Basic Physics Flashcards
What is beam intensity?
total amount of energy per unit area travelling per unit time
Does all electromagnetic radiation travel at speed of light in vacuum?
Yes
What are secondary electrons?
Are electrons produced during compton
Their range depends on density of material and initial energy
**The more energy the photoelectron receives the higher the scatter angle of the photon**
Recoil electrons in compton
- Can only go forwards or sideways
Photons can be scattered in any direction
- can be alpha or beta particles
- ionising
How may types of radiation can radionuclides emit?
Alpha
Beta
Gamma
What is atomic number of tungsten?
What is its K edge ?
Atomic number = 74
K edge 70
What is atomic number of lead?
Atomic number = 82
K edge = 88
What is atomic number of iodine?
What is K edge?
Atomic = 53
K edge = 33
What is atomic number and K edge of barium?
Atomic = 56
K edge = 37
What is the mean energy of the x-ray beam relative to the operating kV?
Mean energy is approx 50% of operating kV
The operating kV is the max energy possible
What does K alpha radiation result from?
Electron falling from L to K shell
What does K beta radiation result from?
Electron falling from M to K shell
What effect does increasing tube current have on x rays and curve?
Increasing mA (tube current) increases NUMBER of electrons hitting anode and therefore number of x- rays
Double tube current = double amount of x rays
Increasing mA does not affect curve shape, just makes it go upwards increasing amplitude
How does increasing kV affect curve shape?
Known as Tube Potential
Potential = kV
Curve up and to the right
Increases:
- number of x-rays
- energy of electrons
What is tube output equal to?
= kV2
What qualities does tube filament have?
High melting point
High resistance
Low vapour pressure
Probability of photoelectric reaction?
- Proportional to the Atomic number3
- Inversely proportional to the kV3 (ie low energy event)
- 1 / kV3
IsoBARS have same…
Mass number
different atomic number
Alpha Particles
What happens in decay?
Mass number decreases by 4
Atomic number decreases by 2
- High energy and very damaging
- Particles carry a charge of +2
- Travel 0.1cm in TISSUES
- Have energy of 4-7MeV
What is included in electromagnetic spectrum?
- Gamma
- X ray
- UV
- Visible light
- Infrared
- Microwave
- Radio
X-rays produced by electron reactions
Gamma rays produced by nucleur reactions
- Both cannot be distinguished by frequency and wavelength
What voltage passes through tube?
10V
10A
What dictates chemical properties of element?
Electrons in outermost shell are responsible for chemical properties
What is 1 MBq equal to?
1 million decays per second
Inverse Square Law
Doubling of will reduce intensity by 1/4
The inverse square law states that the intensity of radiation emitted from a point source will reduce in intensity, proportional to the square of the distance from that point
How it HVL calculated?
0.69/LAC
Does electromagnetic radiation have a mass?
NO
All electromagnetic radiation travels at the speed of light in a vacuum
What is definition of HVL?
The thickness of a material required to reduce the INTENSITY of a beam by half
HVL increases as a beam pass through materials
Does increased kV result in less side scatter?
Yes
Therefore reduced kV results in more side scatter
What is intensity equal to?
The total ENERGY per unit time and area
Increased filter thickness will reduce intensity
What propoerties do isomers have?
Same atomic and mass numbers
Different half lives as they are metastable
What effect predominates in low atomic number materials?
Compton
- Air
- Soft tissue
- Water
What effect predominates in higher atomic number materials?
Photoelectric
- Bone
- Contrast
What is Crurie equal to?
3.7x1010 transformations per second
A bequerel is 1 transformation per second
Decay constant is inversley proportional to half life
How is absorbed dose measured in Radiography?
Ionisation chambers
How is radiation dose read out on electronic dosimeters?
Silicon diodes
Film Badges
Calibrated with caesium source
Have open window for detection of beta particles
What is atomic number equal to?
Just the number of Protons
What is K edge of calcium?
K edge = 4
Most natural elements in the body have a low K edge
What is speed of light?
3x108
What is Mass attenuation coefficient unit?
m2/kg
cm2/g
What is mean beam energy?
50% of the operating tube kV
What is max photon energy equal to?
The operating kV
What is the decay constant?
The fracttion of nuclei decaying per unit time
What is accelerating voltage in x-ray tube?
60 - 120kV
What determines physical properties of an atom?
Mass number
Can protons with sufficient energy be forced into a nucleus?
Yes
As seen in cyclotron
What is linear attenuation coefficient?
The fraction of attenuated incident photons in a monoenergic beam per unit thickness of material
Depdendent on density
Units are cm-1 or mm-1
Does a change in kV or mA affect characteristic energy peaks?
NO
Doesnt affect distribution of peaks or energy but does result in more characteristic radiation
What happens in bremmstraglung?
Filament electrons penetrate K shell but get deflected by nucleus
Continuous spectrum graph only represents Bremmstrahlung
What increases probability of compton?
High electron density
High physical density
Does increasing the kV affect number of filament electrons produced?
NO
Just increases total amount of x-rays produced at the target
