US2463743A - Hydrogen tube - Google Patents

Description

March 8, 1949.

H. H. CARY ETAL HYDROGEN TUBE Filed D60. 29, 1945 INVEN TOPS HENQY CARY 5/ WARREN f? BAXTER HARP/5, /ECH, FOSTER (ff/A RRIS QFAQOZ FOR THE FIRM A TTORNE vs Patented Mar. 8, 1949 HYDROGEN TUBE Henry 1!. Gary, Alhambra, and Warren 1'. Baxter, Pasadena, Calif alslgnors to National Technical Laborateries, Pasadena, Calif.\a corporation of California Application December 29, 1945, Serial No. 638,062

1 .16 Claims. Our invention relates to gas-filled electron tubes and, more particularly; to a. novel hydrogren tube of small size and long life particularly suited for use in spectrophotometry where it is desirable to have a concentrated source of continuous ultra violet radiation in the region of about-300450 miilimicrons but without stron lines in the spectrum within this. band. The invention is primarily concerned with the so-called low voltage or thermionic hydrogen discharge tubes in which voltages ranging from about 50- 100 are suflicient to maintain the discharge.

Heretofore. hydrogen tubes of this type have been quite bulky and open to many objections. The most common construction provides a relatively large glass envelope having a. quartz or fused silica window sealed across an aperture of the glass for transmitting the ultra violet radiation from the tube. Within the glass envelope, such tubes provide a metallic enclosure surrounding the cathode and having a small opening through which the electron stream moves on its way to an arcuate anode positioned between the enclosure and the glass envelope and having a larger opening disposed between the window and the small opening of the enclosure. The interior of the glass envelope is filled with hydrogenand electrons from the heated cathode move outward through the small opening under the attraction of the positively-charged anode.

Attempts to reduce the size of such conventionally-constructed hydrogen tubes have heretofore resulted in an unexplained and very substantial decrease in tube life, accompanied by rapid darkening of the window and/or by reduction in intensity of the discharge itself.

It is an object of the present invention to provide a small hydrogen tube of long effective life. By a long-lived tube we have reference to a hydrogen tube having a useful life of at least 200 hours. According to the teachings of the present application, the life can be made over 1000 hours, a life of 3000 hours being quite common.

We have found that very substantial and unexpected advantages arise from a. general reversal of the customary position of the cathode and ani-de, and it is an object of the present invention dispose the anode within a metallic enclosure mounted in the tube envelope, this enclosure having a small aperture, and to dispose the cathode outside this enclosure at such position that the electron flow through the small aperture is inward rather than outward. In small hydrogen tubes, in which the window must necessarily be placed close to the small aperture, the window is 2 prone to darken rather rapidly due to a deposit of metal or metal oxides. We have found that the particles causing the deposition travel from cathode to anode whereby, in conventional tubes,

these particles travel in a direction causing some proportion of them to fall on the window. In the modified inside-out construction herein disclosed, such particles move in an opposite direction and tend to deposit on the metallic internal elements of the tube. This inside-out construction alone tends substantially to increase the life of small hydrogen tubes by substantially preventing depositions on the window from this source, but such reversal of anode and cathode will not, in itself, eliminate some of the other difliculties to be hereinafter mentioned.

Extensive research has shown that the life of a small hydrogen tube in affected by window depositions from other sources and by chemical reactions within the tubeduring or prior to its operation, and it is an object of the invention to minimize such depositions. The chemical reactions responsible for the depositions have apparently not heretofore been recognized as taking place in hydrogen tubes. They may be classified generally as water-forming and hydrogen-consuming reactions.

We have discovered that, even with the electron flow reversed, there is still some tendency for the window to darken. The primary cause has been traced to a disintegration of the tungsten usually employed to bound the small opening of the metallic enclosure. In this connection, a small amount of water vapor may be present in the atmosphere of the tube due to any one of the water-forming chemical reactions hereinafter mentioned. This water reacts slowly with the tungsten to form tungsten oxide which is vaporized at the existing temperature, the vapors being condensed on the cooler portions of the tube, including the window. This disintegration of the tungsten bounding the small opening produces a gradual enlargement of the opening.

