Radiation Safety Course Radiation Monitoring

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Radiation Safety Course Radiation Monitoring. Heath de la Giroday Dispensing Chemist Radiation Safety Officer. RADIATION MONITORING. Dose rate instruments Personal dosimetry TLDs Survey meters Contamination instruments Liquid scintillation counter Survey meters. Dose Rate Instruments. - PowerPoint PPT Presentation

Transcript of Radiation Safety Course Radiation Monitoring

  • Radiation Safety CourseRadiation MonitoringHeath de la GirodayDispensing ChemistRadiation Safety Officer

  • RADIATION MONITORINGDose rate instrumentsPersonal dosimetry TLDsSurvey metersContamination instrumentsLiquid scintillation counterSurvey meters

  • Dose Rate InstrumentsPersonal dosimetryThermoluminescent dosimeters (TLDs), and x-rayLandauer

  • Dose Rate InstrumentsTLD proper use and careWear badge inside or outside lab coat at chest levelWear ring on dominant hand with text facing radioactive materialBest practice to wear on inside of gloves to match actual exposure and prevent contaminationBe careful not to contaminate TLDsReturn TLDs to storage box after use

  • Dose Rate InstrumentsDose rate metersDisplays Sv/hr or mR/h Can be used to calculate doseRSO uses dose rate meters when receiving radioisotopes to measure radiation field

  • Liquid Scintillation CounterUsesAlpha, beta, and gammaOnly method able to detect H-3Only detect loose surface contaminationExtremely sensitive

  • Liquid Scintillation CounterPrinciples of operationSample added to vial of liquid scintillation cocktailParticle or photon energy is transferred to a solvent molecule, causing it to enter an excited stateEnergy is eventually transferred to a fluor moleculeFluor decays to ground state with emission of photonLight is detected by photomultiplier tubePhotomultiplier tube generates electrical signal

  • Liquid Scintillation CounterLSC operation, e.g. wipe testMap wipe spotsWet absorbent wipe, e.g. filter paper soaked w/ethanolWipe 100cm2 areaLabel all vials and include a control vialFill vials with scintillation cocktail to cover wipes

  • Liquid Scintillation CounterTechnical issuesChemiluminescenceChemical reactions generate photon emissionsPhotoluminescenceExcitation of fluors by ambient like results in photon emissionQuenchingMolecules absorb energy, preventing photon emissionsGive false readings

  • Liquid Scintillation CounterHeat adapting37C for 1-2 hoursSpeeds chemical reactions

    Dark adaptingPut in dark for 5-10 minutesStops absorption of external photons

    Quenchingaddress if it becomes a problem

  • Contamination InstrumentsSurvey metersLudlum model 3 survey meter detectorGeiger-Mueller probeThin end window or pancakeNaI probe

  • Survey MetersGeiger-Mueller probeThin end window or pancakePrinciples of operationParticle causes ionization of gas inside tubePotential causes ion to accelerate to inner wire or outer wallSuccession of ionizations occurThis causes meter to register a count

  • Survey MetersGeiger-Mueller probeUseNearly all beta emittersIncluding beta/gamma emittersNot H-3 because the beta particles do not have sufficient energy to penetrate the windowSome pure gamma emittersDoes not detect low-energy gamma rays (I-125) efficientlyDoes not detect low-energy x-rays efficientlyBoth CPM and mR/h scales are calibrated

  • Survey MetersNaI probeSolid scintillatorPrinciples of operationParticle or photon interacts with a NaI crystalA solid crystal is better than a gas-filled tube at absorbing low-energy gamma rays and x-rays (density)Light is emitted by crystalEmitted light falls on photomultiplier tubePhotomultiplier tube generates a signal

  • Survey ProbeNaI probeUseLow-energy gamma radiation (e.g. I-125)Low-energy x-rays (e.g., Bramsstrahlung)CPM scale is calibratedDose rate (mR/h) scale is not calibrated

  • Survey Meters-Ludlum Model 3Audio always onF for rapid monitoringS for accurate monitoringAlways start at most sensitiveMaster dialBattery CompartmentCalibration dials (normally covered)Probe plugResetAudible/muteSampling rateF/SDisplay

