US3405304A

US3405304A - Electron discharge device for emission of atomic resonance lines

Info

Publication number: US3405304A
Application number: US571498A
Authority: US
Inventors: Wallace Gillies; George Kiyoshi Yamasaki
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1966-08-10
Filing date: 1966-08-10
Publication date: 1968-10-08
Anticipated expiration: 1985-10-08
Also published as: NL6710952A; GB1192184A; DE1673325C3; DE1673325B2; DE1673325A1

Description

m 4 2. mu vo. No. o oo. 8 q w R 3 633 .552 1 553%? l uztmzwm wwwwm zocaa W. GILLIES ETAL ELECTRON DISCHARGE DEVICE FOR EMISSION OF ATOMIC RESONANCE LINES Filed Aug. 10, 1966 NdI Dot. 8, 1968 Om em L 8 w E wN QN INVENTORS Wclluce Gillies & George Kiyoshi Yornosokl BY %z&

ATTORNEY United States Patent 3,405,304 ELECTRON DISCHARGE DEVICE FOR EMISSION OF ATOMIC RESONANCE LINES Wallace Gillies, Pine Valley, and George Kiyoshi Yamasaki, Horseheads,- N.Y., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 10, 1966, Ser. No. 571,498 9 Claims. (Cl. 313218) ABSTRACT OF THE- DISCLOSURE This invention relates to electron discharge devices of the hollow cathode type illustratively including first and secondelectrodes for respectively generating beams of differing characteristic spectral radiation, and an anode element. The first electrode generates from a hollow portion the first beam of radiation along a given path. The second electrode has an aperture therethrough and is so disposed that the path of the first beam of spectral radiation passes through the aperture.

This invention relates to atomic absorption spectrometry,'and more particularly to electron discharge devices of the hollow cathode type whichare adapted for emitting light having sharp atomic spectral lines.

Generally, the constituents of an unknown chemical sample may be disco'vered'by introducing a solution of the unknown sample in the form of a mist into a suitable flame to cause the solution to vaporize. Next, radiation having known spectral lines is directed through the sample vapor with the result that certain spectral lines of the radiation will be absorbed by the atomic vapor. Then, the radiation can be analyzed to determine which spectral lines have been absorbed and the degree to which these lines have been absorbed by the sample vapor to determine the constituent and the concentration of the constitu: ent in the unknown sample.

It is presently known to provide radiation having defined spectral lines by means of electron discharge devices of the hollow cathode type. In such devices the cathode element is usually shaped in the form of a hollow cylinder closed at one end. Typically, the anode may be either a metallic ring, wire or plate which is disposed in the vicinity of the cathode element in a position so as not to. prevent the radiation emitted from the hollow portion of the cathode element from being directed to the outside of the electron discharge device. The cathode element is generally made of the metal whose spectrum it is required to produce.

Further, it has been suggested that more than one electrode may be disposed within the envelope of the electron discharge device to provide a radiation having a plurality of spectral lines corresponding to the materials of which the cathode elements are made. More specifically, the electrodes of these prior art devices have been placed side-by-side with their axis parallel to each other. Further, a suitable alternating current is applied between these electrodes so that radiation will be alternately emitted from first one electrode and then the other depending upon which of the two electrodes is acting as the cathode element. Upon reversal of the potential, the other electrode will act as the cathode element thereby emitting radiation. The radiation emitted from these electrodes tends to be directed along the electrode axes which as stated above are parallel to each other. Therefore, a significant problem associated with these devices resides in the difficulty of focusing the radiation emitted from the electrodes disposed side-by-side through the same point or portion of the vapor to be analyzed.

Further, there has been suggested in US. Patent No. 3,183,393 of Patterson, assigned to the assignee of this invention, that radiation having a plurality of spectral lines may be obtained by making the cathode element of more than one element corresponding to the desired spectral lines. More particularly, there is suggested that radiation having spectral peaks at a wavelength of approximately 2852 angstrom and the second peak at a wavelength of approximately 4227 angstrom may be obtained from a single cathode element made of an alloy of magnesium, calcium and aluminum. One limitation of such a device lies in the number of elements (and thus the corresponding spectral lines) which may be incorporated into the cathode element. More particularly, the intensity of an individual spectral line is dependent upon the proportion of the corresponding element that is alloyed to form the material of which the cathode element is made. Although it might appear possible to alloy any number of elements together, it may be recognized that only certain elements may be alloyed together, and further, if a proportion of a certain element is too small, then the intensity of the spectral lines of this element may be too weak to be of any practical use.