It is known that atomic hydrogen can be formed by intense electrical discharges in hydrogen gas, and we have found that this may occur in hydrogen tubes of the type with which the present invention is concerned. Atomic hydrogen is a gas having an exceedingly high chemical reactivity and it can combine with compounds otherwise stable to hydrogen, such as certain constituents of glass. It recombines to form molecular hydrogen readily when in contact with metallic surfaces, but is relatively stable in the absence of a of the hydrogen atmosphere. to renew continuously or from time to time the surface on which the recombination can take place.

One of the objects of our invention is to expose I the gases which havev participated in.-the discharge to surfaces favoring the recombination of hydride.

atomic into molecular hydrogen before the stream of gases comes v into intimate contact with the window or other surface of the glass envelope of the tube on which deposits are undesirable. This It is also an object of the present invention to provide a body of material which presents a reaction surface to any atomic or ionic hydrogen in the tube to convert such atomic or ionic hydrogen may be achieved by employing a suitable shield, into molecular hydrogen and thus tend to prevent usually connected to the metallic enclosure of the tube. to form a chimney to direct the hot gas stream from the discharge against a selected zone of the envelope, usually the upper interior surdisposed ballles. Any atomic hydrogen or tungsten oxide vapors can thus be carried to a selected portion of the enclosure to prevent promiscuous contact with other portions thereof. The shield depletion of the hydrogen atmosphere. A further object is to dispose such material in protecting relationship with a glass envelope of a'hydrogen tube, particularly in a zone thereof most likeface thereof, or against suitably constructed and ly to receive the atomic or ionic hydrogen. Ifthe aforesaid shield is employed to establish convection currents toward a selected zone of the envelope, the invention contemplates the placing of a coating of such material on theenvelope in this m y also Prot ct the window against direct radiazone. The aforesaid metal shield itself presents tion from the cathode. Such a shield may provide a larger aperture transmitting the radiation from the small aperture of the enclosure to the window. and can be made to reduce the area of the an extensive surface which tends to be contacted by such atomic or ionic hydrogen to cause recombination into molecular hydrogen at the surface of the shield. In some instances we have found glass envelope exposed to the arc. It is .an object it quite satisfactory to employ such an extensiveof the present invention to provide a shield of this typ serving at least one of such functions.

Extensive experimentation with hydrogen tubes has shown that the amount of contained hydro,

gen tends to be reduced during operation of the tube. This is particularly serious in small hydrogen tubes and, in many instances, has caused failure of such tubes after a few hours of operation. It is an important object of the present invention to provide a means within the hydrogen tube for reducing the rate of depletion of the hydrogen gas.

Any water-forming reaction within the tube will, of course, tend to consume the hydrogen. For example, oxygen liberated from the metal parts of the tube or from contaminating oxides in the cathode coating will react with hydrogen to cause its depletion.

In addition, low voltage thermionic tubes require the use of an oxide-coated filament, the coating being usually a mixture of barium and strontium oxide. Molecular hydrogen will not appreciably react with and reduce such oxides but our investigation indicates that the oxides surface shield in the production of long-lived tubes, even without the preferred hydride coating, and such a construction is included among the objects of the invention.

I It is also an object of the invention to provide novel methods of making long-lived hydrogen tubes, including the step of insuring complete vaporization of a hydride-forming metal in the presence of excess hydrogen to prevent hydrogen- 5 consuming reactions after the tube is sealed.

Another object is to provide multiple metal-vaporizing steps to insure this complete vaporization and conversion to the hydride.

Another object of the invention is to provide a vacuum tube having a glass envelope, a section of the glass itself being made thin to provide the window, thus avoiding the necessity of sealing quartz or fused silica windows to a glass envelope.

Further objects and advantages of the invention will be evident to those skilled in the art from the follower description of an exemplary embodiment.

Referring to the drawing, in which the prereact with the activated forms of hydrogen, such ferred hydrogen tube is shown of a size approxas atomic hydrogen or various ionic forms which may be produced in the discharge, with the production of water and metallic barium or strontium. Thus, the reaction has two undesirable conimately double that employed in practice:

Fig. 1 is a vertical sectional view of the tube with the internal parts shown in elevation;

Fig. 2 is a vertical sectional view, taken on the sequences, the production of water and depletion line 2-2 of Fig. 1;

It is impractical hydrogen atmosphere, nor is it feasible, particularly in small tubes, to employ enough hydrogen initially to prevent depletion in several hundred hours of operation.

