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X-Ray TubeProduced by accelerating electrons with high voltage and allowing them to collide with metal target (anode), e.g, Tungsten.• Three Events (Two types of x-ray)a) Heat

b)bremsstrahlung(brakingradiation)c)characteristicradiationemission,

Photoabsorption orphotoelectricabsorptionisthedominantinteractionmechanisminthesoftX-rayregimeandforthelowerhardX-rayenergies.Athigherenergies,Comptonscatteringdominates.Which of the materials should be used to produce soft X-ray and hard x rays?

Ba (Z = 56)W (Z = 74) preferred targetMo (Z = 42)Pb (Z = 82)Pd (Z = 64)

What is the minimum energy of the e -beam in the X-ray tube

IfanelectronisejectedfromtheK – shell.ThevacancyisfilledwithasecondelectronfromtheM – shell.Theproducedphotonisreferredtoas:

Thedirectinteractionofanincidentelectronwiththenucleusofanatomresultsin

X-rayproductiong -rayproduction

The Interaction of X-Rays with Matter

AttenuationA process by which radiation loses power (reduce intensity) as it travels through matter due to the interaction with it.half-value-layer (HVL) is the thickness at which the intensity/energy is reduced by halfDeferential AbsorptionThe deference of absorption of radiation (x-ray) by deferent body tissues.e.g., image of the bone is produced because more x-rays are absorbed by bone than by the surrounding soft tissue. Resulted from - Transmitted x-ray through tissue.- Compton scattering by tissue.- Photoelectric effect.Depends on1) Incident radiation (x-rays) energy.2) Tissue atomic number.3) Tissue mass density

The Interaction of X-Rays (high energy photon) with Matter

Attenuation1) Asx-rayenergyincreases

- LessComptonscattering- Slightincreaseinphotoelectricinteraction- Moretransmissionthroughtissue

Absorption edge: when the photon energy reaches the binding energy level for, e.g. EK, interaction with the K-shell electron becomes possible and the probability of photoelectric absorption jumps to a higher value;

The K-absorption edge occurs at different photon energies with different materials.

The Interaction of X-Rays with Matter

Attenuation2)Astissueatomicnumberincreases- VeryslighteffectonCompton

interaction- Morephotoelectriceffect- Lessx-raytransmission

Theydependonnumberofelectrons,ratherthan,

themassnumberofthematter,thevalency ofatargetmatter,thefreebindingenergy–EK (keV),andtheMolecularconfiguration.

3)Astissuemassdensityincreases- IncreaseinComptoninteraction- Increaseinphotoelectric

interaction- Reductionintransmissionthrough

tissue

Exponentialdecay

Ionizing and Non-Ionizing Radiation photons

Non-ionizingRadiationHasenoughenergytomoveatomsinthemolecularrangeorcausevibrationalorrotationalexcitations,butnotenoughtoremoveelectrons.

Uses- Microwaveradiationfor

telecommunicationsandheatingfood- Infraredtoprovideheat- Radiowavesforbroadcasting

Secondary Electrons and Ionization

Photons with enough energy can ionize atoms through the photoelectricand Compton effectsSecondary electron: the recoiled electrons and photoelectrons set moving in the material;- Secondary electrons will have enough energy to ionize more atoms. - As they travel through the material they interact with the outer shells of the atoms and excite (ionize) them;

Effects of Ionization- Air and gases become electrically conducting (the measurement of X-and gamma-rays);- Cause biological damage;- The excitation of atoms makes them emit light (luminescence);- Photographic effect (silver, bromide);- Heating of the material

• Non-ionizingradiationmaycauseelectricalshocksandburns• Ionizingradiationproducegeneralhealtheffects,withvariationwithdifferent

tissuetypes.- damagetheprocessofnormalcellleadingtocancer

• Naturalsourcesofradiationintheenvironment

- Backgroundradiation:naturallyoccursinourenvironmentfromearth,sun,ourgalaxy,othergalaxies,anduniversebackground.Itisverylowintensity.OneCTscancanbeequaltoseveralyearsofbackgroundradiationexposure

-Radon:colorless,odorlessgasthatcomesfromdecayingrocksandsoil;Accountsforhalfofannualexposuretoradiationofaverageindividual.Secondleadingcauseoflungcanceraftersmoking.

- Cosmicandterrestrialradiation:8%ofouraverageyearlyexposuretoradation,e.g.,UVrays.UVrayscandamageDNAintheskinandcausecancer.