Production of x-rays

Question 1

describe the filament cathode

Answer 1

• very fine wire made of tungsten
• small current passed along it 8-10mA
• electrons are excited
• wire gets hot - may give off light
• electrons are lost from outer shells/orbits round the nucleus
• electron cloud forms around the cathode

Question 2

describe the anode

Answer 2

Small tungsten target embedded in copper Large potential difference between anode & cathode– e.g. 70kV -ve electrons bombard +ve anode High energy electrons come to sudden stop ordecelerate & energy form changes 99% HEAT 1% X-RAYS

Question 3

what are the 2 types of x-ray spectra?

Answer 3

1) continuous spectrum
2) characteristic spectrum

Question 4

describe continuous spectrum

Answer 4

• bremsstrahlung (Bremsstrahlung is a very well-known physical phenomenon, used, for example, in any type of radiology equipment. When an electron or a beta particle passes through matter, it slows down, and a fraction of its energy is directly converted into X-rays) or breaking radiation
• wide range of photon energies

Question 5

describe characteristic spectrum

Answer 5

• depends on material used in anode
• emitted by loss of electrons from K & L shells

Question 6

describe continuous spectrum further

Answer 6

Wide range of photon energies Small deflections are most common – many lowenergy photons Little penetrating power – need filtering out Large deflections less likely – few high energyphotons Maximum photon energy directly related to kVacross the x-ray tube

Question 7

describe characteristic spectrum further

Answer 7

Characteristic of anode atom – tungsten Line spectra relating to K and L shells K lines of diagnostic importance with photon energylevels of 58 – 69.5kV (L lines are less than 10kV) X-ray tube needs to be operating above 69.5kV

Question 8

describe scattering

Answer 8

random change in direction after hitting something

Question 9

describe absorption

Answer 9

deposition of energy in tissues

Question 10

describe intensity

Answer 10

number of x-ray photons in a defined area of the beam

Question 11

describe attenuation

Answer 11

reduction in intensity of beam due to scattering & absorption

Question 12

describe ionisation

Answer 12

removal of electron from neutral atom to give electron & positive ions

Question 13

describe penetration

Answer 13

the ability of photons to pass through or into tissues/materials

Question 14

what are x-ray interactions?

Answer 14

• completely scattered with no loss of energy
• absorbed with total loss of energy
• scattered with some absorption & loss of energy
• transmitted unchanged

Question 15

describe the properties of x-rays 1

Answer 15

• travel in straight lines in free space
• x-ray photons form a divergent beam
• can travel through a vacuum
• penetrate matter
• can be absorbed
• can be scattered

Question 16

describe the properties of x-rays 2

Answer 16

• not detectable by human senses
• produce a latent image on film emulsion
• cause ionisation
• can cause biological damage
• cause certain salts to fluoresce & emit light

Question 17

what is the radiation dose?

Answer 17

is the amount of radiation absorbed by the patient
- low energy photons often are absorbed by soft tissues

Question 18

describe electromagnetic radiation

Answer 18

• divided into ionising & non-ionising radiation
• properties depend on the wavelength
• some properties are harmful to living tissues
• biological harm is not limited to ionising radiation