Therefore, it is an object of this invention to provide a new and improved source of spectral radiation which overcomes the limitations of the prior art.

It is a more particular object of this invention to provide a new and improved electron discharge device of the hollow cathode variety which is capable of providing a radiation having the spectral lines of a plurality of elements. I

It is a still further objectof this invention to provide a new and improved electron discharge device of the hollow cathode variety capable of emitting radiation with a plurality of spectral lines and of precisely directing the radiation emitted therefrom. 1

Another object of this invention is to provide an electron discharge device of the hollow cathode variety capable of emitting radiation With a plurality of spectral lines and of selectively varying the intensity of selected spectral lines with respect to the remaining spectral lines.

These and other objects are accomplished in accordance with the teachings of the present invention by providing a new and improved electron discharge device including a plurality of electrodes for emitting radiation with a plurality of spectral lines corresponding to the material of which the electrodes are made. Generally, the electron discharge device of this invention includes at least two electrodes which are disposed in a tandem relation for emitting beams of radiation therefrom along substantially a single line. Illustratively, the electron discharge devices may include a first and second cathode element and an anode element disposed to cause a discharge between each of the cathode elements and the anode element. The first cathode element may have a hollow portion therein from which one beam of radiation is emitted. Further, the second cathode element has an opening therethrough which is disposed about the beam of radiation of the first cathode element to ensure that the beams of a radiation emitted from the first and second cathode elements approximately coincide with each other.

These and other objects and advantages of the present invention will become more apparent when considered in view of the following detailed descriptioin and drawings, in which:

FIGURE 1 is a diagrammatic view of a system for performing atomic absorption measurements; and

FIG. 2 shows a perspective view, partially broken away and partially in section of a discharge device embodying the present invention.

Referring now to the drawings and particularly to Patented Oct. 8, 1968 FIG. 1, there is generally shown a system for performing atomic absorption measurements including an electron discharge device of the hollow cathode variety for providing a beam of radiation having a plurality of spectral lines. The beam of radiation emitted by the electron discharge device 10 is focused by a suitable optical assembly 96 through a means 98 for evaporating a solution of the unknown sample into a monochromator 100. As explained above, certain spectral lines are absorbed by the vapor of the unknown sample from the beam of radiation as it passes through the flame means 98. By adjusting the monochromator 100 to the wavelength of the spectral lines which is to be absorbed by the sample vapor, a beam of radiation of a narrow bandwidth about the wavelength to be absorbed can be obtained through an opening within the monochromator 100. The resultant beam of radiation is directed onto a radiation sensitive device 101 which provides an output signal which is amplified and applied by an amplifier 102 to a meter 104 which provides an indication of the intensity of the radiation directed through the opening of the monochromator 100. It is contemplated that the degree of absorption may be measured by comparing the indication displayed by the meter 104 when an unknown sample is introduced into the flame means 98 and when no sample is introduced into the flame means 98.

Referring now to FIG. 2, there is shown an illustrative embodiment of the electron discharge device 10 which may be incorporated into the system shown of FIG. 1 to provide a plurality of substantially coincident beams of radiation having a plurality of spectral lines. The electron discharge device 10 includes an envelope 12 made of a suitable insulating material such as glass and being enclosed at one end by a window 14 made of a suitable material efliciently transmissive to the radiation produced by this device and upon the other end by a stern header 16. There is disposed within the envelope 12 a first cathode element 22 which is supported therein by a terminal rod 19 having one end secured to the cathode element 22 and the other end extending through and supported by the stern header 16. The terminal rod 19 is made of a suitable electrically conductive material such as nickel for providing an electrical connection to the cathode element 22 as well as supporting the cathode 22 within the envelope 12. The cathode element 22 is substantially cylindrical in shape and has a central bore or hollow portion 24 extending from an upper edge 23 nearest the window 14 into the cathode 22.

