Film Badges

Report
Personal Monitoring
Dosimetry
IRAD2731
RADIATION DETECTION AND
MEASUREMENT II
Agenda
 Color dosimeters
 Film
 TLDs
 PICs
 OSLs
 Track Etch
 EPD
Characteristics
 Small
 Light weight
 Sensitive to only the radiation of interest
 Insensitive to other influences
 Cheap
 Tissue equivalent
 Linear response
 Rugged
 No dosimeter has all these properties
Early
 Colorimetric Method – color change
 Small metal box containing several clear tubes of
liquid
 The solution consists of chloroform and the dye
brome-creosol purple. When the chloroform
absorbs radiation energy, hydrochloric acid is
produced which changes the dye color from purple
to yellow.
 Sodium hydroxide is added to adjust the
sensitivity.
 High ranges 50R and above
Personnel Radiation Monitoring Devices
Film Badges: Photographic film used for measurement of
ionizing radiation exposure for personnel monitoring
purposes. The film badge may contain two or three films of
differing sensitivities, and it may also contain a filter that
shields part of the film from certain types of radiation.
Pocket ion Chamber: A small tubes that has a charged on a
piezoelectric crystal, when ionizing radiation interact with
the crystal the it is discharge. This discharge moves the
needle down the scale indicating total dose.
Personnel Radiation Monitoring Devices
Thermoluminescence Dosimeter: A small device
used to measure ionizing radiation by measuring
the amount of visible light emitted from a crystal in
the detector. Heat is used to release trapped
energy in the form of visible light.
Optically Stimulated Luminescence: A small device
used to measure ionizing radiation by measuring
the amount of visible light emitted from a crystal in
the detector. A laser is used to release trapped
energy in the form of visible light.
Examples of
Personnel Monitoring Devices
Dosimeters-Film Badges
 Film Badges - the amount of exposure of the film is
proportional to the dose that the badge was exposed
to.
 Oldest from of dosimetery


1903 used for patients
1920s first film badge
 Film badge holder is designed to be able to obtain
photon energy and direction.
 Where should you wear it?
Dosimeters-Film Badges
 Good permanent record of dose.
 Time lag between exposure and reading
 Used to be industry standard, replaced by TLDs and
OSLs

Still used when pregnant female badge is requested
 Will over respond at low energies
Materials
 Silver Halide grains are mixed with gelatin matrix
 Ionizing radiation “sensitizes” the grains
 Development converts to metallic silver and washes
away unused grains
 Color change (optical density)of film is compared to
calibrated dose color change
 Color change can be influenced by temperature,
humidity, light, and processing
 Can be used either as a cumulative dose or single
particle tracks
Film Holder
 Special design
 Used to flatten response curve of the film out over
larger energy rage

unfiltered film will over estimate at low energies
 Can be used to determine energy of incoming
photons by the use of different filters
 Can be made to determine thermal neutron exposure
All filters are locked in and provide for separation of different
types of radiations. They make possible the elimination of
energy dependence of the film when exposed to different
radiation energies.
Open Window
Plastic Filter #1
Plastic Filter #2
Aluminum Filter
Lead/Tin Alloy
Filter
Another filter may be added for
thermal neutron determination.
Dosimeters-TLD
 Thermoluminencent Device (TLD) is a material that
absorbs radiation and traps the energy in the matrix
of the crystal

As opposed to scintillators that release the energy right away
 When heated the crystal releases this energy as light
 The amount of light released is proportional to the
energy absorbed by the TLD
 Energy absorbed is proportional to dose
TLD electrons
Dosimeters-TLD
 Can be used many times over.
 Process of annealing clears out the electrons and readies the
crystal for reuse
 Needs special machine to read.
 Time lag between exposure an reading
 No permanent record after reset.
 Fading
 Spontaneous loss of stored energy over time
 Each material has its own fading rate
 Can be affected by heat
TLD materials
 CaSO4:Mn- very sensitive due to traps are close to
the band gap, but also fades rapidly
 CaF2:Mn- not as sensitive as CaSO4:Mn, but fades a
great deal less, suitable for long term use
 LiF- most popular, negligible fading or energy
dependence, atomic number close to tissue
 Neutron badges 6Li/7Li- -6Li is sensitive to slow
neutrons

Can be used to determine dose due to beta/gamma/neutron in
mixed field
Glow curve
Optically Stimulated Luminesence
 Same as TLDs but the light is released when the
crystal is hit by a laser rather than being heated up
 Has same characteristics as TLDs but


OSLs do not fade
Can be read several times.
 Al2O3 is most common material used
 Not affected by many external things
Dosimeters-PIC
 Pocket Ion Chamber (PIC)- a charged piezoelectric





cell discharges as it interacts with radiation and
moves a needle across a screen to indicate
exposure.
Can check on exposure real time
Can use over many times
several persons can use
But permanent record is lost when reset
Can be confusing if multiple people use it and no
good records are kept
Pocket Chamber and Charger
Track Etch
 Same idea as film but emulsion is thicker
 Simple and inexpensive
 Used for heavy charged particle monitoring
 Insensitive to electrons, gamma rays and fast
neutrons
 Used for Rn detection and space applications
 Can be used to determine direction of radiation
Track Etch
 Radiation interacts with emulsion
 Leaves physical and ionizing tracks in emulsion
 Emulsion is processed
 Chemicals are washed over the emulsion
 Chemical enlarges the holes made by the particles
 Computer can count number of holes per unit area
 Used to be done by eye and a bright light
 Number of holes is proportional to particle flux
 Size of holes is proportional to particle energy
Electronic Dosimeter (EPD)
 Combines the ability to have permanent
record and notify person immediately of
changing dose rates
 Can set alarms for total dose and dose
rate
 Info can be loaded to computer
 Can be used by several
people with proper record keeping
Not all good
 Mechanical failure
 Data loss
 Heavier than TLD
 Response vs battery life
 Some EPDs do not detect betas or neutrons
 Affected by magnetic fields
 Several external influences affect EPD
Issuing PDs
 Film, TLDs, OSLs are all person specific
 Should not share or swap badges
 EPDs and PICs can be used by several people
 In order to be used as dose records need good record keeping
 Person it was checked out to and their initials
 Serial number of unit
 Date and time of issue and return
 Initial reading , final, and net reading
 Can be used as supplemental info(along with other
dosimetry) or if used as official dose record need to
be calibrated annually
Questions?

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