Fundamentals of Ionizing Radiation

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Fundamentals ofIonizing Radiation

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Radiation Fundamentals

• What is radiation?

• Where does it come from?

• How does it interact with matter?

• What is radioactivity?

• What are fission/fusion?

• How are radiation and radioactivity quantified?

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What is Radiation?

• Radiation Energy in transit

The transfer of energy by waves or particles

• Ionizing Radiation Has sufficient energy to
  produce energetic ions in ordinary matter

Alpha particles, Beta particles, Gamma X-rays,
Neutrons

• Non-Ionizing Radiation Does not produce
  energetic ions

Radio, Microwaves, UV, IR, Visible
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Radiation Interaction byIonization
Electron ejected from orbit
Ion
Ion
- Ion
- Ion
Ionizing radiation
Ionizing radiation
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Atoms and Radiation
Typical Atomic Radius 10-10 m
Typical Ionizing Radiation Wavelength 10-11 m
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Electromagnetic Spectrum
Particles can also be described by a wave
function !
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Matter And Energy
E mc2

Proton
938 MeV
Neutron
939 MeV
-
0.511 MeV
Electron
(typical)
0.1 - 1 MeV
Photon
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Matter Energy
Neon-20 20Ne
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Protons
(1.007276 amu)
Neutrons (1.008665 amu)
Electrons (0.0005486 amu)
Binding Energy
Actual Atomic Mass
0.172462 amu
Total Rest Mass

160 MeV
20.164896 amu
19.992434 amu
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Where Does Radiation Come From?
Nuclear Decay - Radioactivity
Atomic Processes - X-rays
Nuclear Processes
Fission
Fusion
Others
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Nuclear Decay - Radioactivity
Radioactivity The spontaneous transformation
(decay) of unstable nuclei, resulting in a more
stable daughter, accompanied by emission of
ionizing radiation Radioactive Material A
substance in any physical form that contains
unstable atoms, and therefore emits ionizing
radiation Radioisotope (radionuclide) An
unstable, radioactive isotope of an element.
Well over 2000 radioisotopes have been identified.
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Radioactivity a Decay
Daughter Nucleus Np-237 Th-234 Ra-228 Rn-222
???????
Parent Nucleus Am-241 U-238 Th-232 Ra-226
Alpha Particle (Helium Nucleus) (4.00147 amu)
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Radioactivity ?- Decay
Daughter Nucleus Nickel -60 Calcium-40
?
Antineutrino
Parent Nucleus Cobalt -60 Potassium-40
??
Beta Particle (electron)
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Radioactivity ? Decay
?
Daughter Nucleus Boron-11 Carbon-13
Neutrino
??

e
ionization
-
e
Positron Particle (Positive electron)
Parent Nucleus Carbon-11 Nitrogen-13
A Y ?? ??
Annihilation Radiation
A X
z
Z-1
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Radioactivity Electron capture
Gamma ray
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Gamma Emission
??
Daughter Nucleus Nickel-60
Parent Nucleus Cobalt-60 (Beta decay)
Gamma Rays
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Radioactive Half-life
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Nuclear Reactions - Fission
Induced fission
slow neutron
Neutrons
Fission Products
Original Nucleus Uranium-235
Each fission event releases 200 MeV
As kinetic energy
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Nuclear Reactions - Fusion
deuterium-tritium fusion
Each fusion event releases 17.6 MeV
As kinetic energy
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Atomic Processes X-rays
Bremsstrahlung Radiation
High-energy electron
Deflected (slowed) electron
X-Ray
Energy is conserved when x-ray is emitted Kinetic
energy is converted to radiative energy
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Comparison of Radiation Types
Lead
Concrete
Paper
Plastic
Alpha
??
Beta
?
Gamma and X-rays
g?
Neutron
n
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Radioactivity Calculation
Related Formulae A N?
N number of radioactive atoms A
activity in decays per unit time ? decay
constant (probability of atom decaying
per unit time) 0.693
At Ao e-(? t ) At activity at some
time, t Ao activity at time t 0
e base of the natural log
T½
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Units for Exposure and Dose

• Exposure Generically, exposure is the
  condition of being exposed. Exposure is also
  used to quantify the amount of ionization
  produced by photons as they pass through air. The
  unit of exposure is the Roentgen (R).
• 1R 1 esu/cc in air
• Absorbed Dose Absorbed dose is the amount of
  energy deposited in any material by ionizing
  radiation. The unit of absorbed dose used in the
  U.S., the rad, is a measure of energy absorbed
  per gram of material. The S.I. unit is the Gray
  (Gy). One Gray equals 100 rad.
• 1Gy 1 J/kg in any material
• Dose Equivalent A special concept relating
  absorbed dose to biological detriment. In the
  U.S. the unit is the rem. The S.I. unit is the
  Sievert (Sv). One Sievert equals 100 rem.

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Converting Absorbed Dose to Dose Equivalent

• The quality factor takes into account the
  relative amount of biological harm done by the
  various types of radiation.
• It is usually denoted by Q.
• Absorbed dose (D) is related to dose equivalent
  (H) through the formula
• H QD
• Thus, rem rads x Q and
• Sv Gray x Q