Discovery of X-rays
The science of x-ray crystallography can be traced back
to two major discoveries.
• The discovery of x-rays is one of these.
• The other, Laue's discovery that crystalline materials
can act as diffraction gratings when interacting with
electromagnetic radiation of the proper wavelength.
Discovery of X-RaysNovember 1895, Würzburg
Wilhelm Conrad Röntgen
Roentgen's Wurzburg Laboratory
Crooke's Tube Similar to That Used in Roentgen's Discovery of X-rays
Cathode ray tubes were known to glow when a current was passed
between the cathode and anode. Röntgen shielded his tube with black
cardboard to darken the room. This is probably because he was either
interested in observing faint fluorescence in materials such as barium
platino cyanide or interested in the laws of absorption of "cathdode
rays“. Cahthode rays (electrons) were easily absorbed by the walls of
the glass enclosure and air. So the glow would be faint.
Röntgen was shocked to note in the darkened room that a barium
platino cyanide screen lying on a nearby table (9 feet) showed a
flash of fluorescence every time an induction coil discharged into
the tube. This could not be from the easily absorbed cathode rays.
By the end of the year 1895, Röntgen discovered many properties of
his X-rays.
• They traveled in a straight line from the point that the cathode
rays in the tube struck the glass wall of the tube.
• They were exponentially absorbed by matter but very much less
so than cathode rays.
• They possessed photographic properties.
Many of the early investigations of X-rays were aimed at
finding if they were electromagnetic wave-like phenomenon or
particles. One way one could show wave-like characteristics
was to use a suitable "diffraction grating." The nature of x-ray
properties continued until the work of Laue and others such as
Thompson, Barkla, and Compton proved that x-rays were
electromagnetic phenomena.
What about Diffraction Effects
Roentgen and Diffraction
From W. C. Rontgen's Third Communication, March 1897: 'The experiments on the permeability (for X-rays) of plates of constant thickness cut from the same crystal in different orientations, which were mentioned in my first Communication, have been continued. Plates were cut from calcite, quarz, turmaline, beryl, aragonite, apatite and barytes. Again no influence of the orientation on the transparency could be found.
'Ever since I began working on X-rays, I have repeatedly sought to obtain diffraction with these rays; several times, using narrow slits, I observed phenomena which looked very much like diffraction. But in each case a change of experimental conditions, undertaken for testing the correctness of the explanation, failed to confirm it, and in many cases I was able directly to show that the phenomena had arisen in an entirely different way than by diffraction. I have not succeeded to register a single experiment from which I could gain the conviction of the existence of diffraction of X-rays with a certainty which satisfies me.'
Using the photographic property, he was able to produce photo's of
brass weights in a wooden box and, soon thereafter, the first photo of the
bones in a living hand (his wife’s). He also discovered that the output of
x-rays could be increased by impinging the cathode rays on a heavy
metal "anticathode" which could also be the anode of the tube. This
arrangement is today the basis of the modern x-ray tube.
The left picture taken at a lecture in January 1896 by Roentgen. The
right by Mr. Haschek and Dr. Lindenthal, in Professor Franz Exner's
physicochemical institute in Vienna was obtained by injecting a mixture
of lime, cinnabar (mercury) and petroleum in the hand of a cadaver.
The photographic use of x-rays advanced quickly. X-ray photographs
were used as early as February 1896 in the U.S. to diagnose bone
fractures.
X-ray Shoe Fitting Device
In the late 1940's and early 1950's, the shoe-fitting x-ray unit was a
common shoe store sales promotion device and nearly all stores had
one. It was estimated that there were 10,000 of these devices in use.
This particular shoe-fitting x-ray unit was produced by the dominant
company in the field, the Adrian X-Ray Company of Milwaukee WI, now
defunct. Brooks Stevens, a noted industrial designer whose works
included the Milwaukee Road Olympian train and an Oscar Meyer
Wienermobile, designed this machine.
The primary component of a shoe-fitting x-ray unit was the fluoroscope which
consisted essentially of an x-ray tube mounted near the floor and wholly or
partially enclosed in a shielded box and a fluorescent screen. The x-rays
penetrated the shoes and feet and then struck the fluorescent screen. This
resulted in an image of the feet within the shoes. The fluorescent image was
reflected to three viewing ports at the top of the cabinet, where the customer, the
salesperson, and a third person (mom) could view the image at the same time.
The radiation hazards associated with shoe fitting x-ray units were recognized as
early as 1950. The machines were often out of adjustment and were constructed
so radiation leaked into the surrounding area.
X-ray Tube Circa 1900
Modern X-Ray Tube
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