Physics exam 2 Robinson

the xray beam can be described by:

quality and quantity

what describes the shape (energy) of the xray spectrum?

quality

true or false: changing the beam quantity (mA) will change the shape of the xray spectrum.

false

penetration of X-rays=

quality

intensity of xrays=

quantity

a soft xray spectrum has more ______energy photons

lower

a hard xray spectrum has more ____energy photons

higher

what terminology is used to describe the SHAPE of the spectrum?

hard/soft

the beam quality will inherently affect the _____ of the image

contrast

a softer xray beam has lower average energy will give you a _______image contrast

higher

a harder xray beam that has better penetration ability will have a ______ image contrast

lower

true or false: beam filtration decreases beam intensity while increasing average beam energy.

true

what are the three things needed to produce X-rays?

1. a source of electrons (filament)

2. acceleration of the electrons (potential difference)

3. stopping the electrons (target=anode)

the electrons that form the thermionic cloud strike the anode target at what speed?

nearly half the speed of light

what is the distance from the cathode to the anode?

less than 2cm

the greater the number or speed of the incident electrons, the ______ the quality (energy) and quantity (number) of photons produced

greater

what is the target material made of?

tungsten

all target interactions occur within _______ mm of the surface of the target

0.25-0.5

what is tube loading?

The amount of heat energy deposited during an x-ray exposure is known as the tube loading. 99% of the kinetic energy of the incident electrons is heat, 1% are photons.

incident electrons seldom transfer enough energy to the outer shell of target atoms to cause ________

ionization

incident electrons transfer just enough energy to excite the outer shell electrons of the target atoms to where they will emit _____

infrared radiation (heat)

what are the two target interactions within the diagnostic range?

1. Bremsstrahlung

2. Characteristic

how is the type of target interactions that occur determined?

1.by the kinetic energy of the incident electrons

2. the binding energy of the electron shells of the target

what target interactions is the most common within the xray beam?

bremsstrahlung interactions

how are bremsstrahlung xrays energy produced?

by the energy lost from the incident electron as the nucleus slows it down, creating an xray photon

the amount of energy lost from a bremsstrahlung interaction is determined by the distance the electron is from the _______

nucleus

the energy of the brem photon is dependent on:

1. the energy of the incident electron

2. the proximity of the incident electron to the nucleus of the atom

Characteristic interactions only occur when the incident electron ____________

ejects an inner shell electron from orbit

what is tungstens K-shell binding energy?

69.5 keV

characteristic interactions only can occur when kvp is above_____

70 kvp

true or false: characteristic target interactions do not ionize the atom.

false

what determines the x-ray photon energy of the characteristic target interactions?

the difference between the binding energy of the outer and inner shells from which the electron dropped

true or false: characteristic x-rays have VERY PREDICTABLE ENERGY because they are calculated from binding energies.

true

what is tungstens atomic number?

74

what is the binding energy of the L-shell of tungsten?

12.1 keV

what shell needs to produce the characteristic photons that are within the diagnostic range?

k-shell

Between 80-100 kVp, brem interactions are _______%of the primary beam.

80-90

between 80-100 kVp, characteristic interactions are ______% of the primary beam.

10-20

when filtration is added, ______-shell characteristic emissions do not have sufficient energy and are absorbed by the filter.

L; but are included within the total spectrum

what percentage of the kvp are the average of the primary beam photons?

30-40%

changing the mAs changes what in the emission spectrum?

amplitude (quantity)

changing the kVp changes what in the emission spectrum?

changes amplitude AND average energy (quantity and quality)

at what kVp are the characteristic peaks of the emission spectrum?

70 kVp

which of the following statements is true regarding x-ray production?

almost all of the kinetic energy of the incident electrons is converted to heat

which of the following occurs when the kinetic energy of the incident electrons is transferred to the outer-shell electrons during x-ray production?

the outer-shell electrons vibrate, resulting in the emission of infrared radiation

which factor determines the types of target interactions that occur in the production of x-ray photons in the diagnostic range?

the energy of the incident electrons

which of the following best describes the energy of a bremsstrahlung photon?

the energy of the bremsstrahlung photon is the difference between the entering and exiting kinetic energies of the incoming electrons

which of the following occurs at the end of the characteristic cascade?

the outermost shell is missing an electron

which interaction produces x-ray photons only if the kVp is 70 or above?

characteristic

what three processes can xrays undergo?

1. transmission through matter

2. total absorption by matter

3. interact with matter and change direction

interactions with photons can occur with.....