We have found that the life of a hydrogen tube can be greatly increased if it contains a chemical compound capable of reacting with water to take Fig. 3 is a horizontal sectional view, taken on the line 3-3 of Fig. 2; and

Fig. 4 is a side view of the internal elements of the tube, taken as indicated by the arrow 4 of Fig. 1.

up the oxygen and release the hydrogen, and it manufacturing process, is connected to a suitable is an object of the invention to employ such a compound for this purpose, typically a metal hydride. In this way, the actual amount of hydrogen within the tube can be maintained subglass tube through which the envelope l0 may be evacuated or supplied with a hydrogen atmosphere. The lower indented end of the envelope l0 provides an element-supporting member l2 stantially constant or even increased with use of in which are sealed conductors l3 and It for supthe tube. It is another object of the invention to deposit such a chemical compound on internal surfaces of the tube by vaporizing a suitable metal in the tube, the vapors reacting with hydrogen plying filament current, and conductor I5 for supplying anode potential. That portion of the element-supporting member I 2 around the conductor I5 is formed as a head it. The conto form the hydride and these vapors condensing ductors l3, l4, and I! are connected to suitable flexible leads or to the prongs of a suitable base, as desired.

A vertically-elongated portion ll of the glass envelope II is blown outward during its manufacture and, after selective reheating, is sucked inward to form a window 26 of the general shape shown in Figs. 2 and 3. The window 20 is relatively thin as compared with the remaining walls of the glass envelope Ill. Very satisfactory results have been obtained by using a glass particularly suited to the transmission of ultra violet radiation, e. 8., a glass known in the art as Corning No. 974. The window 20 is usually made of a thickness of only about .005" to increase the transparency to ultra violet radiation,.and the resulting window is practically as transparent as a quartz window 1 mm. thick. This construction avoids the difficult problem of sealing separate windows to the envelope.

Within the envelope In is a metal enclosure, best shown in Figs. 2, 3, and 4 and indicated generally by the numeral 25. This enclosure can be formed of tubular or sheet stock nickel bent to form a front wall 26, side Walls 21 and 28, and a rear wall 29, defining an upright space 30 closed at its upper and lower ends by flanged plates 3i and 32. The plate 32 provides an opening having a lip 33 which rests, on, and is supported by, the upper hemisphere of the bead l6. The enclosure 25 is also supported by welding of the side wall 28 to the conductor H. A small tungsten plate 34 is spot welded to the front wall 26 at the midsection of the tube, and provides a small aperture 35 aligned with a larger opening of the wall, this small aperture serving to concentrate the electron flow.

Disposed in the enclosure 25, and preferably out of alignment with the small aperture 35, is an anode 31, conveniently a nickel plate welded to the top of the conductor i and extending fore and aft of the tube.

The cathode, indicated generally by the numeral 40, is disposed outside the enclosure 25, preferably adjacent a corner thereof so as to be spaced from a line joining the window 20 and the small aperture 35. Preferably, this cathode is a narrow strip of metallic screen stretched between upper and lower supports 4| and 42, respectively welded to the upper ends of conductors M and i3. correspondingly, one end of the oathode M is electrically connected to the enclosure iii. At least the central portion of the metallic screen is oxide coated to produce adequate electron emission when heated to relatively low temperatures, a preferred coating being a mixture of barium and strontium oxides. I

A member 45 is welded to the side walls 21 and 26 and provides a portion extending transversely of the tube between the front wall 26 and the window 20. This member 45 extends around the cathode 40 in a manner best shown in Fig. 3. Its height is preferably equal to the height of the enclosure 25. A baiiie l6 divides the space bounded by the member 45 and the enclosure 25 into an upright space 41 immediately in front of the front wall 26 and an upright cathode-receiving space 48. Both upright spaces are open at their upper and lower ends, and the temperature therein is such as to establish strong convection currents toward the upper interior of the glass envelope l0, thus serving to establish circulation paths within the hydrogen atmosphere, indicated generally by the arrows 49. The bailie 46 provides an aperture 50 near the midsection of the cathode l0 and in horizontal alignment with the small aperture 36. Similarly, the member 45 provides an aperture 52 substantially larger than the aperture 35 and disposed between the latter and the window 20 to frame the ultra violet radiation and confine this radiation to the central portion of the window 20. That portion of the member- 45 extending forward from the side wall 21 and to the baiiie 46 is hereinafter referred to as a shield 55.

