IL32247A

IL32247A - X-ray diffractometer

Info

Publication number: IL32247A
Application number: IL32247A
Authority: IL
Original assignee: Yeda Res & Dev
Priority date: 1969-05-20
Filing date: 1969-05-20
Publication date: 1972-08-30
Also published as: DE2023646A1; NL7007274A; FR2048551A5; US3728541A; IL32247A0; CH519171A; GB1307570A

Description

improved RESEARCH DEVELOPMENT LIMITED 30202 The invention relates to an improved techniques have widely used for many years in the study of the structure of matter and are capable of yielding detailed information on the structure of cated main in the use of such techniques is to he found in the extremely large amount of data which is required structural analysis and which can even in relatively modest to well over 1000 individual Two main techniques are employed in order to record the intensities of The first technique involves photographically recording the whilst the second technique involves counting the individual quanta by means of a radiation counter such as a proportional or scintillation Whilst the use of photographic techniques involve cameras which are relatively compact and simple in design and operation and have the advantage of yielding a permanent the integrated intensity each reflection estimated either visually or metrically from the density of the correspondin spots on the film and this procedure is slow and yields only relatively low quality Radiation on the other are commonly used with where each reflecting piano of the crystal successively brought into its Bragg angle and the integrated intensity of the reflection from that plane is meacured directly by the The disadvantage associated with conventional apparatus using radiation counters lies in the complexity of the means by which the crystal is oriented in the beam and the detector brought into a known position both in relation to the crystal and the incident Such means conventionally take the of complex mountings for the crystal and the detector to give each the degrees of freedom to properly orient the crystal and the Depending on the type of cradle three or four angular settings are required in order to establish the desired orientation of the crystal relative to the beam and the required position of the detector relative to the As a consequence conventional apparatus is very expensive and requires relatively large and costly computers for control and It is an object of the present invention to provide a new and improved using a direct counting device wherein the above referred to disadvantages substantially reduced or The present invention is based on the method described in full in the book preoession by published b John Wiley and copyright The ollowing is a short summary of the method including the definition of parameters and concepts essential for the understanding of the mode of operation of the present The method use of the fact that the diffracted reflections of the various planes of a irradiated by an lie along the generators of Laue cones with rational directions in that The terra means a direction in the crystal defined by a vector where and are vectors specifying the unit cell of the crystal under consideration and and are small In order to obtain a photograph the Buerger precession camera may be used in which a photographic plate is fixed in a plane perpendicular to a particular rational direction of a crystal that is mounted in such a way as to permit that particular rational directio to precess about the in incident beam at a preselected angle without undergoing any pure The various orders of the Laue cones iated with the particular rational direction will intercept photographic plate and define a set of concentric during one full precession the various planes of the crystal are each at its own phase of the into their reflecting positions and the reflected beams are recorded on the film as spots of different densities arranged in such a manner as to form the set of concentric circles described Each reflectio conventionally specified by three known as the Mille indices of that the precession phase of a given reflection will therefore be denoted the azimuth angle of the spot associated with the which is measured around the circle from a predetermined poin is denoted by All reflections lying on the nth circle Laue have one Miller in common and are to to the nth order or All such nkl reflections have the same elevation the angle of the nth Laue and a circle radius In this manner each and every reflection is uniquely specified by the followin arameterss the precession angle the elevation angle of nth order the phase a and the azimuth angle the unit cell dimensions and chosing the rational direction and the precession angle the rest o the parameters may be calculated by appropriate crystallographic In the diffractometer of the present the photographio plate of the Euerger precession camera used to obtain replaced by a radiation counter whose aperture is selectively i elevation and The rea of the countor is suitably masked so as to permit the recording of only one reflection at a time and to out down the amoun of background The angular opening and the radial chosen so as to exclude unwanted reflections and to minimise the background are computed from the known unit cell the instrument the radiation wave and physical dimensions properties of the By choosing a particular rational direction and by the mechanical parameters of the the precession angle the aperture radial distance the angular opening and radial height of the Δ0 and the nth order circle of the set of concentric be in order to record the intensity of a