Xray Tube

Question 1

charge of cathode vs anode

Answer 1

c - negative

a - positive

Question 2

filament and focusing cup are located in the?

Answer 2

cathode

Question 3

role of focusing cup

Answer 3

focus beam

directed beam where it needs to go

Question 4

charge of focusing cup

Answer 4

negative

Question 5

define space charge

Answer 5

charge in vacuum due to thermionic emission which prevents further liberation of electrons

Question 6

what are qualities of tungsten that make it a good target

Answer 6

high atomic number
thermal conductivity
high melting point

Question 7

define focal spot

Answer 7

the area of the target from which xrays are emitted or the actual xray source

Question 8

smaller focal spot results in better _____ ______

Answer 8

spatial resolution

Question 9

what is the line focus principle

Answer 9

angling target allows for more area for electron interactions with target and thus more photons
results in a smaller effective target area (focal spot)

Question 10

what does line focus principle result in

Answer 10

smaller effective target area therefore better spatial resolution and heat capacity

Question 11

why must the angle of the anode not be too steep (LFP)

Answer 11

must allow for max field size coverage

Question 12

what is the heel effect

Answer 12

a consequence of the line focus principle in which electrons are attenuated on the anode side and therefore a lower intensity of photons on that side of the image
results in underexposed anode side, over exposed cathode side on image

Question 13

how is thermionic emission achieved

Answer 13

mA applied to the filaments making them hot thus ejecting electrons (now thermions) into the envelope

Question 14

what is the potential difference between cathode and anode

Answer 14

the cathode is negative and the anode is positive therefore electrons will always move towards the anode

Question 15

what are the 3 main things that have to occur/be present in order to get a photon

Answer 15

thermionic emission
potential difference between anode and cathode
target interaction

Question 16

what are the 3 outcomes of electrons interacting with the anode

Answer 16

heat
infrared radiation
photons

Question 17

what is the difference between characteristic and brem radiation

Answer 17

characteristic - electron interacts with an inner shell electron which is completely removed, resulting in an outer shell electron dropping down to fill the void, in the process releasing a photon
brem - electron slows down as it approaches the nucleus thus losing KE and releasing photons

Question 18

a diagnostic xray beam consists mostly of _____ xrays and some _____ xrays

Answer 18

mostly brem

some characteristic

Question 19

brem xras create a spectrum of zero to maximum ____ ____ ____

Answer 19

projectile electron energy

Question 20

how is xray output intensity determined

Answer 20

output intensity = # of useful electrons in a beam
determined by the amount of electrons reaching the target set by mA as well by the velocity off the cathode stream (kVp) and pathway of exiting beam (absorption)