1. the entire atom

2. orbital electrons- most common in diagnostic xray range

3. atomic nucleus

low-energy photons interact with _____

the whole atom

moderate-energy photons interact with _____

orbital electrons

high-energy photons interact with _______

the nucleus

what are the five basic interactions of the photons?

1. coherent scattering (within diagnostic range)

2. photoelectric (PE) absorption (within diagnostic range)

3. Compton scattering (can happen at any range)

4. pair production (outside of diagnostic/therapeutic range)

5. photodisintegration (outside of diagnostic/therapeutic range)

which interactions are the least likely of all the photon interactions?

coherent scattering

which photon interaction is initially absorbed by the whole atom?

coherent

does ionization occur with coherent scattering?

no

true or false (coherent): the energy of the photon is ejected out of the atom as a photon with the same energy, just in a different direction.

true

which photon interaction is absorbed by the atom, excites the atom, and then leaves with the same energy?

coherent scattering

true or false: coherent scattering has NO effect on the patient dose.

true

true or false: coherent scattering has an effect on image quality but decreasing contrast and adding noise.

true

true or false: coherent scattering can go by other names such as Rayleigh, Thompson, Classical, and unmodified.

true

true or false: coherent scattering occurs at very high x-ray range.

false; occurs at very low x-ray range

true or false: photoelectric absorption happens mainly at lower kVp levels

true

in photoelectric absorption, the photon is completely absorbed by an ___________ electron

inner-shell

true or false: ionization does not occur in photoelectric absorption

false

what is the ejected atom called in photoelectric absorption?

a photoelectron

what is the photon energy of a photoelectron?

slightly greater than the binding energy of the inner shell electron

what does the cascade effect produce with photoelectric absorption?

characteristic photon

a characteristic photon has less energy and will __________ by the surrounding tissues

just be absorbed

which interaction with matter is the primary source of patient radiation dose?

photoelectric

why is the primary source of patient radiation dose from photoelectric absorption?

the patient's dose comes from the original absorbed photon AND more comes from the characteristic photons

true or false: characteristic photons are NOT scatter, they are secondary radiation.

true

how are characteristics photons from matter different from characteristic photons from the tube?

characteristic photons created by the interactions with matter have much lower energies

true or false: photoelectric absorption is more possible when the x-ray photon's energy and the inner shell binding energy are close to the same.

true

true or false: having a low atomic number increases the probability of photoelectric absorption

false

in diagnostic x-rays, image contrast is mostly because of _____

photoelectric absorption

does ionization occur with photoelectric absorption?

yes

true or false: photoelectric absorption has a large effect on bystanders.

false

what is the most common type of interaction with matter?

Compton

which interaction with matter happens at all energy levels and becomes the main interaction at high energies?

Compton

which shell does the partially absorbed x-ray photon interact with in the atom?

an outer shell

does ionization occur with Compton interactions?

yes

when the electron is kicked out with compton interactions and the atom is ionized, what is the ejected electron called?

Compton (recoil) electron

what happens at the x-ray photon is partially absorbed and the Compton electron is ejected from the outer shell of the atom?

the remaining photon energy is carried away as a scattered photon (with less energy)

true or false: the scattered photon of Compton interactions retains more of the energy than the ejected electron because little energy was needed to eject the electron from the outer shell

true

which direction of compton scatter results in the degradation of image contrast?

forward scatter

which direction of compton scatter results in occupational exposure?

side scatter

which direction of scatter results in patient exposure?

back scatter

true or false: with compton scatter, the higher the energy of the incident photon, the more likely it will travel in the relatively same direction after scattering.

true

what are ways to decrease scatter production?

1. use increased collimation

2. use optimal kVp for the exam you are doing (higher kvp, higher scatter produced)

3. use compression (more matter, more scatter)

ways to decreased the scatter from reaching the IR?

1. use a grid

2. increase the OID (air-gap technique)

ways to decrease scatter from reaching the technologist?

1. increase distance from the source (patient)

2. shielding

true or false: compton interactions do not affect image quality.

false

in pair production, x-ray photon interacts with what part of the atom?

nucleus

in pair product, an x-ray photon is converted to what?

2 electrons (one positron, one negatron)

what is the energy needed to produce a pair production interaction?

a minimum of 1.02 MeV

with pair production, the negation is _____

absorbed

in pair production, what will become of the positron?

combines with an electron and is converted into 2 x-rays; each contains 0.51 MeV of energy (this is known as annihilation radiation)