The Production Of Xrays Flashcards
The two types of transformer in the tube head are…?
1- step-up transformer
2- step-down transformer
What is the tube head composed made of and what is included in that (3 things)
Glass which has 1. Filament 2. Copper block 3. Target
What is the function of the step-up transformer
Steps up the mains voltage (240v) to the high voltage (kV) required across the X-ray tube
Step-down transformer function…
Step-down the mains voltage (240v) to the low voltage current (mA) required to heat the filament
The 5 main components of the X-ray tube
1- the tube head 2- the positioning arm 3- the control panel 4- circuitry 5- the collimator (part of the tube head)
What is the function of the lead shield?
To minimise radiation leakage (may have an unleaded window though)
What is the function of oil in the tube head?
To facilitate heat removal
What metal is in the filter that removes the harmful low energy x-rays?
Aluminium
What does the collimator do?
Restricts the size and shape of the X-ray beam to a rectangle
Name a part of the collimator also known as a spacer cone?
BID - beam indicating device
What is the fsd?
Focus to skin distance
Above 60kV what is the ideal fsd?
200mm
Below 60kV what is the ideal fsd
100mm
1 quantum of energy = ?
1 photon
How many photons are in one x-ray beam?
Millions
You usually get (more/less) energy out than was put in
Less
1st step in the production of energy is…
Electricity on = vibration/excitation of electrons
What does electron excitation create?
A small current (8-10mA)
Where does the small current pass through and what happens?
Through the step-down transformer which alters the current
The altered current then …
Passes through the filament
How is the filament heated?
By the vibrating electrons
Name the type of filament in the x-Ray tube?
Tungsten
What does extreme excitation lead to?
The loss of electrons from the outer shell
What happens after electrons are lost from the outer shell?
The electron cloud of newly free electrons gather at the filament (giving it a -ve charge) making the filament a cathode
A large potential difference is between…
Th cathode (-ve) and anode (+ve)
What is the voltage change after passing though the step up transformer?
240v to 50-90kV
Name the important part on the cathode?
Focusing cup
What is the important part on the anode?
Target point
Where are the electron clouds at the cathode (tungsten filament) attracted to?
The positive anode
When high energy electrons hit the target point on the anode they…(3 points)
- decelerate
- release 99% heat
- release 1% X-rays
What happens to the heat released? 2 stages
- absorbed by the copper
2. dissipated into the oil
what happens to the X-rays released? 2 things
- the anode directs the X-rays through the unleaded window
2. the leaded glass will absorb them (more than through unleaded window)
Name the two spectrum that lead to X-ray producing collisions
- the continuous spectrum
2. the characteristic spectrum
What is continuous spectrum?
- breaking radiation giving WIDE RANGE of photon energies
what is breaking radiation also known as?
bremsstrahlung radiation
what is characteristic spectrum?
- X-rays emitted by loss of electrons from K AND L shells
Which spectrum of X-ray producing collins is used in dentistry?
the characteristic spectrum as energy levels in K AND L shells nicely produce the desired X-rays
what is the characteristic spectrum dependant upon?
the type of material used in the anode.
what is the most common material used in the anode in dentistry? and why?
tungsten because it can be pulled into a fine wire without breaking
what happens when an outer electron is lost from the K shell (leaving it unstable)?
An outer electron from the L shell moves down leaving it unstable.
Give 8 properties of X-rays.
- ionising (biological harm)
- travel in straight line in open space (even in vacuum where no air molecules present)
- X-ray photons form a divergent beam
- they are not detectable by human senses
- they produce a LATENT image on film EMULSION
- they cause certain salts to fluoresce and emit light
- they can be absorbed and scattered
- they penetrate matter (through)
define scattering
- random, unpredictable change in direction of X-rays after hitting something
- can cause an issue with radioation protection as unpredictable
define absorption
deposition of ENERGY in tissues
define intensity
the NUMBER of X-ray photons in a DEFINED AREA of the beam
define attenuation
the REDUCTION in the INTENSITY of a beam
what can cause attenuation? 2 things
-scattering & absorption
define ionisation
the removal of an electron from a NEUTRAL ATOM to give a NEGATIVE ION and a POSITIVE ION
give a positive and a negative of ionisation
positive = required to produce and image negative = can be harmful to lining tissues
define penetration
the ability of photons to pass THROUGH or INTO tissues
give the 4 possible interactions of the X-ray beam
- completely scattered (no loss of energy)
- scattered (some absorption and energy lost)
- absorbed (total loss of energy)
- transmitted unchanged
what is the photo electric effect?
where you have pure absorption of X-rays and a total loss of energy at an atomic level
what is the first stage in the photo electric effect?
incoming X-rays interacts with the K shell (INNER shell)
what is the 2nd stage in the photo electric effect?
an electron is ejected from the K shell with HIGH energy (now it is called a photo electron)
what happens to the X-ray photon during this 2nd stage?
it is totally absorbed and has deposited all its energy
what is the 3rd stage in the photo electric effect? and what is given out during this stage
- outer shell electron cascade to try and stabilise the the inner shell
- excess very low radiation is given out - light
what does the ejected photo electron act like?
the initial high energy X-ray photon - initiates the ejection of other electrons as it passes through the tissues
what is responsible for the ionising interactions in the tissues?
the high energy electrons being ejected
how is atomic stability achieved in both the photoelectric effect and the compton effect?
a free electron will join the outer shell
what is the compton effect?
where you have scatter radiation and absorption at an atomic level
what is the first stage of the compton effect?
incoming X-ray photon interacts with loosely bound, OUTER shell electron
the 2nd stage in the compton effect is..?
where the electron is ejected with SOME energy of the X-ray photon and is now called the compton recoil electron
what happens to the X-ray photon during this stage of the compton effect?
it is scattered from it’s original path as a scattered photon. This can still cause ionisation as it still has energy
what does the compton recoil electron cause?
ionisation in the tissues.
what can the compton recoil electron undergo?
further cotton reaction or photoelectric reactions
give another name for being fully scattered with no energy loss
the rayleigh (unmodified) scattering
what is responsible for producing contrast between tissues?
the photo-electric effect