An anode element 26, which is illustratively shown to be in the form of a plate, is positioned within the envelope 12 at a point olf center from the central axis of the electron discharge device 10 in close proximity to the upper edge 23 of the cathode element 24. The anode element 26 may be made of a suitable electrically conductive material such as tantalum which when operated in a reverse mode may serve as a getter for the electron discharge device 10. The anode element 26 is supported within the envelope 12 by an electrically conductive terminal rod 20 having one end secured to the anode element 26 by spot welding and the other end extending through and supported by the stem header 16.

In accordance with the teachings of the present invention, a second cathode element 28 having an aperture 30 extending therethrough is disposed within the envelope 12 to be coaxial with the axis of the electron discharge device 10. More specifically, the second cathode element 28 is disposed about the beam of radiation which is emitted from the bore 24 of the first cathode element 22 and is spaced from the first cathode element 22 a sufficient distance to prevent contamination by particles sputtered from the first cathode element 22. The second cathode element 28 is supported within the envelope 12 by a terminal rod 18 having one end thereof connected to a cantilever supporting member 42 and the other end extending through and supported by the stem header 16. Further, the cantilever member 42 extends radially inward and has a tab portion which is secured to the periphery of a second cathode element 28 as by clamping or spot welding.

In order to provide the desired beams of radiation, a potential diflerence is applied between, the anode element 26 and the first cathode element 22, and between the anode element 26 and the second cathode element 28. Referring to FIG. 1, a potential source is connected with its positive terminal to the anode element 26. Further, the first and

second cathode elements

22 and 28 are respectively connected in series through the

resistive impedances

92 and 94 to the negative terminal of the potential source 90. As shown in FIG. 1, a connection is made between the first variable resistive impedance 92 and the first cathode element 22 whereas an electrical connection is made between the second variable resistive impedance 94 and the second cathode element 28. The envelope 12 is evacuated and filled with an inert atmosphere such as argon or neon to a pressure of approximately .5 to 40 millimeters of mercury. As a result of the potential differences between the anode element 26 and the first cathode element 22, and between the anode 26 and the second cathode element 28, electron discharges occur between the respective elements which in turn provide positive ions which are attracted to the negatively disposed

cathode elements

22 and 28. The positive ions so produced bombard the first and

second cathode elements

22 and 28 to thereby excite beams of radiation in accordance with the material of which the first and

second cathode elements

22 and 28 are made. It is noted that the currents flowing between the first and second cathode elements and the anode element 26 may be controlled as by varying the resistance of the

impedances

92 and 94. As a result, the intensity of the beams of radiation associated with either of the

cathode elements

22 and 28 may be varied with respect to each other.

In accordance with the teachings of this invention, the first and

second cathode elements

22 and 28 are disposed in a tandem relationship with each other. More specifically, the ion bombardment of the first cathode element 22 is directed into the hollow portion 24 to provide a beam of radiation which is directed along a line which is determined by the shape of the hollow portion or bore 24. More specifically the bore 24 is of a cylindrical configuration whose depth is equal to or preferably greater than the diameter of the bore 24 to ensure that the radiation emitted from the first cathode element 22 is in a narrow pencil beam. Further, the second cathode element 28 is disposed so that the cylindrically shaped aperture 30 is disposed coaxially about the axis of the envelope 12 and also about the line of direction of the beam of radiation emitted by the first cathode element 22. In this manner, the beams of radiation originating from either of the

cathode elements

22 or 28 are directed along substantially the same line and may be easily focused in any desired manner. Although the electron discharge device 10 has been illustratively shown in FIG. 2 with only two cathode elements, it is evident that more than two cathode elements may be disposed in a tandem relationship with each other. The number of cathode elements is limited only by the spacing of the first cathode element from the window 14. If the first cathode element 22 is disposed too remotely from the transmissive window 14, the beam of radiation therefrom may become unduly attenuated. Further, the cathode elements cannot be disposed too close to the window 14 or deposits from the cathodes will cause the window to' be coated and to thereby be rendered non-transmissive.

