US2945144A - Secondary electron multipliers - Google Patents

Description

July 12, 1960 sc lD ETAL 2,945,144

SECONDARY ELECTRON MULTIPLIERS Filed July 11, 1958 mxmxwggtfqin'g nggawnm i d Fig.5

Jnventbrs= Patent SECONDARY ELECTRON MULTIPLIERS Lothar Schmidt and Eberhard Hahn, Jena, Germany, assignors to VEB Carl-Zeiss Jena, Jena, Germany Filed July 11, 1958, Ser. No. 748,101 8 Claims. or. s s-4s of secondary electron multipliers. To this end, two sep arate -multipliers have generally been applied, bug a secondary-electron multiplier is known which comprises two multiplier systems and two cathodes in one evacuated vessel whose vacuum-technical properties serve the purposes of bothsystems. Yet, the existence in this .so-called twb-way multiplier of two separate photocathodes and the a fact that the two multiplier systems are not symmetric to each other may, however, have unwanted and-deleterious consequences.

7 Patented July 12, 1960-.

symmetric systems than in single multipliers or in a valve with separate and asymmetric cathodes.

In the accompanying drawings, which represent several constructional examples of multipliers according to the invention, Figs. 1 and 2 show schematically a multiplier system in longitudinal and in cross section, respectively.

Fig. 3 illustrates the lines of force of a particular case, and Figs. 4, S and 6 show two further embodiments.

'The two-system multiplier arrangement illustrated in Figs. 1 and 2 has in a cylindrical evacuated vessel 1 a 3 and 3 are symmetrical. Opposite the cathode 2 isan 'transparent cathode 2 in which two multiplier systems auxiliary electrode 4 to which cathode potential is applied and which constitutes together with the cathode a doubly slotted cylinder. When the same potential, i.e. cathode potentiaLis applied to these cylinder parts, they produce an electron-optical elfect which is practically that of an;

The present invention, which aims at providing a multi system multiplier exempt from the disadvantages inherent in the known constructions, equips a secondary-electron multiplier having one photocathode and two, or more dynodejsystems disposed in one evacuated vessel,]w'ith electrostatic or magnetic deflecting means of great dir ectionalbcam effect influencing the field in closeproxi'rnity tothe cathode directing the photo electrons released by separate light beams from the common photocathode into'one each of the systems.- It is advantageous to coordinate the electrode systems symmetrically to the cathode. When' using two' multiplier systems, it is pos-'" sible, for instance in the 'space.--surrounding the cathode, by applying corresponding potentials tothe iinputelectrodes ofthe two multiplier systemspin connection with; an auxiliary cathode at cathode potential, which may be;

the cathode itself, to produce such a field distribution that two light beams incident at a certain distance from each other convey the photo-electrons releasedfrom the cathode surface in difierent', preferably opposite directions and," accordingly, into one each of the multiplier systems.

Arnultiplier construction of this kind oifers considerableadvantages over known apparatus. The spectral distribution of the sensitivity of the .photocathode in the multiplier apparatus according to the invention holds good for all photo-electrons released in this apparatus. Changes in the properties of the photocathode also take effect on all released photo-electrons alike. Furthermore, the sym- -:""*metrical arrangement of the multiplier systems permits the thermal dark current of'the photo-cathode to be distributed statistically uniformly over all systems. This symmetry moreover guarantees a uniform formation, which results in uniform properties of thecntire valve with respect to vacuum, fatigue and amplification factor. The symmetric construction of the systems offers manifold possibilities ofcomparative photometric measurements, particularly when compensation and coincidence methods are concerned, since in apparatus elfecting such measurement also the uniform distribution of the capacities is particularly advantageous. A still further advantage consists in a comparatively simple construction. Finally, conditions of linearity as well as the dependence of the over-all amplification on the over-all voltage can evidently be correlated individually and much better in undivided cylinder; Applying to the input electrodes 5,

5' of the two multiplier systems positive potential relative to the cathode calls forth the potential lines schematically a shown. in Fig. l, viz. an anticlinal formation typical withelectrostatic electron lenses designed for electrodes of the kind of 3-4, 4-3.

If two light pencils 6, 6' spaced.

deviated by the potential field effect into ditferentdirec tions. .These photo-electrons: travel through the apertures in the electrodes 5 and 5' and arrive in one each of the two multiplier systems. An arrangement of this kind permits 1 in a comparatively simple manner to obtain- "elfects which are advantageous in measuring technique, it being possible, for instance, to alternately deviate ,also, the two photo-electron fluxes released by the'lightpencils 6 and; 6' into one of the multiplier systemsby alter nately applying negative potential to one of theelecti'odes 5 and 5'.

This process will -now ,he explained: with reference "to Fig," 3, which illustratee the .magneticflux typical of the case. here concerned. .According to the adjustment of the potential 'of the, electrodes 5 and 5f;

relative to that of the cathode, it is also possible, for.

7 instance, to direct the electrons released the -light pencil 6 through; the aperturein-the electrode 5,;whi le.. the photo-electronsrejleased bythelight pencil 6' are intercepted by this; electrode 5.. By reversing the polarityf V of the electrodes 5 and 5', theelectrons released by ,thef light pencil 6' can'be directed in the same manner by way of the aperture in the electrode 5 into the multiplier systemS, while the electrons released bythe light pencil g are intercepted by the electrode 5.

