. H. Negendank, patent attorney, Hamburg 36, Neuer Wall 43

Claimed priority: V. St. v. America August 10, 1953

31. The first plate 16 receives primary particles from the ion source 10 of a mass spectrometer through the window 12 provided in the armor plate 14. In front of one of the plates of the set, namely 26, the control electrode 30 consisting of a grid of parallel wires is arranged.

In the example described, the distances between the successive electrodes and armor plate 14 are as follows:

Plate 16 5.65 mm

Plate 20 5.59 mm

Plate 22 4.45 mm

Plate 24 3.81 mm

Grid 30 4.45 mm

Plate 26 6.35 mm

Plate 31 4.57 mm

The width of the plates 16, 20, 22, 24, 31 and of the grid 30 is each approximately 9 mm. The first four plates 16, 20, 22, 24 adjoining one another edge to edge, are arranged in planes slightly displaced from the perpendicular of the plates, so that the distance between these successive plates from the armor plate 14 becomes smaller and smaller. The distance between the plate 26 and the armor plate 14 is greater than the distance between the plate 24. The plate 26 has a

709 Ϊ57 / 354

Claims (1)

3 4 larger width than the other plates, and one case, however, the control pulse source to the grating 80 Part of it is arranged behind the plate 24. Imposing a sufficient negative tension begins Plate 31 has a smaller distance from the pan- the grid carries the electrons sent out by plate 76 zerplatte than the plate 26. The grille 30 covers the tronen push back, so that the same a new one free part of the plate 26 in order to move all through the previous 5 trajectory 96 in the direction of the following plate 80 Plate 24 in the direction of plate 26 sent, etc., in order to finally create a strong secondary Catch electrons. electron emission through the last plate 86 to The electrodes 16, 20, 22, 24, 30 and 31 are in effect and are caught by the plate 88 the following negative potentials: are to which the cathode ray oscilloscope 89 Plate 16 ....,; - 1800 V xo is connected. Plate 20 ........... - 1600 V The secondary electron multiplier can be Plate22 ........... - 1400 V connected to a mass spectrometer Plate 24 ........... - 1200 V den to indicate the presence or absence of Grid30 ........... —1250V to display particles of exactly a certain mass. In Plate 31 - 1400 V 15 in this case the primary particle source is the ion With the plate 26 is a cathode ray oscilloscope source of the mass spectrometer. tied together. This plate 26 is also about a
Resistance connected to ground. The grid is connected to a pulse source. Finally lies lot- claims: right to the device level an even 20 magnetic field. In the example under consideration, 1. secondary electron multiplier with a this magnetic field has a field strength of 400 Gaussian series of secondary electron-emitting plates. th and a control electrode for controlling the electrons emitted by the source 10 electron flow between two plates of the series, or other primary particles hit the plate 16 35, characterized in that the control electrode and cause secondary (28, 80) electrons to be emitted in front of an auxiliary electrode (26, 78), which, a cycloid trajectory 58 is ordered that the electrons at a determinative, meet on the next plate 20, th size of the applied to the control electrode this in turn sends out secondary electrons, voltage can enforce this control electrode run along the trajectory 60, and so on. The voltage applied to the grid 30 can be that of 78) to be captured so that the electrons of the Plate 24 sent out and stopped along the trajectory nut by the multiplier, 62 secondary electrons running neither the plate 26 while at a different size of the to the can still reach the surface of the grid 30, but control electrode applied voltage the electrons are, a new cycloidal arc 64 describe 35 not enforce the control electrode and thereby bend, continued to the plate 31. The through this their normal way through the secondary electrolater Plate 31 emitted secondary electron multipliers can continue, describe the arc 66 and are through the 2nd secondary electron multiplier after the An collector plate 32 intercepted. The cathode ray spoke 1, characterized in that the control oscilloscope 27 therefore does not normally respond. 40 electrode (30) biased with a potential If the grid 30 is due to the action of the electrons at a penetration of the Control pulse to a compared to the plate 24 control electrode towards the auxiliary electrode (26, Fig. 1) positive potential is raised, it attracts those prevented by the. Electrons arrive at the plate 24, and these electrons trons penetrate the grid to reach the plate 26 45 saying 2, characterized in that the and thus the cathode ray oscilloscope showing device, for example a cathode 27 to cause notification. beam oscilloscope (27) attached to the auxiliary electrode According to the embodiment shown in FIG. 2 (FIG. 1). game is the arrangement of the plates, compared to the 4th secondary electron multiplier according to the above, changed a little. With the exception of 50 claim 1, characterized in that the tax by the control grid 82 hidden plate 78 are electrode (80) biased with a potential all plates progressively in the same sense that the electrodes can penetrate through the pushed by moving more and more of the armor plate control electrode to the auxiliary electrode (78 in 14 stand closer. For example, the values in FIG. 2) are permitted. for the distance between certain plates and the armor 55 5. Secondary electron multiplier according to Anplatte 14 as well as claim 4 applied to these plates, characterized in that the AnPotentials: pointing device, for example a cathode plate 76 3.15 mm, -1200 V beam oscilloscope (89), to the last plate (88) Plate 84 3.10 mm, - 1000 V of the multiplier is connected. Plate 86 3.05 mm, - 800 V 60 6. Secondary electron multiplier after a In addition, in the present case, the grid 82 of the preceding claims, in which the under a voltage of -1150 V. Multiplier plates next to one another in a In the absence of a series connected by the control pulse source, stepwise perpendicular to The control pulse applied to the grid 82 attracts their level offset, thereby which in comparison to the previous plate 76 positive 65 characterized in that the control electrode is in shape tively tensioned grids 82 which are arranged at one point by a grid (30, 80) formed by this plate sent and the trajectory 90 describing elec- trons on, and these electrons penetrate the grid multiple times, while the auxiliary ter in 92 to be captured by plate 78 to electrode (26,78) parallel to and close to the will. 70 control electrode on the side of the latter that is secluded from the multiplier plates is. 7. Use of a secondary electron multiplier according to one of the preceding claims with a spectrometer operating on the basis of time-of-flight measurement, characterized in that that the control electrode (28, 80) is fed with control voltage pulses of such dimensions is that the indicator (cathode ray oscilloscope 27, 89) only the ion groups with a certain Indicates mass number. Considered publications:
British Patent No. 501740. 1 sheet of drawings . © 709 957/354 3.58