Radiation Production & Characteristics Summary Lecture PDF

electron shells electron shells nucleus electrons electrons neutrons electrons neutrons protons  Atoms make up elements An element is composed on only one type of atom  Example: - + Hydrogen atom Molecules are combinations of atoms...

electron shells electron shells nucleus electrons electrons neutrons electrons neutrons protons  Atoms make up elements An element is composed on only one type of atom  Example: - + Hydrogen atom Molecules are combinations of atoms.  - - + - hydrogen + hydrogen + oxygen A chemical compound is any quantity of one type of molecule.  - - - - - - - - - - + + - ++++++ + + - ++++++ ++- ++- - - - - - - - - - - - - + + + + - - - - - ++++++ - ++++++ ++- ++- - - - - - - chemical symbol  atomic mass protons + neutrons atomic number number of protons Elements are arranged according to their atomic number 130 132 132 132 132 Ba Ba Ba Ba Ba 56 56 56 56 56 130 132 134 136 138 Ba Ba Ba Ba Ba 56 56 56 56 56 130 132 134 136 138 Ba Ba Ba Ba Ba 56 56 56 56 56 143 143 143 143 143 N P Cl K Ca 7 15 17 19 20 143 143 143 143 143 N P Cl K Ca 7 15 17 19 20 102 110 112 114 115 N P Cl K Ca 7 15 17 19 20 102 110 112 114 115 N P Cl K Ca 7 15 17 19 20 102 –7 110 –15 112 –7 114 –19 115 –20 = 95 = 95 = 95 = 95 = 95 Tc-99m Tc-99 emits 140-keV gamma ray Arrangement Atomic Number Atomic Mass Number Neutron Number Isotope Same Different Different Isobar Different Same Different Isotone Different Different Same Isomer Same Same Same Questions?  - - The Atomic - + + + + + - Structure -  - - In a neutral atom, the total number of electrons in the orbital shells is exactly equal to - + + - the number of protonsin the + + nucleus. + - = + - - - If you answered no, you are wrong. - + + - + + + - Is this a neutral atom? - - - + + - + + + - This atom is neutral because it has the same number of protons and electrons.  All neutral atoms have the same number of protons and electrons. If an atom has an extra electron, or has had an electron removed, it is said to be ionized. What do we mean by ionization? Ionization is the removal or addition of an orbital electron from an atom.  - - - + + - + + + -  - Questions: - 1.How many protons are there? 2.How many electrons are there? - + + - + + + - - Questions: - 1.How many protons are there? - 2.How many electrons are there? - + + - + + + There are 5 protons in the - - nucleus Questions: - 1.How many protons are there? - 2.How many electrons are there? There are 6 + + - - electrons in the + orbital shells + + - - Questions: 1.How many protons are there? - - 2.How many electrons are there? 3.What is the charge of the atom? - + + - + + + 5 protons –6 electrons = -1 - - The charge of the atom is -1 Questions: 1.How many protons are there? - 2.How many electrons are there? - 3.What is the charge of the atom? - + + - 4.Is the atom neutral? + + + - - No, the atom is not neutral because it has a negative charge, meaning it has more electrons than protons.  - - - - - + + - - + + - + + + + + + - - - - 5 protons –4 electrons = 1 5 protons –8 electrons = -3 Since there are more protons than Since there are more electrons than electrons, the charge of the atom is +1 protons, the charge of the atom is -3 Shell # 1 ++ K -Shell + + + Shell # 2 ++ L -Shell + + +  Shell # 3 ++ M -Shell + + +  Shell # 4 ++ N -Shell + + +  Shell # 5 ++ O -Shell + + + Shell # 6 ++ P -Shell + + +  Shell # 7 ++ Q -Shell + + +  Number of Shell Number Shell Symbol Electrons 1 K 2 - - 2 L 8 3 M 18 - + + - + 4 N 32 + + 5 O 50 6 P 72 - 7 Q 98  Maximum Number of Electrons Per Shell Question: What is the maximum number of electrons that can exist in the O shell? 2n2 Answer: The O shell is the fifth shell from the nucleus; therefore: n=5 2n2= 2(5)2 = 2(25) = 50 electrons 2n2 electron shells electron shells nucleus electrons electrons neutrons electrons neutrons protons  Atoms make up elements An element is composed on only one type of atom  Example: - + Hydrogen atom Molecules are combinations of atoms.  - - - - - + + +++- + - ++++ - - - hydrogen + hydrogen + oxygen A chemical compound is any quantity of one type of molecule.  - - - - - - - - - - + + - ++++++ + + - ++++++ ++- ++- - - - - - - - - - - - - + + + + - - - - - ++++++ - ++++++ ++- ++- - - - - - - chemical symbol  atomic mass protons + neutrons atomic number number of protons Elements are arranged according to their atomic number 130 132 132 132 132 Ba Ba Ba Ba Ba 56 56 56 56 56 130 132 134 136 138 Ba Ba Ba Ba Ba 56 56 56 56 56 130 132 134 136 138 Ba Ba Ba Ba Ba 56 56 56 56 56 143 143 143 143 143 N P Cl K Ca 7 15 17 19 20 143 143 143 143 143 N P Cl K Ca 7 15 17 19 20 102 110 112 114 115 N P Cl K Ca 7 15 17 19 20 102 110 112 114 115 N P Cl K Ca 7 15 17 19 20 102 –7 110 –15 112 –7 114 –19 115 –20 = 95 = 95 = 95 = 95 = 95 Tc-99m Tc-99 emits 140-keV gamma ray Arrangement Atomic Number Atomic Mass Number Neutron Number Isotope Same Different Different Isobar Different Same Different Isotone Different Different Same Isomer Same Same Same Questions? Click to watch the production of characteristics radiation: https://www.youtube.com/watch?v=FjeF1xQHdwk Click to watch the production of bremsstrahlung radiation: https://www.youtube.com/watch?v=UkywJG9QPuE Questions?  