electromagnetic waves and x-ray creation

Question 1

gamma rays (10^-12m - 10^-16m)

Answer 1

• highest energy photons and have extremely short wavelength
• generated by changes in energy levels of the nucleus of atom
• used in nuclear medicine and PET scans

Question 2

x-rays

Answer 2

• 10^-10m
• high energy photons
• generated by deceleration of fast moving e-s
• generated by changed in energy of innermost orbital e-s of atoms
• gamma n x are detected by photography, ionisation chamber and phosphorescence

Question 3

properties of gamma and x

Answer 3

• penetrate matter
• ionise gas (remove e-s)
• cause fluorescence
• photoelectric emissions from metals
• reflected and diffracted by crystals

Question 4

uv radiation

Answer 4

• 10^-8 m - 10^-9 m
• detected with light sensitive circuits (CCDs, photography and fluorescence
• absorbed by glass
• causes chem reactions e.g sun damage- skin damage
• the ionosphere, ayer high in atmosphere, was created by UV radiation from sun ionising atoms in this layer
• generated by orbital e-s of atoms
• also by sun and generated mercury vapour lamps

Question 5

infrared radiation

Answer 5

• 10^-6m
• generated by outer e-s in atoms and molecules and changes in vibrational and rotational energies of molecules (all bonds between atoms vibrate and the freq of vibrations is characteristic of atomic bones involved
• makes colourful images depicting elevated skin temp
• night sights use IR radiation, thermal cameras

Question 6

microwaves

Answer 6

• 10^-4 m - 10^-1m
• emerging biomedical imaging modality
• noninvasive assessments of functional and pathological conditions of soft tissue
• ultrawide band microwave imaging is promising method for detection of breast cancer

Question 7

radio waves

Answer 7

• 10^3m
• astronomy
• MRI
• communication
• generated by oscillating e-s in special circuits to radioactive aerials (the transmitter)
• tuned oscillatory circuit (radio receiver)

Question 8

electromagnetic waves

Answer 8

• single frequency EM wave exhibit a sinusoidal variation of electric and magnetic fields in space
• magnetic variation is perpendicular to electric field
• EM waves travel in straight lines

Question 9

electromagnetic wave description

Answer 9

• sinusoidal wave
• amplitude- height of wave
• wavelength- length of one cycle
• frequency- cycles per second

Question 10

electromagnetic wave equation

Answer 10

c=f x lambda

c= speed of wave (ms-1)
f= frequency (Hz)
lambda= wavelength

Question 11

energy of electromagnetic radiation equation

Answer 11

E= h x f
h= plancks constant (6.626x10^-34)
f= frequency

Question 12

photon

Answer 12

• think of light as a series of particles or photons
• elementary particle
• em radiation therefore consists of discrete quantises packets of energy which we call photons
• no mass, no electric charge and does not decay spontaneously
• consists of oscillating electric field component E and oscillating magnetic field component B

Question 13

inverse square law

Answer 13

• expresses the way radiation energy propagates though space
• E= I / r^2
• E= energy
• I= radiation intensity
• r= distance from source
• rule states that the “power intensity per unit area from a power source, if the rays strike the surface at a right angle, varies inversely according to the square of the distance of the source”

Question 14

x-ray creation

Answer 14

there are 2 types of interactions of electrons with the anode target produce radiation
1. interaction with the atomic nucleus produce bremsstrahung x-ray photons
2. interaction with e- shells which produces characteristic x-ray photons

Question 15

bremsstrahlung spectrum

Answer 15

• energy distribution for a 90 kVp acceleration potential

Question 16

bremsstrahlung radiation

Answer 16

• characterised by continuous distribution of radiation
• referred to as the continuous x-ray spectrum
• an e- with kin energy of 70 keV can lose all, none and any intermediate level of its kin energy in a bremsstrahung interaction
• for e-s with kin energy of 70 keV, the brem. emissions can have an energy in the range of 0-70 keV
• 70keV in joules corresponds to the cut off wavelength

Question 17

bremsstrahlung equation

Answer 17

• E= h x c / lambda
• min lambda=. h x c / E max
• h= plancks
• c=. velocity of em radiation in a vacuum 3 x 10^8ms-1

Question 18

characteristic radiation

Answer 18

• atomic electron from innermost shell is ejected by incoming high energy e-, creating a vacancy in the shell
• e- from next shell drops down to fill vacancy so charactertic x-ray unique to thus element is emitted
• produced a vacancy in that shell- transitions depend on differences in energy between shells

Question 19

x-ray spectrum

Answer 19

2 production processes occur: bremsstrahlung rad. and characteristic x-rays