~ HISTORY OF X-RAY ~

[MysteRy]

HISTORY OF X-RAY




The history of X-Rays is a little murky. There were many independent experiments involving cathode vacuum tubes that resulted in the creation of X-Rays in the late 19th century. Initial experimenters, however, were either not aware that X-Rays had been created (they are invisible in most conditions) or observed their effects but did not know what caused them. Early scientists that observed the effects of X-Rays included William Crookes, Heinrich Hertz, Nikola Tesla, and Thomas Edison. Wilhelm Röntgen, a German physicist, is widely attributed as the “true” discoverer of X-Rays because he studied them in-depth beginning in 1895 and gave them their name. Because what he observed was then an unknown form of radiation, he initially called it “X” radiation, “X” standing for “unknown”. The initial name has remained since, although they are also sometimes referred to as Röntgen rays in honor of his contributions.

Exact accounts of his discovery conflict, but most agree that he was working with a cathode tube that he had covered in black cardboard. A screen that had been treated with a fluorescent paint stood a few feet away, and as the cathode tube began emitting a highly charged electron stream, Röntgen saw that the screen began to glow lightly. Because all visible light had been blocked by the cardboard, Röntgen realized something else, although invisible, had traveled through the glass tube and cardboard to make the screen glow: X-Rays.

[MysteRy]

The Discovery of X-Rays


ONE OF THE WELL KNOWN STORIES in physics is the tale of the discovery of X-rays. While the null search for the ether indeed ushered in the modern physics world, the connection between that phenomenon and the rapid understanding of the fundamentals of matter comes much later. The accepted birth of modern physics of matter begins in the remarkable few years between 1895 and 1898. In Germany, England, and France, laboratory surprises occurred which have promoted Michelson's ill-timed comment about the future of physics to embarrassing prominece for its wrongheadedness!

     The stage for the first surprised was set by Philipp Lenard [1862-1947], who was an assistant of Hertz's (and a later ardent Nazi and an embarrassment to his former scientific colleagues). In 1892 he managed to coat the end of a Crooke's tube with a very thin layer of aluminum...through which he was able to transmit the cathode rays into air beyond the tube. Now, this was quite spectacular: the cathode rays penetrated what was presumed to be an opaque, solid wall of metal. It was this experiment that led a careful and rather unspectacular German professor to world-wide recognition.

William Roentgen-The First Nobel


William Konrad Roentgen [1845-1923] in the 1890's was a middle aged professor of Physics at Wurzburg. He had been transfered within the German university system four different times and was not likely to go much higher. At Wurzburg, he lived upstairs from his laboratory and from there, he continued his pedantic and careful work. A competent experimenter, he made good measurements of standard quantities in electromagnetics and materials. Indeed, Lorentz dubbed a pheonomenon that Roentgen had painstakingly discovered and characterized as the "Roentgen Current" (the observation of a magnetic field generated by a moving dielectric placed in a homogeneous electric field). He was productive, an author of 48 careful, unspectacular papers at the age of 50 when lightening struck.

     The year that Babe Ruth was born was the turning point. During the evening of November 8th, 1895 Roentgen was working alone in his laboratory, studying the Lenard effect, the penetration of cathode rays through different materials. In his darkened room, he covered his Hittorf tube (a variant on the glow tube of Hertz) with black cardboard. Quite by accident, on the wall six feet from the end of his tube, was a sheet of paper which had been treated with the salt barium platinum-cyanide which he used as a screen for other experiments. Because it was dark he noticed that the paper was glowing, flourescing. Further study demonstrated that this flourescent glow originated from the tube and that it exibited amazing properties! He knew from his earlier work that source of the glow could not be the cathode rays themselves, as they seemed unable to penetrate the tube's glass wall and the cardboard. Rather, they were of unknown origin, so he called them "X-rays".

