Production and properties of X rays

Question 1

atomic mass unit

Answer 1

1/12 mass of carbon atom

Question 2

mass of proton, neutron and electron

Answer 2

proton and neutron= 1amu

electron= 1/1840

Question 3

structure of an atom

Answer 3

nucleus of protons and neutrons

electrons in orbit around nucleus

Question 4

what is Z

Answer 4

proton number

and electron number

Question 5

what is A

Answer 5

atomic number. number of protons and neutrons in nucleus

Question 6

define excitation

Answer 6

moving electron inner –> outer shell to excite the atom (move to higher energy level)

Question 7

define ionisation

Answer 7

complete removal (or addition) of an electron from an atom, causing it to gain or lose charge

Question 8

what is binding energy

Answer 8

attraction between -ve e- and +ve protons (nucleus)

Question 9

where is binding energy greatest

Answer 9

K shell (greater for electrons closer to nucleus)

Question 10

what is a photon

Answer 10

packet of X ray energy, equivalent to a quantum of energy

Question 11

what kind of radiation is x rays

Answer 11

electromagnetic radiation, ionising

high frequency, short wavlength

Question 12

what is the biggest source of ionising radiation

Answer 12

radon (gas released from soil/rocks)

Question 13

what % of ionising radiation is artificial

Answer 13

13%

Question 14

name the other type of ionising radiation

Answer 14

gamma rays

Question 15

wavelength and freq of x rays/ gamma rays

Answer 15

short wavelength

high freq

Question 16

how fast do x rays travel in a vacuum

Answer 16

speed of light

Question 17

range of x ray wavelengths

Answer 17

0.01-0.05nm

Question 18

x rays obey the inverse square law. what is this

Answer 18

intensity of radiation reduces to 1/4 when distance from source is doubled

Question 19

why must x ray production be in a vacuum

Answer 19

otherwise atoms of air would be in the way of electron movement

Question 20

3 steps to produce x rays

Answer 20

1. produce lots of electrons
2. accelerate them to very high energy
3. smash them in to target

Question 21

main components of tube head and their function

Answer 21

• glass x ray tube (filament, copper block, target)
• step up transformer (high voltage to accelerate electrons)
• step down transformer (low voltage to heat filament
• lead casing (to stop x rays escaping)
• oil (conduct heat away from insert)
• aluminium filtration (removes unwanted low energy electrons)
• collimator
• beam indicating device

Question 22

what direction do electrons flow?

Answer 22

negative (cathode) to positive (anode)

Question 23

how are electrons produced

Answer 23

thermionic emission from heating the filament at the cathode

Question 24

what is tube current?

Answer 24

the amount of electron flow

Question 25

how to increase tube current

Answer 25

increase heating of filament

Question 26

how are electrons accelerated to anode

Answer 26

high potential difference

Question 27

what happens when the electrons reach the anode

Answer 27

hit a small target area, stop moving (lose energy) | energy lost as heat (99%) or x rays (1%)

Question 28

how is the heat removed

Answer 28

copper block and surrounding oil

Question 29

why is the tungsten used for the target

Answer 29

- high melting point (not affected by heat from electrons) | - high atomic number (74) so lots of interaction for electrons

Question 30

what happens to produce a) heat-producing reaction | b) x ray producing reaction

Answer 30

a) heat-producing reaction: incoming electron hits an outer-shell tungsten electron b) x ray producing reaction: incoming electron avoids outer shell tungsten electrons and comes very close to tungsten nucleus. the electron-nucleus attraction causes the electrons to lose energy as x rays. the further round the nucleus the electrons are deflected, the higher energy the photons

Question 31

tube current value for dental radiographs

Answer 31

7-10mA

Question 32

kV value for dental radiographs

Answer 32

60-70kVp

Question 33

why is high kV used?

Answer 33

less dose to patient because electrons more accelerated, more likely to reach nucleus

Question 34

function of kV

Answer 34

- determines quality of X ray beam ie energy of photons - determines penetrating power of photons - affects film contrast

Question 35

function mA and time

Answer 35

determine quantity of x ray photon | affects degree of blackening of film (optical density)

Question 36

name 2 methods of x ray production

Answer 36

Bremsstrahlung radiation | characteristic radiation

Question 37

describe Bremsstrahlung radiation

Answer 37

incoming electron penetrates outer electron shells and passes close to nucleus of tungsten atom this is slowed down and reflected by nucleus with large loss of energy emitted in the form of x rays

Question 38

what is maximum potential energy

Answer 38

enough energy given to moving electron so that it fully stops at the target nucleus

Question 39

what is filtration

Answer 39

removal of low-energy photons produced when bombarding electrons are only partly deflected. they have little penetrating power so are not useful

Question 40

describe and explain spectrum produced by Bremsstrahlung radiation

Answer 40

continuous. incoming electrons slowed down/ deflected to varying degrees

Question 41

describe characteristic radiation

Answer 41

incoming electron collides with inner shell tungsten electron, displacing it to outer shell (excitation) or displacing it from atom (ionisation). an outside electron jumps down to fill gap. this decrease in energy causes x ray production

Question 42

describe pattern of x ray production in characteristic radiation

Answer 42

always the same amount of x ray produced (hence characteristic) because same amount of energy lost when electrons move rings L-->K on the tungsten atom

Question 43

what electrons are useful for diagnosis and why

Answer 43

K shell elctrons because they have the highest binding energy

Question 44

what kV is needed to displace K shell electron to produce x ray?

Answer 44

69.5kV

Question 45

what is k alpha k beta

Answer 45

k alpha: L to K electron movement | k beta: M to K electron movement

Question 46

what type of radiography uses filtration?

Answer 46

both