Extending upward from, and welded to, the rear wall 29 is an arm 58 carrying a plate 59 concave toward the front of the glass envelope l0. Mounted on this plate is a small metal tab 60. This tab contains metal or substances forming metal on heating, which metal is adapted to be vaporized during manufacture of the hydrogen tube in a manner similar to that employed in the vaporization of a getter in the manufacture of high vacuum tubes, namely, by inductive heating thereof from a position. outside the glass envelope Ill. The resulting vapors or reaction products thereof will move to the upper interior surface of the glass envelope and condense to form a coating 62. Some advantages arise from the presence of this coating entirely aside from its composition. For example, any material coated on the upper interior of the glass envelope will tend to form a protective surface therefor. Atomic or ionic hydrogen, carried by the circulation indicated by arrows 49, will contact such a coating 62 so that the atomic or ionic hydrogen will tend to recombine into molecular hydrogen. thus tending toprevent hydrogen depletion within the envelope.

However, itis particularly advantageous that this coating be a metal hydride. To produce such a coating, we prefer to vaporize, in a hydrogen atmosphere, a hydride-forming metal and the tab 60 may be composed of, or may include as a component, or may partially enclose, such a metal or substances adapted to produce such a metal. This metal may be either a hydrideforming alkali metal or alkaline earth metal. the latter being distinctly preferable as the alkali metal hydrides are quite volatile and tend quite rapidly to decompose to re-formthe alkali metal and liberate hydrogen at the operating temperature of the tube. Such alkali metals can be em.- ployed in certain circumstances but the alkaline earth metals have been found generally superior for the intended purpose.

For example, if the small tab '60 is made of calcium, vaporization thereof in a hydrogen atmosphere causes the vaporized calcium to react with the hydrogen to produce the hydride which deposits to form the coating 62. Thereafter and during normal use of the tube, this calcium hydride is available to react with any water vapor present or formed, according to one or both of the following formulae:

' Reaction in accordance with Equation 1 is slow and that in accordance with Equation. 2 predominates. A further reaction, though very slow as involving the reaction of two solids, may also be present, as follows:

Ca (OH) 2+CaH2- 2 Ca0+2H2 (3) Each of the above reactions is hydrogen-liberat ing and, in itself, tends actually to increase, during use of the tube, the total amount of gaseous hydrogen within the glass envelope. We have than normal.

found that hydrogen-liberating reactions can be made to balance or over-balance other hydrogenconsuming reactions in the tube, particularly when the shield 55 is employed to establish con.- vection currents previously mentioned.

Similarly, strontium or barium can be employed as the hydride-forming alkaline earth metal and, from equations similar to those above, it will be seen that any water vapor forming during operation of the tube will react with the hy dride to renew, or prevent depletion of, the hydrogen atmosphere. It is important, however, that the hydride-forming metal of the tab 60 be completely vaporized. Our experience has shown that, unless this is done, the remaining metal may slowly react with the sealed-in hydrogen atmosphere in a manner tending to consume same. However, as will be later pointed out, it is not always essential that all of the metal be vaporized in the presence of hydrogen during the tubemanufacturing process as some advantages can be derived from partial vaporization while the tube envelope is evacuated.

'In practice we prefer to employ as the small tab 60 an alloy of barium with magnesium and/or aluminum and to employ the following procedure in the manufacture of the hydrogen tubes of the invention:

After the tube elements are in place and while the upper end of the glass envelope is connected to a suitable glass tube by which the envelope and its elements can be supported, evacuated, or pressured with hydrogen, the envelope is exhausted by suitable means, usually by the combined use of a mechanical vacuum pump and a diffusion pump, until the internal pressure is about 10- mm. of Hg. The envelope is then filled with hydrogen to a pressure of about one atmosphere and is surrounded by an electrically heated oven which brings its temperature to about 525 C., after which it is cooled to about 345 C. This anneals and removes the strains from the glass envelope. When the temperature drops to about 345 C., the envelope is evacuated to about .05

mm. of Hg and the temperature is again raised to about 425 C. during continued evacuation to an even lower pressure, thus baking out the glass and removing water vapor therefrom. The tube is then permitted to cool to about 400 C., with the vacuum applied, after which the oven is removed.

The filament is then outgassed under vacuum ,while operating at a bright red heat, much higher Hydrogen is then admitted to the envelope and the internal elements are heated to a red heat by an induction coil surrounding the envelope to continue the outgassing operation. In the preferred operation, the heat applied at this point is not sufficient to vaporize the metal of the tab 60. The envelope is then again evacuated and the filament is further outgassed at a bright red heat in the manner noted above.

