(IUCr) Bragg Lecture 2001

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style="width:66px;margin-top:-10px;margin-right: 24px;margin-bottom:6px;" /></a></div> <a href="https://www.iucr.org/education" title="[Education Home Page]"><h2>Resources for crystallographic education</h2></a></div></div>          <div id="breadcrumb"> <a href="https://www.iucr.org">iucr</a>  >  <a href="https://www.iucr.org/education">education</a>  >  <a href="https://www.iucr.org/education/teaching-resources">teaching resources</a>  >  <a href="https://www.iucr.org/education/teaching-resources/bragg-lecture-2001">bragg lecture 2001</a> </div>         <div class="wrapper row3" id="page_body"> <main class="hoc container clear">  <div class="motd"> </div>  <div class="clear">   <div id="_layout_34Q" class="content three_quarter first"></div> <div id="_layout_34" class="content three_quarter"></div> <div id="_layout_full" class="content"><script type="text/javascript"> var r1="This is a home-made apparatus involving a 2-D grid/mesh in a holder that allows transmission of a laser beam thus giving a 2D red-laser array of spots; a motorised fan belt rotates the holder thus giving a powder pattern of rings. The adjustment of the speed of the motor allows the transition between spots and rings to be readily seen by the audience. The grid is represented by a pair of 35mm projection slides each holding an optical diffraction grating purchased from a physics teaching supplier. In this Public Lecture the usual dimming of lights was needed and there is a large distance between the rotating gratings and the projection onto the Lecture theatre side wall. The video cameraman does capture the rings to 2D pattern of spots nicely. The sharpness of the 'powder' rings in the video is not as good as the live demonstration."; var r2="The Fourier summation is of diffraction waves added via one viewgraph, so that the projection view of hexachlorobenzene gradually builds up. The projection allows the hexchlorobenzene to be viewed 'in plane' and the whole unit cell shows several molecules. The Lecture Theatre has to have lights dimmed but not off as the audience needs to see the viewgraphs being added one by one. A limitation of viewgraphs is that they are not completely transparent; and so each viewgraph represents the addition of three reflection waves. Overall a total of approx 30 reflections gives an atomic resolution image. The video cameraman in the final shot of this zooms away from the screen and the longer distance shot of the several molecules in view I found particularly pleasing. A little later on in the main Lecture I return to this collection of stacked viewgraphs and emphasise the need for each viewgraph to be carefully aligned to get the image of the molecules. By shuffling the viewgraphs out of alignment one shows the loss of alignment i.e. the loss of the phases relative to one another in losing the clarity of the molecules in the image."; var r3="This is a commercially available piece of apparatus sold by Griffin and George. It comprises a source of microwaves of wavelength 2.8cm and a microwave receiver. A simple rotary turntable was connected via metal rods to the source and the receiver (detector) thus making a simple diffractometer where the crystal sample was a metal framework model of sodium chloride with inter-ion spacing being 5.6cm. [The spacing in the Face Centred Cubic lattice of ions of NaCl is 5.6Å.] The University of Manchester School of Chemistry Electronics workshop linked the output of the reading-dial of the microwave receiver to a loudspeaker; thus a reflection was a loud sound and absence of reflection was 'quiet'. By rotation of the sample on the rotary stage the (100) and (110) microwave reflections could easily be found by adjustment of the receiver angle; thus Bragg's Law of diffraction via reflection at specific angles for (100) and (110) planes could be demonstrated. The limitations of this apparatus were (i) that the divergence angle of the emitted microwave beam was significant and at low angles the receiver would pick up