Radiation Physics

Question 1

***for this lecture, know structure and function. Don’t just memorize

Answer 1

: )

Question 2

part that surrounds the other parts, creates vacuum for x-ray production

Answer 2

glass tube

Question 3

cathode ____ electrons, and has a ____ charge

Answer 3

generates, negative

Question 4

anode ____ electrons and ______

Answer 4

receives, produces x-rays

Question 5

Tungsten filament is connected to a _____ circuit

Answer 5

low-voltage

Question 6

negatively charged concave reflector is a…

Answer 6

focusing cup

Question 7

site of x-ray production, where is it? what is its charge?

Answer 7

focal spot

located in anode, positively charged

Question 8

focal spot attracts _____

Answer 8

electron cloud from cathode

Question 9

ideal target should have. Tungsten satisfies all except which?

Answer 9

• high Z#
• high melting points
• high thermal conductivity
• low vapor pressure

Tungsten does not satisfy thermal conductivity

Question 10

how do we address Tungsten’s poor conductivity of heat?

Answer 10

copper block and cooling oils in glass tube

Question 11

focal should be large to assist in _____
focal spot should be small to increase ____

what’s the solution?

Answer 11

heat dissipation, image sharpness

solution: line focus principle

Question 12

line focus principle practicals

Answer 12

putting focal spot at an line

Question 13

importance of glass tube vacuum

Answer 13

no gas to prevent collision of e- to the gas molecules (which impairs x-ray production)

Question 14

what type of systems do dental x-ray systems use?

Answer 14

stationary (non-rotating)

Question 15

what are the features of a rotating anode?

Answer 15

• beveled anode disk rotates while tube is operating
• e- strike successive small areas of target (small focal spot)
• distributes heat over larger areas d/t actual focal spot

Question 16

two big concerns in anode/focal spot

Answer 16

heat dissipation, image sharpness

Question 17

image sharpness in rotating anode: e- strike ________

Answer 17

successive small areas of target

Question 18

heat dissipation in rotating anode: actual focal spot is the _______ which helps to distribute heat over ____

Answer 18

circumference of the disk, larger areas

Question 19

low voltage circuit powers ____; high voltage powers ___

Answer 19

filament, cathode to anode

Question 20

purpose of low voltage circuit

Answer 20

heat filament to cause thermionic emission

Question 21

_____ increases or decreases resistance in circuit and changes the current in the filament

Answer 21

variable resistor

Question 22

increase mA, _____ electrons sent to anode

Answer 22

increase

Question 23

e- from heated filament to the target ___ the x-ray tube constitute mA current

Answer 23

within

Question 24

increase mA for a given exposure time, ____ receptor exposure

Answer 24

increase

Question 25

increase kVp, ______

Answer 25

increase mean energy of polychromatic x-ray beam

Question 26

purpose of high voltage circuit

Answer 26

create high potential difference between cathode/filament and anode/target

Question 27

increasing kVp will ultimately influence ____

Answer 27

image quality

Question 28

as kVp increases, _______

Answer 28

• velocity of e- increases
• photon energy increases
• # of photons increases

Question 29

as photon energy (quality, penetrability) increases…

Answer 29

• fewer photons interact in patient

- radiographic contrast decreases

Question 30

of photons increases, ______

Answer 30

receptor exposure increases

Question 31

item used to change kVp that compensates for variations in incoming line (voltage stabilizer)

Answer 31

autotransformer

Question 32

measure of total x-ray beam exposure to the sensor/detector/recpetor

Answer 32

receptor exposure

Question 33

how is receptor exposure controlled?

Answer 33

• kVp
• mA
• exposure time (seconds)
• other factors to be discussed later…..

Question 34

kVp controls _______ and _____

Answer 34

beam quality (image contrast), beam quantity (exposure)

Question 35

mA controls _____

Answer 35

beam quantity (exposure)

Question 36

exposure time is measured in ____

Answer 36

pulses

Question 37

1 pulse equals…

Answer 37

1/60th of a second

Question 38

amount of radiation per second (mA)

Answer 38

exposure rate

Question 39

duration of radiation production (seconds)

Answer 39

exposure time

Question 40

overall measure of exposure (assuming kVp is fixed)

Answer 40

milliamp-seconds (mAs)

Question 41

for constant receptor exposure, exposure time and mA are _____

Answer 41

inversely related

Question 42

mAs is a product of _____

Answer 42

mA and exposure time (in sec)

Question 43

for constant receptor exposure, mAs must be the ___

Answer 43

same

Question 44

when exposure time is increased, mA _______

Answer 44

must be decreased and vice versa

Question 45

if 10mA x 1 sec = 10mAs, then 5mA x ___ = 10mAs

which would be most ideal?

Answer 45

2 seconds

the lower time exposure (less time for exposure)

Question 46

if sufficient cooling time is not allowed, damage to ____ can occur

Answer 46

target or filament

Question 47

x-ray production is inefficient, as seen by…

Answer 47

1% x-ray production, 99% heat production

Question 48

2 guidelines for cooling time

Answer 48

1. duty cycle

2. tube rating (heat capacity)

Question 49

cooling time applies when one is anticipiating a single, long exposure

Answer 49

tube rating

Question 50

cooling time that applies when several minor exposures are made in a clinical setting

Answer 50

duty cycle

Question 51

radiation that originates at focal spot, leaves tube through window and is useful in image formation

Answer 51

primary (usable beam)

Question 52

radiation that originates at focal spot, leaves the tube through barriers around the tube

Answer 52

leakage radiation

Question 53

radiation that originates in tissues that causes image noise

Answer 53

secondary/scatter radiation

Question 54

what helps minimize leakage radiation?

Answer 54

glass, oil, metal enclosures