O SU RE EXP C TO RS FA  XPOSURE OF A E PROPER TO RADIATIONE A T PATIEN RY TO PRODUC H SA AP ISNECES STIC RADIOGR DIAGNO Exposure Factors are factors that control the density (blackening) and contrast of a radiographic image. used by radiologic technologists to produce high quality radiographs. kVp mA time  QUALITY Controls the quality of the beam PENETRABILITY Increase in kVp results in increase in x-ray beam penetrability CONTRAST KILOVOLTAGE PEAK Adjustments in kVp results in change in image contrast therefore kVp controls radiographic contrast  Vp k er qu alit y x-ray bea m is o to ne p w e ith higher netrate t he Ah igh e likely tha t is thus mor st. energ y n atom y of intere a  Vp k ith increasing kV p, mo r e x he -r ays are em r energy itted W ha ve h ig and they ity. rea te r penetrabil and g  Vp k Vp c ontrols the sc a le of contras s kVp t on the increases , The k cause a e d rad iograph be ion occurs. finish b s o rp t rential a less diffe  Vp k V p c on trols the s ca le of c s ontrast o kVp in n the creases, The k ause a io graph bec urs. finished rad l ab s o rption occ rentia less diffe  LOW HIGH CONTRAST CONTRAST Low kVp results in High kVp results in poor image contrast reduced image contrast  QUANTITY Controls the number of x-rays produced DOSE An increase in mA will result in an increase in patient dose DENSITY The more x-rays that hit the image receptor, the greater the image density MILLIAMPERE  AS SHORT AS POSSIBLE To minimize motion blur as a result of patient movement EXPOSURE TIME  s A pere seconds m milliamtal number of x-rays e to affects th uring exposure d produced  As m product of mA and time it is the  mA and exposure time are usually combined and used as one factor: mAs mAs controls density, radiation quantity and dose It does not influence radiation quality or penetrability An Increase in X-ray Quantity X-ray Quality Kilovolt peak Increase Increase Milliampere Increase No change Exposure time Increase No change Screen-Film Radiographic Technique Are you ready for this session?  Exposure factors are a few of the tools that radiographers use to create high quality radiographs. p o s u r e Ex The prime exposure factors are: Factors kVp mA exposure time source-to-image receptor distance Radiographic Technique Combination of settings selected on the control panel of the x-ray imaging system to produce a high quality image.  kVp Exposure Factors mA The factors that influence and s determine the quantity and quality of x-radiation to which the patient is exposed are called exposure factors. SID  Primary control of x-ray beam quality, and kVp therefore beam penetrability. The higher the kVp, the higher the quality and penetrability of x-rays. 75 kVp 79 kVp kVp Also affects the quantity of x-rays in the x-ray beam - but to a lesser degree. As kVp increases, x-rays have higher energy and interact more by Compton effect and produce more scatter radiation, resulting in reduced image contrast.  The mA selected determines the number of x- rays produced, and therefore radiation quantity and the patient radiation dose. ma The higher the mA, the more electrons produced in the filaments and flow through towards the anode, the more x-rays are produced.  A change in mA does not change the kinetic energy of electrons flowing from cathode to anode. It only changes the number of electrons. ma Therefore, the energy of x-rays produced is not changed; only the number of x-rays.  The radiographic exposure times are usually kept exposure as short as possible. The purpose is not to minimize patient radiation dose but rather to time minimize motion blur that can occur because of patient motion.  The Source-to-Image largely determines the distance intensity of the x-ray beam at the image receptor.  filtration Three types of x-ray filtration are used: Inherent Added Compensating  All x-ray beams are affected by the Inherent Filtration inherent filtration properties of the glass or metal envelope of the x- ray tube. Inherent Filtration Required total filtration of 2.5 mm Al.  For general-purpose x-ray tubes, the Inherent Filtration value of inherent filtration is approximately 0.5 mm Al equivalent.  The variable-aperture light-localizing Inherent Filtration collimator usually provides an additional 1.0 mm Al equivalent.  