Preparatory to vaporization of the small tab 80, hydrogen is admitted to the envelope until the pressure is about 60 mm. of HE. A small induction heater is then brought close to the back of the envelope adjacent the tab 60. The barium evaporates and forms barium hydride on its way to the upper interior wall of the glass envelope,

this hydride depositing on the glass to produce a' 'spongy deposit. The magnesium in a bariummagnesium-aluminum alloy will also deposit but, during this first flash vaporization, most of the aluminum remains in the tab 50. When the alloy in the tab contains no magnesium, the deposit 8 at this time is almost invisible because most of the barium has been reacted to form the colorless hydride.

It is important that all of the barium in the tab be evaporated and converted into its hydride before the tube is placed in use. If this is not done, the barium will continue to react with the hydrogen during use of the tube, it being understood that this reaction will be slow as only the barium on the relatively small surface of the tab would enter into this reaction. While a small residual amount of barium will be converted into its hydride in the subsequently-mentioned aging step, it is distinctly preferable to flash-vaporize substantially all of the barium by induction heating.

It is preferable to have complete vaporization in the first flash-vaporizing step, but this requires intense inductive heat applied for a sufficient length of time to insure such complete vaporization, and sometimes is difficult to accomplish in practice. To insure complete vaporization of thebarium, we prefer to re-heat the tab to a higher temperature by re-application of the induction heater. In the preferred practice, this is done after the envelope has been evacuated to aid in insuring complete barium vaporization. The residual barium thus vaporized does not form a hydride during its movement to the interior wall of the envelope but, instead, deposits as metallic barium on the previously-deposited spongy hydride coating. The observed result in practice is that the coating now becomes substantially opaque, albeit the coating is not necessarily continuous. The layer of metallic barium is extremely thin and, because of the spongy nature of its foundation deposit of hydride and also because of the relatively extensive area of the upper interior of the envelope, it presents a large surface area to any hydrogen later introduced into the tube, e. g., in the subsequently-mentioned aging step, whereby the metallic barium is completely converted into hydride within a few hours and before sealing of! the envelope.

It is next preferred again to outgas the filament by heating it to higher than normal temperature while the system is evacuated, as previously defined. Pure hydrogen gas is then introduced into the envelope to a pressure of about 7.6 mm. of Hg. If the hydrogen is not pure, it is desirable to introduce it through a cold trap to condense any condensabie material therein. The tube is then connected to a power supply and aged for about 16 hours, while still connected to the source of hydrogen to replenish any of the hydrogen used up during the aging. During this aging step, any metallic barium in the coating 62 is converted into its hydride. The tube is then sealed off and, after the usual tests, is ready for use.

As an alternative ofthe above procedure, involving flash vaporization of the barium in the tab 60 in the presence of a hydrogen atmosphere, it is possible to vaporize all of the barium while/the envelope is evacuated. In this instance all of the barium deposits on the inner wall of the envelope 'in a very thin coating and is entirely converted into its hydride in the later aging step when a continuously-replenished hydrogen atmosphere is present.

In the construction of the tube, we have found it very dfflicult to insure complete vaporization of/ the hydride-forming metal if, for example, the small tab 60 is placed on the exterior of the enclosure 25 and if an attempt is made to vaporize the hydride-forming metal during the enclosure-heating step mentioned above. In this instance the application of sumciently high temperatures, by induction heating, to insure vaporization of the hydride-forming metal is usually impractical as it often results in partial or complete destruction or burning of the enclosure 25, usually formed of nickel, not to mention heating of the glass to such temperature that it will melt. Such problems are solved .by mounting the tab 50 at a position spaced from the enclosure 25 so that it can be selectively heated to the flash-vaporizing temperature. The flag-like mounting of Figs. 1, 2, and 4 has been found particularly effective.

