US2922904A - Target window for x-ray microscopes - Google Patents

Description

Jan. 26, 1960 M. J. ZUNICK v 2,922,904

TARGET WINDOW FOR X-RAY MICROSCOPES Filed Dec. 30, 1957 MICHAEL .1 zu/v/c/r I f By E ATTRA/EKS United Sttes TARGET WINDOW FOR X-RAY MICROSCOPES Michael J. Zunick, West Allis, Wis., assignor to General Electric Company, a corporation of New York Application December 30, 1957, Serial No. 705,959

1 Claim. (Cl. 313-60) This invention relates to improvements in anodewindows particularly adapted for use as target windows in X-ray microscopes.

Major objects are as follows:

(a) To extend the commercial limitations of known X-ray microscopes in a manner to permit increased heat application to the focal spot which, for example, may be a 1 to micron spot.

(b) Substantially to increase the radiation factor of heat dissipation from very thin anode-windows, such windows as presently employed being, for example, in the .002 thickness range.

(0) To provide a target window assembly particularly adapted for use with present types of objective lens assemblies.

(d) Virtually to obtain a rotating target affect and the known advantages attendant thereof through employment of structure compatible with existing types of X-ray miscroscopes.

(e) To provide the above advantages in a manner also permitting employment of the guiding concept in respect to interval targets.

The single figure drawing is deemed adequate to teach the concept andone application to an objective lens assembly of a known type of X-ray microscope, it being evident that the principles illustrated are equally applicable to a plurality of structural modifications without departure from the broad inventive concepts, the parameters of which are defined in the appended claims.

The inventive concept nets to an improved method of safely increasing unit area loading of a thin anodewindow, and improved apparatus for carrying out the method, including the employment of a bellows-like, or other non-rigid coupling in sealing relation between a target window support constrained against movement along the axis of the beam while permitted free movement in a transverse plane; and portions of the tube envelope, to permit both rotational and linear target movement transversely of the beam while maintaining tube evacuation.

In the drawings:

Fig. 1 illustrates, in diametric section, an X-ray microscope tube and window incorporating the present invention.

Fig. 2 is a plan view of the device of Fig. 1, showing one form of anode-Window drive mechanism.

Referring to the drawings, a terminal portion of an X- ray microscope tube envelope 10, which may be of suitable metal, provides support for an objective lens assembly, generically designated 11 and comprising a centrally apertured plate 12 in complemental engagement with the inner wall of envelope and rigidly secured thereto, and a pair of cup-shaped centrally apertured lens elements 1.3 and 14 which find their support on plate 12 in the manner shown for alignment of their apertures 15 and 16, respectively, with an electron beam generated by a cathode structure generically designated 18, at the opposite end of the tube envelope. Cathode 18 may inelude a filament 19 connected to a suitable source of elec tric power 19a. A beam accelerating and shaping electrode 22 is'maintained at high positive potential by voltage source 24, it being understood that electrode 22 may comprise a plurality of elements for accelerating and shaping the beam which need. not be described. The structure described above is shown, and its function described in US. Patent 2,814,729 issued November 26, 1957 to Sterling Newberry and Theodore Summers and also assigned to the General Electric Company, the

- present assignee.

vided with a bonding ring 27, disposed" marginally thereof, to which the upper end of bellows 20 is suitably bonded to complete the enclosure of tube envelope 10 in fluid sealing relation to the atmosphere.

Target member 17 is constrained against vertical movement by a guideway 25, shown as an inwardly directed marginal channel provided in annulus 26, the guideway being of a vertical dimension snugly to engage the marginal areas of member 17 and of suflicient depth to per mit some horizontal movement of member 17 in either direction, bellows 20 'beingdesigned for easy deformation to permit horizontal, oscillation of member 17 as well as some rotational movement inrespect to tube en- Velope 10. The are through which'target member 17 may be rotationally oscillated is: of course limited by the flexing properties of bellows 20.

Member 17 is shown provided with an upwardly open frusto-conical channel 28' to define a central portion of reduced thickness, apertu'red at 29 for reception of a metallic target window 30 in concentric alignment with lens apertures 15 and 16' to receive a high energy electron beam from cathode 18, accelerated and shaped by electrode 22 and lens elements 13 and 14 to define a small focal spot. The high energy electrons pass through the window which is conventionally of thin metal such as beryllium or tungsten as, for example, in the order of .002 thick to form the vortex of an X-ray cone extending upwardly from window 30 to produce, by the shadow graph principle, well known inthe art, a microscopic image of an object placed above-window 30. The above cited patent may be referred to for other details of such a microscope which form no part of this invention.

