Lecture19BiolEffectsofRadiation_001

Lecture19BiolEffectsofRadiation_001 - Lecture 19:...

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Lecture 19: Biological Effects of Radiation I. Radiation Chemistry Interaction of Radiation with Matter: Emphasis on effect of medium on incident radiation Biological Effects of Radiation: Emphasis on effect of radiation on medium A. Chemical Species Formed in Medium 1. Cation-Electron Pairs a. Gases and Liquids mobile ions – facilitates detection e . g . , C H 4  CH 4 + + e biological systems: alters electrolyte balance b. Solids trapped electrons and lattice defects modified conduction bands: impurities, Si bit upsets 2. Free Radicals Bond cleavage CH 4  CH 3 + H a. Radioalysis: Decomposition of compounds; esp. H 2 O, by radiation H 2 O  H + OH H + H H 2 (reducing agent) Body mostly H 2 O OH + OH H 2 O (oxidizing agent) TMI b. Compounds C x H y O z  CO 2 , H 2 O, H 2, etc. recombinants may alter properties – negative or positive Negative: biological alterations (DNA) Positive: cross-linking of polymers (Cook, Inc.) dE/dx AZ 2 /E for charged particles dE/dx E
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3. Excited Atoms and Molecules a . Excitation Fluorescence b. Application Scintillation detectors (both liquid and solid) Widely used in biochemistry and medical sciences for counting 3 H, 14 C, 32 P B. Radiation Dosimetry DOSE – Quantity of Radiation Exposure 1. Rad – Basic unit of radiation dose measurement (Gray – SI unit) = Gy a. Definition: 1 rad = 10 2 J/kg of absorbed material = 100 ergs/g = E mass 1 0 2 J 1 kg 1 eV = 1.60 10 19 J 1 Gy = 1 J/kg = 100 rads (1) Charged particles E = energy of particle if stopped ( d E / d x ) ( x) if transmitted and derivatives anthracene phenathrene stilbene Resonance stabilization ; aromatic hydrocarbons highly susceptible to excitation (good scintillators)
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(2) Photons E = E /cm 2 b. Example: A 2.0 g sample absorbs 1.0 Ci of 100 keV electrons in 10.0 min. What is the dose in rads? E = (1.00 10 5 eV)(1.60 10 19 J/eV)(3.70 10 4 dps)(600 s) E = 3.6 10 7 J Dose = E mass J 2.0 kg kg 10 J -2 36 10 10 7 3 . = 1.8 10 2 rads = 18 mrads=1.8 10 4 Gy 2. Biologically Permissible Doses a. Depends on type of radiation charged ions: dE/dx high ; range low  : dE/dx intermediate ; same for range , n: low dE/dx ; long range b. Quality Factor (QF), or Relative Biological Effectiveness (RBE)
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Lecture19BiolEffectsofRadiation_001 - Lecture 19:...

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