DI L1 Physics

drhartz's version from 2017-09-07 15:56

Radiation Physics

Question Answer
X-rays have what 2 types of radiationelectromagnetic and ionizing
X-ray velocity travels at what rateconstant
energy is proportional to frequency
frequency is inversely proportional to wavelength
wavelength is inversely proportional to frequency / energy
X rays travel in what direction straight lines
Do xrays have an electric charge? What are they unaffected by?No electric charge. Unaffected by magnetic fields
How do xrays interact with matterpass through, absorbed, or scattered
where are xrays generated xray tube
what interactions produce xrays collisional and radiactive
xray tube components cathode & anode
Cathode (tungsten filament) is + or - charged? Anode(rotating tungsten disk)? Cathode negative Anode Positive
the electrons strike the anode over a small area called the _____ its size affects ____focal point
quality / sharpness of radiograph
Electrons are produced at the ___ by running ___ through it cathode (tungsten filament) , electric current (heat)
why is tungsten filament used for electron production?produces a large number of electrons & has a high melting point
Amount of current is determined by the production of _____ at the cathode electrons (negative charge)
QUANTITY of current/electrons aka NUMBER of xrays is controlled by?the mA (electric current)
mA is directly proportional tonumber of xrays produced --> if mA is doubled twice a many xrays will be produced
Electrons are accelerated due to ______ between filament (cathode -) and target (anode +)voltage differential
ENERGY / speed of xrays produced at the target anode is a function of?KvP (velocity)
How does the temperature of the filament affect quantity of electrons? what controls the temperature thus the quantity?higher temperature more electrons produced. the mA
location on the target (anode) where electrons strike?focal spot
90% of energy created by electrons hitting the target is transformed into what? what is it not transformed into?transformed into Heat NOT xrays
why does the target anode rotate? dissipation of heat --> needs a high melting point, tungsten: 6192 F
focal spot of anode associated with electron collision/heat concentration? actual focal spot
focal spot of anode associated with image sharpness effective focal spot
effective focal spot is small or large to create a sharper image small effective focal spot = sharper image
what 2 things affect the effective focal spot? filament size & anode focal spot angle
Question Answer
Actual focal spot is what?area of TARGET on ANODE that electrons hit - want larger prevents damage to anode -also rotating the anode prevents damage
a smaller cathode filament..
advantage: small effective focal size
disadvantage: smaller actual focal size, small filaments overheat more rapidly, limited mAs,
what can be done to compensate disadvantages?
1. Angle the target anode 20 degrees (lrg actual fs w small effective) 2. Rotate anode
by rotating the target 20 degrees what 2 things are accomplished?1. electrons hit a larger actual focal spot preventing anode damage 2. creates a smaller finer effective focal spot which creates the xray beam
effective focal spot does what? size?creates the xray beam - want smaller creates fine beam
rotating the anode target does what?high number of electrons can hit a small focal spot without damage bc the target is constantly changing
what is VERY IMPORTANT the anode be doing before exposure is made?rotating
what type of rod is attached to the tungsten anode? it does not conduct what? why does this matter?MOLYBDENUM
does NOT conduct HEAT
heat energy would damage the motor a small effective focal spot achieves a sharper image by a ____filament and a _____ angle
small filament and small angle

Xray Tube Components/ Problems/ Solutions

Question Answer
what is the fx of the xray tube? 1. heating the tungsten filament (cathode) to produce electrons using electric current (mA) & 2. accelerating the electrons from the cathode to the anode using kV
4 components of the xray tubepower supply to tungsten filament, high voltage transformer, auto-transformer, rectifier
5 main problems of xray generation and what what is the solution to all of them? 1. mA current for filament too high (going to burn) 2. kV too low 3. level of incoming current fluctuates 4. alternating current directional 5. amount of heat generated ....solution: TRANSFORMERS
what type of transformer reduces A to mA current?step down transformer
what type of transformer increases voltage V to kilovolts kV? step up transformer
what type of transformer eliminates INCOMING CURRENT fluctuation/voltage variation Autotransformer --> called the line voltage compensator
alternating current must be rectified to direct current. why is an alternating current bad? how is it fixed? multidirectional flow of electrons will hit and damage cathode.
fixed with a RECTIFICATION generator to make flow UNIDIRECTIONAL from Negative cathode to Positive anode
how do we deal with an inc of amount of heat generated?Anode tilted aprox 20 degrees (17-22) --> Larger ACTUAL focal spot (heat concentrated over larger area) while still maintainig EFFECTIVE focal spot is small (sharper image)

Xray Machine Controls

Question Answer
Xray machine controls (6)kV, mAs, Exposure button, Timer, Light beam diaphram, support for xray machine
mAs (mA x seconds) = number of xrays
if you inc. mA you must (inc or dec) time?decrease time
if you increase time you must (inc or dec) mAsdecrease mAs
if you decrease mA you must (inc. or dec.) time?increase time
kVp = speed = energy of xrays = penetrating power
kV & mA are inversely proportional or portional?inversely proportional
xray EXPOSURE is determined by kVp and mAs
collimation does what 3 things1. dec scattered radiation 2. improves image quality 3. method of radiation safety

Types of Radiation

Question Answer
collisional interaction produces what type of radiation? characteristic
electron from filament: ejects an electron from inner shell and its energy is released as an xray. Outer shell electron fills inner shell void. what type of INTERACTION is this? What type of RADIATION is this? Interaction: Collisional
Radiation: Characteristic
Radiactive interaction produces what type of radiation? Bremsstrahlung braking radiation
electron from filament: bends around nucleus and brakes/deccelerates from electric charge difference ...its energy is released as an xray.
interaction: Radiactive
radiation: Bremsstrahlung braking radiation
the deceleration of an electron causes kinetic energy loss this loss is used to produce an xray. what type of radiation is this?bremsstrahlung
an electron from an inner shell is ejected from an atom and the electron in an outer level falls into its place the difference in energy between the 2 shells is emitted an an xray. what type of radiation is this?characteristic
Most xray spectrum produced is what type of radiation? Bremsstrahlung
xray produced from difference in energy between 2 shells --> what type of radiation?Characteristic
xray produced from loss in kinetic energy --> type of radiation?Bremsstrahlung