      He fussed for some time in his little lab. He moved the screen away....it continued to glow. He turned the treated side to the wall....it still glowed. He changed from a Crooke's tube to a Lenard tube. He started to put various objects between the tube and the paper and most materials appeared to actually be transparent: the screen continued to glow. The rays coming from the end of the tube were even capable of discharging electrified objects placed in their path. But, when he inserted his hand in the beam...he saw his bones! (The photograph is actually Rontgen wife's hand and her ring).

Roentgen Has Gone Crazy...
You can imagine how incredible this must have seemed. Imagine standing in the dark in your basement realizing that you knew something that nobody else had evern known...that it would likely raise a ruckus. Because of this, he was careful. For weeks afterwards, he secretly kept repeating the experiments, telling nobody but his wife. He told her that he was doing something so strange that if people learned about it they would say that "Rontgen has really gone crazy." Finally, on January 1st, 1896 he sent numerous copies of a report of his findings, with a picture of the bones of his hand, to various labs around Europe. Then he waited.

      One of those to receive his mailing was Henri Poincare [1854-1912], who hastened to transmit it the French Academie des Sciences on January 20, 1896. Roentgen's paper was quickly reprinted in Nature, Science and other journals within weeks. He received letters of congratulations from around the world. Rutherford wrote about his boss to his fiancee in late January, 1896, "The Professor [J.J. Thomson] has been very busy lately over the new method of photography discovered by Professor Roentgen...nearly every Professor in Europe is now on the warpath."

     The reaction, world-wide was proportional to the magnitude of this discovery: five more observations were reported in a week of the Paris announcement. Within three more weeks, X-rays were used to set the broken arm of a young boy in Dartmouth, New Hampshire. Within a year, a thousand papers were published on the phenomenon.

     Roentgen only gave one talk on his discovery. In late January of 1896, he addressed the Physical-Medical Society from his home institution where he was received with tumultulous applause. Inexplicably, Rontgen, himself, published only two more papers on the subject, returning instead to his previous work. In 1900 he moved to Munich where he became the director of the Institute for Experimental Physics and then received the first Nobel Prize for Physics in 1901. Shy about public speaking and the publicity that his work had generated, he literally snuck out of Sweden to avoid having to give the Nobel Lecture. While Nobel required a speech on the subject of the prize, the specific requirements did not require that speech to be given at the ceremony, as it is traditionally done now. Rather, Roentgen managed to substitute his single Physical-Medical Society talk.

      The rest of Roentgen's life was not a storybook tale. He suffered terribly during WWI, as did many in the institutes around Germany. He never allowed himself to profit financially from his discovery and died in poverty during the post-war inflation at the age of 73.

[MysteRy]

X-Rays




What are x-rays?
X-rays use invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs on film or digital media. Standard x-rays are performed for many reasons, including diagnosing tumors or bone injuries.

X-rays are made by using external radiation to produce images of the body, its organs, and other internal structures for diagnostic purposes. X-rays pass through body structures onto specially-treated plates (similar to camera film) or digital media and a "negative" type picture is made (the more solid a structure is, the whiter it appears on the film).

When the body undergoes x-rays, different parts of the body allow varying amounts of the x-ray beams to pass through. The soft tissues in the body (such as blood, skin, fat, and muscle) allow most of the x-ray to pass through and appear dark gray on the film or digital media.  A bone or a tumor, which is more dense than the soft tissues, allows few of the x-rays to pass through and appears white on the x-ray. At a break in a bone, the x-ray beam passes through the broken area and appears as a dark line in the white bone.

X-ray technology is used in other types of diagnostic procedures, such as arteriograms, computed tomography (CT) scans, and fluoroscopy.

Radiation during pregnancy may lead to birth defects. Always tell your radiologist or physician if you suspect you may be pregnant.

How are x-rays performed?
X-rays can be performed on an outpatient basis, or as part of inpatient care.
Although each facility may have specific protocols in place, generally, an x-ray procedure follows this process:

1.The patient will be asked to remove any clothing or jewelry which might interfere with the exposure of the body area to be examined. The patient will be given a gown to wear if clothing must be removed.

2.The patient is positioned on an x-ray table that carefully positions the part of the body that is to be x-rayed - between the x-ray machine and a cassette containing the x-ray film or specialized image plate. Some examinations may be performed with the patient in a sitting or standing position.