nkl reflection the particular rational direction is to the required phase angle nkl the aperture is rotated about the rotational direction to the required angle angular positions and reflection will be the output of the detector yields the grated intensity of this By changing the pair of angles and 0 the complete set of nth order reflections can be According to the present there is provided an diffractoraeter for positioning a crystal in an beam and measuring the intensity of radiation a yoke on which a crystal can be mounted that a particular rational direction thereof intersects the axis of the beam at a a tor mounted on the yoke and selectively positionable in azimuth and elevation with respect to the particular rational direction of the output of the detector being proportional to the intensity of the reflected tion intercepted by the and the yoke being structed and arranged to effect precession of both the icular rational direction of the crystal and the detector about the axis of the For a hotter understanding of the present invention and to show how it can be carried out in reference should be made to the accompanying 1 is a schematic representation showing the mounting of a crystal in a Buerger precession camera in preparation for making a is a top plan view of a diffractometer ing to the present is a front elevation of the diffractometer shown in 4 is a side elevation of the diffractometer shown in 2 with the gimbal rotated to make an angle with the incident and 5 is a schematic representation of precession diffractometer system in accordance with the present Referring first to Figure crystal 1 rigidly linked with a recording medium hotographic 2 by means of a rigid link The crystal is oriented in such a way that a particular rational direction is disposed normally to the recording medium An beam is incident on the crystal at a preselected angle with respect to the particular rational direction t The mechanism of the Buerger camera causes the crystal and the recording medium to move such that the particular rational t generates a conic section whose coincides with the The resultant reflections roduce the In the first embodiment of the invention shown in 2 5 of the a first vertical gimbal comprises a pair of vertically disposed spaced limbs 6 and 7 coupled together by a horizontal gimbal beam A vertical tube 100 attached to beam 0 is rotatably mounted on a vertical gimbal 9 which in fixedly mounted on a turntable Fork 5 thus vertically rotatable abou axis 101 of shaft turntable 10 is rotatably mounted on base beams 11 are supported with respect to a support surface by means of levelling screws turntable 10 is provided with a turntable lock 13 by means of which1 the turntable can be locked in any desired angular position with respect to the base beams A pair off short horizontally aligned gimbal shafts nd 15 are respectively rotatably mounted in ball bearings 16 and nalled in the upper bifurcated ends of the vertical gimbal limbs 6 and horizontal gimbal shaft 14 formed on one end with an extended horizontal shaft 18 of the gimbal which i coupled to a goniometer head 19 which supports a crystal The crystal is located at that point at which the axis 101 intersects the axis which is the axis of aligned horizontal shafts 14 and The other end of the horizontal gimbal shaft 14 is couplod a crystal translation adjustment mechanism 21 via a dial 23 and vernier The mechanism 21 is provided with a crystal translation screw 24 or selectively moving the crystal along A second gimbal comprises a pair of yoke arras 27 which into the bifurcated ends of the vortical gimbal fork limbs 7 and are rigidly secured to the short horizontal gimbal shafts The yoke arras 27 are rigidly secured together by rear intermediate cross beams 28 and The second gimbal fork 25 is thua mounted on the gimbal 5 pivotal the horizontal axis A support shaft whose passes through the intersection of the axes 101 and projects through and is rotatably mounted in the cross beam Vernier rigidl mounted on beam cooperates with 0 dial 30 rigidly attached to and rotatable with shaft free end of shaft 103 projects and is rotatably mounted in a suitable bearing in coupling collar 32 which can freely slide on arcuate member 33 and thus position 25 relative to limbs and 7 of 5 so that the axis 104 of shaft 103 will make the desired angle μ with a horizontal beam through the section of 101 In such the collar 32 can be to arcuate member 33 which itself is rigidly attached to a drive shaft 34 journalled in a frame withi hich supported drive motor The output the motor 36 transmitted via a worm and gear 37 coupled to the drive By means of locking screw the dial 38 rigidly attached to and rotatable with shaft Dial is cooperable wit vernier 39 which is rigidly attached to frame The end 103 remote the bearing in 32 is attached to and supports one end of radiation counter drum 41 which is mounted in fork 25 for rotation about the 0 an annular drum 42 means of angularly spaced apart drum supports respectively held in support holders 44 secured to the frame 42 and respectively provided with drum support adjustment screws rear end of the drum is formed integrally a ø gear wheel 46 which meshes with a 0 pinion 47 coupled to an output shaft 48 of a 0 drive motor 49 al30 supported by the yoke Thus the drum 41 can be rotated about axis 104 through the angle 0 by the drive motor 49 wliilst supported on the drum supports Located1 within the drum 41 is a radiation counter 50 in dottod lines in longitudinal axis is parallel to 9 but spaced apart from the longitudinal axis 104 of the drum The front aperture