X-ray tube/Cathode

Question 1

What is the charge on the cathode side?

Answer 1

negative

Question 2

What does the cathode house?

Answer 2

large and small filaments
focusing cup

Question 3

The cathode is the site of…

Answer 3

electron production

Question 4

What is applied to the focusing cup to achieve a negative charge? During when?

Answer 4

low negative potential

during electron production

Question 5

What is applied to the cathode end of the tube during an exposure?

Answer 5

large negative potential

Question 6

What is the focusing cup made of? Why?

Answer 6

nickel

its high heat capacity

Question 7

The focusing cup houses what?

Answer 7

the 2 (large and small) filaments

Question 8

What does the focusing cup do?

Answer 8

helps accelerate electrons toward the anode

Question 9

During what process do the focuses produce electrons?

Answer 9

thermionic emission

Question 10

Thermionic emission

Answer 10

the boiling off of electrons due to the heating of the small coil of thoriated tungsten wire (electron cloud)

Question 11

List 2 reasons why Tungsten is an ideal target material.

Answer 11

high melting point (6192 degree F)
high Z number (74)

Question 12

Why are the tungsten filaments coated in Thorium?

Answer 12

it’ll burn off about 2% more electrons, resulting in a more efficient thermionic emission process

Question 13

what do electrons form when the Tungsten filament is heated up?

Answer 13

“thermionic cloud”
“space charge”

Question 14

What is the most common type of x-ray tube failure

Answer 14

tungsten filament vaporization

Question 15

most x-ray tubes are considered to be what?

Answer 15

dual focus (2 filaments)

Question 16

What is the small focal spot used for?

Answer 16

greater spatial resolution and smaller body parts

Question 17

What is the large focal spot used for?

Answer 17

larger body parts (requires more electrons)

Question 18

What is the principal advantage of using the large filament?

Answer 18

increased heat capacity

Question 19

What can the electrons of the large focal spot be turned into?

Answer 19

x-ray photons

Question 20

What is the x-ray tube made of and why?

Answer 20

Pyrex glass to enable it to withstand the heat generated

Question 21

The x-ray tube is __________ to the heat produced by the heating of the filament and the electron interaction with the anode.

Answer 21

resistant

Question 22

In what way do electrons travel to the anode?

Answer 22

unimpeded (freely)

Question 23

What helps dissipate the heat generated during x-ray production in the tube?

Answer 23

oil bath

Question 24

What process does the surrounding of the oil bath help aid?

Answer 24

convection

Question 25

What makes a gassy tube?

Answer 25

electrons strike the heat residue of tube, creating a gassy substance

no longer a vacuum tube

Question 26

What things are needed to efficiently produce x-rays?

Answer 26

1. source of electrons
2. acceleration of electrons
3. a vacuum
4. a target

Question 27

What is a space charge?

Answer 27

cloud of free electrons made from Tungsten filament heating up

Question 28

The space charge affect limits the mA of the x-ray tube to approximately:

Answer 28

1000 mA