Rad Physics

Question 1

Z-number is?

Answer 1

protons

Question 2

A-number is?

Answer 2

mass number

Question 3

Higher Z# means what for binding energy?

Answer 3

higher

Question 4

Particulate vs Electromagnetic radiation

Answer 4

particulate: alpha, beta, cathode
kinetic energy of small mass

electromagnetic: x-rays, gamma rays, light
electric/magnetic fields

Question 5

X-rays mass? electric charge?

Answer 5

no mass, no charge

Question 6

Wavelength of xrays

Answer 6

0.1A to 0.5A

Question 7

Bremstrahlung is what interaction? How are x-rays created this way?

Answer 7

electron to nucleus interaction

x-rays generated when high velocity electrons interact with high atomic # atoms and decelerate suddenly

Question 8

characteristic radiation is what interaction? How are x-rays created this way?

Answer 8

electron to electron interaction

Direct hit knocks electron out of orbit. When a higher-energy electron fills this spot, the movement to a lower level gives off x-ray.

Question 9

Two named mechanisms for x-ray production?

Answer 9

bremsrahlung and characteristic radiation

Question 10

Which mechanism creates the greatest source of xrays?

Answer 10

Bremstrahlung

Question 11

In the x-ray tube, the tungsten filament is the…

Tungsten target?

Answer 11

Filament - cathode

Target - anode

Question 12

What is the source of electrons?

Answer 12

cathode

Question 13

What concentrates electrons?

Answer 13

focusing cup

Question 14

what accelerates electrons?

Answer 14

high voltage

Question 15

What is the target to stop electrons?

Answer 15

anode

Question 16

How are electrons generated in the cathode?

Answer 16

thermionic: current heats cathode to 2200 C which emits an electron cloud

Question 17

What does the step down transformer do?

Answer 17

Steps voltage down so cathode doesnt melt

Question 18

What does the step up transformer do?

Answer 18

increases potential difference between cathode and anode, increasing speed of electrons

Question 19

effective focus spot is _____ to improve ____?

Answer 19

small to improve image sharpness

Question 20

actual focus spot is _____ to increase _____?

Answer 20

large to increase heat dissipation

Question 21

Factors controlling x-ray beam (5)

Answer 21

Tube voltage (KVp)
Exposure time (S)
tube current (mA)
Filtration
Collimation

Question 22

Tube voltage effect on x-ray beam?

Answer 22

shifts curve up and to right - greater # of higher energy photons

Question 23

HVL - characterizes what about an xray beam?

Answer 23

penetrating quality and mean energy, found by thickness of an absorber that reduces quantity of photons by half

Question 24

As KVp increases, HVL…?

Answer 24

increases

Question 25

Tube current effect on xray beam?

Answer 25

Increases # photons

Question 26

Exposure time vs # photons recieved?

Answer 26

Double exposure = double photons

Question 27

FIltration filters out what?

Answer 27

low energy electrons that don't contribute to radiograph but do to patient risk

Question 28

What is responsible for inherent filtration in xray tube? | Added filtration in x-ray tube?

Answer 28

Inherent - glass/oil | Added - aluminum disk

Question 29

Filtration levels for 50-70 kVp? | 70+?

Answer 29

1. 5mm aluminum equivalent | 2. 5mm

Question 30

Filtration increases exposure time by what? Reduces pt dose by?

Answer 30

50% more exposure, 80% reduced dose

Question 31

Filtration effect on photon curve?

Answer 31

down and peak to right

Question 32

collimator does what?

Answer 32

metallic barrier with aperture that 1. reduces size and modifies shape of beam 2. reduces volume tissue irradiated 3. improves image quality

Question 33

Distance versus dose of xray

Answer 33

intensity inversely proportional to square of distance

Question 34

Should put x-ray tube how far from pt?

Answer 34

as close as possible without touching

Question 35

Types of interaction of xrays with tissue (3)

Answer 35

Coherent (7 %) Photoelectric effect (27%) Compton (57%) (other 9% is no interaction)

Question 36

Coherent scattering is what?

Answer 36

Incoming low energy electron comes near outer electron, , causes it to vibrate at same frequency and dies. The new electron radiates a new x-ray with same frequency and energy as old xray.

Question 37

Which type of interaction is the primary contributor to image formation?

Answer 37

Photoelectric effect

Question 38

How does photoelectric effect work?

Answer 38

incoming photon collides with inner shell electron electron absorbs all photon's energy and is ejected (ionization) Higher energy electron fills vacancy, emits characteristic radiation Recoil electron (photoelectron) also given off, all absorbed.

Question 39

Photoelectric effect depends on what 3 things?

Answer 39

1. wavelength/energy of photon energy/kVp 2. Atomic # of material 3. density of material PE = Z^3/kVp^3

Question 40

Compton scattering works how?

Answer 40

Incoming photon interacts with outer shell electron, electron ejected Incident photon deflected with lower energy Scattered photons travel in all directions

Question 41

What do the scattered photons from compton scattering contribute to image?

Answer 41

no useful information due to altered path; only fogging/darkening

Question 42

Distinguishing radiopaque/radiolucent on film due to?

Answer 42

differential absorption

Question 43

Exposure defined as?

Answer 43

capacity of x-rays to ionize air - amount of charge per mass of air, coulombs per kg

Question 44

Conventional unit of exposure?

Answer 44

Roentgen: 2.58 x 10e-4 C/Kg

Question 45

Absorbed dose defined as

Answer 45

amt energy imparted by ionizing radiation to a mass of tissue.

Question 46

Absorbed dose unit?

Answer 46

1 Gray (Gy) = 1 joule of energy deposited in 1 kg 1 Gray = 100 Rads

Question 47

Equivalent dose measures? How to calculate?

Answer 47

biological effectiveness of different types of radiation Sum of products of absorbed dose (Gy) and quality factor (QF)

Question 48

Unit of equivalent dose?

Answer 48

Rem, 100 Rem = 1 Sv (Sievert)

Question 49

Effective dose measures? How to calculate?

Answer 49

compares risk of different types of expsoures Sum of products of equivalent dose to each organ and tissue weighing factor

Question 50

Effective dose takes into account (3)

Answer 50

Volume Radiosensitivity of tissue irradiated Biologic effectiveness of radiation

Question 51

For dental x-rays, 1 roentgen = ? rads = ? rems?

Answer 51

1 roentgen = 1 rad = 1 rem

Question 52

For dental xrays, 100 rads = ? Gy = ? Sv

Answer 52

100 rads = 1 Gy = 1 Sv