US2189972A - Secondary electron emitter - Google Patents

Description

Feb. 13, 1940.

r R. WARNECKE ETAL SECONDARY ELECTRON EMITTER Filed April 19. i939 l/OZTS y INVENTOR. ROBER WRNEC/END ANDRE R/OT EY MW 'Zd/f" ATTORNEY.

Patented Feb. 13, 1940 2,189,972 l SECONDARY aLacTaoN EMITTER Robert Wamecke and Andre riot, Paris, France,

assignors to Compagnie Generale de Telegraphie Sans Fila corporation of France Application April 19, 1939, Serial No. 268,734

In France April 22', 1938 4 claims.` (o1. 25o- 174) The present invention relates to materials having a high secondary to primary electron emission ratio and primarily useful for electrodes for electron multipliers and similar discharge devices 5 which utilize secondary electron emission.

It is known to coat secondary `electron emitters with layers having either an alkaline earth oxide base or with complex layers having a caesium base. The emitters with the oxide base are stable and can be easily prepared, but have a rather low coefficient of secondary electron emission, which `is the quotient or ratio obtained by dividing the number of. secondary electrons bythe number of primary electrons.` The emitters 'having the caesium base have a substantially higher secondary electron emission coefcient, but are difficult to prepare and are susceptible to deterioration on rather slight in.

creases in temperature; furthermore, it is diicult to obtain several identical surfaces which have the same coeflicient of secondary electron emission.

The principal object of our invention is to provide a secondary electron emitter which has a greater coeiiicient of secondary electron emission and substantially as good stability as prior emitters with alkaline earth oxide bases. Another 'object is to facilitate the making of such emitters.

In accordance with our invention we make the surfaces or electrodes of high secondary electron emissivity of a base consisting of. alloys of light metals, such as aluminum and beryllium, with the addition of a small amount of ferrous metal, such as iron, and of a metalloid, preferably silicon.

We have found that by adding a small amountr oi iron and silicon we can obtain alloys which consist predominantly of aluminum and contain up to 30% of beryllium; No prior alloys of this kind which contain more than a Vsmall percent' age of beryllium are known to us. Theaddition of the iron and silicon to the alloys of aluminum with beryllium produces a new material, `as vit seems to modify the physical structure so that" the proportions of beryllium` to the other light metal, such as aluminum. For example, the beryllium may constitute from 10% to 30% of the alloy, the iron and silicon addition about 1% `least half or more of the addition.

`electron emissivity.

to 10%, with the remainder the other light metal,

such as aluminum. 1 The ratio of iron to silicon in the addition may vary widely, although in general it is `desirable that the silicon constitute at ciiic alloy which we have found to be especially suitable for secondary electron emitters is of the pressed in volts, the secondary electron emissioni coenicient obtained with the above alloy. For a velocity of 400 volts of theprimary electrons,

the secondary emission coefficient exceeds the value of 5, which is somewhat below the values ing a caesium base. On the other hand, emitters made of this alloy in accordance with our invention have marked advantages over the caesiated type because of facility in preparing the. electrodes, regularity of the results obtained, and the very high stability; and our emitters also have advantages, as the secondary electronemission obtainedirom emitters of this alloy is substantially greater than can `be obtained from the surfaces with alkaline earth oxide base ordinarily employed. 1

, 'Ihe preparation of electrodes made from the alloy in accordance with `our invention is simple. For instance, the electrode made from such alloy is placed in a glass vessel in which is created a high vacuum (of the order of 10%'7 millimeter mercury), whilethe electrode is freed from occluded gases by heatingit with high frequency inductive heating or electronic bombardment. No treatment other thandegassing in high vacuum is necessary to develop the high secondary The electrodes or emitters thus obtained have the advantage of a high thermic stability. They are of particular use in tubes with multiplying emitters or electrodes which dissipate through radiation a rather large amount ofenergy and t which therefore should be able to stand relatively high temperatures such as (300 C.) `without "losing their emitting properties.

We claim: l. A secondary electron emitting electrode for electron multipliers and the like having a sur- `face of' high secondary electron emissivity and composed of `an alloy consisting of 10% to 30% the balance4 aluminum;

One spe- 2. A secondary electron emitting electrode cOmposed of an alloy consisting of 15% to 25% beryll5 obtained with complex or caesiated surfaces liav-v` lium, 1% to 10% of an addition consisting of iron and silicon in which the silicon equals or yexceeds the iron, and the balance aluminum.

3. A secondary electron emitting electrode com- 5 posed of 74% aluminum, 21% beryllium, 2% iron and 3% silicon.

y 4. A secondary electron emitting electrode composed of an alloy consistingof a basev constitut- ROBERT WARNECKE. ANDRE BRIOT.

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