User:Twlk42/sandbox X ray microscope

'EG: Great work, Zeguan. Only minor things--see below. Eric'

Main article: X-ray microscope

X-ray optics
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Detection devices
=== Invention and development === The history of X-ray microscopy can be traced back to the early 20th century. After the German physicist Rontgen discovered X-rays in 1895, scientists soon illuminated an object using an X-ray point source and captured the shadow images of the object with a resolution of several microns. In 1918, Einstein pointed out that the refractive index for X rays in most mediums should be just slightly less than 1, which means refractive optical parts would be difficult to use for X-ray applications.

"Early X-ray microscopes by Paul Kirkpatrick and Albert Baez used grazing incidence reflective X-ray optics to focus the X-rays, which grazed X-rays off parabolic curved mirrors at a very high angle of incidence. An alternative method of focusing X-rays is to use a tiny Fresnel zone plate of concentric gold or nickel rings on a silicon dioxide substrate. Sir Lawrence Bragg produced some of the first usable X-ray images with his apparatus in the late 1940s.

In the 1950s Sterling Newberry produced a shadow X-ray microscope which placed the specimen between the source and a target plate, this became the basis for the first commercial X-ray microscopes from the General Electric Company."

After a silent period in the 1960s, X-ray microscopy regained people's attention in the1970s. In 1972, Horowitz and Howell built the first synchrotron-based X-ray microscope at the Cambridge Electron Accelerator. This microscope scanned samples using synchrotron radiation from a tiny pinhole and showed the abilities of both transmission and fluorescence microscopy. Other developments in this period include the first holographic demonstration by Aoki and Kikuta in Japan, the first TXMs using zone plates by Schmahl et al. , and Stony Brook’s experiments in STXM.

The uses of synchrotron light sources brought new possibilities for X-ray microscopy in the 1980s. However, as new synchrotron source-based microscopes were built in many groups, people realized that it was difficult to perform such experiments due to insufficient technological capabilities at that time, such as poor coherent illuminations, poor quality x-ray optical elements, and user-unfriendly light sources.

Entering the 1990s, new instruments and new light-sources greatly fueled the improvement of X-ray microscopy. Microscopy methods including tomography, cryo, and cryo-tomography were successfully demonstrated. With rapid development, X-ray microscopy found its new applications in soil science, geochemistry, polymer sciences, and magnetism. The hardware was also miniaturized so that researchers could perform experiments in their own laboratories.

With the applications continued to grow since 2000, X-ray microscopy has become a routine, proven technique used in environmental and soil sciences, geo- and cosmo-chemistry, polymer sciences, biology, magnetism, material sciences. With this increasing demand for X-ray microscopy in these fields, microscopes based on synchrotron and laboratory light sources are being built around the world. X ray optics and components are also being commercialized rapidly.

Biological applications
One early applications of X-ray microscopy in biology was contact imaging, pioneered by Goby in 1913. In this technique, soft x-rays irradiate a specimen and expose the x-ray sensitive emulsions beneath it. Then, magnified tomographic images of the emulsions, which correspond to the x-ray opacity maps of the specimen, are recorded using a light microscope or an electron microscope. A unique advantage that X-ray contact imaging offered over electron microscopy was the ability to image wet biological materials. Thus, it was used to study the micro and nanoscale structures of plants, insects, and human cells. However, several factors, including emulsion distortions, poor illumination conditions, and low resolutions of ways to examine the emulsions, limit the resolution of contacting imaging. Electron damage of the emulsions and diffraction effects can also result in artifacts in the final images.

X-ray microscopy has its unique advantages in terms of nanoscale resolution and high penetration ability, both of which are needed in biological studies. With the recent significant progress in instruments and focusing, the three classic forms of optics—diffractive, reflective, refractive optics—have all successfully expanded into the X-ray range and have been used to investigate the structures and dynamics at cellular and sub-cellular scales. In 2005, Shapiro et al. reported cellular imaging of yeasts at a 30nm resolution using coherent soft X-ray diffraction microscopy. In 2008, X-ray imaging of an unstained virus was demonstrated. A year later, X-ray diffraction was further applied to visualize the three-dimensional structure of an unstained human chromosome. X-ray microscopy has thus shown its great ability to circumvent the diffractive limit of classic light microscopes; however, further enhancement of the resolution is limited by detector pixels, optical instruments, and source sizes.

A longstanding major concern of X-ray microscopy is radiation damage, as high energy X-rays produce strong radicals and trigger harmful reactions in wet specimens. As a result, biological samples are usually fixated or freeze-dried before being irradiated with high-power X-rays. Rapid cryo-treatments are also commonly used in order to preserve intact hydrated structures.