Space Radiation Radiation Biology Overview

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Space Radiation -Radiation Biology Overview
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Overview

• Composition and Energies of Ionizing Radiation in
  Space
• Electromagnetic v. Particle Interactions with
  Matter
• Biological Impacts of Space Radiation
• Read Online U.N. Text, pages 22 - 36

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Ionizing Radiation in Space

• Ionizing Electromagnetic Radiation
• X-Rays
• Gamma Rays
• Particles
• Mostly protons and electrons
• Large component of alpha particles
• Low flux of HZE particles

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Radiation Energies

• Visible light has an energy of 1 eV
• UV light has an energy of 10 eV, which is
  enough to burn skin
• Gamma Rays have energies of 1012 eV
• Particle energies are typically measured in
  eV/nucleon
• Protons can have energies up to a few hundred MeV
• Electrons have typical energies of keV
• HZE particles can have energies of GeV/nucleon
• Neutrons

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Electromagnetic RadiationInteraction with Matter

• Primary modes of interaction
• Photoelectric Effect
• Compton Scattering
• Pair Production
• Diffuse energy deposition
• Delivers most of energy near surface
• Exponential decline in energy deposition with
  depth

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Charged Particle RadiationInteraction with
Matter

• Interaction described by the Bethe-Bloch Equation
• Typically determined by Coulomb Interactions
• Energy loss proportional to z2/v2
• Penetrates matter in localized tracks
• Secondary particle production furthers the impact
• Most energy deposited at stopping distance,
  called the Bragg Peak

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Linear Energy Transfer

• Energy Deposition per Unit Path Length
• For biological purposes, LET in water is
  typically used

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What happens to a cell when it is struck by an
energetic proton?
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Biological Impact of Ionizing Radiation

• Production of free radicals
• Reactive molecules cause either oxidation or
  breakage of chemical bonds in DNA
• Direct interaction of particle with DNA
• Breaks DNA molecule again
• Cellular level impacts
• Cell Death
• Cause Mutations
• Induce Cancer

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DNA Damage

• Radiation can cause the following changes in DNA
• Changed or deleted base pairs
• Breaking H-bond between base pairs
• Breaking DNA strand(s)
• Creating cross-links
• Any change in base pairs can result in mutation

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DNA Damage

• Direct Interactions take place within 10-15 s
• Free Radicals are produced within 10-9 s
• A free radical can only travel 3nm before
  reacting
• The timescale for direct interactions makes it
  difficult for enzymatic DNA repair
• Timescales for free radicals are reparable
• Particle interactions produce unique effects not
  demonstrated by EM radiation

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What is the best measure of radiation risk for
space exploration?
How is dose measured now?
How do we determine the relative effectiveness of
different types of radiation?
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Health Effects

• Acute
• Long-term