Question | Answer |
X-ray wavelength range | 0.0001nm to 10nm |
Analytical methods based on | 1. emission
2.absorption
3.fluorescence
4.scattering
5.diffraction |
How x-ray radiation is produced? | 1.primary x-ray radiation produce by bombardment of metal target with high energy electrons
2. secondary x-ray rad.- expsoing material to a beam of primary radiation
3. by the decay of radioactive source
4. from a synchrotrom |
What kind of spectra does an x-ray produce | Both continuum and line spectra:
1. production of continuum of x-ray radiation only
2. production of a continuum of x-ray radiation on whichh a line spectrum is super-imposed |
other name for continuum spectra | white radiation; bremsstrahlung |
what is the continuum characterized by? | short wavelength lambda not(lo) |
what does lambda not(lo)depend on | Volatage; higher V- shorter lo |
does lo depend on the target material? | NO! x-ray continuum radiation will be the same from any metal target at particular voltage |
What are K-series | group of lines at shorter wavelnegth.
produced by by elements with smaller atomic number then 23
consists of two line Ka and KB
result when electron is ejected for k orbital :n=1 |
What are l-series | longer wavelength.
Consist of three line LB2,LB1, La
result when electrons are lost from l-orbitals n=2 |
When the highest probability of the atom absorbing the radiation occurs? | It occurs when energy of x-ray radiation=energy required to remove electron from the inner orbital
KE electron=0 |
Formula for mass absorption coefficient | ln(Po/P)=mx
ln(Po/P)=Mmrx
1.Mm-mass absorption coefficients: independent of the physical and chemical state
2. mass absorption coefficients are additive functions.Mm=wa+ma+wb+mb.... |
difference between fluorescence and absorption | fluorescence lines occur at slightly longer wavelength than the corresponding adsorption edge. |
is x-ray fluoresce a destructive technique? | NO |
what are the requirements for diffraction? | 1. distance between planes of the crystal must be of the same order of magnitude as the wavelength of the x-radiation
2. scattering centers of the crystal must be distributed in a regular manner: MUST BE REGULAR CRYSTAL LATTICE |
Bragg's Law | nl=3dsinF |
Detctors in X-ray | 1. Gas-Filled detectors
2. Scintillation counters
3. Semiconductor detectors |
Type of Gas filled detectors | 1.ionization chamber
2. proportional counter
3. geiger counter |
different Voltage Regions in the gas-filled tube | 1. Ionization chamber region
2. Proportional counter region
3.Geiger region |
Ionization chamber region | 1.current is very small 10^-12 to 10^-16; independent of voltage
2. Not very sensitive is not used in x-ray spec |
Proportional counter region | 1.# of electron increase with applied voltage
2. number of electrons depends on the frequency of x-ray rad
2. deadtime is small |
Geiger region | 1.number of electrons independent of energy of x-ray rad.
2.deadtime is large
3.not widely used in x-ray spectrometers |
Scintillation counter | 1.consists of a crystal activated NaI
2. number of photons is proportional to the energy of incident radiation |
Semiconductor detector consists of these levels: | 1st layer:p-type material. Coated with thin Gold layer protected with beryllium layer
2nd layer: Li-drifted zone.
3rd layer: n-type material coted with layer of AL |