US2946886A

US2946886A - Adjustable ion collector slit for mass spectrometer

Info

Publication number: US2946886A
Application number: US617019A
Authority: US
Inventors: Beldon A Peters; James A Rickard
Original assignee: Jersey Production Research Co
Current assignee: Jersey Production Research Co
Priority date: 1956-10-19
Filing date: 1956-10-19
Publication date: 1960-07-26
Anticipated expiration: 1977-07-26

Description

July 26, 1960 B. A. PETERS ETA 2, 6,88

ADJUSTABLE ION COLLECTOR SLIT FOR MASS SPECTROMETER Filed Oct. 19, 1956 2 Sheets-Sheet 1 ION SOURCE W 4 2 I I ION BEAM FIGJ.

INVENTORS. BELDON A. PETERS. JAMES A. RICKARD.

" ywm ATTORNEY.

July 26, 19601 B, A, PETER ETAL ADJUSTABLE ION COLLECTOR SLIT FOR MASS SPECTROMETER 2 Sheets-Sheet 2 Filed Oct. 19, 1956 ION SOURCE R O T C E L L o C N O ION SOURCE ION SOURCE hzmtznu 20- TIME.

(MAGNETIC FIELD VARYING TIME I DISPERSION 1 VARYING TIME I COLLECTOR SLIT WIDTH F'IG. 9.

TIME, MAGNETIC FIELD hzummao ZO INVENTORS. BELDON A PETERS,

JAMES A. RICKAR D. BY j Z ATTORNEY.

United States Patent 6 ADJUSTABLE ION COLLECTOR SLIT FOR MAS SPECTROMETER Filed Oct. 19, 1956, Ser. No. 617,019

7 Claims. (Cl. 25041.9)

This invention concerns an adjustable slit device for use in mass spectrometers. More specifically, it is directed to an adjustable ion collector slit for use in mass spectrometers.

Referring briefly to the figures wherein identical numerals designate identical parts, I j

Fig. 1 is a sectional view of a vacuum chamber of a mass spectrometer showing the adjustable slit device arranged thereon in operative position;

Fig. 2 is a view taken on lines 22 of Fig. 1;

Fig. 3 is an elevation of the device of Fig. 2 with the slit adjusting plate removed;

Fig. 4 is' a view of the removed slit adjusting plate;

Figs. 5 to 7 are schematic illustrations of the operation of a mass spectrometer; and

Figs. 8 and 9 are plots of ioncurrent versus time (magnetic field varying time) for different slit width openings.

A mass spectrometer commonly analyzes an unknown sample by ionizing the molecules or atoms of the sample by passing the sample in gaseous form through an electron'beam. As seen in Fig. 5, the ion source 10 emits an ion beam, the ions of which are accelerated by an electric field through collimating slits 11, the moving ions indicated at 12 are then passed in a vacuum through a magnet-ic field as at -13 where the ions are deviated in different paths according to their masses. The lighter ions being indicated by the line 14 and the heavier ions being indicated by the line '15. The ion beam designated 16 passes through a primary collecting slit 17 and' the ion current is measured in the ion collector .18 by any suitable means. An additional secondary collecting slit, not shown, may be employed in conjunction with the collecting slit 17. However, because the collimating slits 11 are not infinitely narrow and because defocusing effects are always present, each ion beam is not perfectly collimated as it leaves the collimating slits 11. Hence, a beam composed of ions of only one mass would appear as shown in Fig. 6. This figure has been enlarged and the imperfect collimation has been exaggerated for illustration purposes. If the mass spectrometer is properly constructed and the magnetic field properly shaped, the aberration of the moving ions 12 after passing through collimating slits 11, as shown by the arrowed lines in Fig. 6, may be compensated for to a large extent.