the edge of the incident beam; (ii) the set up was not an ideal Fraunhofer far field geometry but more of a Fresnel near-field geometry. Thus the distance of the receiver to the sample, which was adjustable to be closer to or further from the sample, also led to maxima and minima of the received microwaves. In the Public Lecture the viewing angle of the videoing camera from the demo did not allow a view from above, i.e. the Lecturer's view, or from the audience for that matter. Thus this demo would work best in a tutorial or small classroom setting. Nevertheless the Public Lecture gave a reasonable view of the components of the diffractometer and of the ideas behind Bragg's Law."; var r4="The optical effect of calcite, known originally as Iceland Spar,  was first written about by Bartholinus in the late 17th century. I purchased a large single crystal of calcite from our local, Stockport Crystal and Gems shop measuring 11.5cm x 4 x 3.5cm. The School of Chemistry Mechanical Workshop drilled a linear array of ten holes in a metal plate; each hole was diameter 2mm and spaced 1cm apart so that the total length of the array was less than the long length of this calcite crystal. Overall the plate was of sufficient size to cover completely the illuminated area of the overhead projector i.e. 31.5 x 31.5cm. Thus a single array of lit up spots is projected onto the Lecture Theatre screen facing the audience. By placing the calcite crystal onto the array of holes a double array of holes is now seen. The connection to the atomic layout of the calcium carbonate in calcite is shown via a combination of viewgraphs of figures in W L Bragg's book 'The Development of X-ray Analysis', the key feature being the planar trigonal arrangement of each of the carbonates and the polarisation selection of the light coming up through the calcite crystal. I also show a neat diagram from WLB sketching out the ray paths of the ordinary and the extraordinary ray. The climax of the demo is to show that each of the two lines of ten lit-up spots now involves differently polarised states of light. Thus by rotating a piece of Polaroid directly above the crystal one can show one row and then the other appearing and disappearing."; var r5="Since its origins 150 years ago the University of Manchester has had many famous staff and students in the history of science including a variety of Nobel Laureates. The University had a significant involvement in the development of science at the global level and included Ernest Rutherford's 'splitting of the atom'. W. L. Bragg succeeded Rutherford both in Manchester and in Cambridge and Bragg in his 18 years in Manchester contributed a major part of that science history. Bragg's scientific interests embraced crystallographic methods, strongly based on physical optics, and their applications in chemistry and biology, the latter during his Cambridge ie final part of his career. A Publc Lecture was given by Professor John R. Helliwell as the 'W. L. Bragg Lecture', delivered at the University of Manchester's Physics Department ('Schuster Laboratory'), on 5th February 2001 as part of the University's 150th Anniversary Celebration. A detailed article was prepared for the Manchester Literary and Philosophical Society Memoirs and subsequently was reproduced in Z. Krist., with permission of the Society, as a contribution to Z. Krist's 125th Anniversary."; var v1='<iframe width="640" height="360" src="https://www.youtube.com/embed/o-DWLSCWhZo?autoplay=1" frameborder="0" allow="autoplay; fullscreen"></iframe>'; var v2='<iframe width="640" height="360" src="https://www.youtube.com/embed/51z-1yEXqN4?autoplay=1" frameborder="0" allow="autoplay; fullscreen"></iframe>'; var v3='<iframe width="640" height="360" src="https://www.youtube.com/embed/hjNO4QBf7dg?autoplay=1" frameborder="0" allow="autoplay; fullscreen"></iframe>'; var v4='<iframe width="640" height="360" src="https://www.youtube.com/embed/uzUDwI8RliU?autoplay=1" frameborder="0" allow="autoplay; fullscreen"></iframe>'; var v5='<iframe