DE2613116A1 - ELECTRON MULTIPLIER - Google Patents

Description

EIKENBERG & BRÜMMERSTEDT PATENT LAWYERS IN HANOVER

EMI LIMITED 100/473

Electron multiplier

The invention relates to an electron multiplier, the one in an evacuated flask has a dynode electron multiplier element is provided from which when Primary electrons secondary electrons are triggered with at least five-fold multiplication.

Electron multipliers have been proposed in which a channel multiplier is provided to counteract upon impingement to cause a secondary emission multiplication of primary electrons. A channel multiplier has a high overall gain factor, since secondary electrons are not only triggered when an input electron hits a channel side wall

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are, but the secondary electrons in turn on the channel side wall meet so that the number of secondary electrons is increased. The multiplication in a channel multiplier is at usually only twice or three times, so that Numerous hits are required to achieve the desired overall multiplication factors in the range of 10 to 10, and furthermore the signal-to-noise ratio when encountering a lower one Amount of electrons bad.

There are also known electron multipliers in which dynode stacks are provided. Compared to the channel multiplier the dynode stack is space-consuming, and the time interval between the output pulses depends only statistically on the time interval Distance between the input impulses, however, is the sensitivity and the signal-to-noise ratio is better, in particular, when only small amounts of electrons impinge.

The invention is based on the object of an electron multiplier of the type mentioned above, which is characterized by a good signal / noise ratio and a high multiplication factor from ζ calibrates.

The object set is thereby achieved according to the invention solved that the released secondary electrons are directed to the entrance of a channel electron multiplier, in which they are multiplied again and a current depending on the amount at a collector adjacent to the output of the impinging primary electrons.

It has surprisingly been found that the signal / noise ratio is better than using just one channel multiplier.

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The arrangement according to the invention is also at low levels Quantities of primary electrons suitable. The arrangement can contain a photocathode or a heatable cathode to generate the primary electrons. The arrangement can also be in one Piston be arranged, which is opened for the replacement of the dynode and then sealed again with connection to a vacuum system can be.

The invention is explained in more detail below with reference to exemplary examples shown in the drawing. Fig. 1 and FIG. 2 each show embodiments of a photomultiplier tube according to the invention in cross section.

The electron multiplier assembly is in an evacuated one Piston 10 arranged, which has a permeable part, so that light or other radiation on a photocathode 1 can fall.

Primary electrons, indicated by the arrow A, released from the photocathode 1 by the incident radiation migrate to a dynode 2, where necessary assistance from the action of an electric field from the grid 11 takes place. A suitable electrical potential can be applied between the terminals 12 and 21 in order to create the electrical field to create. The primary electrons striking the dynode 2 trigger secondary electrons from the surface of the material of the dynode, the number of which is greater than the number of primary electrons. The construction described so far is known. The dynode can be made of a metal or an alloy, which easily emits secondary electrons, or it may be coated with such a metal or alloy. The piston can be designed so that it can be opened so that

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the dynode can be exchanged and thus throwing away the entire tube can be avoided.

The secondary electrons are moved by the dynode 2 due to their shape and possibly by an electric field to the entrance opening 31 of a channel multiplier element 3 passed. The element 3 can consist of a horn 32, which acts as a preamplifier for the actual multiplier 33 is used. Such horn designs are known in the art. The inside The horn is coated with a material that easily emits secondary electrons. The multiplier 33 can consist of one or consist of several tubular strands of glass, which have such a high conductivity that one between the ends of each Strands applied potential difference in the tube and in the strand creates an electric field through which secondary electrons, which are generated by an electron striking the horn 31 or directly on the multiplier, passed through the tube will. The electrons hit the wall of the tube and generate by emission from the wall or one located on it Coating more and more secondary electrons. Instead, you can use two parallel plates with a resistive layer be provided on their adjacent, larger surfaces, so that in the same way in one by a potential difference an electric field generated between the ends of a plate occurs. The potential difference can between terminals 35 and 36 are fed.

In either case, the multiplier is preferably curved or twisted in order to avoid a straight path between its ends and thus the backward scattering in a known manner to diminish. An opaque wall 13 prevents stray radiation from the channel multiplier to the dynode 2 or to the input 31

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The secondary electrons exit at the exit 34 and are collected at a collector 4.

For the person skilled in the art, it is important that a corresponding potential must be present at the cathode.

A more compact arrangement is shown in FIG. 2, in which the same parts have the same reference numbers as in FIG. 1 are provided. Here the channel multiplier 3 is curved around the entrance area, but it is separated from it by a Wall 13 separated. A cone 14 becomes the dynode 2 enclosing cylindrical input area in the piston 10 fixed, which consists of a larger cylinder with a usual tube base can exist. In both embodiments these are "end views", but the arrangement according to FIG. 2 in the piston 10 can also be used as a "side view type" be arranged, giving the duct duplicator the required curvature.

The arrangements described above represent electron multipliers which have very high gain, but with the noise and other disadvantages of previous proposals The fact that a dynode is placed in front of a channel multiplier can be reduced from the high single-stage Use can be made of, for example, five to about fifteen times amplification of the dynode. at The channel multiplier works with low incident radiation levels with an input signal level at which the signal-to-noise ratio is better without the need for bulky stacks of Dynodes must be used. The arrangement according to the invention is particularly suitable for low-voltage photometry, the. Spectro-photometry, photon counting, thermo-luminescent

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Data display and astronomy. The primary electrons can be emitted from a photo-cathode in the manner described or generated by a heated cathode or other source. The arrangement is therefore not only for light but also for others Radiations suitable.

A multi-channel electron multiplier can also be provided in a piston, with each channel having a dynode, contains a channel amplifier and a collector. The dynode element can also contain more than one dynode, so that above In addition, the signal-to-noise ratio is further improved without the space requirement increasing unduly,

-Patent claims-

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Claims (9)

Patent claims: ί1.J electron multiplier, in which a dynode electron multiplier element is provided in an evacuated flask, from which secondary electrons are released when primary electrons strike, characterized in that the released secondary electrons are sent to the input (31) of a channel electron Multiplier (33) are directed, in which they are multiplied again and generate a current at a collector (4) adjacent to the output (34) depending on the amount of primary electrons incident. 2. Electron multiplier according to claim 1, characterized in that it contains an electrode grid (11) on the side of the dynode on which the primary electrons impinge, to which a potential can be applied to effect the impingement of electrons. 3. Electron multiplier according to claim 1 or 2, characterized in that a photocathode (1) is provided on the inner surface of a transparent part of the piston next to the dynode (2). 4. electron multiplier according to one of claims 1 to 3, characterized in that the piston can be opened and closed again and the dynode can be replaced. 5. electron multiplier according to any one of the preceding claims, characterized in that numerous in the piston 6 0 9 B Ia 3/0 7 U 7 Groups of dynodes, channel multipliers and collectors are provided to form a multi-channel electron multiplier. 6. Multi-channel electron multiplier according to claim 5, characterized in that a single photocathode is provided for generating the primary electrons for the dynodes. 7. electron multiplier according to one of the preceding claims, characterized in that the channel multiplier has a horn preamplifier. 8. Electron multiplier according to one of the preceding claims, characterized in that the channel multiplier is returned to the dynode and is separated therefrom by an opaque wall (13). 9. electron multiplier according to one of the preceding claims, characterized in that the dynode element consists of two dynodes connected in cascade. Bs / dm 6098 4 3/07 / ₊ 7 Blank page