Though the

electrode

22 and 28 have been described as cathode elements, it is noted that in another embodiment of this invention that the anode element may be deleted and a source of alternating current may be interconnected between the

electrodes

22 and 28. In this embodiment, first one electrode and then the other will act asa cathode element depending upon the instantaneous polarity of the voltage applied thereto. The disadvantage of this embodiment resides in the fact that the electrodes, which are made of different elements or compounds, present differing impedances to the alternating source for differentperiods of the cycle. As a result, the relative intensities of the radiation emitted from the different electrodes may vary. However, where an anode element is included, the current flow from each of the

electrodes

22 and 28 may be controlled to ensure that the intensities of the beams of radiation emitted therefrom are approximately equal or in any other desired relation. Further, it is noted that the first cathode element 22 could be of an annular configuration, whereas it appears to be necessary that the second electrode 28 should be annular to allow the beam of radiation from the first electrode to pass therethrough.

The discharge between the anode element 26 and the

cathode elements

22 and 28 is limited to the bore 24 and to the aperture 30 through the use of insulating disks which substantially isolate all but the bore 24 and the aperture 30 from the anode element 26. Referring now to FIG. 2, a disk 34 made of a suitable insulating material such as a ceramic or mica is disposed between the anode element 26 and the first cathode element 22. Further, the insulating disk 34 has a central aperture 72 with a diameter larger than that of the bore 24. In addition, the insulating disk 34 is disposed in proximity to or to abut the upper edge23 of the first cathode element 22 with the central aperture 72 substantially coaxial with the bore 24. A second insulating disk 32 is disposed in a substantially parallel relation with the insulating disk 34. Further, the insulating disk 32 has a central aperture 70 whose diameter is substantially equal to the diameter of the first cathode 22. Both the insulating disks 32 and 34 extend to the inner periphery of the envelope 12 to prevent the discharge 26 from leaking about the insulating disks 34 and 32 to the remote portions of the first cathode elements 22.

Further, the discharge between the anode element 26 and the second cathode element 28 may be limited to the aperture 30 by the use of insulating

disks

44 and 46. The insulating disk 44, which is in close proximity to or abuts one end of the second cathode element 28, has a central aperture 74 disposed concentrically about the aperture 30. The insulating disk 46 is disposed a short distance from and in parallel relationship with the insulating disk 44. Further, the insulating disk 46 has a central aperture 76 of substantially the same diameter as that of the second cathode element 28. In order to prevent an electrical discharge from being directed from the anode element 26 through the aperture 30 to the remote portions of the second cathode element 28, there may be incorporated insulating

disks

48 and 50 to effectivel isolate the second cathode element 28. More specifically, the insulating disk 50 would be disposed adjacent one end of the second cathode element 28 and have central aperture 80 disposed concentrically about the aperture 30. The insulating disk 48 is spaced closely to and in parallel relationship with the insulating disk 50, and has a central aperture 78 of approximately the same diameter as that of the second cathode element 28.

In order to substantially isolate the various elements from each other, it may also be necessary to place suitable insulating members about the terminal rods associated with the various electrodes. More specifically, an insulating sleeve 36 made of a suitable insulating material such as aluminum oxide is disposed about the terminal rod 18 and extends between stem header 16 and the insulating disk 32. A ring 37 of an appropriate insulating material is disposed about the terminal rod 18 between the insulating disks 32 and 34. Further, an insulating sleeve 38 is disposed about the terminal rod 18 between the insulating disk 34 and the insulating disk 44, and an insulating ring 39 is disposed about the terminal rod 18 between the insulating

disks

44 and 46.

The insulating disks and rings associated with the terminal rod are held axially in place by the support member 42 which is secured to one end of the terminal rod 18 'to abut against an insulating ring 40 which is disposed between the member 42 and the insulating disk 46.

In a similar manner, the terminal rod is isolated from the exposed portion of the first cathode element 22 and the terminal rod 19 associated therewith by an insulating sleeve 52 which is disposed about the terminal rod 20 between the button stern header 16 and the insulating disk 32. Further, an insulating ring 53 is disposed between the insulating disks 32 and 34 about the terminal rod 20. An insulating ring 54 is disposed about the terminal rod 20 between the insulating disk 34 and the anode element 26. It may be understood that the anode element 26 serves to axially position the insulating rings 54 and 53 and the insulating sleeve 52.

