RAD03-2002 How are X-Rays produced?

Question 1

What is the main part of the X-ray unit called?

Answer 1

Tubehead

Question 2

What is within the tubehead the produces the x-rays themselves?

Answer 2

Glass x-ray tube

Question 3

What is the cathode?

Answer 3

At one end of the glass tube there is a coil of wire called the filament

Question 4

What is the anode?

Answer 4

At the other end of the glass tube there is a target made of tungsten set into a block of copper

Question 5

What is the entire X-ray tube surrounded by?

Answer 5

Oil

Question 6

What unit is within the tube head?

Answer 6

Step up transformer

Question 7

What part of the tube head is in contact with the patients face?

Answer 7

Spacer cone

Question 8

What is the function of the step-up transformer?

Answer 8

To step up the mains voltage to 60,000 to 70,000

Question 9

What is the function of the surrounding oil?

Answer 9

Removes heat that is produced during x-ray production

Question 10

What is the function of the spacer cone?

Answer 10

Indicates the direction of the beam and sets the ideal distance of the X-ray tube’s target to the skin of the patient’s face

Question 11

What is the density off any substance described as?

Answer 11

Atomic number (z)

Question 12

What is the atomic number

Answer 12

Number of protons

Question 13

What occurs the glass x ray tube during x-ray exposure?

Answer 13

As electric current flows through the filament and heats up
The electrons from the tungsten atoms are boiled off and released, and a cloud of electrons forms around the end of the filament
60k voltage is provided from the step up transformed, which allows the electrons to travel across the gap to the tungsten target

Question 14

What happens to the heat produced?

Answer 14

Conducted away down the big copper block

Question 15

What are the implications of some photons leaving the target in other directions?

Answer 15

Must never hold the tubehead because your hand could be directly irradiated by leaked radiation

Question 16

What happens when the accelerated electron approaches tungsten?

Answer 16

The electron passes near the nucleus and is attracted towards and deflected and slowed in its path

Question 17

What are the effects of the electron slowing down as is it deflected in tungsten?

Answer 17

The electron loses some of its energy, which is converted into an x-ray photon and emitted

Question 18

How does the proximity of the electron to the nucleus affect the defection?

Answer 18

The closer the electron is to the nucleus, the larger the deflection therefore will be a stronger and longer X-ray

Question 19

What type of spectrum does the deflection of the accelerated electron result in?

Answer 19

Continuous spectrum

Question 20

Which energy photons are more dangerous for the patient?

Answer 20

Low energy

Question 21

What is the overall energy of the photon determined by?

Answer 21

The energy of the incoming electrons which is determined by the size of the voltage

Question 22

How does the size of the voltage affect the energy of the electron?

Answer 22

The bigger the voltage, the greater the energy given to the electron

Question 23

How does the number of low energy photons differ from high energy photons?

Answer 23

There are very many low energy photons whilst relatively few high energy photons

Question 24

What is Emax?

Answer 24

The maximum energy any one photon can have

Question 25

What is the Emax for a 60kV machine?

Answer 25

60,000 volts

Question 26

How does a higher kV affect the number of photons?

Answer 26

A higher kV produces more photons

Question 27

What is an alternative method X-rays can be produced?

Answer 27

X-ray producing collision

Question 28

How are x-rays produced via x-ray producing collisions?

Answer 28

The incoming electron passes into the atom of tungsten and interacts with one of the orbiting electrons The electron is knocked out of the atom and the incoming electron is deflected in its path and leaves the atom The displacement of an inner shell electron means the atom is unstable so an electron from the adjacent shell drops to fill the gap As one electron drops to the next shell, it is dropping from one energy to another, so energy is emitted in the form of an x-ray photon. There will be a similar cascade of electrons to fill the void, again energy being released as a photon Eventually a free electron is captured and the atom is returned to it stable state

Question 29

What type of spectrum is formed as a result of rearrangement of the electrons?

Answer 29

Characteristic

Question 30

Why is rearrangement of electron known as characteristic spectrum?

Answer 30

The electrons are only of specific energy levels thats are specific to the size of the gap

Question 31

When will photons from the characteristic spectrum be formed?

Answer 31

When the voltage is 70kV or more | As lower kV do not give the incoming electrons enough energy to knock out an inner shell electron from tungsten atom

Question 32

How are lowest energy photons removed from the beam before hitting the patient?

Answer 32

Passing the beam through an aluminium sheet, which absorbs and filters out lowest energy photons that are most harmful

Question 33

What is the recommenced thickness for aluminium?

Answer 33

1. 5mm for x-ray units operating at less than 70kv | 2. 5mm for x-rays operating at more than 70kV

Question 34

What are the 3 main controls on the control panel?

Answer 34

kV milli amperage (mA) Time

Question 35

What controls are fixed in dental sets?

Answer 35

kV an mA is fixed and you cannot alter it | But time can change

Question 36

What does kV determine?

Answer 36

The energy of the photon and hence their penetrating power | Affects the film contrast

Question 37

What does a lower kV mean in terms of contrast?

Answer 37

Lower kV shows bigger contrast with less shades of grey | The difference between black and white is more obvious

Question 38

Why is a higher kV more ideal for patients?

Answer 38

More photons penetrate hence less absorption

Question 39

What has happened in grey areas of an x-ray image?

Answer 39

Some photons have passed through and hit the film and there is scattering of photons

Question 40

What has happened in white areas of the x-ray image?

Answer 40

Photons have been stopped by a filling

Question 41

What has happened in black areas of an x-ray image?

Answer 41

All photons have passed through and hit the film

Question 42

What do mA and time determine?

Answer 42

Determines quantity of electrons leaving tube hence quantity of photons

Question 43

How does increased photons affect the x-ray image?

Answer 43

Leads to increased blackening and over exposure

Question 44

What does an over-exposed look like?

Answer 44

Too dark

Question 45

How is rectification achieved?

Answer 45

Via either half wave pulses where X-ray fire only on positive waves Or single phase full wave rectification where negative is flipped to positive

Question 46

Why are X-rays firing only only positive waves very inefficient?

Answer 46

Longer exposure and X-ray fires from 0 on every new pulse

Question 47

What type of current is recommended?

Answer 47

DC but it is expensive

Question 48

What is FSD?

Answer 48

The distance form focal spot on the target to the end of the spacer cone that touches the patients head

Question 49

What is the effect of a long FSD?

Answer 49

Smaller beam hence patient has less irration

Question 50

What FSD is recommended?

Answer 50

200mm

Question 51

What is the collimator?

Answer 51

The device that restricts beam size