In the normal operation of the tube the electrons given oil from the cathode 40 move as a stream through the aperture 50 into the upright space ll, the stream turning therein and being confined by the small aperture 35 and moving to the anode 31 through the upright space 30 inside the enclosure 25. Without the shield, there will still be a substantial tendency for the window 20 to darken due to th spattering of tungsten oxide from the aperture-forming plate 34 and for loss of hydrogen to occur by reaction of the atomic or ionic form with the glass of the window. The presence of the shield 55 tends to prevent these actions and the interior surface thereof tends to receive such tungsten deposits and also tends to provide a metallic surface contactable by the atomic or ionic hydrogen and on which recombination can take place to re-form molecular hydrogen. Such functions of the shield 55 are probably aided by the upward thermally-induced flow of the hydrogen through the upright space 41. It is distinctly preferable that this upright space have its upper and lower ends open to the atmosphere of the tube. Tubes with the internal construction shown and employing the shield 55 are long lived, although it has been found that removal of the shield 55 will substantially shorten the life of the tube, and these statements hold even though the tube does not contain a coating 62 of hydride or metal on the surface of which the atomic or ionic hydrogen can recombine.

On the other hand, the tube life can be additionally extended and depletion of its hydrogen atmosphere further prevented by employment of the coating 52. This is true to some degree even if the coating 52 is formed of any protective material preventing contact of atomic or ionic hydrogen with the glass of the envelope. It is true to a very marked extent if the coating 62 is a hydride, thereby replenishing the hydrogen atmosphere, and in some instances even increasing the amount of hydrogen, during operation of the tube.

Various changes and modifications can be made without departing from the spirit of the invention as defined in the appended claims.

We claim as our invention:

1. In a long-lived hydrogen tube, the combination of: an envelope providing a window for passage of ultra violet radiation, the "interior of said envelope containing hydrogen gas; an enclosure within said envelope and providing a wall having a small aperture facing said window; an anode within said enclosure and on one side of said wall; a cathode outside said enclosure to be on the other side of said wall and adapted when heated to produce an electron stream moving inward through said aperture and to said anode; said electron flow tending to produce activated hydrogen reactable with the material of said window; and means within said envelope for converting said activated hydrogen into molecular hydrogen to avoid such reaction with the material of said window and to prevent depletion of said hydrogen gas.

2. A hydrogen tube as defined in claim 1, in which said small aperture is bounded by tungsten which tends to disintegrate and form a deposit on said window, and including a shield electrically connected to said enclosure for preventing such deposition on said window, said shield providing an aperture aligned with said small aperture of said enclosure for transmitting the radiation to said window.

3. In a long-lived hydrogen tube, the combination of: an envelope providing a window for passage of ultra violet radiation, the interior of said envelope containing hydrogen gas; an enclosure within said envelope and providing a wall having a small aperture facing said window; an anode within said enclosure on one side of said wall; a cathode outside said enclosure to be on the other side of said wall and adapted when heated to produce an electron stream moving inward through said aperture and to said anode. said cathode being disposed to one side of a line joining said aperture and said window; and a shield having an aperture larger than said small aperture and disposed between said window and said small aperture.

4. In a long-lived hydrogen tube, the combination of: an envelope providing a window for passage of ultra violet radiation, the interior of said envelope containing hydrogen gas; means for'establishing an electron flow through said hydrogen gas and for confining said electron flow opposite said window to produce intense ultra violet radiation, said electron flow tending'to produce atomic hydrogen; and means for preventing depletion of said hydrogen gas during use of said tube, said means including a surface exposed to said hydrogen gas and to said atomic hydrogen within said tube and on which said atomic hydrogen reacts with itself to produce molecular hydrogen.

5. A hydrogen tube as defined in claim 4,-ineluding means for guiding such atomic hydrogen to said surface.

6. A hydrogen tube as defined in claim 4, in which said envelope is glass whereby said atomic hydrogen tends to react therewith, and in which said surface comprises a layer of inert material not reactable with molecular hydrogen, said layer covering at least a portion of the inner surface of said glass.

'7. In a long-lived hydrogen tube, the combination of: a glass envelope providing a window for passage of ultra violet radiation, the interior of said glass envelope containing hydrogen gas; means for establishing an electron flow through said hydrogen gas of sufficient intensity to pro duce said ultra violet radiation and toproduce atomic hydrogen and thus tending to deplete the amount of hydrogen gas in said glass envelope; means for establishing a thermal circulation in said hydrogen gas from the vicinity of said electron flow and toward a selected zone of said glass envelope to carry atomic hydrogen toward said zone; and a body of material incapable of reaction with atomic hydrogen and disposed in the circulating hydrogen gas at a position to shield said zone of said glass envelope from substantial contact with the atomic hydrogen in the stream of circulating hydrogen gas, said material providing a surface contacted by said stream and on which the atomic hydrogen combines with itself to re-form molecular hydrogen and thus diminish depletion of said hydrogen gas.

