Part No...., Module No....Lesson No Module title IAEA Regional Training Course on Radiation Protection of patients for Radiographers, Accra, Ghana, 11-15 July 2011 Interaction of radiation with matter, X-ray production and X-ray beams Part …: (Add part number and title) Module…: (Add module number and title) Lesson …: (Add session number and title) Learning objectives: Upon completion of this lesson, the students will be able to: … . (Add a list of what the students are expected to learn or be able to do upon completion of the session) Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.) Duration: (Add presentation time or duration of the session – hrs) Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate) References: (List the references for the session) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Interaction of radiation with matter

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

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

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 50 100 150 200 5: Interaction of radiation with matter

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

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

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

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

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 = 0.693 / 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

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

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

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

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

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

X-ray production 5: Interaction of radiation with matter

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

X Ray tubes 6: X Ray production

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

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

Example of a cathode 6: X Ray production

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

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

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

X-ray beam 5: Interaction of radiation with matter

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