the counter 50 is located opposite a aperture 51 formed in an end face of the Selective rotation of drive motor 49 will rotate the counter about axis 104 until the surface is at the desired asimuth angle relative to axi3 Superimposed on the end of the drum is a first metal disc which is on the end face for rotation about axis A aperture 52 formed in the first metal disc corresponds to the aperture formed in the fixed end by the first metal disc with respect to the end face of the the apertures 51 and 5 may be misaligned to the extent necessary to mask of the surface of counter 50 except for the aperture 53 having the desired angular width The relative position of the two apertures 51 and 52 and in rotatable disc dial and vernier arrangement A disc 55 is also rotatably mounted on the end face of the drum and is provided with a plurality of annular slots of differing radii corresponding to the differing radii of the cone axis The radial width of each establishes the height of aperture for the By rotating the second disc on the end face of the a of the slots can be positioned opposite the aperture 51 and 52 to establish the radial position of the Λ pair of radially spaced apart locking screws 57 and 58 are provided for securing the additional disc 55 in the required The end face of the in cooperation with the first and second discs selectively masks the pho surface of the counter establishing a detector with a limited field of By rotating the drum on the yoke 25 and by rotating the first and second discs on the end face of the the detector can be positioned at azimuth and elevation with respect to the rational direction t of the crystal corresponding to a particular reflection to be In the required aperture size Δ and to prevent recariation simultaneous reflections will also bo achieved0 an collimator supported in a collimator holder 60 and is provided with a collimator lock mechanism the collimator holder 60 being located fixedly with respect to the turn table collimator 59 is aligned with the drive shaft In operation the precession diffractometer turntable is rotated so as to align the collimator 59 in the direction of the source and the turntable 10 is clamped in this position by means of the turntable lock The horizontal axis dial mechanism 21 is then rotated so as to bring the horizontal into the appropriate position wherein the desired rational direction of the crystal is correctly orientated with respect to the collar 32 is thereupon and io slid on the arc member 33 until the axis 104 orients the crystal at the predetermined angle with respect to Incident so orientated the oollar 32 is clamped in first metal disc on the end face of drum 41 is rotated so as to define a predetermined angular width of aperture Δ0 as indicated is predetermined in accordance with the conditions for avoiding the detection of Similarl the second metal disc 55 is rotated so as to superimpose on the aperture that annular slot corresponding to the predetermined height and radial position of the aperture in which measurements are to A detector is now established at the desired elevation angle to measure the reflected energy from a particular nth level of the Measurement can now be obtained in any one of following modes In accordance with a first mode of operation and drive motors and 49 are actuated so as to set the read on the respective dials 40 and The the crystal and the is maintained stationary in thio particular and the reflection intensity is measured over a predetermined period of time in terms the electric pulses from the counter which are fed to spectrometer which together with the counter constitutes a standard counting In accordance with a second mode of operation the drive motor 36 is arranged to displace the instrument to a value of which corresponds but is somewhat less than the predetermined value corresponding to the particular reflection to be The 0 drive motor 49 then rotates the drum to the required position and a predetermined number of discrete stepping pulses are successively fed to the drive motor so as to drive the instrument by small discrete steps into and slightly beyond the predetermined at each step the intensity of reflection being In this way scanning of the range obtained Preferably stepping motors are used for both the nd 0 These motors were chosen because they offer two important advantages over continuous they can be conveniently used in open loop control is no need for from digitizer other position detecting to stop motor when the required setting is redetermined number o electrical pulses being all that is needed to rotate the motor to its specified such a motor avoiding drift of the drive The motor drive preferably consists of an electronic pulse generator whose pulses are fed into the Manual control switches can be provided for selecting the required motor operation and its Λη automatic control may be used to supervise the operation of the various components of the precession ractometer system in order to the data of a complete As seen in automatic control is effected by means of an computer assembly The computer assembly 71 consists of a a programmer and an auxiliary storage An interface 72 connects the output of the computer assembly 71 to a motor drive control to the spectrometer 74 and to a scaler printout control 75 and teletype unit A suitable programme controls the Input parameters for this programme comprises crystallographic operation instructionsβ status Using these data the computer assembly of computing and controlling the data collection of a se of reflections belonging to a given insufficientOCRQuality

