Lecture5InteractionofRadiationwithMatter_001

Lecture5InteractionofRadiationwithMatter_001 - LECTURE 5:...

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LECTURE 5: INTERACTION OF RADIATION WITH MATTER All radiation is detected through its interaction with matter! INTRODUCTION: What happens when radiation passes through matter? Emphasis on what happens to emitted particle (if no nuclear reaction and MEDIUM (i.e., atomic effects) RELEVANCE: (1) Detection of Radiation (2) Radiation Safety (3) Environmental Hazards (4) Biological Effects "Radiation Hypochondria" (5) Risk Assessment – Alternative Medicine TYPES OF RADIATION: (1) Positive Ions: X +q , fission, cosmic rays, beams (2) Electrons: , IC, Auger, cosmic rays (3) Photons: x-ray uv visible (4) Neutrons: nuclear reactors, nuclear weapons, accelerators
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I I. Posi A. B. itive Ions Definitio Overvie 1. Po R 2. Q a. b. c. Stages o 1. El a. on: Catio ew ossible inte esult: ion- ualitative P v I < < c Mass (io Trajector Analogy of Energy lectronic S Stripping n = Z A X eractions: electron c Properties (usually ~ n) > > Ma ry: straigh : bowling Loss Stopping: : Z Aq X ion (e q , whe Nuclei Orbital ollisions d of ion-elec ~ 0.01 0. ss (e ) ; ht line ball – ping v I > > v medium electron se ere q = at l e s dominate in ctron Colli 1 c) Many co g-pong bal e - in ato Z AZ X ; ea) tomic ioniz ~ 10 2 ~ 10 1 nteractions isions ollisions re ll collision omic orbita e.g., 8 16 2 O zation state 24 cm 2 16 cm 2 equired to ns als (95%) ~ ion of p in e stop ion 8 16 8 O ~ 10 8 ;
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i.e., ion loses all electrons (usually) in passing through matter ( X~100 atoms) b. Ion-Electron Collisions Multiple, sequential collisions ; straight-line trajectory c. Medium Effects (1) Ionization Creation of multiple cations (from medium) – electron pairs (2) Electronic Excitation: fluorescence (uv, x-rays, etc.) (3) Molecular Dissociation (free radical formation) 2. Intermediate Stopping: v I v e (inner shells) a. Pickup: Incident ion begins to pick up electrons from stopping medium. K-shell first, since they have highest velocity (binding energy). b. Moderate Directional Changes (Dramatic size increase) O +e - v(1s) e - e - 87 5        6 O 1,0 1 s 1 1s 2 1s 2 2s 1 1s 2 2s 2 2p 4 1 c. Ion slows down at each step and ionic charge is neutralized 3. Atomic ("nuclear") stopping: v I v e (valence shell) a. Ion charge 1,0
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b. Elastic ion-atom collisions
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Lecture5InteractionofRadiationwithMatter_001 - LECTURE 5:...

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