basic radiation interactions, definition of dosimetric ... ?· basic radiation interactions,...

Download Basic Radiation Interactions, Definition of Dosimetric ... ?· Basic Radiation Interactions, Definition…

Post on 04-Dec-2018

213 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Basic Radiation Interactions,Definition of Dosimetric Quantities,

    and Data Sources

    J.V. SiebersVirginia Commonwealth University

    Richmond, Virginia USA

    2009 AAPM Summer School2009 AAPM Summer School

  • Learning Objectivesg j

    T i d d ib th b i f 1. To review and describe the basics of radiation interactions for understanding radiation dosimetry

    2 To review definitions of quantities 2. To review definitions of quantities required for understanding radiation dosimetrydosimetry

    JVS: 2009 AAPM SS

  • Constants Units Conversions

    JVS: 2009 AAPM SS

  • JVS: 2009 AAPM SS

  • ScopeRadiation Types

    IonizingIonizingInteractions can remove atomic orbital electrons Non-Ionizing

    Particulate ElectromagneticParticulate-electron-positron

    Electromagnetic

    -proton-neutron- alpha

    JVS: 2009 AAPM SS

    p- etc.

  • Types of ionizing radiationyp g

    Di tl i i i di ti Directly ionizing radiation Direct interactions via the Coulomb force along a

    particles track Charged particles

    electrons positrons

    protons protons heavy charged particles

    JVS: 2009 AAPM SS

  • Direct IonizationCoulombic Interaction

    e-Coulombic Interaction

    A charged particle exerts exerts electromagnetic forces on atomic Energy transfer can electrons result in the ejection

    of an electron (ionization) (ionization)

    JVS: 2009 AAPM SS

  • Indirectly Ionizing Radiationy g

    Uncharged particles that must first transfer energy to a charged particle which can then further ionize matterT t Two step process

    ExamplesEl t ti di ti Electromagnetic radiations: x- or -rays

    Neutrons

    JVS: 2009 AAPM SS

  • Indirectly Ionizing RadiationPh t l t i Eff tPhotoelectric Effect

    e-

    Ej t d

    hEjected

    electrons further ionize ionize matter

    JVS: 2009 AAPM SS

  • Radiant Energy Rgy

    R Total energy excluding rest mass R Total energy, excluding rest mass, carried by particles Photons: E = h = hc/ Electrons + other CPs: kinetic energy T

    JVS: 2009 AAPM SS

  • Energy imparted

    - Energy impartedR R Q - Energy imparted i l i

    in outR R Q Q mass to energy conversion resultingfrom interactions or radioactive decayQ

    if(mE), Q>0

    inR outRhe-

    he-

    JVS: 2009 AAPM SS

    if(Em), Q

  • Dose

    GydD

    Energy deposited per unit mass

    ydm

    Energy deposited per unit mass

    1 Gy = 1 J/kg

    Knowledge of D is the object of dosimetry

    JVS: 2009 AAPM SS

  • Equilibrium Part 1: R di ti E ilib iRadiation Equilibrium

    R Rh

    e-

    in outR Rhe- e-

    hhe-

    R R QQ d Qd RE in outR R Q Q d QdDdm dm

    RE RE

    JVS: 2009 AAPM SS

  • Radiation SourcesS

    Radioactive decay Radioactive decay Alpha-decay Beta-decay Electron capture Electron capture Isomeric transitions

    Accelerated charged particles Direct Direct X-ray generators

    Atomic energy transitionsCharacteristic X rays Characteristic X-rays

    Auger electrons Interaction products

    JVS: 2009 AAPM SS

  • Radioactive Decayy

    General balance equationsGeneral balance equationsR R

    R R

    A A AAZ Z Z ZP D R Q

    P D RQ M M M

    JVS: 2009 AAPM SS

  • Q

    JVS: 2009 AAPM SS

  • Radioactive Decay

    ActivitydNA Ndt

    0t

    tA A e

    1ln 2t

    JVS: 2009 AAPM SS

    12

  • Radioactive Decay

    4 42 2A AZ ZP D He Q

    s have short range /

    01 1A AZ ZP D Q

    01 1A AZ ZP D Q

    Neutrino ( , ) results in spectrum of energies( ) p g maxE and E are tabulated ( , ) are non-ionizing

    Electron Capture 0A AP D Q 01 1A AZ ZP e D v Q

    Can occur when energetically prohibited Followed by characteristic x-rays or Auger electron

    Isomeric Transition so e c a s o * 00

    A AZ ZP P Q

    decay from meta-stable state Internal Conversion

    * 0 0A AP P Q

    JVS: 2009 AAPM SS

    0 01 1A AZ ZP e P e Q

    Competes with isomeric transition Results in ejection of atomic electron

  • JVS: 2009 AAPM SS

  • 15 15 0 0 1 732O N M V + 15 15 0 08 7 1 0 1.732O N MeV

    15 0 15 08 1 7 0 1.732O e N MeV Electron Capture

    +

    JVS: 2009 AAPM SS

    8 1 7 0Capture

  • JVS: 2009 AAPM SS

  • Accelerated Charged Particlesg

    Di t Direct use Electrons, protons,

    Indirect via production of electromagnetic radiationradiation Synchrotron radiation Bremmstrahlung Bremmstrahlung

