Chapter 5 Notes

Question 1

x-ray production requires what

Answer 1

a source of electrons, an appropriate target material, a high voltage, and a vacuum

Question 2

the x-ray tube consists of

Answer 2

a cathode and anode enclosed within an envelope and then encased in a protective housing

Question 3

the cathode is the _____ side of the x-ray tube

Answer 3

negative

Question 4

function of the cathode

Answer 4

produce a thermionic cloud, conduct the high voltage to the gap between cathode and anode, and focus the electron stream as it heads for the anode

Question 5

cathode assembly consists of

Answer 5

the filament or filaments, focusing cup, and associated wiring

Question 6

what is the filament

Answer 6

a small coil of thin, thoriated tungsten wire

Question 7

the focusing cup serves to

Answer 7

narrow the thermionic cloud as it is driven to the anode

Question 8

the anode is the _____ side of the x-ray tube

Answer 8

positive

Question 9

anodes are divided into what two types

Answer 9

stationary and rotating

Question 10

anodes are made using what

Answer 10

tungsten

Question 11

tungsten is used to make anodes because

Answer 11

high atomic number, high melting point, and good heat-conducting ability

Question 12

anode assembly consists of

Answer 12

anode, stator, and rotor

Question 13

the portion of the anode where the high-voltage electron stream impacts is called

Answer 13

target, focus, focal point, focal spot, or focal track

Question 14

effective focal spot describes

Answer 14

the area of the focal spot that is projected out of the tube toward the object being radiographed

Question 15

line-focus principle is used to

Answer 15

reduce the effective area of the focal spot (permits the best detail in as large of an area as possible)

Question 16

effective focal-spot is controlled by

Answer 16

the filament size and the anode target angle

Question 17

when the target angle is less than _____ degrees, the effective focal spot is smaller than the actual focal spot

Answer 17

45 degrees

Question 18

anode heel effects states that

Answer 18

radiation intensity is greater on the cathode side than on the anode side

Question 19

what can cause serious degradation of radiographic image quality?

Answer 19

off-focus or extrafocal radiation

Question 20

off-focus radiation comprises

Answer 20

photons that were not produced at the focal spot

Question 21

three types of heating charts

Answer 21

radiographic tube rating charts, anode cooling charts, and housing cooling charts

Question 22

heating charts are available to help radiographers

Answer 22

avoid thermal damage to x-ray tubes

Question 23

which heating chart is most valuble

Answer 23

radiographic rating charts because they provide a guide regarding the maximum technical factor combinations that can be used without overloading the tube

Question 24

what is the melting point of tungsten

Answer 24

3,370 degrees C

Question 25

what are also good choices for filament material

Answer 25

rhenium and molybdenum

Question 26

most modern x-ray tubes will last between how many exposures

Answer 26

10,000-20,000 exposures

Question 27

focusing cup is composed of

Answer 27

nickel

Question 28

grid-biased tubes changes charge of focusing cup from

Answer 28

negative to positive

Question 29

grid-biased tubes permit

Answer 29

very short, rapid sequencing of exposures

Question 30

rotating anode made of

Answer 30

tungsten-rhenium alloy

Question 31

anode layering assists with

Answer 31

heat loading

Question 32

when should tube warm-up procedure be performed

Answer 32

if tube has been idle for an extended period of time (>2 hours)

Question 33

rotating anode can increase heat capacity by

Answer 33

300x

Question 34

the actual focal spot is

Answer 34

the physical area of the focal track being hit by electrons

Question 35

the effective focal spot is

Answer 35

the projected area of x-ray beam

Question 36

with the anode heel effect, beam intensity can vary as much as

Answer 36

45%

Question 37

what is the only part of the x-ray tube located outside the envelope

Answer 37

stator

Question 38

rotor is made of

Answer 38

copper cylinder connected to anode disk by molybdenum stem

Question 39

what is the Gyroscopic effect

Answer 39

when high speed anode rotations add stress to x-ray tube design

Question 40

envelope is made of

Answer 40

heat tolerant Pyrex glass or metal

Question 41

two functions of envelope

Answer 41

supports anode/cathode assemblies and maintains a vacuum

Question 42

off-focus radiation contributes up to what percent of the total primary beam

Answer 42

25%

Question 43

ways to extend x-ray tube life

Answer 43

1. follow recommended tube warm-up procedures 2. avoid frequent and successive "boosting" of tube 3. use low mA settings when possible 4. use low speed rotor rotation when possible 5. follow rating charts 7. avoid rough handling of x-ray tube head 8. listen for unusual sounds