8. A hydrogen tube as defined in claim 7, in which said body of material is a coating on the inside of said glass envelope occupying said zone thereof. 1

9. A hydrogen tube as defined in claim 7, in

which said material is a metal hydride capable 'to react with and liberate hydrogen when contacted by any water resulting from water-forming chemical reactions in said tube, said tube being further characterized by the substantial absence of any hydride-forming metal in contact with the hydrogen gas within said envelope and which would react with such hydrogen during operation of the tube.

11. As an article of manufacture, a long-lived hydrogen tube including in combination: an envelope providing a window for passage of ultra violet radiation, the interior of said envelope containing hydrogen gas; an enclosure within said envelope and providing a wall having a small aperture facing said window; an anode and a cathode on opposite sides of said wall and adapted to produce an electron stream moving through said aperture; and a vapor-deposited coating of metal hydride covering a portion of the interior of said envelope, said tube being further characterized by the substantial absence of any hydride-forming metal in contact with the hydrogen gas within said envelope and which would react with such hydrogen during operation of the tube.

12. As an article of manufacture: an envelope providing a window for passage of ultra violet radiation, the interior of said envelope being adapted to contain hydrogen gas; an enclosure within said envelope and providing a wall havinga small aperture facing said window; an anode and a cathode on opposite sides of said wall and adapted to produce an electron stream moving through said aperture; a small body of hydrideforming metal within said enclosure and selected from the class consisting of hydride-forming alkali metals and hydride-forming alkaline earth metals; and means for mounting said small body of hydride-forming metal in spaced relationship with said enclosure and sufiiciently close to said envelope to be completely vaporized by induction heating through said envelope whereby such heating will vaporize said hydride-forming metal and the resulting vapors will react with the hydrogen within said enclosure to form a hydride of said metal, said hydridedepositing on the interior surface of said envelope.

13. As an article of manufacture, a long-lived hydrogen tube including in combination: an envelope providing a window for passage of ultra violet radiation, the interior of said envelope containing hydrogen gas; an enclosure within said envelope and providing a wall Having a small aperture facing said window; an anode within said enclosure and on one side of said wall; a cathode outside said enclosure to be on the other side of said wall and adapted when heated to produce an electron stream moving inward through said aperture to said anode; a shield between said wall and said window and spaced from said wall to define an upright space open at its upper and lower ends, said shield providing an aperture framing the ultra violet radiation moving toward said window; and a coating of a metal hydride covering the upper interior of said envelope to be disposed in the path of a stream of hydrogen gas rising in said upright space, said tube being further characterized by the substantial absence of any hydride-forming metal in contact with the hydrogen gas within said envelope and which would react with such hydrogen during operation of the tube.

14. A long-lived hydrogen tube as defined in claim 3 in which said enclosure is formed of meta1, and in which said shield is also formed of metal and is electrically connected to said enclosure.

15. A long-lived hydrogen tube as defined in claim 3 in which said shield provides a space open at its upper and lower ends to the hydrogen gas in said envelope, said electron flow establishing a discharge moving through said space to heat the gas therein, the heated gas tending to rise in said space, said discharge tending to produce activated hydrogen, and in which said shield provides an extensive-area surface on which such activated hydrogen recombines to form molecular hydrogen.

16. In a long-lived hydrogen tube, the combination of an envelope providing a window for passage of ultra violet radiation, the interior of said envelope containing a body of hydrogen; means for establishing an electron flow through said hydrogen to produce ultra violet radiation; and means for preventing depletion of said hydrogen because of any water-forming reactions within said envelope, said means including means for establishing a thermal circulation in said body of hydrogen gas from the zone of said electron flow to a. selected zone inside said envelope and spaced from said window to carry to said selected zone any water in the circulating hydrogen, said last-named means including a metal hydride in the path of said circulating hydrogen to react with such water and release hydrogen.

HENRY H. CARY. WARREN P. BAXTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,917,848 Marden et a1 July 11, 1933 1,922,281 Dawson Aug. 15, 1933 1,991,479 Williams Feb. 19, 1935 1,999,653 Case Apr. 30, 1935 2,047,175 Braselton July 14, 1936 2,162,505 James et al June 13, 1939

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