x-ray production Flashcards
1
Q
functions of glass envelope
A
creates air free vacuum around cathode and anode and protects tube from oxidation
2
Q
function of tube housing
A
- prevents x-rays being emitted through exam room
- good insulator
- rounded shape prevents dissipation of static charge
3
Q
what is the glass envelope made of
A
borosilicate glass
4
Q
what does the cathode consist of
A
- filament
- focussing cup
5
Q
what is the focussing cup made of
A
- nickel and stainless steel
- can remain a negative charge very easily
6
Q
reason for filament and what is it made out of
A
- made of tungsten
- help increase SA
- increase light
7
Q
why do we use small filaments
A
- high spatial resolutions
8
Q
why do we use tungsten
A
- low work function - can give off electrons at low voltage
- high melting point
- low vapour pressure
- high atomic number
9
Q
why is a high atomic number good
A
- loads of electrons in outer shells
- doesnt need much energy
- gives efficient x-ray production
10
Q
dual focus filaments
A
- 2 filaments
- dual focus increases number of electrons you can fire
11
Q
why is the oil surrounding the circuit
A
oil surrounds the tube because oil is a good thermal conductor
11
Q
why is the oil surrounding the circuit
A
oil surrounds the tube because oil is a good thermal conductor
12
Q
what two forces to electrons experience
A
- one towards the anode
- one towards the central axis of the beam
13
Q
tube housing shield
A
- earthed aluminium or steel
- electrical and radiation safety for staff and patients
-radiation should not escape 3mm of lead lining
14
Q
how is the x-ray tube shield made safe?
A
- by connecting the copper wire braiding of HT cables to both shield and HT transformer casing thats securely earthed
- insulated with robber
