IRAD2731RADIATION DETECTION AND

MEASUREMENT II

Personal MonitoringDosimetry

Agenda

Color dosimetersFilm TLDsPICsOSLsTrack EtchEPD

Characteristics

SmallLight weightSensitive to only the radiation of interestInsensitive to other influencesCheapTissue equivalentLinear responseRuggedNo dosimeter has all these properties

Early

Colorimetric Method – color changeSmall metal box containing several clear

tubes of liquidThe 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 DevicesFilm 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 ofPersonnel 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 readingUsed 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 grainsDevelopment converts to metallic silver and

washes away unused grainsColor change (optical density)of film is

compared to calibrated dose color changeColor change can be influenced by

temperature, humidity, light, and processingCan 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 awayWhen heated the crystal releases this energy

as light The amount of light released is proportional

to the energy absorbed by the TLDEnergy 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 reuseNeeds special machine to read.Time lag between exposure an readingNo 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 usedNot 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 timeCan use over many timesseveral persons can useBut permanent record is lost when resetCan 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 thickerSimple and inexpensiveUsed for heavy charged particle monitoringInsensitive to electrons, gamma rays and fast

neutronsUsed for Rn detection and space applicationsCan be used to determine direction of

radiation

Track Etch

Radiation interacts with emulsionLeaves physical and ionizing tracks in

emulsionEmulsion is processed

Chemicals are washed over the emulsionChemical enlarges the holes made by the

particlesComputer 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 computerCan be used by several people with proper record keeping

Not all good

Mechanical failureData lossHeavier than TLDResponse vs battery lifeSome EPDs do not detect betas or neutronsAffected by magnetic fieldsSeveral 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?