  • Ludlum Pre-Operation ChecksFour ChecksCalibrationVerify calibration from sticker1 year in CanadaBatteryRotate master knob from Off to BatVerify needle is in Bat Test region of scaleBackground count rateCheck source (if available)

  • Survey Meter OperationScanning for contaminationMove at a steady pace and be systematic-1/sIf a hot spot is found ,use a spiral pattern to find the edges of a hot spot

    Monitoring surfaceFinding edges of contamination

  • Ludlum OperationContamination CheckIf meter chirp rate increases above background rate, find location of highest count rateIf necessary, slowly rotate master knob counterclockwise until needle is on-scalePush reset button to speed equilibration after switching to lower sensitivityWhen site of contamination is located, flip response fast/slow switch to slow for more accurate readings

  • Keep in MindCPM and dose rate of survey meters is variable between radioisotopesDetection efficiency

    Do not contaminate the probe or meter

  • Survey Meter Operation-SummaryCheck calibration stickerEnsure unit is in good conditionTurn unit on and check batteryTurn switch to lowest multiplication scaleCheck backgroundPerform positive checkMeasure radioactivityNote highest count rate in CPMTurn unit off when finished (Be green-use less batteries)

    **Different instruments are used to detect the different types of radiation. It is very important that the equipment you are using can detect the type of radiation you are working with.

    A radiation survey meter is used to detect moderate to high energy beta, gamma and x-ray radiation. This kind of meter is unable to measure low energy radioisotopes like tritium (H-3).

    The unit is composed of a probe to detect radioactivity, the base containing the electronics, and the meter face.

    Radiation detection equipment are broken down into two groups: contamination instruments (measure activity in CPM or CPS) and dose rate instruments (measure dose in milliR or microSv).

    Most survey meters at UNBC have two scales for contamination monitoring and dose rate measurements.

    *It is mandated by the CNSC that all NEWs have their radiation doses monitored by an approved dosimetry service provider. They recommend that non-NEWs have their doses monitored, and UNBC does monitor individual doses to ensure that they are below 1 mSv/year.

    Rings are provided in some labs to detect the dose to the hands. Badges are provided to detect whole body dose.

    TLDs are returned to Landauer for analysis and reports are returned to UNBC.

    This service and all records are managed by RSO. You can ask you supervisor at any time for your exposure report.*Do not store dosimeters in the hotroom*Survey meters displaying milliR or microSv are dose rate meters.

    They can be used to calculate dose, if you know how long you were working in a particular radiation field.

    *LSC is also used for wipe tests to detect removable contamination on lab surfaces.*A control vial is always used.

    Samples are soaked in a scintillating substrate (cocktail). Beta particles transmit their energy to the solvent molecules in the cocktail, which transmit energy to fluors added to the cocktail, which emit light to release the energy. These pulses of light are detected by the photomultiplier tube. The PMT amplifies the effect, allowing for accurate measurement of very low activity radioisotopes, like tritium.

    Print out will show CPM.

    Chemiluminescence-false highPhotoluminescence-false highQuenching-false low**Date of calibration (dose rate meters) or verification (contamination meters) is it current?

    Battery check battery must be fully charged

    Check background

    Check source response remember effect of distance, must hold probe very close to source for best response

    *Check for a calibration sticker. If the calibration date has passed, contact the RSO. Check that the unit is in good condition and for tightness of cable connections. Loose cable connections can cause instrument damage or cause false readings. Perform a battery check. Batteries must be fully charged. If you need new batteries, contact the RSO.

    Turn the on/off switch to the lowest multiplication scale. Turn on the audio and ensure the unit is on the "F" position, if there is a F/S switch. Allow the unit to warm up (15-20 seconds). Determine the background. This should be done away from sources of radioactivity. Typical background readings are 0-200 CPM or 0.05 mR/hr.

    Measure the area of radioactivity by placing the probe as close as possible to the area being monitored without actually touching it. Note the audio function will guide you to the source of contamination. Find the highest count rate and record it in cpm. Determine the spread of the contamination. Take a wipe to determine if the contamination is removable. Never forget to turn off the survey meter once the work is completed.