Radiation physics
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Transcript of Radiation physics
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Physics Applied to Radiology
Chapter 5 Chapter 5
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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
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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
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Electromagnetic Spectrum Chart
ultraviolet
10
10
10
10
10
10
10
10
5
0
-5
-10
-15
-20
energy (eV) frequency (Hz)
1025
1020
1015
1010
105
100
10-5
wavelength (m)
10
10
10
10
10
10
10
-15
-10
-5
0
5
10
15
xray
infrared
microwave
TV/FM radio
radio
long waves
gamma
light
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EMS RelationshipsWhich of the following has the highest energy?
Radio waves or visible light
frequency = 3.2x1019Hz or 4.9x1014Hz
wavelength = 8.5x10-6m or 4.2x10-12m
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EMS Relationships (cont.)
Which of the following has the longest wavelength?
microwave or ultraviolet waves
energy = 2.3x10-5eV or 57keV
frequency = 3.1x108Hz or 8.9MHz
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EMS Relationships (cont.)Which of the following has the lowest frequency?
Red light or yellow light
energy = 980 eV or 6.25x10-2keV
wavelength = 8325 mm or 4.78x10-3m
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General Characteristics of EMS no mass or physical form travel at speed of light (c) in a vacuum (or air)
c = 3 x 108 m/s travel in a linear path (until interaction occurs)
dual nature: wave vs. particle unaffected by
electric or magnetic fields gravity
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Characteristics (cont.) obeys the wave equation
c = obeys the inverse square law
I1d12 = I2d2
2
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EM Interactions with Matter sections may overlap general interactions with matter include
scatter (w or w/o partial absorption) absorption (full attenuation)
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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
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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
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PARTICLE vs. WAVE (in general) Wave
extended in space always in motion repeating
Particle (mass) localized in space moving or stationary
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Wave Characteristics cycle:
one complete wave form or repetition
crest
trough
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Wave (cont.) amplitude
max. displacement from equilibrium
+
-
0
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Wave (cont.) wavelength
distance traveled by wave
= d/cycle Unit meter
m
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Wave (cont.) frequency f or
number of cycles per unit time
Unit hertz Hz #/t Example below: 2 cycles/s = 2 Hz
time = 1 s1 2
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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
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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
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Mathematical Relationships for EM Waves wave equation
general: v = forv EM radiation: c = for c
constant velocity at c
v = c = 3x108m/s
of EM are inversely proportional
for vice versa
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Inversely Proportional as one goes up other goes down
v = fsame 100 = 1 100100 = 2 50100 = 4 25100 = 5 20100 = 10 10
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Example An x-ray photon has a wavelength of 2.1nm.
What is its frequency?f= 2.1x10-9m c = 3x108m/s
c = f
f= c / = [3x108m/s] / [2.1x10-9m]
= 1.428571428571 x 1017 /s
= 1.4 x 1017 Hz
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Example #2 A radio station broadcasts at 104.5 MHz.
What Is the wavelength of the broadcast?
= ?? 104.5 x 106 /s = [c = 3 x 108 m/s]
c = f= c / f= [3 x 108 m/s] / [104.5 x 106 /s]
= 0.028708134 x 102 m
= 2.871 m
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Example #3 What it the frequency of microwave
radiation that has a wavelength of 10-4 m?
f= ?? 1 x 10-4m = [c = 3 x 108 m/s]
c = f= c /
= [3 x 108 m/s] / [1 x 10-4m ]
= 3 x 1012 Hz
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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
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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
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Example What is the energy (keV) of an x-ray photon
with a frequency of 1.6 x 1019 Hz?
E = ?? 1.6x1019Hz = f [h = 4.15 x 10-15 eVs]
E = h f
= [4.15 x 10-15 eVs] [1.6 x 1019 Hz]
= 6.64 x 104 eV
= [6.64 x 104 eV] / [103 ev/keV ]
= 6.64 x101keV = 66 keV
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Example #2 What is the energy in MeV of an x-ray
photon with a frequency of 2.85 x 1021 Hz?
E = ?? 2.85x1021Hz = f [h = 4.15 x 10-15 eVs]
E = h f= [4.15 x 10-15 eVs] [2.85 x 1021 Hz]= 11.8275 x 106 eV
= [11.8275 x 106 eV] / [106 ev/MeV]= 11.8 MeV
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Wave & Particle Theories Combined
= inverse relationship =
E & = direct relationship = E
E & should have ??? .
inverse relationship = E
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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 108m/s]
m
[12.4 x 10-7 eVm]
m
hcm
EeV =
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Shortcut FormulaeEeV = hc/ = [12.4x10-7eVm] / m
by incorporating changes in prefixes you can
arrive at the following shortcut formulae:
[12.4 keV A]
A
EkeV = A = 10-10m
[1.24 keVnm]
nm
EkeV = nm = 10-9m
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ExampleWhat is the of an 85 keV x-ray photon?
?? 85 keV = energy need h & c
EeV= hc m
m = [4.15 x 10-15eVs] [3 x 108m/s] EeV
= [12.4x10-7eVm] 85 x 103 eV
= 0.1458823529412 x 10-10m = .15 x 10-10m or .15A
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Shortcut method?? 85 keV = energy
shortcut h & c
EkeV = 12.4 / A
A = 12.4 / EkeV
= 12.4 / 85
= 0.1458823529412
= .15 A
EkeV = 1.24 / nm
nm = 1.24 / EkeV
=1.24/85
= 0.01458823529412
= .015 nm
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Example #2What is the energy of a .062nm x-ray photon?
keV = ?? .062 nm = nm shortcut h & c for nm
EkeV = 1.24 / nm
= 1.24 / .062 nm
= 20 keV
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Matter and Energy Relativity Formula
2cmE Enables calculation of matter equivalence
for any photon Must convert E in keV to E in J
1 J = 6.24x1018eV
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Relativity problem example: What is the matter equivalence of a 86keV x-ray photon?
? = mass E = 86keV [c = 3x108 m/s]
kg
kg
J
eV
c
EmcmE
sm
sm
eVJ
32
32
16
15
28
1024.613
22
104.1
104250.1
109
108205.1
103
1086
2
2
18
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Relativity problem example: How many electron-volts are contained in .25kg of matter?
? = E m = .25 kg [c = 3x108 m/s]
eV
J
eVJ
J
kg
cmE
s
mkg
sm
35
1816
1616
28
2
104.1
1
1024.61025.2
103.21025.2
)103(25.
2
2