As seen in Fig. 7, some of the ions are not perfectly focused and feathering caused by imperfect focusing occurs as indicated at 19. If the collection slit 17 were finite in width, although small compared to the dispersion (the dispersion being the distance from one focus point to the next designated 20 in Fig. 5) and if the magnetic field were varied sufliciently slowly that each mass beam were passed through the collection slit in turn, a graph of ion current vs. time would be as shown in Fig. 8, wherein three different masses are represented by the

curves

25, 26 and 27, respectively. The collection slit width is designated at 28' and the feathering Kid caused by aberration is indicated at 29. No aberration caused by imperfect focusing and instrumental discriminations occurred, the curve of ion current vs. time would follow the

dotted lines

30, 31 and 32 for the masses represented by

curves

25, 26 and '27, respectively.

. If the dispersion is large, compensation may be made by adjusting the slit width 28. For example, if the, collector slit width 28 were increased, the curves of the masses represented by 25, 26 and 27 in Fig. 8 would be as shown by

curves

35, 36 and 37 respectively in Fig. 9. This procedure of adjusting the slit width to compensate for dispersion may be used as long as the slit 'width is smaller than the dispersion. However, the dispersion changes with mass, sothat a proper slit width for masses of

atomic mass units

44, 45 and 46, for example, may not be usable for masses of atomic mass units 144, 145 and 146. It is, therefore, desirable to be able to change the collector slit width while the mass spectrometer is in operation.

It is known to vary the width of collector slits in mass spectrometers by employing a magnet or iron bar and screw thread device whereby an internal magnet or iron bar mounted in the vacuum chamber of a mass spectrometer is twisted by an external magnet mounted ads jacent the vacuum chamber to thereby actuate the screw thread device which in turn adjusts the slit width. However such an arrangement is disadvantageous in many respects. For example, it is somewhat complicated to construct; there is inherent backlash in the screw threads; the apparatus may stick or be otherwise diflicult to operate due to the relatively small torque which can be transmitted by the magnetic fields; and the magnet may have a harmful efiect on the ion beam path. The present invention'is an improvement over such apparatus.

An object of this invention is, therefore, to provide an adjustable ion collector slit for mass spectrometers; which has no backlash; which can transmit considerable torque thereby preventing sticking of the slit width control mechanism; which does not employ a magnet; and which can provide a continuous indication of the width of the collection slit.

Briefly, the invention comprises a device for use in the vacuum chamber of. a mass spectrometer includinga first plate member formed to provide an opening therein and positioned in the path of an ion beam projected from an ion source; a second plate member is slidably'arranged on the first plate member and is adapted to cooperate with the first plate member to vary the size of the opening upon movement thereof; resilient means is positioned between the first and second plate members adapted to urge the second plate member in a direction whereby the area of the opening is enlarged; movable rodmeans is provided extending sealingly into the chamber and engaging the second plate adapted to move the second' plate against the bias of the resilient means and scale means is provided connected to the rod adapted to indicate the size of the opening.

For a detailed description of the adjustable slit mechanism, reference is now made to Figs. 1 through 4. In these figures is shown a vacuum chamber housing 40 in which is positioned cylindrical member 41 through which an ion beam is projected from an ion source, designated 42. A cylindrical plate member 43 is secured to an end of cylindrical member 41 by means of screws 44 and a positioning pin 44. to provide an opening 45 and is also formed to provide an indented portion 46 extending from one side of opening 45 to the periphery of plate 43. Additional plate members 47, as seen more clearly in Fig. 2, are secured to plate member 43 by means of screws 48. The plate members 47 are spaced apart as shown and provide slots or trackways adjacent the indented portion 46 of plate The plate 43 is formed 43. A plate member 50is slidably arranged in the indented portion of plate 43 on protuberances 50 which are slidably arranged in the slots formed by plates 47. Plate member 50 cooperates with opening 45 in plate member 43 to form an adjustable slit opening 45'. A flange 51 is-formed on plate member 50- and a spring member 52 is arranged betweenplate member 4-3 and plate member 50, as-shown. Each end of spring member 52 ispositioned between one of the plates 47 and plate 43 and the center engages flange 51 thereby biasing: the plate member 50 away from plate member 43; that is, in a direction-whereby the slit 45 is widened. The inner end ofa push rod 53 engages flange 51 and extends through the wall of the vacuum chamber 40. A third plate member 65 is :positionedbetween plate member 43 and an ion'collector 66 and is formed to provide an opening 67 arranged in alignment with opening 45'. Plate member 65 is secured-to plate member 43 by means of bolts 68; Plate member 65' is used in a well known manner and does not form a part of this invention.

