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X-RAY INTERACTION WITH MATTER. COLLIMATE OR NOT TO COLLIMATE?!. SCATTER . X-RAYS WITH LOW ENERGIES –APPROX. 10 KEV INTERACT WITH MATTER THROUGH COHERENT SCATTERING.

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Thomson scattering (R) MATTER THROUGH COHERENT SCATTERING, also known as Rayleigh, coherent, or classical scattering, occurs when the x-ray photon interacts with the whole atom so that the photon is scattered with no change in internal energy to the scattering atom, nor to the x-ray photon. Thomson scattering is never more than a minor contributor to the absorption coefficient. The scattering occurs without the loss of energy. Scattering is mainly in the forward direction.


Coherent scattering
Coherent Scattering MATTER THROUGH COHERENT SCATTERING


Λ MATTER THROUGH COHERENT SCATTERING1= Λ2


μ MATTER THROUGH COHERENT SCATTERING1= μ2


Approx 5 of x rays undergo coherent scattering at
APPROX. 5% OF X-RAYS UNDERGO COHERENT SCATTERING AT MATTER THROUGH COHERENT SCATTERING

70 KVP


Scatter
SCATTER MATTER THROUGH COHERENT SCATTERING


Compton effect incoherent scattering
COMPTON EFFECT-INCOHERENT SCATTERING MATTER THROUGH COHERENT SCATTERING


Compton Scattering (C) MATTER THROUGH COHERENT SCATTERING, also known a incoherent scattering, occurs when the incident x-ray photon ejects a electron from an atom and an x-ray photon of lower energy is scattered from the atom. Relativistic energy and momentum are conserved in this process and the scattered x-ray photon has less energy and therefore greater wavelength than the incident photon. Compton Scattering is important for low atomic number specimens. At energies of 100 keV -- 10 MeV the absorption of radiation is mainly due to the Compton effect.


Most likely to occur with outer shell electrons
MOST LIKELY TO OCCUR WITH MATTER THROUGH COHERENT SCATTERINGOUTER SHELL ELECTRONS


Angles of deflection of photons 0 180 degrees
ANGLES OF DEFLECTION OF PHOTONS MATTER THROUGH COHERENT SCATTERING0-180 DEGREES

0 DEGREE DEFLECTION

0 ENERGY TRANSFER


Backscatter
BACKSCATTER MATTER THROUGH COHERENT SCATTERING


Compton
COMPTON MATTER THROUGH COHERENT SCATTERING


Probability 1 e
PROBABILITY= MATTER THROUGH COHERENT SCATTERING1E

Atomic number No effect on Probability!!

Energy Probability


ENERGY TRANSFER= MATTER THROUGH COHERENT SCATTERING

THE ENERGY OF SCATTERED X-RAY

+

THE ELECTRON BINDING ENERGY

+

THE KINETIC ENERGY OF RECOIL ELECTRON


Photoelectric (PE) MATTER THROUGH COHERENT SCATTERING absorption of x-rays occurs when the x-ray photon is absorbed resulting in the ejection of electrons from the inner shell of the atom, resulting in the ionization of the atom. Subsequently, the ionized atom returns to the neutral state with the emission of an x-ray characteristic of the atom. This subsequent emission of lower energy photons is generally absorbed and does not contribute to (or hinder) the image making process. Photoelectron absorption is the dominant process for x-ray absorption up to energies of about 500 KeV. Photoelectron absorption is also dominant for atoms of high atomic numbers.


Probability z 3 e 3
PROBABILITY= MATTER THROUGH COHERENT SCATTERINGZ3E3

Atomic number Probability

Energy Probability


Energy transfer
ENERGY TRANSFER MATTER THROUGH COHERENT SCATTERING

ENERGY OF INCIDENT PHOTON=

THE ELECTRON BINDING ENERGY

+

THE KINETIC ENERGY OF THE ELECTRON



Probability of compton interaction and photoelectric interaction is the same
PROBABILITY OF COMPTON INTERACTION AND PHOTOELECTRIC INTERACTION IS THE SAME:

  • IN SOFT TISSUE AT 20 keV

  • IN BONE AT 40 keV


Compton vs photoelectric
Compton vs Photoelectric INTERACTION IS THE SAME:

bone

Probability of

interaction

s. tissue

Compton

40 keV

Photoelectric

20 keV

X-ray energy


Pair Production (PP) INTERACTION IS THE SAME: can occur when the x-ray photon energy is greater than 1.02 MeV, when an electron and positron are created with the annihilation of the x-ray photon. Positrons are very short lived and disappear (positron annihilation) with the formation of two photons of 0.51 MeV energy. Pair production is of particular importance when high-energy photons pass through materials of a high atomic number. Energy: > 1.02 MeV


Annihilation
ANNIHILATION INTERACTION IS THE SAME:


Photodisintegration (PD) INTERACTION IS THE SAME: is the process by which the x-ray photon is captured by the nucleus of the atom with the ejection of a particle from the nucleus when all the energy of the x-ray is given to the nucleus. Because of the enormously high energies involved, this process may be neglected for the energies of x-rays used in radiography


Energy 10 mev
ENERGY > 10 MeV INTERACTION IS THE SAME:


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