X rays

X-Rays 16/4/2016

Properties of x-rays: The X-rays are a form of electromagnetic radiation similar to radio waves, microwaves, visible light and gamma rays. X-ray photons are highly energetic and have enough energy to break up molecules and hence damage living cells. When x-rays hit a material some are absorbed and others pass through. Generally, the higher the energy the more x-rays will pass through. This is what gives x-rays the power to “see inside” things. X-rays cannot be steered by electric and magnetic fields like alpha, beta and other charged particles.
Production of X-rays: X-ray production whenever electrons of high energy strike a heavy metal target(figure1), like tungsten or copper. When electrons hit this material, some of the electrons will approach the nucleus of the metal atoms where they are deflected because of there opposite charges (electrons are negative and the nucleus is positive, so the electrons are attracted to the nucleus). This deflection causes the energy of the electron to decrease, and this decrease in energy then results in forming an x-ray(figure2).
figure(1)



There are two types of X-ray generated: characteristic radiation and bremsstrahlung radiation.
1.Characteristic X-ray generation
When a high energy electron collides with an inner shell electron both are ejected from the tungsten atom leaving a 'hole' in the inner layer. This is filled by an outer shell electron with a loss of energy emitted as an X-ray photon(figure2 ).
2.Bremsstrahlung/Braking X-ray generation
When an electron passes near the nucleus it is slowed and its path is deflected. Energy lost is emitted as a bremsstrahlung X-ray photon.
Bremsstrahlung = Braking radiation
Approximately 80% of the population of X-rays within the X-ray beam consists of X-rays generated in this way.

figure(2)

Maximum energy: all electron’s energy is converted into the photon’s energy
- Kinetic energy = photon energy
- Kinetic energy = charge of electron × voltage
eV = hf h = Planck’s constant
and… c = fλ
so… eV = hc/λ


Absorption of X-rays: occurs when x-rays pass through materials due to energy loss by: photo electric effect, Compton Scattering, Pair Production.
Compton effect:The Compton effect (also called Compton scattering) is the result of a high-energy photon colliding with a target, which releases loosely bound electrons from the outer shell of the atom or molecule(figure3).

figure(3)

Photoelectric effect is a phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it(figure4).

figure(4)

Pair production can only occur if the incident photon energy is at least 1.022 MeV. As the photon interacts with the strong electric field around the nucleus it undergoes a change of state and is transformed into two particles :one electron and one positron. These two particles form the pair referred to in the name of the process(figure5).

figure(5)

Attenuation of X-rays: intensity reduces with distance(figure6)
I = I0 e-μx
I is the photon intensity of x-rays at depth x from the surface.
I0 is the initial intensity of x-ray.
x is the depth of x-rays from the surface.
μ is the absorption coefficient


figure( 6):attenuation of x- rays.
Uses of X-rays:
1- diagnosis
2- treatment of cancers (radiotherapy) with high energy X-rays.
X-ray workers…
1) wear a film badge to check the amount of radiation they get.
2) wear lead aprons while the machine is in use.
3) verify that the machine is in an enclosed room and the controls
are in a separate room.
4) ensure that that there is no entry into the X-ray room while the
machine is in use.

Dangers of X-rays:

1- water ionises to produce free radicals which produce H2O2
2- enzymes & DNA are damaged
3- parts of cells are damaged
4- cell division is damaged ( mutations)
5- tissue & organ damage
6- life expectancy shortens
7- mutations cause gene alterations in populations