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