Applide AScience Physics

1. Course: Diploma
Subject: Applied Science Physics
Unit: V
Chapter: I

2. Production of X-rays
 X-rays are produced when rapidly moving electrons
that have been accelerated through a potential
difference of order 1 kV to 1 MV strikes a metal target.
Evacuated
glass tube
Target
Filament

3. Production of X-rays
 Electrons from a hot element are accelerated onto a
target anode.
 When the electrons are suddenly decelerated on
impact, some of the kinetic energy is converted into
EM energy, as X-rays.
 Less than 1 % of the energy supplied is converted into
X-radiation during this process. The rest is converted
into the internal energy of the target.

4. Minimum wavelength in the X-ray Spectra
 When an electron hits the target its entire kinetic
energy is converted into a photon.
 The work done on each electron when it is
accelerated onto the anode is eV.
 Hence hƒ = eV and the maximum frequency
h
eV
f max
Therefore,
eV
hc
min

5. Ex.1 : A X ray tube operates at 30 keV.
Calculate wavelength of X rays
produced
 h= 6.62 x 10-34 Js
 C=???????
eV
hc
min

6. Continuous X-ray Spectrum
 Bremsstrahlung X-rays can be produced at any
projectile electron energy. In diagnostic radiography
most of the x-rays are Bremsstrahlung x-rays.
 The Bremsstrahlung x-ray energies range from zero
to a peak and back to zero.
 This is referred to as the Continuous X-ray Spectrum.
 The majority of the useful x-rays are in the
continuous spectrum.
 The maximum energy will be equal to the kVp of
operation.
 This is why it is called kVp (peak).

7. Characteristic X-ray Spectra
 Different target materials give different wavelengths
for the peaks in the X-ray spectra.
 The peaks are due to electrons knock out inner-shell
electrons from target atoms.
 When these inner-shell vacancies are refilled by free
electrons, X-ray photons are emitted.
 The peaks for any target element define its
characteristic X-ray spectrum.

8. Properties of X-rays
 X-rays travel in straight lines.
 X-rays cannot be deflected by electric field or
magnetic field.
 X-rays have a high penetrating power.
 Photographic film is blackened by X-rays.
 Fluorescent materials glow when X-rays are directed
at them.
 Photoelectric emission can be produced by X-rays.
 Ionization of a gas results when an X-ray beam is
passed through it.

9. Properties of X rays
 Affect photographic film.
 They cause the phenomenon of fluorescence.
 They are classified in hard X-rays(High energy, short
wave length) & soft X-rays(low energy, long wave
length).Soft are dangerous compared to hard x-rays.
 Absorbed by material through which they travels.
 They travel in straight line. Speed is equals to light.
 They undergo reflection & refraction.

10. Applications of X rays
 X-ray photons carry enough energy to ionize atoms
and disrupt molecular bonds. This makes it a type
of ionizing radiation and thereby harmful to living
tissue.
 A very high radiation dose over a short amount of
time causes radiation sickness, while lower doses can
give an increased risk of radiation-induced cancer.
 In medical imaging this increased cancer risk is
generally greatly outweighed by the benefits of the
examination.

11.  The ionizing capability of X-rays can be utilized
in cancer treatment to
kill malignant cells using radiation therapy. It is also
used for material characterization using X-ray
spectroscopy.
 Attenuation length of X-rays in water showing the
oxygen absorption edge at 540 eV, the energy-
3 dependence of photo absorption, as well as a
leveling off at higher photon energies due to Compton
scattering.
 Hard X-rays can traverse relatively thick objects
without being much absorbed or scattered. For this
reason X-rays are widely used to image the inside of
visually opaque objects.

12.  The most often seen applications are in
medical radiography and airport security scanners,
but similar techniques are also important in
industry (e.g. industrial radiography and industrial
CT scanning) and research (e.g. small animal CT).
 The penetration depth varies with several orders of
magnitude over the X-ray spectrum.
 This allows the photon energy to be adjusted for the
application so as to give sufficient transmission through
the object and at the same time good contrast in the
image.

13.  X-rays have much shorter wavelength than
visible light, which makes it possible to probe
structures much smaller than what can be seen
using a normal microscope.
 This can be used in X-ray microscopy to
acquire high resolution images, but also in X-
ray crystallography to determine the positions
of atoms in crystals.

14. Moseley’s law and its importance.
The English physicist Henry Moseley
(1887-1915) found, by bombarding high
speed electrons on a metallic anode, that
the frequencies of the emitted X-ray
spectra were characteristic of the material
of the anode. The spectra were called
characteristic X-rays.

15. Moseley’s law and its importance.
He interpreted the results with the aid
of the Bohr theory, and found that the
wavelengths λ of the X-rays were
related to the electric charge Z of the
nucleus. According to him, there was
the following relation between the
two values (Moseley’s law; 1912).

16. 1/λ = c(Z - s)2
where c and s are constants
applicable to all elements, and Z is an
integer.

17.  When elements are arranged in line according
to their position in the Periodic Table , the Z
value of each element increases one by one.
 Moseley correctly interpreted that the Z values
corresponded to the charge possessed by the
nuclei. Z is none other than the atomic
number.

18. It was found that the characteristic X-ray of an unknown
element was 0.14299 x 10-9 m. The
wavelength of the same series of the characteristic X-ray
of a known element Ir (Z = 77) is 0.13485
x 10-9 m. Assuming s = 7.4, estimate the atomic number
of the unknown element.
 
 
 
 
2
9
9
1
c Z s
1
c Z s
1
c 77 c
0.13485 10
c 1222
1
1
69.6
222 Z
0.14299 10
75
7.4
7.4


 

 

 

 
  




19. Importance of Moseley’s law
 Atomic no. is more important than Atomic weight as it is
equals to charge of nucleus.
 Difference between Ni,Co,Te & I etc., is explained when
periodic table was constructed with atomic no.
 Moseley predicted the existence of elements with atomic
no. 43,61,72 & 75.Thus X ray spectrum analysis new
elements can be discovered.

20. REFERENCE BOOKS AUTHOR/PUBLICATION
ENGINEERING PHYSICS S S PATEL (ATUL PRAKASHAN)
MODERN ENGINEERING
PHYSICS
A S VASUDEVA
ENGINEERING PHYSICS K. RAJGOPALAN

21. Image reference links
1. http://www.wadifatima.net/up/do.php?img=8471