Radiation safety: principles of radiation protection Flashcards
x-ray production requires 4 conditions. What are they?
1.) source of free electrons
2.) acceleration of electrons
3.) focusing of electrons
4.) deceleration of electrons
Source of free electrons
The source of electrons is a filament at the cathode end of the tube.
The current is passed through the tungsten filament and heats it up.
-as it’s heated up the increased energy enables electrons to be released from the filament through thermionic emission.
what does the filament consist of?
Small coil of tungsten wire
As tungsten is heated…..
electrons in the tungsten atoms orbits spin faster, moving farther from the nucleus.
-electrons in outer orbits are flung out of the atoms forming an “electron cloud” or space charge
The space charge provides…..
the electron source for x-ray production
If you increase the mA, you increase the _______ current, which in turn increases the _______ current- this leads to more x-ray photons being created.
filament; tube
Acceleration of electrons
The free electrons must be accelerated across the x-ray tube from cathode to anode
Kvp forces electrons across the tube giving them what kind of energy
kinetic energy
The higher the kvp the more energy the ________ electrons will have
accelerating
“Pre-workout”
Focusing of electrons
a focusing cup houses the filament wires
-made of molybdenum or nickle
if you increase kvp then what else increases?
-electron energy increases
-x rays energy increase
when the kvp is applied during the exposure the electrons are focused…
-into a narrow beam
-directed from the cathode to the anode
deceleration of electrons
the electrons decelerate when they strike the anode
what is the anode target made out of?
Tungsten disk which has a high atomic number of (74) and a high melting point
-rehenium makes it last longer **
what are the 2 possible Target interactions?
There are two interactions that occur at the target (anode)
-Brems
-Characteristic
** BOTH start with an electron and result in a photon
X-Ray Productions happens…..
In the tube!! at the anode target
Explain Bremsstrahlung
-Braking radiation
-Electron in & a photon out
-Produces x-rays of all energies
-90% of all x -ray production
-x-rays below 70 KVP are a 100% Brems!
Explain Characteristic
-Electron in & Photon out
-The incident electron Collides with a shell electron, crashing it out of orbit and causing a cascade of electrons to fall into each shell closer to the nucleus, each time an electron cascades it causes characteristic x-rays closer to the nucleus to have a higher photon energy
What is K-shell binding energy of Tungsten?
69.5 or 70 keV
what is the Frequency of an X-ray mean?
It’s the number of times per second the electric and magnetic fields generate themselves.
** Number of waves
The higher the energy of the x-ray, the _______ the frequency
higher
what is the Unit of frequency?
Hertz (Hx)
or cycles per second
What is wavelength mean?
It is the distance the X-ray travels during one regeneration of electric and magnetic fields.
* the distance between two successive peaks. ALSO MEANS: Distance between the tops of the waves.
What is the unit of Wavelength?
Angstrom
Frequency and wavelength have an ________ relationship
inverse
if frequency increase than wavelength decreases
higher frequency would have either short or a long wavelength. which one?
SHORT
Low frequency will either have a short or long wavelength. which one?
LONG wavelength
Energy (kvp) and Frequency have a ________ relationship
direct
** E&F= closer together in the alphabet
Energy (Kvp) and wavelength are _______ related?
inversely
*meaning if you increase kvp, you will get shorter wavelengths!
low frequency
extremities!
high frequency
chest x ray
where we use a high kvp
beam characteristics
-quantity (# of x ray photons)
-quality (energy or the x-ray photons)
Quality
-the energy of the x-ray photons
-the ability to penetrate
-the KVp determines the quality (energy) of the x-ray beam
-the higher the kvp, the higher the quality of the beam
Quantity
Refers to the number of x-ray photons
-mAs determines the quantity (number)
-higher the mA= the higher the quantity
-think money-more money = more quantity
Primary beam
refers to the x/rays that are produced by the x-ray tube and strike the patient
-either brems, characteristic or BOTH
Remnant beam or exit beam
means remaining
-the remaining beam after it leaves (exits) the patient
-made up of primary and secondary radiation
describe the inverse square law
the inverse square law states that the intensity of radiation is inversely proportional to the square of the distance between the x-ray tube and the image receptor
inverse square law formula
I1/ I2 = (D2)^2/ (D1)^2
when distance is doubled…..
intensity is decreased by 4 times
When distance is cut in half…..
intensity is increased by 4x
* go basic, as radiographers we know that standing farther from the source reduces dose!
