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    Rtfi Notes 2

    Uploaded by

    Ajith Payyanur
    This document discusses the interactions between radiation and matter, including primary radiation, scattered radiation, and three major interaction mechanisms: the photoelectric effect, Compton scattering, and pair production. It also summarizes techniques to minimize radiation exposure, including increasing time and distance from the source, and using shielding. Finally, it provides an overview of film processing steps including development, stop bath, fixing, washing, and drying.

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    Rtfi Notes 2

    Uploaded by

    Ajith Payyanur
    76 views27 pages
    This document discusses the interactions between radiation and matter, including primary radiation, scattered radiation, and three major interaction mechanisms: the photoelectric effect, Compton scattering, and pair production. It also summarizes techniques to minimize radiation exposure, including increasing time and distance from the source, and using shielding. Finally, it provides an overview of film processing steps including development, stop bath, fixing, washing, and drying.

    Original Description:

    inter rt notes

    Original Title

    RTFI NOTES 2 (1)

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    This document discusses the interactions between radiation and matter, including primary radiation, scattered radiation, and three major interaction mechanisms: the photoelectric effect, Compton scattering, and pair production. It also summarizes techniques to minimize radiation exposure, including increasing time and distance from the source, and using shielding. Finally, it provides an overview of film processing steps including development, stop bath, fixing, washing, and drying.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    76 views27 pages

    Rtfi Notes 2

    Uploaded by

    Ajith Payyanur
    This document discusses the interactions between radiation and matter, including primary radiation, scattered radiation, and three major interaction mechanisms: the photoelectric effect, Compton scattering, and pair production. It also summarizes techniques to minimize radiation exposure, including increasing time and distance from the source, and using shielding. Finally, it provides an overview of film processing steps including development, stop bath, fixing, washing, and drying.

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    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
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    You are on page 1of 27

    SCATTERING AND

    CHEMICAL PROCESSING
    PART 2
    Scattered Radiation

    Primary radiation
     Photons which passes
    through matter without
    any interaction

    Scattered radiation
     Photons affected by
    interaction with matter
    Three major interaction mechanisms are:
    • Photoelectric effect .
    • Compton scattering .
    • Pair production.
    Photoelectric Effect
    • Photon impacts on one shell electron(Ground
    state)
    • All Photon energy is transferred to electron.
    • Photon is absorbed (stops existing).
    • when the photon energy is less than 600 keV or
    0.6 MeV
    Compton Scattering
    • From 600 keV to approximately 6 MeV Compton
    scattering predominates.
    Pair Production
    • a high energy photon progress near to atom nucleus
    • Pair production may occurs only above a threshold
    energy of 1.02 MeV
    • Under influence of nucleus energetic field it converts to
    an electron(-1e0 )and positron+1e0 (pair)
    MINIMISE THE EFFECT OF RADIATION
    1. TIME
    2. DISTANCE
    3. SHIELDING

    Distance
    Inverse Square Law
    Half value Layer (HVL)
    Tenth value Layer (TVL)
    • The amount of shielding required to reduce the incident radiation
    levels by 1/10 th is called Tenth value Layer (TVL)
    • Backscatter Control
    • A lead plate (~2 mm) will be placed behind the cassette to protect
    film from Backscatter
    • A lead letter B is attached to the back of the film cassette during
    exposure.
    Backscatter Control
     Backscatter presence is indicated by light image
    of ‘B’ (not acceptable).
     A dark image of ‘B’ does not indicate
    backscatter!!!

         
    Radiographic Film

    Radiographic film is similar to photographic…


    Emulsion contains AgBr grains
    Optical Density
    Optical density = Degree of Darkening the film
    Characteristic Curve
    Characteristic curve – the relationship between optical density and
    exposure.
    Graininess

    Fine grain film Coarse grain film


    Film Speed
    • The coarse grain is faster as it needs less exposure time to reach
    required optical density.
    • The film factor cF serves to compare film speeds
    Film Fog
    • Film Fog may be caused by:
    • Opacity of the film base
    • Incorrect storage (influence of heat, pressure, or unwanted exposure etc.
    • Is reduces the contrast
    • Shall be monitored (maximum acceptable for is usually 0.3D)
    Film Latitude
    • Ability of a radiographic technique to display a wide range of material
    thickness at an acceptable film density.
    • The Latitude is opposite to the Contrast
    Intensifying Screens
    • The following types of the screens are in use:
    • Metallic foil intensifying screens.
    • Fluorescent (salt) screens.
    • Fluoro-metallic screens.
    Metallic Foil Intensifying Screens
    • Metallic screens usually contain Lead (Pb).
    • Their use has the following effects:
    • Exposure time is reduced (~ 2x or 3x) (therefore are called intensifying).
    • Scatter influence is reduced.
    • Unsharpness is reduced.
    Fluorescent (Salt) Screens
    • Fluorescent screens contains Calcium Tungstate (CaWO4) which is a
    good scintillator.
    • Their use has the following effects:
    • Dramatic intensifying effect (up to 500 x)
    • Significant increase of inherent unsharpness.
    • Negligible filtering effect
    In order to boost the filtering effect the salt screen must be combined
    with metallic layer (Fluoro-metallic screens)
    Film Processing
    Processing sequence
    1) Development
    2) Stop bath
    3) Fixing
    4) Washing
    5) Drying
    • Until film is processed, any additional exposure
    must be avoided.
    • Processing is carried out in the dark room
    Film Processing
    Developing
    • Developer is alkali solution
    • Standard temperature 20 °C (manual process)
    • Standard processing time 5 minutes
    • Ag+ + 1e- » Ag (Black metallic silver)
    Film Processing
    Stop bath
    • Water or solution of acetic acid (~ 1:35)
    • Standard temperature – same as developer
    • Standard processing time – depends on agent ( 5 to
    30 sec)
    Film Processing
    Fixing
    • Fixer is an acidic solution
    • Chemical- sodium thiosulphate (hypo)
    • Standard temperature – same as developer
    • Standard processing time 2x clearing time

    • Fixer has 2 functions


    • Fixing
    • Hardening
    Film Processing
    Fixing
    • Fixing – dissolve all unexposed AgBr
    grains from gelatine (will make it
    transparent)
    • Hardening – will harden gelatine (fix
    silver in place and allow safe
    handling).
    • After Fixing
    • Film is transparent
    • Emulsion is hard, safe to be handled
    • Emulsion contains thiosulphate
    Film Processing
    Washing
    • Water
    • Standard temperature – same as developer
    • Standard processing time – 10 to 30 minutes
    (manual process)
    • Wetting agent may be used at the end of washing
    (avoid water marking)
    • Washing will:
    • Wash out thiosulphate from emulsion and
    secure durability of radiograph
    Film Processing
    Drying
    • At room temperature or with hot air
    • Dust free environment required
    • Drying time depends on air temperature and
    humidity, circulation and if wetting agent was used.

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