x-ray production Flashcards
functions of glass envelope
creates air free vacuum around cathode and anode and protects tube from oxidation
function of tube housing
- prevents x-rays being emitted through exam room
- good insulator
- rounded shape prevents dissipation of static charge
what is the glass envelope made of
borosilicate glass
what does the cathode consist of
- filament
- focussing cup
what is the focussing cup made of
- nickel and stainless steel
- can remain a negative charge very easily
reason for filament and what is it made out of
- made of tungsten
- help increase SA
- increase light
why do we use small filaments
- high spatial resolutions
why do we use tungsten
- low work function - can give off electrons at low voltage
- high melting point
- low vapour pressure
- high atomic number
why is a high atomic number good
- loads of electrons in outer shells
- doesnt need much energy
- gives efficient x-ray production
dual focus filaments
- 2 filaments
- dual focus increases number of electrons you can fire
why is the oil surrounding the circuit
oil surrounds the tube because oil is a good thermal conductor
why is the oil surrounding the circuit
oil surrounds the tube because oil is a good thermal conductor
what two forces to electrons experience
- one towards the anode
- one towards the central axis of the beam
tube housing shield
- earthed aluminium or steel
- electrical and radiation safety for staff and patients
-radiation should not escape 3mm of lead lining
how is the x-ray tube shield made safe?
- by connecting the copper wire braiding of HT cables to both shield and HT transformer casing thats securely earthed
- insulated with robber
what does lead lining of tube do
prevents leakages of tube
what is the anode heel effect
A phenomenon in which the the intensity of the x-ray beam is greater towards the cathode side of the tube than the anode side of the tube
when are x-rays produced
- when electrons are accelerated from cathode to anode
- number of electrons controlled by mA selector
what is kinetic energy of electrons controlled by
kV selector
what does KVp control
peak potential difference across tube
- if increased then higher energy x-rays produced