The constructional examples illustrated in Figs. 4, 5 and Z 6 show that the multiplier systems can be coordinated to common cathode also in another manner. Inthe arrange-} ment represented in Fig. 4, a section through lineX--X' of which is shown in Fig. 5, an evacuated vessel 7 contains a transparent cathode 8 and two symmetrical multiplier systems 9 and 9, which are parallel to each other and have collector electrodss 10 and 10', respectively. To avoid mutual interference, the multiplier systems are separated from each other by a web 11 to which is supplied a potential precluding changes of the electrons from the one system to the other. Suitably chosen potential relations between the cathode and the auxiliary electrodes 12 and 13 permit the field in the space around the cathode to be given a shape as indicated by the dash-lines 14. It is of importance in this case to obtain quite near the cathode a field distribution guaranteeing a comparatively high directional-beam value. Photo-electrons not emanating at right angles to the cathode surface are thus prevented from getting into the wrong multiplier system. High directional-beam values canbe obtained in different ways. In the arrangement according to Figs. 4 and 5, the

desired eflect is arrived at by a relatively strong field near the cathode.

The embodiment shown in Fig. 6 has two multipher systems 15 and 15' so placed opposite to each other that bothsystems'havein each stage one electrodetlti, 17,

18, 19) incommon, Between the cathode 20 andthe input electrodes 21, -21 of the multiplier systems is disposed another auxiliary electrode, 22, which may contain in a small cup 23 the evaporation coil for the cathode-support metal. t e

We claim: 1

1. A secondary electron multiplier for amplifying the photoelectric current of at least two separate beams of light, comprising in an evacuated vessel a common' photocathode, a separate dynode system for each of said beams, and deflecting means disposed in close proximity to said cathode, said deflecting means having a great directional-ray effect and directing the photo-elec said photocathode into the corresponding of said separate dynode systems. v U 3. A secondary electron multiplier for amplifying the photoelectric current of two separate beamsof light,

comprising in an evacuated vessel a common photocathode, two dynode systems and deflecting means in close proximity tosaidcathode, said deflecting means having a great'directional-ray eflect and directing the photo-electrons released by said separate beams from said photocathode into the corresponding of said dynode systems, said photocathodef having a cylindrical; surface, said surface and those inputelectrodes of said two dynode systems, to whichpositive potential is applied relative to said cathodeconstituting an electrostatic lens. e

4. A secondary electron multiplier'for amplifyingthe photoelectric current of two separate beams of light, comprising in an evacuated vessel a common photocathode, two dynode systems and deflecting means in close proximity to said cathode, said deflecting means. having a great directional-ray efiect and directing the photo-electrons released by said separate beams from said photocathode into the corresponding of said dynode systems, said photocathode having a spherical surface, said surface and those input electrodes of said two dynode systems to which positive potential is appliedrelative to said cathode constituting an electrostatic lens.

5. A secondary electron multiplier for amplifying the photoelectric current of two separate beams of light. comprising in an evacuated vessel a' photocathode, two dynode systems and deflecting means in close proximity to said cathode, said deflecting means having a great directional-ray effect and directing the photo-electrons released by said separate beams from said photocathode into the corresponding of said dynode systems, said photocathode being divided into at least two parts insulated from each other to which cathode potential can be applied selectively.

6. A secondary electron multiplier for amplifying the current of two separate beams of light, comprising in an evacuated vessel a photocathode, two dynode systems and deflecting means in close proximity to said cathode, said deflecting means having a great directional-ray effect and directing the photo-electrons released by said separate beams from said photocathode into the corresponding of said dynode systems, the surface of said photocathode being divided into at least two parts insulated from each other to which .a potential difierent from that of said cathode can be applied singly or in pairs.

7. A secondary electron multiplier for amplifying the current of two separate beams of light, comprising in an evacuated vessel a photo cathode, two dynode systems and deflecting means in close proximity to said cathode, said deflecting means having a great directional-ray effect and directing the photo-electrons released by said separate beams from said photocathode into the corresponding of said dynode systems, said photocathode having a cylindrical surface, said surface and the input electrodes of said two dynode systems to .which the same positive potential is. applied relative to said cathode constituting an electrostatic lens.

&,A secondary electron multiplier for amplifying the current of two separate beams of light, comprising in an evacuated vessel a photocathode, two dynode systems and deflectingrneans in close proximity to said cathode said deflecting means-having a great directional-ray effect and directing the photo-electrons released by said sep-, arate beams 'from said photocathodeinto the cor; responding otsaid dynodersystems, saidphotocathode. having a spherical surface, said surface and the inputelectrodes of said two dynode systems to which the'same positive potential is applied relative to said cathode constituting' an electrostatic'lena- I ReferencesCited thefile of this patent UNITED STATES PATENTS.

2,160,797 Teal May '30, 1939 2,431,510 Salinger Nov. 25, 1947 2,433,700 Larson Dec. 30, 1947 FOREIGN PATENTS 7 748,720 Germany Nov. 8, 1944

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