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Chap 9 Interactions
Equipment. Chap 9. Interactions with matter
| Question | Answer |
|---|---|
| ______ is also called classical or thompson scattering. | Coherent scattering |
| 5 ways an x-ray could interact with matter? | coherent, compton, photoelectric effect, pair production, photodisinigration |
| What 2 ways can an x-ray interact that is important to diagnostic radiology? | compton scattering and photoelectric |
| below 10 keV what interaction occurs? | coherent |
| Incident x-ray interacts with target atom, excites it. Target atom releases this excess energy as a _________ with wavelength _____ to that of the incident x-ray. | scattered x-ray, equal. |
| The energy of the compton scattered x-ray is equal to the.... | difference between the energy of the incident and energy of ejected x-ray. |
| The wavelength of the scattered x-ray is greater than that of the incident x-ray. Which interaction? | compton scattering |
| Outer shell interaction, reduces its energy and ionizes the atom. Which interaction? | compton. |
| The ejected electron in a compton scatter interaction is called ______ or ______. | compton electron or recoil e-, or secondary e-. |
| In a compton interaction, after the incident x-ray interacts, it continues in a different direction with _____ energy. | less. (coherent has equal) |
| What is the compton effect equation? | Ei= Es + Eb + Eke. (Ei is incident, Es is scattered, Eb is binding energy, Eke is kinetic energy of electron) |
| Usually, the scattered x-ray retains most of the energy. But both have sufficient energy to undergo additional ionizing interactions before loosing all energy and being absorbed PE. Which interaction? | compton scatter |
| At a deflection of 0 degrees, how much energy is transferred? | none |
| As the angle of deflection increases to 180, _____ energy is transferred to the __________. | more, compton electron. |
| *Probability of compton scattering is inversely proportional to x-ray energy (1/E) and _________________ | independant of atomic #. |
| __________ does not depend on the atomic number of the atom involved. Any given x-ray is just as likely to undergo this interaction with an atom of soft tissue or of bone. | compton |
| In photoelectric effect, the electron removed from the atom is called ________, and escapes with kinetic energy that is equal to what? | a photoelectron, difference between energy of incident x-ray and binding energy of electron. |
| What is the photoelectric effect equation? | Ei= Eb + Eke |
| What happens to the incident photon/x-ray in the photoelectric effect? | It disappears/ gets absorbed. The photoelectron is ejected. |
| As mass density of absorber increases, what happens to compton scattering? | Proportional increase. (no effect on compton is atomic # changes..) |
| The probability of the PE effect is inversely proportional to the ........ | third power of the x-ray energy. (1/E)^3. (DIRECTLY proportional to 3rd power of the Z# of the absorbing material) |
| The probability of __________ is directly proportional to the third power of the atomic # of the absorbing material (Z^3). | PE effect. (INVERSELY proportional to the 3rd power of the x-ray energy) |
| If the incident x-ray has sufficient energy, the probability that it will undergo a PE effect _______ with the 3rd power of the photon energy. | decreases. (1/E^3) |
| What is a log scale? | power of 10 scale to plot data that cover several orders of magnitude. |
| On a _____ scale, equal intervals have equal numeric value. On a ____ scale, equal intervals represent equal ratios. | linear, log |
| For the PE effect, a small variation in atomic number of the tissue or in x-ray energy results in a large change in the chance of a PE interaction. Why? | When the probability of interaction is proportional to the third power, the change is very rapid. |
| X-ray interacts with nuclear field, x-ray disappears. In its place what is formed? What is this called? | Two electrons (positive and neg), pair production |
| An x-ray with less than _____MeV cannot undergo pair production. Why? | 1.02 MeV. Because energy equivalence of the mass of an e- is .51 MeV.. and two e- are formed in pair production. |
| In pair production, the positron unites with a free electron, and the mass of both particles is converted to energy in a process called | annihilation radiation |
| X-rays with energy above 10 MeV can be absorbed by the nucleus, the excited nucleus emits a nucleon. This process is called | photodisintigration |
| Image results from difference between x-rays that are absorbed PE and those transmitted to the IR. This is called | Differential absorption |
| Differential absorption increases as the kVp is | reduced |
| Reducing the kVp to increase differential absorption and therefore image contrast results in ______ patient dose | increased |
| At low energies, most x-ray interactions with tissue are ______. At high energies, ________ predominates. | PE. Compton |
| As x-ray energy is increased, the chance of any interaction _______. | decreases. |
| Polyenergetic beam? | x-rays emitted over an entire spectrum of energies, not just one same energy (monoenergetic) |
| quantity of matter per unit volume is mass density, what is it specified in? (units) | kilograms per cubic meter (kg/m^3) or grams per cubic centimeter (g/cm^3) |
| When mass density is doubled, why is the chance for interactions doubled? | Twice as many e- are available for interaction |
| *As x-ray energy increases: There are fewer _________ interactions but even fewer ________ interactions. | Compton, PE |
| *As tissue atomic number increases: what happens to Compton and PE? | no change in compton, many more PE. (also, there is less x-ray transmission) |
| *As ___________ increases, There is a proportional increase in compton and PE interactions, and a proportional reduction in x-ray transmission. | tissue mass density |
| What 3 interactions are absorption processes? | PE, pair production, photodis. |
| Attenuation is the total reduction..... | in the # of x-rays remaining in the beam after penetration through a given tissue |
| _____ is the product of absorption and scattering | attenuation |
| X-rays are attenuated exponentially, which means what? | They do not have a fixed range in tissue. (they are reduced in # by a given % for each incremental thickness of tissue they go through) |
| In 5 cm of tissues how many x-rays have been attenuated? | 50%. |
| Differential absorption and attenuation depend on what 3 things | Z# of atoms in tissue, mass density of tissue, xray energy |
| x-rays have very short wavelengths, approx ______ - ________ m. | 10^-8 to 10^-9m. |
| A 30 keV x-ray ionizes an atom of barium by ejecting an o-shell e- with 12 keV of kinetic energy. What is the energy of the scattered x-ray? (binding energy of o-shell e- of barium is .04 keV) | (Ei= Es + Eb + Eke) 30 keV= Es + .04 keV + 12 keV. Es = 30keV - .04 + 12. =30 - 12.04. =17.96 keV |
| A 50 keV x-ray interacts PE with (a) a carbon and (b) a barium atom. What is the kinetic energy of each photoe- and the energy of each characteristic x-ray if an L to K transmission occurs? k shell BE is .3 keV for carbon. 37 keV BE for k shell barium. | (a) ((Eke= Ki - Kb)) Eke= 50keV - .3 keV. |
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Zoest35
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