Rad Physics Flashcards
Z-number is?
protons
A-number is?
mass number
Higher Z# means what for binding energy?
higher
Particulate vs Electromagnetic radiation
particulate: alpha, beta, cathode
kinetic energy of small mass
electromagnetic: x-rays, gamma rays, light
electric/magnetic fields
X-rays mass? electric charge?
no mass, no charge
Wavelength of xrays
0.1A to 0.5A
Bremstrahlung is what interaction? How are x-rays created this way?
electron to nucleus interaction
x-rays generated when high velocity electrons interact with high atomic # atoms and decelerate suddenly
characteristic radiation is what interaction? How are x-rays created this way?
electron to electron interaction
Direct hit knocks electron out of orbit. When a higher-energy electron fills this spot, the movement to a lower level gives off x-ray.
Two named mechanisms for x-ray production?
bremsrahlung and characteristic radiation
Which mechanism creates the greatest source of xrays?
Bremstrahlung
In the x-ray tube, the tungsten filament is the…
Tungsten target?
Filament - cathode
Target - anode
What is the source of electrons?
cathode
What concentrates electrons?
focusing cup
what accelerates electrons?
high voltage
What is the target to stop electrons?
anode
How are electrons generated in the cathode?
thermionic: current heats cathode to 2200 C which emits an electron cloud
What does the step down transformer do?
Steps voltage down so cathode doesnt melt
What does the step up transformer do?
increases potential difference between cathode and anode, increasing speed of electrons
effective focus spot is _____ to improve ____?
small to improve image sharpness
actual focus spot is _____ to increase _____?
large to increase heat dissipation
Factors controlling x-ray beam (5)
Tube voltage (KVp) Exposure time (S) tube current (mA) Filtration Collimation
Tube voltage effect on x-ray beam?
shifts curve up and to right - greater # of higher energy photons
HVL - characterizes what about an xray beam?
penetrating quality and mean energy, found by thickness of an absorber that reduces quantity of photons by half
As KVp increases, HVL…?
increases
Tube current effect on xray beam?
Increases # photons
Exposure time vs # photons recieved?
Double exposure = double photons
FIltration filters out what?
low energy electrons that don’t contribute to radiograph but do to patient risk
What is responsible for inherent filtration in xray tube?
Added filtration in x-ray tube?
Inherent - glass/oil
Added - aluminum disk
Filtration levels for 50-70 kVp?
70+?
- 5mm aluminum equivalent
2. 5mm
Filtration increases exposure time by what?
Reduces pt dose by?
50% more exposure, 80% reduced dose
Filtration effect on photon curve?
down and peak to right
collimator does what?
metallic barrier with aperture that
- reduces size and modifies shape of beam
- reduces volume tissue irradiated
- improves image quality
Distance versus dose of xray
intensity inversely proportional to square of distance
Should put x-ray tube how far from pt?
as close as possible without touching
Types of interaction of xrays with tissue (3)
Coherent (7 %)
Photoelectric effect (27%)
Compton (57%)
(other 9% is no interaction)
Coherent scattering is what?
Incoming low energy electron comes near outer electron, , causes it to vibrate at same frequency and dies. The new electron radiates a new x-ray with same frequency and energy as old xray.
Which type of interaction is the primary contributor to image formation?
Photoelectric effect
How does photoelectric effect work?
incoming photon collides with inner shell electron
electron absorbs all photon’s energy and is ejected (ionization)
Higher energy electron fills vacancy, emits characteristic radiation
Recoil electron (photoelectron) also given off, all absorbed.
Photoelectric effect depends on what 3 things?
- wavelength/energy of photon energy/kVp
- Atomic # of material
- density of material
PE = Z^3/kVp^3
Compton scattering works how?
Incoming photon interacts with outer shell electron, electron ejected
Incident photon deflected with lower energy
Scattered photons travel in all directions
What do the scattered photons from compton scattering contribute to image?
no useful information due to altered path; only fogging/darkening
Distinguishing radiopaque/radiolucent on film due to?
differential absorption
Exposure defined as?
capacity of x-rays to ionize air - amount of charge per mass of air, coulombs per kg
Conventional unit of exposure?
Roentgen: 2.58 x 10e-4 C/Kg
Absorbed dose defined as
amt energy imparted by ionizing radiation to a mass of tissue.
Absorbed dose unit?
1 Gray (Gy) = 1 joule of energy deposited in 1 kg
1 Gray = 100 Rads
Equivalent dose measures? How to calculate?
biological effectiveness of different types of radiation
Sum of products of absorbed dose (Gy) and quality factor (QF)
Unit of equivalent dose?
Rem, 100 Rem = 1 Sv (Sievert)
Effective dose measures? How to calculate?
compares risk of different types of expsoures
Sum of products of equivalent dose to each organ and tissue weighing factor
Effective dose takes into account (3)
Volume
Radiosensitivity of tissue irradiated
Biologic effectiveness of radiation
For dental x-rays, 1 roentgen = ? rads = ? rems?
1 roentgen = 1 rad = 1 rem
For dental xrays, 100 rads = ? Gy = ? Sv
100 rads = 1 Gy = 1 Sv
