What is X-Ray ?
X-Ray is an electromagnetic wave with frequency 3x10E16Hz to 3x10E19 Hz or in wavelength scale 0.01 to 10 nano meters i.e. shorter than UV and longer than gamma radiation. In energy scale 120eV to 120 KeV. these are em waves with High penetrating Power.
What are the Properties useful for Us?
Penetration power: this ray can penetrate deep into metals atteneuting throughout. So can used probe into solid blocks.
optical Resolution: as per raleigh criterion the resloution of an optical microscope increases with decrease in wavelength and these are em waves with lowest wavelength.
Diffraction:Wavelength suitable for crystalography. The planes of crystals produce a diffraction pattern when radiation of suitable wavelength target on it. the xray wavelength suitable for this.
as pern barggs equation
2dsin(theta)=n x Lambada
Spectroscopic Analysis: The emission / absorption is not just a single line or just a single band. It is a set of quantized bands. Now you can say then sodium(Na) has only two lines 589.0 and 589.6 nm , yes it is true if you are looking only at the visible spectra.
there are more spectras which belongs to transition other than 3p1/2->3s1/2(589nm) and 3p3/2->3s1/2(589.6nm).
We have more no of spectra for most of the elements in X-ray region.
What are the classes ?
These rays are categorised according to penetrability through matter. Hard Xrays (12ev to 120Kev)/0.1 to 0.01nm wavelength. and soft xrays (0.12 to 12KeV)/(10->0.1nm).
These are sometimes also classified as per the method of generation or its spectrum.
Continuous / white X-ray
Discrete / Characteristic X-ray
Generation Methods:
There are two methods two generate x-ray based on two physics processes.
Flouroscence: when a high energy photon stikes a electron it ejects out the electron from the shell leaving a blank space. That blank space filled by a electron from upper shell which means dexcitation of the electron so there is a emission of a photon.
Bremhallstrahlung: This is radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton number) nuclei. These X-rays have a continuous spectrum. The intensity of the X-rays increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the X-ray tube.
So the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines.
X-ray Generation Techniques:
X-ray is generated by X-ray tubes. I have diagram of the two oldest tubes and the commercial tube. The basic design is same as we have to achieve the process "bombardment of high eneergy electron beam over some metal surface". The enhancements in this tube is
1) Enhancement of the cathode (use of filaments, use of isolated filament)
2) Use of cooling systems for anode.
3) Replaceable anode as the anode is continuously corroded.
4) Rotating anode tube
The output of the X-Ray tube is dependent on the enrgy of the electron beam, which in turn dependent on the electric field provided by the applied potential.
So the applied potential will be one key parameter for the output energy.
Another Key factor is the anode temperature, how much heat the anode can sustain,
only 0.05% of the electron beam is converted to x-Ray then what happen to rest part is converted to heat. So this amount of heat should be dissipiated in anyway otherwise our anode will melt down.
Figure 1. Schematic of an X-ray tube for X-ray diffraction analysis: (1) metallic anode block (usually grounded); (2) beryllium window for exit of X-radiation; (3) hot cathode; (4) glass envelope insulating the anode part of the tube from the cathode part; (5) cathode leads, to which the filament voltage and high (with respect to the anode) voltage are supplied; (6) electrostatic electron-focusing system; (7) anode (anticathode); (8) inlet and outlet pipes for the flowing water that cools the anode block