Target member 1'7 is subjected to both rotational and linear movement as above stated by suitable driving mechanism. Member 17 is provided with circumferentially disposed apertures 33 into which pins 34 loosely project. Pins 34 are fixed to depend from radially disposed arms 35, fixed to annulus 26 by screws 37 to position the pins inwardly from the rings and substantially centrally of apertures 33 with bellows 20 unstressed. A drive arm 41, associated with suitable mechanism for movement of the arm in the arrow direction and return, has a loose link connection with pin 40, fixed to member 17. Member 17 is marginally provided with a cam lobe 42, and as arm 11 rotates member 17 clockwise as viewed in Fig. 2, (a movement permitted by bellows 20) earn lobe 42 engages the inclined surface of a radially disposed cam arm 43, positioned in a guideway provided in annulus 26 (not shown). Arm 43 is slotted at 44 for radial adjustment, the arm being fixed in an adjusted position by screw 45. Rotation of the windowed member 17 by arm 3 r 41 thus causes member 17 to also move linearly in channel 25, hence member 17, and window 30 are simultaneously subjected to both rotational and linear movement. As is apparent, withdrawal of arm 41 onaback stroke results in the return of member 17 to the position shown under an urge frombellows 20 as the distortional stresses caused by the rotationthereof are relieved. .Bysubjecting arm 41 to continuous reciprocation, window 30 is thus continuously subjected to a combination. of linear and oscillatory movement. I 7

As will be readily. apparent to persons familiar with rotating anode type X-ray tubes, unit area heat loading is a limiting output factor, and in view of the very thin target window employed in X-ray microscopes this factor becomes especially critical. While X-ray tubes lend themselves to employment of rotating anodes for the purpose of feeding fresh metal to the electron beam for increased loading, it is apparent that no such solution is available to the designer ofX-ray microscopes. The structure above described permits continuous supply of fresh metal to the electron beam upon application of a combination of oscillatory and rotational movement to target window 30, which is applied through member 17, and those two motions may be so correlated in their application as to feed a substantial area of target window 30 to the beam before returning to the starting position. While the invention is notlimited to any specific type of drive mechanism for subjecting member 17 to the desired oscillatory and rotational movements, one type of mechanism that may advantageously be employed is illustrated and operates as follows. Window support plate 17, of circular configuration, is provided with a plurality of circumferentially disposed arcuate slots 33 for reception of guide pins 34, mounted to depend from radially disposed support arms 35 attached to guide member 26 by screws 37. Pins 34 are a diameter substantially less than the width of slots 33 to permit lateral as well as transverse movement of plate 17 while constraining the plate against binding engagement with the inner wall of guide channel 25. A reciprocably driven arm 41, in loose engagement with pin 40, imparts a combination of rotational and transverse movement to plate 17. Plate 17 is peripherally provided with a cam portion 42 positioned for engagement with a cam follower 43, adjustably secured to guide member 26 by screw 45 to impart transverse deflection of plate 17 as it is rotated. The simple structure illustrated to combine rotational and transverse movement of plate 17 within guide channel 25 may be modified as desired without departure from the inventive principle of subjecting window 30 to those combined movements. The distortion of bellows 20 resulting from rotational oscillation by drive arm 41 may result in suflicient transverse displacement of plate 17 to permit elimination of cam 42 and follower 43, for example.

It is thus seen, as stated in the objects, that the invention, and its adaptation in the illustrated embodiment shown and above described, is productive of the advantages of a rotating target while presenting a structure which lends itself for use in connection with an X-ray microscope. Since the focal spot size may be only about 1 to 5 microns in diameter, it follows that only a small movement of the target window is required continuously to shift the spot sufficiently to obtain a substantial gain in loading. In the event an interval target, distinct from the window, is used, the proper motion can be imparted to it by a cam type drive mechanism sealed into the tube envelope through a bellows similar to the bellows construction above described.

The parameters of the above described invention are limited only as defined by the following claim.

I claim:

An X-ray shadow microscope comprising an evacuable rigid housing, means for initiating and focusing an electron beam within said housing, a moveable member re-. mote from the beam source and disposed in the path of the beam, fixed guide means slidably supporting said member for movement in only one plane that is in perpendicularity with the axis of the electron beam, a thin planar metallic window in said member adapted to intercept said beam at its focal spot and to develop a point source of X-rays at the beam remote side thereof, and a hollow flexible member surrounding the beam and scal ingly fastened between said rigid housing and said moveable member, whereby said target window may be moved to present a different surface area to said beam without changing the position of the X-ray point source, drive means connected to said moveable member remotely from i 1 the beam axis for applying reversible rotational forces in parallelism with the plane of movement within limits established by said guide means, and cam means interposed between said fixed guide means and said movcable member for imparting translational movement to said member concurrently with its rotational movement.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES X-ray Microscopy and Microradiography; published by Crosslett, Engstrom and Patee; 1957.

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