A bellows 54, as seen in Fig. l, is secured and hermetically sealedto one end of push rod 53 as at 60. The other end of bellows 54 is secured and hermetically sealed about an opening 61 in the wall of housing it? as seen at 617. The push rod 53 is movable into and out of housing 40. through opening 61. The bellows 54 and push rod 53 are arranged in a housing 56 which is connected to the exterior wall of chamber 40 by means of bolts 58. A micrometer having a micrometer head 57 provided with a scale indicator, not shown, is connected to housing 56. The micrometer head 57 extends through housing 56 and'engages with the outer end of push rod 53;.

In operation when it is desired to narrow slit opening 45 the micrometer is rotated in one direction to move pushrod. 53 against the bias of spring 52, thereby narrowing the width of slit opening 45'; on the other hand, when it is desired to Widen slit opening 45', the microm eter is rotated in a reverse direction'to mo ve push rod 53. away from the flange 51 permitting spring 52 to move plate member 50 in the direction of movement of the push rod 53, thereby enlarging the width of slit opening 45. Thus, the ion beam projected from ion source 42 through opening 45 may be adjustably transmitted through opening 45 and then transmitted to the ion collector 66 through opening 67 in plate member 65. By having the micrometer properly zeroed, the width of the slit opening 45 may be continuously indicated for any selected positions of plate 50.

Having fully described the structure, objects and operation of our invention, .we claim:

1. Adevice for forming an adjustable ion collector slit in a mass spectrometer comprising a housing, a support mounted in said housing, a first plate member secured to said support, a second plate member slidably arranged on said first plate, said first and second plate members cooperating to form a slit opening, the width of said slit opening being varied upon movement of said second plate member, resilient means positioned between said first and second plate members adapted to urge said second plate member in one direction, movable means extending sealingly through said housinga-nd-engaging said second plate member adapted to urge said second plate member against the bias of said spring and means engaging with said movable means adapted to indicate the width of said slit opening.

2. A device as recited in claim 1 wherein said movable means is a rod and said means engaging therewith is a micrometer head.

3. A device for forming an adjustable ion collector slit in a vacuum chamber of a mass spectrometer comprising a first plate member formed to provide a first opening arranged in said chamber in the path of an ion beam, a second plate member slidably' arranged on said first plate member adapted to cooperate with said first plate member to form an adjustable second opening, resilient means positioned between said first and second plate members adapted to bias said second plate member in a direction whereby said second opening is enlarged, movable means extending sealingly into said chamber and engaging said second plate member adapted to move said second plate member against the bias of said resilient means and scale means connected to said movable means adaptedto continuously indicate the size of said second opening.

4; A device as recited in claim 3 wherein said movable means is a rod and said-scale means. is a micrometer. head.

5. A device for forming an adjustable ion collector slit in a vacuum chamber of a mass spectrometer comprising a first plate member formed to provide. an opening arranged in said chamber in the path of anion beam, a second plate member slidably arranged on said first plate member adapted to cooperate with said opening to vary the amount of said ion beam passed through said opening, resilient means positioned between said first and second plate members adapted to bias said second plate member in one direction, movable means extending sealingly into said chamber adapted to move. said second plate member against the bias of said resilient means, and means positioned exterior of said chamber to indicate the amount of said ion beam being passed through said opening.

6. A device as recited in. claim 5 wherein said movable means is a rod and. said exterior means is a micrometer.

7. A device as recited in claim5 wherein a bellows seals olf fluid communication between said exterior means and said chamber.

References Cited in the file of this patent UNITED. STATES PATENTS 2,292,087 Ramo Aug. 4, 1942 2,378,962. Washburn June 26, 1945 2,674,698 Dmorth et a1 Apr. 6, 1954 2,709,222 Lawrence May 24, 1955 2,852,684 Payne Sept. 16, 1958