1. Part No...., Module No....Lesson No
Module title
IAEA Regional Training Course on Radiation Protection of patients for Radiographers, Accra, Ghana, July 2011
Interaction of radiation with matter, X-ray production and X-ray beams
Part …: (Add part number and title)
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

2. Interaction of radiation with matter

3. 1. Electron-nucleus interaction (I)
Part No...., Module No....Lesson No
Module title
1. Electron-nucleus interaction (I)
Bremsstrahlung:
radiative energy loss (E) by electrons slowing down on passage through a material
 is the deceleration of the incident electron by the nuclear Coulomb field
 radiation energy (E) (photon) is emitted.
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

4. Electron-nucleus interaction (II)
Part No...., Module No....Lesson No
Module title
Electron-nucleus interaction (II)
With materials of high atomic number
the energy loss is higher
The energy loss by Bremsstrahlung
> 99% of kinetic E loss as heat production, it increases with increasing electron energy
X Rays are dominantly produced by Bremsstrahlung
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

5. X Ray spectrum energy Maximum energy of Bremsstrahlung photons
kinetic energy of incident electrons
In X Ray spectrum of radiology installations:
Max (energy) = Energy at X Ray tube peak voltage E
Bremsstrahlung
Bremsstrahlung
after filtration
keV
keV
5: Interaction of radiation with matter

6. 2. Characteristic x-rays
Part No...., Module No....Lesson No
Module title
2. Characteristic x-rays
Starts with ejection of e- mainly from k shell (also possible for L, M,…) by ionization
e- from L or M shell fall into the vacancy created in the k shell
Energy difference is emitted as photons
A sequence of successive electron transitions between energy levels
Energy of emitted photons is characteristic of the atom
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

7. Part No...., Module No....Lesson No
Module title
3. Photoelectric effect
Incident photon with energy h
 all photon energy absorbed by a tightly bound orbital electron
ejection of electron from the atom
Condition: h > EB (electron binding energy)
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

8. Factors influencing photoelectric effect
Part No...., Module No....Lesson No
Module title
Factors influencing photoelectric effect
Photon energy (h) > electron binding energy EB
The probability of interaction decreases as h increases
It is the main effect at low photon energies
The probability of interaction increases with Z3 (Z: atomic number)
High-Z materials are strong X Ray absorber
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

9. Part No...., Module No....Lesson No
Module title
4. Compton scattering
Interaction between photon and electron
Compton is practically independent of Z in diagnostic range
The probability of interaction decreases as h increases
Variation of Compton effect according to:
energy (related to X Ray tube kV) and material
lower E  Compton scattering process  1/E
photon energy is transferred to the electron, the remainder to the scattered photon
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

10. Beam characteristics: Half Value Layer (HVL)
Part No...., Module No....Lesson No
Module title
Beam characteristics: Half Value Layer (HVL)
HVL: thickness reducing beam intensity by 50%
Definition holds strictly for monoenergetic beams
Heterogeneous beam  hardening effect
I/I0 = 1/2 = exp (-µ HVL) HVL = / µ
HVL depends on material and photon energy
HVL characterizes beam quality
 modification of beam quality through filtration
 HVL (filtered beam)  HVL (beam before filter)
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

11. X Ray penetration and attenuation in human tissues
Part No...., Module No....Lesson No
Module title
X Ray penetration and attenuation in human tissues
Attenuation of an X Ray beam:
air: negligible
bone: significant due to relatively high density (atom mass number of Ca)
soft tissue (e.g. muscle,.. ): similar to water
fat tissue: less important than water
lungs: weak due to density
bones can allow to visualize lung structures with higher kVp (reducing photoelectric effect)
body cavities are made visible by means of contrast products (iodine, barium).
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

12. X Ray penetration in human tissues
Part No...., Module No....Lesson No
Module title
X Ray penetration in human tissues
60 kV - 50 mAs
70 kV - 50 mAs
80 kV - 50 mAs
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

13. X Ray penetration in human tissues
Part No...., Module No....Lesson No
Module title
X Ray penetration in human tissues
70 kV - 25 mAs
70 kV - 50 mAs
70 kV - 80 mAs
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

14. X Ray penetration in human tissues
Higher kVp reduces photoelectric effect
The image contrast is lowered
Bones and lungs structures can simultaneously be visualized
Note: body cavities can be made visible by means of contrast media: iodine, barium
5: Interaction of radiation with matter

15. Effect of Compton scattering
Part No...., Module No....Lesson No
Module title
Effect of Compton scattering
Effects of scattered radiation on:
image quality
patient absorbed energy
scattered radiation in the room
5: Interaction of radiation with matter
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

16. X-ray production
5: Interaction of radiation with matter

17. Basic elements of the X Ray source assembly
Generator : power circuit supplying the required potential to the X Ray tube
X Ray tube and collimator: device producing the X Ray beam
6: X Ray production

18. X Ray tubes
6: X Ray production

19. X Ray tube components
Cathode: heated filament which is the source of the electron beam directed towards the anode
tungsten filament
Anode (stationary or rotating): impacted by electrons, emits X Rays
Metal tube housing surrounding glass (or metal) X Ray tube (electrons are traveling in vacuum)
Shielding material (protection against scattered radiation)
6: X Ray production

20. X Ray tube components housing cathode 1: long tungsten filament
2 : short tungsten filament
3 : real size cathode
1: mark of focal spot
6: X Ray production

21. Example of a cathode
6: X Ray production

22. Cathode structure (I) Modern tubes have two filaments
a long one : higher current/lower resolution
a short one : lower current/higher resolution
Coulomb interaction makes the electron beam divergent on the travel to the anode
lack of electrons producing X Rays
larger area of target used
focal spot increased  lower image resolution
Focalisation of electrons is crucial !
6: X Ray production

23. This conflict is solved by slanting the target face
Anode angle (I)
The Line-Focus principle
Anode target plate has a shape that is more rectangular or ellipsoidal than circular
the shape depends on :
filament size and shape
focusing cup’s and potential
distance between cathode and anode
Image resolution requires a small focal spot
Heat dissipation requires a large spot
This conflict is solved by slanting the target face
6: X Ray production

24. Anode heel effect (I)
Anode angle (from 7° to 20°) induces a variation of the X Ray output in the plane comprising the anode-cathode axis
Relative higher beam intensity on cathode side The heel effect is not always a negative factor
It can be used to compensate for different attenuation through parts of the body
For example:
thoracic spine (thicker part of the patient towards the cathode side of the tube)
6: X Ray production

25. X-ray beam
5: Interaction of radiation with matter

26. Radiation emitted by the X Ray tube
Primary radiation: before interacting photons
Scattered radiation: after at least one interaction; need for Antiscatter grid
Leakage radiation: not absorbed by the X Ray tube housing shielding
Transmitted radiation: emerging after passage through matter
7: X Ray beam