Radiogrpahic Physics Flashcards
1
Q
Whar are atoms made of?
How is an atom stable?
A
- protons (+) and neutrons live in the nucleus
- electrons (-) orbit the nucleus in shells
An atom is stable if the number of electrons is equal to the number of protons
2
Q
Atomic number?
A
- Z
- the total number of PROTONS in the nucleus
- as protons and electrons are equal in a stable atom, the number of electrons will be the same as the atomic number
3
Q
Mass Number?
A
- A
- total number of protons and neutrons in the nucleus
4
Q
What is electron binding energy?
A
- the minimum energy require to remove an electron from its orbit
- the closer the electron to the nucleus, the greater the binding energy
5
Q
What does Ionising radiation do?
- what do free radicals do?
- dose damage increase with dose?
A
- radiation that raise the energy of an electron and it is freed from the atom
- the atom is then ionised as it is missing an electron
- causes the formation of free radicals which
- free radicals can damage DNA if they if they interact with the nucleus
- The nucleus is small and chances are slim but probibility rises with increased dose
6
Q
What is thermionic emission?
What is the space charge effect?
A
- the emission of electrons from a heated metal
- space charge effect: when the emitted electrons from the metal form a negatively charge cloud, this cloud is attracted to the now positive metal. Electrons will stay here as charge of the cloud is equal to the charge of the metal
7
Q
Describe x-ray tube
A
- cathode (negative and on the left) has a tungsten filament surrounded by a nickel focusing cup. Nickel focusing cup is negative
- high melting point of tungsten means it doesnt vaporise easily
- anode disc (positive) is on the right and rotates to evenly disperse heat
- enclosed in glass to create a vacuum
tungsten Z= 74
x-ray production is 99%, 1% radiation
8
Q
what is mA?
what is kV?
A
mA: charge of filament current - milliamper
kV: potential difference applied across the tube
9
Q
What is bremsstrahulung radiation?
A
- negative electron passes close to the positive nucleus and abruptly changes direction
- the sudden change in direction converts some of the electrons kinetic energy into x-ray energy, reuslting in the generation of an x-ray photon
- below 70kVp, 100% of the beam is bremsstrahlung radiation
10
Q
What is characteristic radiation?
A
- electron hits a k-shell electron out of its shell.
- an outer shell electron drops into vacant k-shell spot but creates an energy difference.
- this energy difference is emitted as an x-ray photon
- k-shell electrons energy is 69keV, x-ray photons with energy less than 70kV are not present in the beam
11
Q
What is characteristic radiation?
A
- electron hits a k-shell electron out of its shell.
- an outer shell electron drops into vacant k-shell spot but creates an energy difference.
- this energy difference is emitted as an x-ray photon
- k-shell electrons energy is 69keV, x-ray photons with energy less than 70kV are not present in the beam
12
Q
What is photoelectric absorption?
A
- collision with orbiting electron
- photon deposits ALL ITS ENERGY
- a photoelectron is produced and exits the shell
- characteristic radiation is then produced as an outer shell electron fills the now empty inner shell. THIS IS SECONDARY RADIATION AND HAS NO EFFECT ON X-RAY
13
Q
What is photoelectric absorption?
A
- collision with orbiting electron
- photon deposits ALL ITS ENERGY
- a photoelectron is produced and exits the shell
- characteristic radiation is then produced as an outer shell electron fills the now empty inner shell. THIS IS SECONDARY RADIATION AND HAS NO EFFECT ON X-RAY
14
Q
What is compton scatter?
A
- high energy photon strieks outer shell electro
- the elctron is ejected, the photon is deflected
- some of the photons energy passes onto the electron, the now lower energy photon changes direction and leaves the body and hits the IR