In order to further support the various insulating disks, a support rod 21 is provided having one end thereof supported by the stern header 16 and extending upward through each ofthe various insulating disks. An insulating sleeve 56 illustratively is disposed about the support rod 21 between the stem header 16 and the insulating disk 32. Further, an insulating ring 57 is disposed about the support rod 20 between the insulating disks 32 and 34. In a manner as described above, an insulatingsleeve 58 is disposed between the insulating

disks

34 and 44, and an insulating ring 59 is disposed between the insulating

disks

44 and 46. Further, an insulating sleeve 60 is disposed between the insulating

disks

46 and 48, and an insulating ring 61 is disposed about the support rod 21 between the insulating

disks

48 and 50. Finally, an insulating ring 62 is disposed about the support rod 21 with a tab 64 secured to the other end of the support rod 21 as by spot welding to thereby axially position the various insulating sleeves and rings and to hold the insulating disks in their position.

For a further description of the advantages and the structure of the insulating members reference is made to the copending application, Ser. No. 289,215 of Yamasaki, now US. Patent No. 3,264,511, and assigned to the assignee of this invention.

In accordance with the teachings of this invention, the first and

second cathode elements

22 and 28 are made of different elements (or compounds) corresponding to the desired spectrum or spectral lines which it is desired to produce. As mentioned above, one of the advantages of this invention is that the relative intensity of the spectral lines of the beam of radiation derived from each of the cathode elements may be adjusted with respect to each other. Further, it is noted that one or all of the cathode elements may be made of an alloy of various elements (or compounds) to thereby derive spectral lines corresponding to each of the elements forming the alloy. In one particular embodiment, the first cathode element was made of an alloy including calcium, barium and strontium and the second cathode element was made of an alloy of iron, copper, nickel and manganese,

Thus, there has been shown a new and improved source of radiation having defined spectral lines, in which the number of elements and thus the number of spectral lines present in the beam of radiation projected therefrom is greatly increased. Further, there has been shown a source of radiation in which the relative intensities of the various spectral lines may be varied with respect to each other. Also, it is noted that the beams of radiation may be modulated or otherwise controlled for use in special applications.

Since numerous changes may be made in the abovedescribed apparatus and difierent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description and as shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A spectral radiation source comprising an anode, and first and second cathodes, said first cathode including a first material for providing a first beam of characteristic spectral radiation, said second cathode including a second material for providing a second beam of characteristic spectral radiation different from that of said first cathode, said first and second cathodes disposed to project said first and second beams of radiation along substantially the same path.

2. A spectral radiation source as claimed in claim 1, wherein said first and second cathodes are spaced apart in a tandem relation with respect to each other.

3. A spectral radiation source as claimed in claim 1, wherein said anode element is disposed for providing an electron discharge between said first cathode and said anode element, and between said second cathode and said anode element.

4. A spectral radiation source as claimed in claim 3, wherein there is included means associated with said first and second cathode and said anode element for controlling the relative intensity of said first and second beams of radiation.

5. A spectral radiation source as claimed in claim 4, wherein said means includes a potential source and variable impedances for regulating the current applied to said first and second cathodes.

6. A spectral radiation source as claimed in claim 1, wherein said first cathode projects said first beam of radiation along a predetermined path, said second cathode being of an annular configuration and disposed about said predetermined path.

7. A spectral radiation source as claimed in claim 1, wherein said first cathode has a hollow portion therein for projecting said first beam of radiation along said path, said second cathode having an aperture therethrough and disposed so that said path passes through said aperture.

8. A spectral radiation source as claimed in claim 7, wherein an anode element is disposed between said first and second cathodes for providing an electron discharge between said first cathode and said anode element, and between said second cathode and said anode element.

9. A spectral radiation source comprising first and second electrodes, said first electrode including a first material providing a first beam of characteristic spectral radiation, said second electrode including a second material for providing a second beam of characteristic spectral radiation different from that of said first electrode, said first electrode projecting said first beam of radiation along a path, said second electrode having an aperture therethrough and so disposed that said path passes through said aperture, and means for applying a negative potential to said first and second electrodes.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

W. J. SCHWARTZ, Assistant Examiner.