Rad Science AEC

Question 1

Device that measure the quantity of radiation reaching the IR

Answer 1

Automatic Exposure Control

Question 2

It automatically terminates the exposure when the IR has received enough radiation to provide the required optical density

Answer 2

AEC

Question 3

only controls time

Answer 3

AEC

Question 4

_must be set in case of AEC failure (150% of anticipated exposure)

Answer 4

Back-up timer

Question 5

-2, -1, +1, +2 increases or decreases densityby _ % for each step

Answer 5

25%

Question 6

_are used to compensate for pathology, not part thickness

Answer 6

Density controls

Question 7

2 types of AEC

Answer 7

phototimer

ionization chamber

Question 8

_ the most common AEC ( ionizes gas inside chamber)

Answer 8

ionization chamber

Question 9

must have accurate

Answer 9

positioning and photocell selection

Question 10

The _ (made of tungsten)are located w/in the focusing cup.

Answer 10

Filament

Question 11

__ has a high melting point and it is hard to vaporize (turn to gas)

Answer 11

Tungsten

Question 12

most common cause of tube failure is _ w/deposits on the inside of the glass envelope

Answer 12

tungston vaporization

Question 13

the filament emits electrons when sufficiently heated. The outer shell of electrons are boiled off. This is _ and requires - amps of current

Answer 13

thermionic emission

4-6

Question 14

Because electrons are negative, they repel each other and sit around the filament waiting to be sent to the anode. This is referred to as the

Answer 14

electron cloud (space charge effect)

Question 15

2 types of anodes

Answer 15

stationary anode

rotationg anode

Question 16

Staionary anode is used in

Answer 16

low powered systems (dental)

Question 17

rotating anode is used in

Answer 17

x-ray tubes

Question 18

The _ is the area of the anode struck by electrons from the filament

Answer 18

target (focal spot, focal tract)

Question 19

The filament is made of

Answer 19

tungston and alloyed rhenium

Question 20

Tungston is used for the target for 3 reasons

Answer 20

atomic #, high 74
thermal conductivity dissipates heat well
high melting point, little pitting

Question 21

the rotating anode allows for _ over a much larger area

Answer 21

electron interactions

Question 22

_ is the source of radiation

Answer 22

focal spot

Question 23

useful radiation; radiation between tube and patient

Answer 23

primary radiation

Question 24

the _ is located between the anode and rotor (made of molybdenum)

Answer 24

stem

Question 25

intensity is greater on the _ side of the tube because some intensity is absorbed by the angle of the _ ((heel)

Answer 25

cathode

anode

Question 26

the smaller the target angle, the larger the

Answer 26

heel effect

Question 27

place the thicker portion of the subject under the _ side of the tube for more intensity

Answer 27

cathode

Question 28

electrons should hit the focal spot of the _. Some hit and bounce off and land outside of the focal spot. This can increase _, reduce _ and image tissue collimated off.

Answer 28

anode
pt. dose
contrast