An additional 1-mm Al filter is inserted Inherent Filtration between the x-ray tube housing and the collimator.  Some x-ray imaging systems have selectable added filtration. Usually, Added Filtration the imaging system is placed into service withe the lowest allowable added filtration.  Are shapes of aluminum mounted Compensating onto a transparent panel that slides in Filters grooves beneath the collimator. Compensating These filters balance the intensity of the x-ray beam so as to deliver a more Filters uniform exposure to the image receptor. Compensating Ex. they may be shaped like a wedge for examination of the spine, Filters or like a trough for chest examination. Radiation Interaction with Matter OVERVIEW When x-rays pass through a medium, interactions occur between the photons and matter. The x-ray photon may undergo the following processes: Attenuation Absorption Scattering Transmission TERMS Attenuation is the reduction in radiation intensity that results from absorption or scattering. Absorption refers to the taking up of the energy from the beam by the irradiated material. It is absorbed energy which is important in radiobiological effects. Scattering refers to a change in direction of the photonsl  Coherent Scattering X-RAY Compton Effect INTERACTIONS Photoelectric Effect Of the five x-ray interactions with matter, only compton effect and photoelectric effect Pair Production are important in making an x- ray image. Photodisintegration COHERENT SCATTERING Classical scattering or Thompson scattering X-rays below approximately 10 keV The incident x-ray interacts with a target atom, causing it to become excited The excess energy is released as a scattered x-ray COMPTON EFFECT Compton Scattering Diagnostic range x-rays Incident x-ray interacts with an outer shell electron and ejects it from the atom The x-ray continues in a different direction with less energy. PHOTOELECTRIC EFFECT Diagnostic range x-rays Incident x-ray interacts with an inner shell electron and ejects it from the atom The x-ray is totally absorbed PAIR PRODUCTION X-ray energies greater than 1.02 MeV Incident x-ray escapes interaction with electrons and come close enough to the nucleus causing the x-ray to disappear In its place, two electrons appear - one positively charged and one negatively charged PAIR PRODUCTION The electron loses energy through excitation and ionization The positron unites with a free electron and the mass of both particles is converted to energy in a process called annihilation radiation PHOTODISINTEGRATION X-ray energies above approximately 10 MeV X-rays escape interaction with electrons and the nuclear field and be absorbed directly by the nucleus The nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment  ANY QUESTIONS?  RADIATION INTERACTION WITH MATTER PART 2  PHOTON BEAM INTERACTIONS A Attenuation B Absorption C Scattering D Transmission  PHOTON BEAM INTERACTIONS ATTENUATION Removal of radiation from the beam by matter. May occur due to scattering or absorption.  ATTENUATION What is it exactly? When mono-energetic radiation passes through any material, a reduction in the intensity of the beam occurs. This is known as attenuation.  ATTENUATION What is it exactly? Primary radiation – Attenuation = Remnant or Exit Radiation  ATTENUATION What are the factors affecting attenuation? X-ray energy Density Atomic Number Electrons per gram  PHOTON BEAM INTERACTIONS ABSORPTION The taking up of energy from the beam by the irradiated material. Absorbed energy is vital in producing radiobiological effects in material or soft tissues.  PHOTON BEAM INTERACTIONS SCATTERING Refers to a change in the direction of photons. Contributes to attenuation and absorption.  SCATTERING What is it exactly? Primary radiation passes through the patient unchanged or is completely removed from the useful beam. Scatter radiation detracts from film quality and contributes to the quality of the film.  SCATTERING What is it exactly? For thick parts such as the abdomen, only 1% of the x-ray photons in the primary beam reach the film. The rest are attenuated, and majority are scattered through Compton scattering.  SCATTERING What is it exactly? For thick parts such as the abdomen, only 1% of the x-ray photons in the primary beam reach the film. The rest are attenuated, and majority are scattered through Compton scattering.  SCATTERING Factors Affecting Scattering Kilovoltage Part Thickness Field Size  PHOTON BEAM INTERACTIONS TRANSMISSION Any photon, which does not suffer the previous interactions mentioned, is transmitted. REFERENCE: Bushong, S. C. (2017) Radiologic Science for Technologists: Physics, Biology, and Protection. (11th Ed.). St. Louis, MO: Elsevier Mosby.