Download RAD 254 Chapt 5 Electromagnetic Radiation

RAD 254 Chapt 4/5
Electromagnetic Radiation
• Photons
– No mass/charge
– Have velocity, frequency, wavelength &
amplitude
– Follow the “duality theory”
– Travel in discrete bundles of energy
“Quantum”
• Velocity is the speed of light
– 3 X 1010 cm/sec OR 3 X 108 m/sec
– Is the smallest quantity of any type
e/m/radiation
– Have both electric (A/C) and magnetic
qualities
– Travel as sine waves
Units of electromagnetic concerns
• Amplitude = height of the sine wave
• Frequency (f) = length of successive
points in the sine wave/cm
– As frequency goes up, so does energy
(energy is DIRECTLY proportional to
frequency)
• As velocity decreases, so does frequency
– Velocity = frequency X wavelength
V=f X λ
Electromagnetic Spectrum
• Three ranges : visible light, RF, X-ray
– All travel the speed of light, but may have differing
frequency and wavelength
– Visible light is I’d by it’s wavelength, RF by it’s
frequency, and x-rays by energy
– Radiation can be ionizing or non-ionizing
• Non-ionizing can be reflected as well as absorbed
• Ionizing cannot be reflected BUT can be absorbed and/or
scattered
• Absorbed = attenuated
– Radiolucent vs. Radiopaque
Inverse Square Law
• Radiation intensity is inversely related to
the square of the distance from the source
• I1 (D2)2
• I2=(D1)2
DRAW THE PICTURE
FILL IN THE KNOWNS/UNKNOWNS
SOLVE
DO A “QUICK MENTAL CHECK”
Planck’s Quantum Equation
• E = h X f ( e= photon energy, h = Planck’s
Constant and f= photon energy in hertz)
• Planck’s Constant = 6.63 X 10-34 J/sec
(or 4.15 X 10-15 eVs)
Photon Energy
• Photon energy is directly proportional to its
frequency
• Photon energy increases as wavelength
decreases
• Photon energy increases as kVp increases
Electricity & Magnetism
The PRIMARY purpose of an x-ray tube is
to convert electric energy into
ELECTOMAGNETIC RADIATION
Laws of electrostatics
• Unlike charges attract
• Like charges repel
• Electrostatic force is DIRECTLY
proportional to the product of the charges
and the SQARE of the distance between
them
• When objects are electrified, the charges
are distributed throughout the object –
BUT tend to be greatest at “pointed” spots
Electric terms
• Electrodynamics = study of electron flow in
MOTION (current – AMP)
• Conductors = Matter that CONDUCTS
electrical current
• Insulators – Matter that INHIBITS current
flow
– Semi-conductor = depending on conditions, can
be either
• Superconductor = like an MRI unit low
resistance (niobium/titanium)
Electric Terms, con’t
• Electric Potential = Volt (V)
• Resistance = Increasing electric resistance
(ohm’s) = LESS current flow in amps (A)
• Ohm’s law = voltage across the total circuit
is equal to the CURRENT X the resistance
• (V= IR) I=current in amps; R= resistance in
ohms; V= potential in volts
• WATT(W) = measurement of electrical
power
Current
• Direct Current (DC) electron flow in only
one direction
• Alternating Current (AC) sinusoidal form
each way (+ & -)
– Magnetism and AC are very closely related
(+/- or N-S pole charges)
– Magnets are classified according to their
origin (natural, permanent, electromagnet)
Magnetic Laws
• Every magnet has TWO poles
• Like poles repel – unlike poles attract
• Magnetic charges and lines may be induced
– Magnetic lines are ALWAYS closed
– Magnetic force and the distance from the
magnet are INVERSELY proportional to the
square of the distance – BUT the attraction is
GREATEST at the POLES rather than the
sides of the magnet