    JVS: 2009 AAPM SS

  • Synchrotron Radiation

    hRadiation

    Magnetic Field

    e-

    JVS: 2009 AAPM SS

    Synchrotron image courtesy of http://www-project.slac.stanford.edu/ssrltxrf/spear.htm

  • Bremmstrahlungbremsh

    Bremmstrahlungbrems

    e-

    JVS: 2009 AAPM SS

  • Atomic Energy TransitiongyCharacteristic x-ray

    xray h

    JVS: 2009 AAPM SS

  • Atomic Energy TransitionAuger Electron

    e-

    JVS: 2009 AAPM SS

  • Quantifying Radiation FieldsQ y g

    Th f Thus far R D

    JVS: 2009 AAPM SS

  • Radiation Fluence

    N is number of particles i h

    dN particles crossing sphere surrounding P with cross-sectional area da

    2

    pda m

    sectional area da

    Integrated over all directions and energies

    Single particle type

    JVS: 2009 AAPM SS

  • Equivalent definition of fluenceq

    l = particle track l l = particle track length through a volume

    nTracksl

    V

    l need not be straight

    Volume can be irregularU f l f M t Useful for Monte Carlo applications

    JVS: 2009 AAPM SS

  • Energy Fluencegy Definition

    dR J 2

    dR Jda m

    Poly-energetic Mono-energetic

    da m

    E Diff ti l fl

    EE E dE E Differential energy fluence

    E E d dE JVS: 2009 AAPM SS

    E E d dE

  • Attenuation

    td n dl tl 0e

    l 1n JVS: 2009 AAPM SS

    l 0 tn m

  • Attenuation coefficient l 0e

    l

    Attenuation coefficient

    t th i t ti ( l) f represents the interaction (removal) of primaries from the beam

    No consideration is given to what occurs as a result of the interaction Secondary particles Energy-to-mass conversion

    To remove density dependence, tabulated as /[ 2/ ]

    JVS: 2009 AAPM SS

    [cm2/g]

  • TERMA Total Energy Release per unit MAss

    Jkg

    TERMA

    *

    Describes loss of radiant energy from uncharged

    kg

    primaries as they interact in material Energy lost can be absorbed locally or at a distance

    JVS: 2009 AAPM SS J

    kgEE

    ETERMA E dE

    For poly-energetic spectra*

  • Aside:Photon InteractionsPhoton Interactions

    To understand what happens with the radiant energy removed, understand the interactions(e.g. interactions)

    JVS: 2009 AAPM SS

  • Photon interactions contributing to Photon interactions contributing to

    -1mRayleigh

    = Rayleigh + Compton scattering = Rayleigh + Compton scattering = photo-electric = pair production = pair production = photo-nuclear

    JVS: 2009 AAPM SS

  • Rayleigh Scatteringy g S g

    Elastic coherent scattering of the photon by an atomy

    Important for low energy photonsC t ib t < 20% t t t l tt ti Contributes < 20% to total attenuation coefficient

    JVS: 2009 AAPM SS

  • Compton ScatteringCompton Scatteringe-

    h

    e

    h

    h 2cmAN Z

    JVS: 2009 AAPM SS

    ge A

  • Comptonp

    JVS: 2009 AAPM SS

  • Photoelectric EffectPhotoelectric Effect

    e-

    h b AeT h E T beT h E

    JVS: 2009 AAPM SS

  • Photo-electric

    3 4

    2 3Zh

    Au

    increases when increases when shell can participate in reactionreaction

    JVS: 2009 AAPM SS

  • Pair ProductionPair Production

    e-h

    +

    pairh

    e+22 ee eavailT T T h m c ee eavail

    2

    diom c

    JVS: 2009 AAPM SS

    radianoT

  • Triplet ProductionTriplet Production

    22avail eT h m c

    e-

    e- tripleth

    e+22h

    JVS: 2009 AAPM SS

    223

    eh m cT

  • Photo-nuclear interactions

    ( n) ( Xn) ( p) (,n), (,Xn), (,p),

    BE (Binding Energies) result in thresholds >~ 10 MeV

    Cross-section is small (

  • JVS: 2009 AAPM SS

  • Pb attenuation coefficient

    JVS: 2009 AAPM SS

  • Relative importance of interactionsRelative importance of interactions

    JVS: 2009 AAPM SS

  • Summary photon interactions

    JVS: 2009 AAPM SS

  • Energy transferred to charged particlesi t ti

    Energy transferred to charged particles per-interaction

    general nonrtr in outu uR R Q photo

    u u

    = compton pair

    ==

    Averagei

    trn

    JVS: 2009 AAPM SS

    itr

    in

  • RecallAttenuation coefficient

    l 0el

    Attenuation coefficient represents the interaction (removal) of represents the interaction (removal) of

    primaries from the beam No consideration is given to what occurs as a No consideration is given to what occurs as a

    result of the interaction Secondary particles Secondary particles Energy-to-mass conversion

    To remove density dependence, tabulated as /[cm2/g]

    JVS: 2009 AAPM SS

  • Mass-energy transfer coefficient

Recommended

View more >