• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Radiation physics
 

Radiation physics

on

  • 2,532 views

 

Statistics

Views

Total Views
2,532
Views on SlideShare
2,523
Embed Views
9

Actions

Likes
0
Downloads
79
Comments
0

2 Embeds 9

http://www.slideshare.net 8
http://translate.googleusercontent.com 1

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Radiation physics Radiation physics Presentation Transcript

    • Physics Applied to Radiology Chapter 5
    • Electromagnetic Energy Spectrum
      • continuous range of energy
        • spectrum indicates that the distribution of energies exist in an uninterrupted band rather than at specified levels
      • released by accelerating charged particles
        • moves through space or matter as oscillating magnetic & electric fields
          • needs no carrier medium but can have one
          • can penetrate or interact with matter
    • Electromagnetic Spectrum
      • transverse energy waves traveling as magnetic & electric fields  to each other
        • maxima and minima of wave occur simultaneously
        • unlike other waves, needs no carrier
    • Electromagnetic Spectrum Chart light
    • EMS Relationships
      • Which of the following has the highest energy?
        • Radio waves or visible light
        • frequency = 3.2x10 19 Hz or 4.9x10 14 Hz
        • wavelength = 8.5x10 -6 m or 4.2x10 -12 m
    • EMS Relationships (cont.)
      • Which of the following has the longest wavelength?
        • microwave or ultraviolet waves
        • energy = 2.3x10 -5 eV or 57keV
        • frequency = 3.1x10 8 Hz or 8.9MHz
    • EMS Relationships (cont.)
      • Which of the following has the lowest frequency?
        • Red light or yellow light
        • energy = 980 eV or 6.25x10 -2 keV
        • wavelength = 8325 mm or 4.78x10 -3 m
    • General Characteristics of EMS
      • no mass or physical form
      • travel at speed of light ( c ) in a vacuum (or air)
        • c = 3 x 10 8 m/s
      • travel in a linear path (until interaction occurs)
      • dual nature: wave vs. particle
      • unaffected by
        • electric or magnetic fields
        • gravity
    • Characteristics (cont.)
      • obeys the wave equation
        • c =   
      • obeys the inverse square law
        • I 1 d 1 2 = I 2 d 2 2
    • EM Interactions with Matter
      • sections may overlap
      • general interactions with matter include
        • scatter (w or w/o partial absorption)
        • absorption (full attenuation)
    • EM Interactions (cont.)
      •  probability if matter size  the wavelength
        • examples:
          • radiowaves vs. TV antena
          • microwaves vs. food
          • light vs. rods & cones in eye
          • x rays vs. atom
      • ionization occurs only EM energy > 33 to 35 eV
        • high ultraviolet, x-ray, gamma
    • Dual Nature of EM Radiation
      • continuously changing force fields
        • energy travels as sine WAVE
        • macroscopic level
      • photon or quantum
        • small bundle of energy acting as a PARTICLE
        • microscopic level
    • PARTICLE vs. WAVE (in general)
      • Wave
        • extended in space
        • always in motion
        • repeating
      • Particle (mass)
        • localized in space
        • moving or stationary
    • Wave Characteristics
      • cycle:
        • one complete wave form or repetition
      crest trough
    • Wave (cont.)
      • amplitude
        • max. displacement from equilibrium
      + - 0
    • Wave (cont.)
      • wavelength 
        • distance traveled by wave
        •  = d/cycle
        • Unit meter
       m
    • Wave (cont.)
      • frequency f or 
        • number of cycles per unit time
        • Unit hertz Hz #/t
        • Example below: 2 cycles/s = 2 Hz
      time = 1 s 1 2
    • Wave (cont.)
      • For the wave depicted below, determine the frequency and wavelength.
        • t = 25 ms d = 58 nm cycles = 4.5
        • f = #/t = 4.5 cycles/25 ms = 4.5/25 x10 -3 = 180 Hz
        •  = d/cycle = 58 nm/ 4.5 cyc. = 58 x 10 -9 /4.5 = 1.3 x 10 -8 m
      time = 25 ms d = 58 nm
    • Wave (cont.)
      • velocity v (general) c (EM radiation)
        • speed each cycle travels
        • Unit m/s
      • total distance wave moves in time period
      • v of EM radiation always = c
    • Mathematical Relationships for EM Waves
      • wave equation
        • general: v =  f  or  v 
        • EM radiation: c =  f  or c    
          • constant velocity at c