10 fundamental properties of x-rays
- Travel in straight lines
- Highly penetrating, invisible rays
- electrically neutral
- wide range or wavelengths (heterogeneous)
- travel at the speed of light
- capable of ionizing matter
- cannot be focused by a lens
- effects digital images
- causes certain crystals to fkuroesce
- produces secondary and scatter radiation
what are the 3 interactions with Matter that occur in diagnostic radiology
- Compton effect- x ray changes direction
- Photoelectric absorption- complete absorption
- Coherent- (classical scatter) least likely to happen
Explain Compton effect
-Most common interaction/ least desirable
-energy partially absorbed by loosely bound outer shell electrons
-knocks electron out of orbit= ionization
-produces scatter photon ( low energy ) going in different direction & Compton electron
-source of the most occupational exposure… REMEMBER Compton = teCh exposure
-straight OUT of compton
-source of the MOST FOG seen on IR
-decreases image contrast
Photoelectric effect
-photon in
-photon energy equals binding energy
-Total absorption* interaction
-inner shell electron* knocked out of orbit= Ionization
-The ejected electron is termed a “ photo electron”
-Photoelectric = Patient
what does attenuation mean?
the reduction in intensity of the x-ray beam as result of absorption, scatter and divergence
what is differential absorption?
different objects absorb radiation differently
Thickness of the body part
More dense areas of the body will attenuate more x-rays
(abdomen vs. chest)
type of tissue
the higher the atomic number of the body part the greater the attenuation of the x-ray beam and the greater the biological effect
subject density
Air - does attuenate
Fat
Water
Muscle
Bone - attuenuates a lot
indirect relationship with receptor exposure
metal
Higher frequency to lower frequency
-gamma rays
-x-rays
-ulta violet
-visible light
-infrared
-microwave
-radio
what to know that brems is
- electron in
-a target reaction
-bends or breaks
-goes around the nuclues
-if the kvp is lower than 70 its brems
what to know about chacteristic
-electron in
-cascade effect or cascading!!
-the binding energy of k shell is 69.5 Kev or sometimes they write 70
-“if there a kardesion they would start with the K shell”
important fundmental properties of x-ray (not all but important ones)
1.Travel in straight lines
2.Electrically neutral, no mass
3.Wide range of wavelengths (heterogeneous)
4. Travel at the speed of light
5. Capable of ionizing matter
scatter radiation is what?
Scatter radiation is a type of secondary radiation that
occurs when the beam intercepts an object, causing
the X-rays to be scattered.
The higher the kvp, the _______ the energy, the _______ the frequency and the __________ the wavelength
-higer
-higher
-shorter
Kilovolts controls how _______ the electrons are sent
across the tube (tube potential)
fast
kvp controls
Beam Quality
○ Subject Contrast (not digital image contrast)
○ Beam Energy
○ Penetrability
Increasing kVp also _________ scattered photons
reducing image quality
increases
-Most kVp settings are set per thickness of bone on
technique charts
Milliamperage (mA) is a measurement of x-ray tube _________.
current
Increase mA =
increase the filament temperature which increases the electrons boiled off from thermionic
emission.
mA determines the _________ of x-ray photons.
number
exposure time
Time or length of exposure is in seconds or fractions of a second.
● 1 second
● 1000 milliseconds
○ Move the decimal point 3 places for milliseconds conversion
Should be kept as short as possible, for most examinations.
● Minimize the risk of patient motion
○ Motion on a radiograph = blurry areas - poor detail
● Longer exposure times increase patient dose.
mAs is the main controller of
receptor exposure
If the patient has more tissue (mass) surrounding the part
than the average patient, you will need to __________mAs.
increase
quantum mottle
not enough mAs
Underexposed image.
● Grainy appearance
● General rule = double original mAs
○ Must increase at least 30% for a visual change
● Follow Exposure Index guides for ranges
mAs does not effect
-scatter
-contrast
-spatial resolution
-distortion
mAs Reciprocity Law
There are multiple ways to combine mA and seconds to equal the same mAs.
The reciprocity law shows us that mA and Time are inversely proportional.
They go in opposite directions!
● If mA is Increased - seconds will need to be decreased
● If seconds are increased - mA will need to be decreased
General Rules
1. If mAs is doubled - Time should be cut in half
2. If mAs is cut in half - Time will need to be doubled.
May be used to prevent motion unsharpness.
higher receptor exposure?
pick the highest mAs
reduce motion or prevent it?
pick the shortest seconds
pediatrics
short time!!!
coherent scatter
-photon in, photon out
-occurs at low energy
-NO effect on patient or occupational
-occurs at low energy
a hyperstenthic patient would absorb ________ x- ray photons
more
ashenic/ hyposthenic will allow __________ more x -ray photons to pass through
more
increasing kvp will _________ attenuation
decrease
increasing kvp will __________ absorption
decrease
increasing kvp will ____________ subject contrast
decrease
increasing kvp __________ the energy
increases
increasing kvp _________ the frequency
increases
(higher frequency)
increasing kvp __________ the wavelength
decreases
(shorter wavelength)
