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# Chap 9 Interactions

### Equipment. Chap 9. Interactions with matter

______ 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.
Created by: Zoest35