3.Body parts not being imaged may be covered with a lead apron (shield) to avoid exposure to the x-rays.

4.The x-ray beam will be focused on the area to be photographed.

5.The patient must be very still or the image will be blurred.

6.The technologist will step behind a protective window and the image is taken.

7.Depending on the body part under study, various x-rays may be taken at different angles, such as the front and side view during a chest x-ray.

[MysteRy]

Making X-rays


Where do x-rays come from?

An x-ray machine, like that used in a doctor's or a dentist's office, is really very simple.Inside the machine is an x-ray tube. An electron gun inside the tube shoots high energy electrons at a target made of heavy atoms, such as tungsten. X-rays come out because of atomic processes induced by the energetic electrons shot at the target.

X-rays are just like any other kind of electromagnetic radiation. They can be produced in parcels of energy called photons, just like light. There are two different atomic processes that can produce x-ray photons. One is called Bremsstrahlung, which is a fancy German name meaning "braking radiation." The other is called K-shell emission. They can both occur in heavy atoms like tungsten.

So do both ways of making x-rays involve a change in the state of electrons?

That's right. But Bremsstrahlung is easier to understand using the classical idea that radiation is emitted when the velocity of the electron shot at the tungsten changes. This electron slows down after swinging around the nucleus of a tungsten atom and loses energy by radiating x-rays. In the quantum picture, a lot of photons of different wavelengths are produced, but none of the photons has more energy than the electron had to begin with. After emitting the spectrum of x-ray radiation the original electron is slowed down or stopped.

What is the "K-shell" in the other way of making x-rays?

Do you remember that atoms have their electrons arranged in closed "shells" of different energies? Well, the K-shell is the lowest energy state of an atom.

What can the incoming electron from the electron gun do to a K-shell electron in a tungsten target atom?

It can give it enough energy to knock it out of its energy state. Then, a tungsten electron of higher energy (from an outer shell) can fall into the K-shell. The energy lost by the falling electron shows up in an emitted x-ray photon. Meanwhile, higher energy electrons fall into the vacated energy state in the outer shell, and so on. K-shell emission produces higher-intensity x-rays than Bremsstrahlung, and the x-ray photon comes out at a single wavelength.

[MysteRy]

How X-Rays work




The x-ray machine is made up of a cathode and an anode that is inside of a glass vacuum tube.  The machine passes current through the cathode, which heats it up and emits electrons off the surface.  The anode, which is made of tungsten, draws electrons across the tube.  The electrons fly through the tube with extreme force due to the voltage difference between the cathode and the anode.  An electron is knocked loose from a lower orbital when an electron collides with a tungsten atom.  This causes the emission of an x-ray.

The x-ray tube is surrounded by a thick lead shield.  This is done to prevent the x-rays from going in all direction.  There is a small slit in the end of the machine that allows a beam of electrons to escape towards the patient.  There is a camera that is placed on the other side of the patient to record the image, much like an ordinary camera.  Doctors normally keep the negative of the image.  This means that anywhere the x-ray hits the camera it appears dark and anywhere that it does not hit the camera it appears light.  Thus, bones appear white and softer materials appear darker.

For x-rays, there are basically two main equations.  The frequency of the x-ray can be found using the equation c=fλ.  The energy of the x-ray can then be found by the equation E=hf.  X-rays are on the order of 1.00x1018 Hz.

c=fλ

f = (3.00x108 m/s) / (3.00x10-10 m)

f = 1.00x1018 Hz

This means that x-rays have a frequency that is greater than that of radio waves and visible light, but less than that of gamma rays.

The energy of the x-ray can be found with the frequency found in the previous equation and Planck's constant, which is 6.63x10-34 Js.

E = hf

E = (6.63x10-34 Js)(1.00x1018 Hz)

E = 6.63x10-16 J or 4143 eV

The only electromagnetic wave that has more energy than x-rays are gamma rays, which means that gamma rays are the only rays with a higher frequency and shorter wavelength.