            • v = c = 3x10 8 m/s
      •  of EM are inversely proportional
        •       f    or vice versa 
    • Inversely Proportional
      • as one goes up other goes down
        • v =   f
        • same   
        • 100 = 1 100
        • 100 = 2 50
        • 100 = 4 25
        • 100 = 5 20
        • 100 = 10 10
    • Example
      • An x-ray photon has a wavelength of 2.1nm. What is its frequency?
        • f    = 2.1x10 -9 m c = 3x10 8 m/s
        • c =   f
        • f  = c / 
        • = [3x10 8 m/s] / [2.1x10 -9 m]
        • = 1.428571428571 x 10 17 /s
        • = 1.4 x 10 17 Hz
    • Example #2
      • A radio station broadcasts at 104.5 MHz. What Is the wavelength of the broadcast?
        •  = ?? 104.5 x 10 6 /s =  [c = 3 x 10 8 m/s]
        • c =  f 
        •    = c / f  = [3 x 10 8 m/s] / [104.5 x 10 6 /s]
        • = 0.028708134 x 10 2 m
        • = 2.871 m
    • Example #3
      • What it the frequency of microwave radiation that has a wavelength of 10 -4 m?
        • f  = ?? 1 x 10 -4 m =   [c = 3 x 10 8 m/s]
        • c =  
        • f  = c / 
        • = [3 x 10 8 m/s] / [1 x 10 -4 m ]
        • = 3 x 10 12 Hz
    • Particle Nature (Quantum Physics)
      • Photon (quantum)
        • view as if a single unit of EM radiation
        • indivisible
      • Views EM radiation as a particle
        • "bundle of energy"
        • acts like a particle (but is not particle)
      • relates E to  (direct relationship)
        • "count" # of photons per unit time
        •   f =  E
    • Mathematics
      • E  f
      • E = h f  
          • h = Planck’s constant
          • = 4.15 x 10 -15 eVs
      • units
        • usual energy units = J
        • EM energy units = variation of J
          • [eVs][/s] = eV
          • x rays & gamma rays usually in keV or MeV
    • Example
      • What is the energy (keV) of an x-ray photon with a frequency of 1.6 x 10 19 Hz?
        • E = ?? 1.6x10 19 Hz = f [h = 4.15 x 10 -15 eVs]
        • E = h f
        • = [ 4.15 x 10 -15 eVs] [ 1.6 x 10 19 Hz]
        • = 6.64 x 10 4 eV
        • = [6.64 x 10 4 eV] / [10 3 ev / keV ]
        • = 6.64 x10 1 keV = 66 keV
    • Example #2
      • What is the energy in MeV of an x-ray photon with a frequency of 2.85 x 10 21 Hz?
        • E = ?? 2.85x10 21 Hz = f [h = 4.15 x 10 -15 eVs]
        • E = h f
        • = [4.15 x 10 -15 eVs] [2.85 x 10 21 Hz]
        • = 11.8275 x 10 6 eV
        • = [11.8275 x 10 6 eV] / [10 6 ev / MeV ]
        • = 11.8 MeV
    • Wave & Particle Theories Combined
      •    = inverse relationship   =  
      • E &  = direct relationship   =  E
      • E &  should have ??? .
      • inverse relationship   =  E
    • Combination of Wave & Practical Theories
      • combine formulas: c =    E = h  
        • solve wave wave equation for frequency:  = c / 
        •  insert solution in quantum formula:
      [4.15 x 10 -15 eVs] [3 x 10 8 m/s]  m [12.4 x 10 -7 eVm]  m hc  m E eV =
    • Shortcut Formulae
        • E eV = hc/  = [12.4x10 -7 eVm] /  m
        • by incorporating changes in prefixes you can arrive at the following shortcut formulae:
      nm = 10 -9 m  [12.4 keV A]  A  E keV = A = 10 -10 m  [1.24 keVnm]  nm E keV =
    • Example
      • What is the  of an 85 keV x-ray photon?
        •  ?? 85 keV = energy need h & c
        • E eV = hc
        •  m
        •  m = [4.15 x 10 -15 eVs] [3 x 10 8 m/s]
        • E eV
        • = [12.4x10 -7 eVm]
        • 85 x 10 3 eV
        • = 0.1458823529412 x 10 -10 m
        • = .15 x 10 -10 m or .15A
    • Shortcut method
        •  ?? 85 keV = energy
        • shortcut h & c
        • E keV = 12.4 /  A
        •  A = 12.4 / E keV
        • = 12.4 / 85
        • = 0.1458823529412
        • = .15 A
        
        • E keV = 1.24 /  nm
        •  nm = 1.24 / E keV
        • =1.24/ 85 = 0.01458823529412
        • = .015 nm
    • Example #2
      • What is the energy of a .062nm x-ray photon?
        • keV = ?? .062 nm =  nm shortcut h & c for nm
        • E keV = 1.24 /  nm
        • = 1.24 / .062 nm
        • = 20 keV
    • Matter and Energy
      • Relativity Formula
      • Enables calculation of matter equivalence for any photon
        • Must convert E in keV to E in J
        • 1 J = 6.24x10 18 eV
    • Relativity problem example:
      • What is the matter equivalence of a 86keV x-ray photon?
        • ? = mass E = 86keV [c = 3x10 8 m/s]
    • Relativity problem example:
      • How many electron-volts are contained in .25kg of matter?
        • ? = E m = .25 kg [c = 3x10 8 m/s]