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Neutron microscope
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<h2 id="applications">Applications</h2> <p>Neutron imaging has potential for studying so-called soft materials, as small changes in the location of hydrogen within a material can produce highly visible changes in a neutron image.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>Neutrons also offer unique capabilities for research in <a href="/facts/Magnetic_material/vvrg6VSk">magnetic materials</a>. The neutron's lack of <a href="/facts/Electric_charge/xxsBfmlB">electric charge</a> means there is no need to correct magnetic measurements for errors caused by stray <a href="/facts/Electric_field/tt4MooBs">electric fields</a> and charges. <a href="/facts/Spin_polarization/S36kxcj2">Polarized</a> neutron beams orient neutron spins in one direction. This allows measurement of the strength and characteristics of a material's magnetism.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>Neutron-based instruments have the ability to probe inside metal objects — such as fuel cells, batteries and engines to study their internal structure. Neutron instruments are also uniquely sensitive to lighter elements that are important in biological materials.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="shadowgraphs">Shadowgraphs</h2> <p><a href="/facts/Shadowgraph/SvbncIPM">Shadowgraphs</a> are images produced by casting a shadow on a surface, usually taken with a <a href="/facts/Pinhole_camera/8JmYNdeL">pinhole camera</a> and are widely used for <a href="/facts/Nondestructive_testing/Czz0Vt0B">nondestructive testing</a>. Such cameras provide low illumination levels that require long exposure times. They also provide poor spatial resolution. The resolution of such a lens cannot be smaller than the hole diameter. A good balance between illumination and resolution is obtained when the pinhole diameter is about 100 times smaller than the distance between the pinhole and the image screen, effectively making the pinhole an f/100 <a href="/facts/Lens_(optics)/ejlH6n5c">lens</a>. The resolution of an f/100 pinhole is about half a degree.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="wolter-mirror">Wolter mirror</h2> <p>Glass lenses and conventional mirrors are useless for working with neutrons, because they pass through such materials without <a href="/facts/Refraction/S8kvSKzM">refraction</a> or <a href="/facts/Reflection_(physics)/BhcjDs79">reflection</a>. Instead, the neutron microscope employs a <a href="/facts/Wolter_telescope/MxpwmMI5">Wolter mirror</a>, similar in principle to <a href="/facts/Grazing-incidence_small-angle_scattering/1HCE5Bdv">grazing incidence mirrors</a> used for <a href="/facts/X-ray_telescope/FDpF14TH">x-ray</a> and <a href="/facts/Gamma-ray_telescope/s59YdwaX">gamma-ray telescopes</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p>When a neutron grazes the surface of a metal at a sufficiently small angle, it is reflected away from the metal surface at the same angle. When this occurs with light, the effect is called <a href="/facts/Total_internal_reflection/Tm0M62NQ">total internal reflection</a>. The critical angle for grazing reflection is large enough (a few tenths of a degree for thermal neutrons) that a curved mirror can be used. Curved mirrors then allow an imaging system to be made.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>The microscope uses several reflective cylinders nested inside each other, to increase the surface area available for reflection.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <h2 id="measurement">Measurement</h2> <p>The <a href="/facts/Neutron_flux/nDE9Nlrx">neutron flux</a> at the imaging <a href="/facts/Focal_plane/7vqmsXJy">focal plane</a> is measured by a <a href="/facts/Charge-coupled_device/l6xffIcz">CCD</a> imaging array with a neutron <a href="/facts/Neutron_detection/8BRncp82">scintillation screen</a> in front of it. The scintillation screen is made of <a href="/facts/Zinc_sulfide/K8l5AF3K">zinc sulfide</a>, a <a href="/facts/Fluorescent/qsJVT2qP">fluorescent</a> compound, laced with <a href="/facts/Lithium/7vXX6BWA">lithium</a>. When a thermal neutron is absorbed by a <a href="/facts/Lithium-6/XC311sQu">lithium-6</a> nucleus, it causes a <a href="/facts/Fission_reaction/LfkIylvm">fission reaction</a> that produces <a href="/facts/Helium/yRul93TG">helium</a>, <a href="/facts/Tritium/HWSa6EHy">tritium</a> and energy. These fission products cause the ZnS <a href="/facts/Phosphor/vTLjrGDE">phosphor</a> to light up, producing an optical image for capture by the CCD array.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Electron_microscope/XtaBktwF">Electron microscope</a></li> <li><a href="/facts/ISIS_neutron_source/oo3jNPoo">ISIS neutron and muon source</a></li> <li><a href="/facts/LARMOR_neutron_microscope/znuCdjal">LARMOR neutron microscope</a></li> <li><a href="/facts/Microscope_image_processing/kBlRgtsg">Microscope image processing</a></li> <li><a href="/facts/X-ray_microscope/SNRNlbgI">X-ray microscope</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Liu, D.; Khaykovich, B.; Gubarev, M. V.; Lee Robertson, J.; Crow, L.; Ramsey, B. D.; Moncton, D. E. (2013). "Demonstration of a novel focusing small-angle neutron scattering instrument equipped with axisymmetric mirrors". Nature Communications. 4: 2556. arXiv:1310.1347. Bibcode:2013NatCo...4.2556L. doi:10.1038/ncomms3556. PMID 24077533. S2CID 34185138. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"New kind of microscope uses neutrons - MIT News Office". Web.mit.edu. 2013-10-04. Retrieved 2013-10-21. <a href="http://web.mit.edu/newsoffice/2013/new-kind-of-microscope-uses-neutrons-1004.html" target="_blank">http://web.mit.edu/newsoffice/2013/new-kind-of-microscope-uses-neutrons-1004.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"New kind of microscope uses neutrons - MIT News Office". Web.mit.edu. 2013-10-04. Retrieved 2013-10-21. <a href="http://web.mit.edu/newsoffice/2013/new-kind-of-microscope-uses-neutrons-1004.html" target="_blank">http://web.mit.edu/newsoffice/2013/new-kind-of-microscope-uses-neutrons-1004.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"What shall we do with a neutron microscope?". Gizmag.com. 21 October 2013. Retrieved 2013-10-21. <a href="http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/" target="_blank">http://www.gizmag.com/mit-neutron-microscope-reactor-prototype/29392/</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> </ol>