attenuation processes

Question 1

what type of matter do low/med/high E radiation interact with?

Answer 1

low - atoms/molecules
med - electrons
high - nuclei

Question 2

what is attenuation

Answer 2

anything that reduces the x-ray beam intensity

Question 3

what is the photoelectric effect

Answer 3

a photon ionizes an atom, ejecting the k-shell electron
ALL ENERGY gets absorbed
outer shell drops down, creating SECONDARY ch rad

Question 4

what is the formula for the energy of a photoelectron

Answer 4

KE = hf - BE

Question 5

when is the photoelectric effect the most probable

Answer 5

when the photon energy is just above the BE

Question 6

how does the photoelectric effect affect the image

Answer 6

no scatter
magnifies subject contrast

Question 7

how does the photoelectric effect affect the pt

Answer 7

very high dose -all energy absorbed
photoelectron can cause new ionizations
secondary characteristic radiation

Question 8

what is coherent scatter

Answer 8

when a photon strikes an atom, and the excitation causes energy (IDENTICAL) to be released

Question 9

which are ionizing interactions?
photoelectric effect
coherent scatter
Compton scatter

Answer 9

photoelectric effect
Compton scatter

Question 10

when is coherent scatter the most probable

Answer 10

with high Z, low energy

Question 11

how common is coherent scatter in diagnostic radiagraphy

Answer 11

<5% of scatter

Question 12

what is Compton scatter

Answer 12

photon ionizes an atom, releasing a Compton electron and changing direction

Question 13

how much of the original photon energy does a scattered Compton x-ray retain

Answer 13

at least 2/3

Question 14

what are the end products of Compton scatter

Answer 14

ion pair (pos atom, Compton electron)
scattered photon

Question 15

when is Compton scatter most likely

Answer 15

when photon E is much higher than the BE

Question 16

how does Compton scatter affect the image

Answer 16

degrades image quality:
reduces contrast
creates noise

Question 17

what are the dose effects of Compton scatter

Answer 17

minimal photon energy loss, but compton electron, bad for pt
high E scatter to staff

Question 18

what is pair production

Answer 18

HIGH E - >1.02 MeV
a photon interacts with the nuclear field, creating an electron and a positron

Question 19

what is photodisintegration

Answer 19

VERY HIGH E - >10MeV
photon interacts with nucleus, ejecting a nucleon or nuclear fragment