Production and properties of X rays Flashcards Preview

Year 3 Radiography > Production and properties of X rays > Flashcards

Flashcards in Production and properties of X rays Deck (46):
1

atomic mass unit

1/12 mass of carbon atom

2

mass of proton, neutron and electron

proton and neutron= 1amu
electron= 1/1840

3

structure of an atom

nucleus of protons and neutrons
electrons in orbit around nucleus

4

what is Z

proton number
and electron number

5

what is A

atomic number. number of protons and neutrons in nucleus

6

define excitation

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

7

define ionisation

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

8

what is binding energy

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

9

where is binding energy greatest

K shell (greater for electrons closer to nucleus)

10

what is a photon

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

11

what kind of radiation is x rays

electromagnetic radiation, ionising
high frequency, short wavlength

12

what is the biggest source of ionising radiation

radon (gas released from soil/rocks)

13

what % of ionising radiation is artificial

13%

14

name the other type of ionising radiation

gamma rays

15

wavelength and freq of x rays/ gamma rays

short wavelength
high freq

16

how fast do x rays travel in a vacuum

speed of light

17

range of x ray wavelengths

0.01-0.05nm

18

x rays obey the inverse square law. what is this

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

19

why must x ray production be in a vacuum

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

20

3 steps to produce x rays

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

21

main components of tube head and their function

-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

22

what direction do electrons flow?

negative (cathode) to positive (anode)

23

how are electrons produced

thermionic emission from heating the filament at the cathode

24

what is tube current?

the amount of electron flow

25

how to increase tube current

increase heating of filament

26

how are electrons accelerated to anode

high potential difference

27

what happens when the electrons reach the anode

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

28

how is the heat removed

copper block and surrounding oil

29

why is the tungsten used for the target

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

30

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

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

31

tube current value for dental radiographs

7-10mA

32

kV value for dental radiographs

60-70kVp

33

why is high kV used?

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

34

function of kV

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

35

function mA and time

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

36

name 2 methods of x ray production

Bremsstrahlung radiation
characteristic radiation

37

describe Bremsstrahlung radiation

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

38

what is maximum potential energy

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

39

what is filtration

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

40

describe and explain spectrum produced by Bremsstrahlung radiation

continuous. incoming electrons slowed down/ deflected to varying degrees

41

describe characteristic radiation

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

42

describe pattern of x ray production in characteristic radiation

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

43

what electrons are useful for diagnosis and why

K shell elctrons because they have the highest binding energy

44

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

69.5kV

45

what is
k alpha
k beta


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

46

what type of radiography uses filtration?

both