Radiation Physics 1

Question 1

Shells in an atom are numbered from?

Answer 1

1 to 7

Question 2

If the shells are labeled with letters, they are?

Answer 2

K to Q

Question 3

The previously mentioned number of letter is known as the shell’s?

Answer 3

Principal quantum number or n

Question 4

What is the formula for the number of electrons a shell can hold?

Answer 4

2n^2

Question 5

How do you calculate atomic mass?

Answer 5

of protons + # of neutrons

Question 6

What causes particulate radiation? What is the capacity to ionize based on?

Answer 6

Moving particles. Mass, velocity, and charge affect the capacity to ionize

Question 7

What is an alpha particle and how ionizing is it?

Answer 7

Helium atom with no electrons. Very ionizing so it doesn’t travel very far

He 2+

Question 8

What is a beta particle and how ionizing is it?

Answer 8

An electron that has been emitted from a radioactive nucleus. It is not very ionizing and thus travels further

Question 9

What is linear energy transfer

Answer 9

Loss of energy as a particle moves through tissue

Question 10

What factors can increase linear energy transfer?

Answer 10

Increasing size and charge and decreasing velocity

Question 11

Other than particulate radiation, the other kind is?

Answer 11

Electromagnetic radiation

Question 12

The x ray machine consists of what 3 parts?

Answer 12

Power supply, control panel, tube head

Question 13

What is used to absorb heat created by the x ray tube?

Answer 13

Mineral oil

Question 14

The filament in the cathode is the source of? What is it made out of?

Answer 14

Electrons, made of a coiled piece of tungsten

Question 15

What is the focusing cup of the cathode?

Answer 15

Negatively charged concave reflector that repels electrons.

Question 16

What is the focusing cup made of?

Answer 16

Nickel or molybdenum

Question 17

The anode is made of?

Answer 17

Tungsten target embedded in a copper stem

Question 18

What does the anode do and how efficient is the process?

Answer 18

Convertes the kinetic energy from the phi lament into photon energy or x-rays. Highly inefficient, 99% lost as heat

Question 19

What 4 properties of tungsten make it the best choice?

Answer 19

High atomic number and efficient in making x-rays

Highest melting point of any metal so it can withstand the heat generated

High thermal conductivity and it dissipates heat into the copper stem

Low vapor pressure which helps maintain the vacuum

Question 20

What type of anode is better for a dental setting, rotating or stationary?

Answer 20

Stationary

Question 21

What is the focal spot? How does focal spot size affect radiographic image sharpness?

Answer 21

The focal spot is where the focusing cup directs electrons from the filament. Sharpness of the image increases as focal spot size decreases

Question 22

What determines the intensity of the x-ray beam?

Answer 22

Tube current or mA and tube voltage or kVp

Question 23

What determines the number of electrons and x-rays produced?

Answer 23

The tube current or mA, higher mA= more electrons

Question 24

What are the two processes that produce x-rays?

Answer 24

Bremsstrahlung and characteristic radiation

Question 25

What produces bremsstrahlung?

Answer 25

Sudden stopping or slowing of the electron at the target

Question 26

Which produces the majority of x-ray photons?

Answer 26

Bremsstrahlung

Question 27

What is exposure?

Answer 27

How many x-ray photons are produced

Question 28

What is the combined unit for current and exposure time?

Answer 28

milliamp seconds

Question 29

Older x-rays used what unit for time?

Answer 29

An impulse which was 1/60th of a second

Question 30

Half wave rectification is AKA? How does it work?

Answer 30

Self-rectification, limits machine to using half the AC cycle

Question 31

Most dental x-rays now use?

Answer 31

DC cycle because it provides more uniform energy

Question 32

What is tube rating?

Answer 32

Maximum exposure time an x-ray may be energized for single exposure or max time you can leave the tube on before it gets too hot

Question 33

What is duty cycle?

Answer 33

Frequency at which exposures can be made

Question 34

When characteristic radiation occur?

Answer 34

When a high speed electron from the filament displaces an electron from the inner shell of the tungsten atom. An outer shell electron drops in and emits a photon

Question 35

What affect does the focal spot have on heat?

Answer 35

Heat increases as the size of the focal spot decreases

Question 36

What is external filtration and what is used?

Answer 36

Removing low energy photons from the beam using an aluminum filter

Question 37

What is the half value layer?

Answer 37

The thickness needed to absorb half of the beams energy

Question 38

What is inherent filtration?

Answer 38

Absorption from anything that is not the aluminum filter

Question 39

How much aluminum equivalent is needed up to 70 kVp and over?

Answer 39

1.5mm under and 2.5mm over

Question 40

What does collimation do?

Answer 40

Limits beam size and patient radiation exposure

Question 41

What shape collimator do we use for intraoral exposures?

Answer 41

Rectangular

Question 42

How does a collimator increase image quality?

Answer 42

By reducing scatter radiation