Claims

322 -2 WHAT 13 CLAIMED IS: 1. An X-ray diffractometer for positioning a crystal in an X-ray bean and measuring the intensit of reflected radiation comprisin s a yoke on which' a crystal can be mounted so that a particular rational direotion thereof intersects the axis of the beam at a predetermined angle» a photon-sensitive detector movably mounted on the yoke and selectively positionable in azimuth and elevation with respeot to the particular rational direction of the crystals the output of the detector being proportional to the intensity of the reflected radiation intercepted by the detector, and the yoke being constructed and arranged to effect precession of both the particular rational direotion of the crystal and the detector about the axis* of the X-ray beam, , 2. An X-ray diffractpmoter acoording to Claim 1, wherein the yoke comprises a first gitabal fork mounted for pivotal movement about first axis intersecting the boam at a right angle,, a second gimbal fork mounted on the firs¾ fork for pivotal movoment about a second axis perpendicular to the first axis and passing through the point wheie the beam intersects the first axisB a drive member mounted for notation about the axis of the beam, and a pivotal connection between the drive member and tho second fork, the axis of the pivotal connection passing throug the poirtt a which the first and second axes intersect with the beam. ' ,; 3. An X-ray diffractometer according to Claim 2R ¾rherein the drive member is arcuate in shape,' the center of curvature of the drive member being the point a which the 32¾ 7-3 4. An X-ray diffractoraeter according to Claim 3» including a drive motor for moving the drive member to preselected angular positions, and an azimuth motor fox-rotating ¾he detector about the axis of the pivotal connection between the drive member and the second fork. 5.. An X-ray diffractometer according to Claim 4» including a drum rotatable όη the second gimbal yoke about the same axis as the pivotal connections the detector being mounted eccentrically in the drum and the azimuth motor serving to move the drum to preselected angular positions, / 6,! , An X-ray diffractometer according to Claim 5 wherein the drive motor and the asimuth motor are stepping motors that impart incremental movement to the drive member jand the drum respectively. 7t An X-ray diffractometer according any of Claims 4, 5 or 6 including motor control means for controlling the drive and drum motors in accordance with a computer controlled program. 8» A method for "using the X-ray diffractometer according to Claim 1, wherein the yoke is operated to cause precession of both the particular rational axis of the ' crystal and the detector about the beam direction, and the azimuth and elevation of the detector are periodicall ohanged in a manner to cause the detector to map the intensity of the reflected beam. 9· An X-ray diffractometer according to Claim 1, x/herein the detector is constituted by a counter havin an aperture defining moans masking the counter and limiting the field of view of the detector for preventing unwanted reflections from reaching the surface.! 10. An X-ray diffractoineter according to Claim 9i including a drum mounted on the yoke so as to be rotatable about the particular rational direction of the crystal, the counter being eccentrically mounted on the drum so that rotation of the drum changes the a iauth of the detector, 11. An X-ray diffractometor according, any of Claims .1, 9 or wherein the axis of the deteotor ia substantially parallel to the particular rational direction of the crystal. 12. An X-ray diffractometer substantially as described above by way of example and with reference to the accompanying drawings. 13. A method for using an X-ray diffractometer substantially as described above by way of example and with reference to the accompanying drawings. For the A pplicants DR. Kt»«0lD COHK AND PARTNERS