Roentgen's X-rays have been used in fields as varied as medicine and metallurgy. Its use has been boosted with developments and modifications in technology. Mammography, digital subtraction angiography, xeroradiography, CT scan, tomography, barium enema (or meal), Intra Venous Urography and oral choecystography are important ramifications of X-ray usage.
Mammography is an useful tool in the detection of breast cancer. Long wavelength X-rays (=> low frequency=> low energy, since E=hv; h being Plank's constant, v being frequency of radiation) are used in mammography, which enables surgeons or radiologists to see if there were any cyst or a cancerous neoplasm in the breast. It is usually done on women above 30 years in whom breast tissue is less dense. In ladies below 30 years in whom the breast is more dense, ultrasound is recommended, as the picture quality of mammograph suffers.
In xeroradiography, a coat of amorphous selenium which is layered on aluminium-oxide coated aluminium plate, is charged uniformly, by a device called scorotron. Whenever and wherever incident X-ray photons impinge on these, charges disappear. The magnitude of discharging of the charges depends on the energy of the photons. Toner particles now are attracted by static electricity of the charges. Other techniques are also used at the same time, so that the adherence of toner to the plate is faithful. Next the pattern of the toner is transferred to a paper, which typically can be re-used. It's use has now fallen out of favor.
If you wanted to visualize renal stones or wanted to investigate ureteric obstruction or anything related to the state of the urinary tract, you could easily do it by performing an Intravenous Urography or IVU. In this procedure the patient is given an intravenous injection of an iodinated radio-opaque contrast dye. The dye circulates in the systemic circulation and is filtered in the kidney, delineating the details. We can now see the structures because we can see the dye. Similarly, oral cholecystography (OCG) employs radiopaque contrast media to be taken orally. It then goes to the liver and thence to the gall bladder.
But how can we see blood vessels in the brain? Even if we inject a contrast, the 
shadow of the dense skull bones will superimpose, spoiling everything. We can circumvent it in digital subtraction angiography (MRI angiography is another option). In DSA, we take an X-ray of the head (suppose); we then take another snapshot after giving the patient a shot of a contrast dye. If we add the negative of the former with the positive of the latter, the shadow due to the skull will cancel out. This is the principle of DSA. A photo is shown on the left.
Tomography of olden times, before the advent of CAT scan, was performed in an ingenious way. The patient was positioned between the X-ray camera and the photo plate (cassette). If you rotated both the camera and the cassette in opposite directions keeping the suspected lesion of the patient as the imaginary center, then all else but the suspected lesion will become blurred. The suspected lesion can be viewed easily, despite the fact that it could have been buried deep into the lung parenchyma. Modern CT scan is much more powerful and complicated.
X-ray never failed to amaze us. Now its grandchildren seems set to rule another decade or so, despite the ionization stigma it has on its shoulders.
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Wilhelm Conrad Roentgen was passing a current through a 'partially' evacuated glass tube from an induction coil. Induction coils typically produce large make and particularly break currents due to collapsing magnetic field that produces electricity in the opposite direction. He noticed that a fluorescent screen glowed, despite the room being dark and the glass tube covered by black paper. He later noticed that this device produced some hitherto unknown 'rays' that could penetrate variety of materials. He could see through his own flesh, down to the bones, and medical application of X-ray was born. Later he captured this in a photographic plate. The photo on the left is that of Rontgen's wife's hand, still wearing the wedding ring, one of the earliest recorded X rays.
When there is a vast potential difference in a partially evacuated glass tube, 
electrons rush towards the anode from cathode. As they impinge on the anode (anode being positively charged, attracts electrons), which is usually made of tungsten (Wolfram), they suddenly decelerate by colliding with the electrons of the anode material. Atoms are made up of protons and neutrons (which constitute the nucleus); and electrons, revolving around them in defined orbits. The electrons have clearly defined shells, spins, orbitals so that Pauli's exclusion principle is obeyed. Upon colliding, the electron knocks out an electron from the inner shell, which jumps to a higher energy level (outer shell). It finally comes down to its original place and emits electromagnetic radiation (photon) or X-Ray in the process. Thus X rays can be said to be produced mechanically (gamma rays are the result of nuclear decay or disintegration). The frequency of radiation is dictated by the equation, e=hv; where e is the energy of the quanta, h the Planck's constant and v the frequency of radiation.
X rays are electromagnetic radiation whose frequencies are higher than ultraviolet rays, but lower than gamma rays. They can be thought of as packets of energy or photons. X rays are ionising radiations. They ionize by either of the three ways: photoelectric effect, Compton effect, or pair production. In diagnostic applications (= at low energies, 30-100keV) photoelectric effects, the process just mentioned, predominate. Photoelectric effects are proportional to the cube of the atomic number that is exposed (Z^ 3). This explains the mechanism why bones (containing calcium) contrast so well with soft tissues. At higher energies, as is employed in radiotherapy, Compton effect, whereby the incident electron transfers some of its kinetic energy (to impart) to the target electrons and the rest as a deflected, less energetic photon. At still higher energy (above1.02 MeV), the energetic electron will form 'matter-antimatter' pair in the exposed material. A positron and an electron will form, which will annihilate later (to form two photons which will fly almost 180 degrees apart, i.e. in opposite directions).
In addition to detection by photographic plates, fluoroscopy; solid state materials like lithium doped germanium or silicon can also detect x rays. Here, the photons cause the formation of electron hole pair, which can then be detected. X ray photons may be transformed into visible photons when they interact with alkali halides such as sodium iodide (NaI). This visible light may then be amplified by photomultiplier tubes. Strictly speaking, they are electron multipliers, because as x ray photons hit the halide surface, typically only a few atoms thick, electrons are emitted. These electrons are accelerated by subjecting them to a cascade of increasing positive voltages (dynodes) in a circular or venetian blind system. Photomultipliers require less x-ray exposure (due to this magnification) and are widely used in nuclear physics.
X rays have various uses in medicine, industry and science. Orthopedic situations such as fracture, joint displacement; cancer; lung parenchyma and associated illnesses like emphysema, pneumonia; calculi (stones: renal, gall stones etc); paranasal sinuses (PNS, in sinusitis) are among them. In physiology, biochemistry and many other fields, X-ray crystallography is a valuable armament in deciphering the structure of crystalline molecules. The photons diffract (scatter) as they travel through the crystal lattice, leaving its imprint in the process. One can decode the molecular structure by deciphering the 'scatterings'. Deducing the structure of DNA molecule is perhaps the best known example till date.
Natural structures can also emanate X rays. Some celestial bodies emit x rays. But don't ask me about X ray specs, I have no idea. Anyway, X-rays are not always invisible themselves. High energy x-rays, make the peculiar sensation of light produced within the eye itself, when someone looks directly into the beam.
References: Stephen M. Hahn, Eli Glatstein, "Environmental and Occupational Hazards", HARRISON'S PRINCIPLES OF INTERNAL MEDICINE, Vol.2 (15th edition) pp. 2586-2587.
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shadow of the dense skull bones will superimpose, spoiling everything. We can circumvent it in digital subtraction angiography (MRI angiography is another option). In DSA, we take an X-ray of the head (suppose); we then take another snapshot after giving the patient a shot of a contrast dye. If we add the negative of the former with the positive of the latter, the shadow due to the skull will cancel out. This is the principle of DSA. A photo is shown on the left.
