Production and properties of xrays

Question 1

history of xrays

Answer 1

• roentgen discoverd xrays in 1895

- first dental xray= 189y by Walkhoff

Question 2

what are xrays?

Answer 2

• form of electromagnetic radiation
• each xray=photon=packet of energy
• has a frequency and wavelenght
• xrays are inoinsing and can knock out electron from an atom
• very high photon energy, and short wavelength

Question 3

what are the properties of xrays?

Answer 3

• invisible and weightless
• no charge
• travels in straight lines-does not bend
• travels at speed of light
• variable wavelength and frequency-diff give diff properties
• penetrating
• ionising
• OBEYS INVERSE SQUARE LAW (intensity of radiation reduces to 1/4 as distance from source is doubled)

Question 4

what is the structure of an atom?

Answer 4

• protons( +ve)and neutrons make up the nucleus at the centre
• e-(-ve) in orbit around the nucleus
• atom is electrically neutral

Question 5

numbers and charges

Answer 5

• Z= atomic number (no. of protons in the nucleus)

- A= atomic mass number (no.of protons and neutrons in the nucleus)

Question 6

electron shells

Answer 6

• e- are limited to certain principle energy levels or “shells”
• K,L,M,N etc
• K=1st shell (2 e-), L=2(8 e-), M=3 (18e-)

Question 7

what is the difference between excitation and ionisation?

Answer 7

• excitation- when e- is moved from one shell to a higher shell
• ionisation-when one or more e- is removed completely from the atom and creates an ion pair (the +ve ion and the e-)
  
  • an atom is electrically neutral so when an e- is removed from atom a +ve ion is formed

Question 8

electron binding energy (EBE)

Answer 8

• EBE is the work needed to overcome attraction and remove e- from the atom (as e- is attracted to the +ve nucleus)
• the binding energy is greatest in K shell and energy gets smaller for outer shells

Question 9

what are the three stages in the production of x-rays?

Answer 9

1. Produce lots of e-
2. Accelerate them into a high energy
3. Smash them into a heavy metal target eg.tungsten (high melting point and high atomic no.) (without destroying it)

Question 10

what are the main components of tubehead?

Answer 10

• glass x-ray tube insert (filament, copper block and tungsten target)
• step up transformer (high voltage to accelerate e- from cathode to anode)
• step down transformer (low volatage to heat filament)
• lead lined casing
• oil surrounds insert
• aluminium filtration
• collimator (points where the beam is going
• beam indicating device

Question 11

production process

Answer 11

• e- produced by filament heating- termioinc emission (cathode)
• TUBE CURRENT (mA)- the extent of filament heating controls the amount of electrons produced and hence the current flowing between cathode and anode
• e- accelerated to anode by high POTENTIAL DIFFERENCE (kV)
• rapid deceleration of e- by target, interaction of e- with (tungsten) target (ANODE)
• the e- that smash into the tungsten are suddenly brought to rest; the energy lost by the e- i transferred into either heat (99%) or X-RAYS(1%). the heat is dissapated and removed by the copper block and surrounding oil