width="640" height="360" src="https://www.youtube.com/embed/Z71rrk9bbJg?autoplay=1" frameborder="0" allow="autoplay; fullscreen"></iframe>'; </script> <img src="https://www.iucr.org/__data/assets/image/0019/10468/JRH.jpg" alt="[John R. Helliwell]" style= "float:right;margin-left:10px;height:180px;width:135px;"> <h1>Bragg Lecture 2001</h1> <h2>X-ray crystal structure analysis and Manchester: from W. L. Bragg to the present day</h2> <h3>Professor John R. Helliwell</h3> <h4>Professor of Structural Chemistry at the University of Manchester</h4> <p>As part of the 150th anniversary celebrations of the University of Manchester, the Department of Physics and Astronomy organised a special lecture, delivered by <b>Professor J. R. Helliwell</b>, reviewing Lawrence Bragg's association with the university and the many consequent contributions to X-ray crystallography. A notable feature of this lecture was the live demonstrations and experiments illustrating some of the scientific principles discussed.</p> <p><a href="https://doi.org/10.1107/S0021889809002775">Helliwell, J. R. (2009). <i>J. Appl. Cryst.</i> <b>42</b>, 365, doi: 10.1107/S0021889809002775</a><a title="Open URL link" href= "https://doi.org/10.1107/S0021889809002775"></a></p> <hr> <p> <table cellpadding="10" width="920"> <tbody> <tr> <td id="_td0_0" valign="top"> <div id="preview"><img alt="display area" src=https://www.iucr.org/__data/assets/image/0017/10466/LectureTitle.gif></div> <br></td> <td id="_td0_1" style="border: 1px solid rgb(102, 0, 0);" valign="top" width="240"> <div style="overflow: auto; height: 520px;"> <h6>Demonstration 1: simulation of powder diffraction pattern</h6> <img src=https://www.iucr.org/__data/assets/image/0018/10467/demo1.gif alt="[Demonstration 1]" style="border: 0px solid rgb(0, 0, 0);" onclick="getElementById('preview').innerHTML=v1;getElementById('rubric').innerHTML=r1;" vspace="0" width="160" height="120" hspace="0"> <br> (3 min 20 sec)<br> <br> <h6>Demonstration 2: phases of reflections in crystallography via a 'viewgraphs' Fourier analysis simulator</h6> <img src=https://www.iucr.org/__data/assets/image/0003/10497/demo2.gif alt="[Demonstration 2]" style="border: 0px solid rgb(0, 0, 0);" onclick="getElementById('preview').innerHTML=v2;getElementById('rubric').innerHTML=r2;" vspace="0" width="160" height="120" hspace="0"> <br> (3 min 40 sec)<br> <br> <h6>Demonstration 3: microwave analogue of diffraction</h6> <img src=https://www.iucr.org/__data/assets/image/0006/10500/demo3.gif alt="[Demonstration 3]" style="border: 0px solid rgb(0, 0, 0);" onclick="getElementById('preview').innerHTML=v3;getElementById('rubric').innerHTML=r3;" vspace="0" width="160" height="120" hspace="0"> <br> (3 min 05 sec)<br> <br> <h6>Demonstration 4: double refraction in calcite</h6> <img src=https://www.iucr.org/__data/assets/image/0008/10502/demo4.gif alt="[Demonstration 4]" style="border: 0px solid rgb(0, 0, 0);" onclick="getElementById('preview').innerHTML=v4;getElementById('rubric').innerHTML=r4;" vspace="0" width="160" height="120" hspace="0"> <br> (4 min 06 sec)<br> <br> <h6>Complete lecture</h6> <img src=https://www.iucr.org/__data/assets/image/0017/10466/LectureTitle.gif alt="[Bragg Lecture 2001]" style="border: 0px solid rgb(0, 0, 0);" onclick="getElementById('preview').innerHTML=v5;getElementById('rubric').innerHTML=r5;" vspace="0" width="160" height="120" hspace="0"> <br> (46 min 36 sec)</div> </td> </tr> <tr> <td colspan="2"> <div id="rubric"></div> </td> </tr> </tbody> </table></div>   <div class="sidebar one_quarter" style="float:right;"></div> <div class="sidebar one_quarter" style="float:right;"></div> </div> </main> </div>                     <div class="wrapper row1"> <div id="quicklinks" class="hoc clear">  <div class="accordion">  <a href="javascript:void(0);" class="accordiontoggle heading">Quick links</a>  <div class="linkblock group"> <div class="one_quarter first">  <ul> <li><a href="https://www.iucr.org/news/notices/announcements">Announcements</a></li> <li><a href="https://www.iucr.org/people/associates">Associates 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(IUCr) Bragg Lecture 2001