Radiation Surveys, Instrumentation and Dosimetry

Laurie S. Vivekanand, CIHLaurie S. Vivekanand, CIHNXP SemiconductorsNXP Semiconductors

Hopewell Junction, NYHopewell Junction, NY

Radiation Surveys, Instrumentation and Dosimetry

Survey TypesSurvey TypesSurvey Instrumentation Survey Instrumentation DosimetryDosimetrySurvey and Dosimetry RecordkeepingSurvey and Dosimetry Recordkeeping

Survey Types

General Area (Dose Rate)General Area (Dose Rate)ContaminationContamination

Fixed ContaminationFixed ContaminationRemovable Contamination Removable Contamination

Leakage Leakage XX--Ray Generator LeakageRay Generator LeakageSealed Source LeakageSealed Source Leakage

Area (Dose Rate) and Contamination Surveys

Conducted in labs and other areas using or Conducted in labs and other areas using or storing radioactive materialsstoring radioactive materialsSurvey for XSurvey for X--Ray, Ray, γγ , high energy , high energy ββHandHand--held survey meterheld survey meterSurvey estimates dose rate exposures, Survey estimates dose rate exposures, identifies potential areas of contaminationidentifies potential areas of contamination

Fixed Contamination Surveys

Fixed contamination Fixed contamination –– cannot be easily cannot be easily removed from surfaces by wipingremoved from surfaces by wipingPortable survey meterPortable survey meter

Held just above surface of potential Held just above surface of potential contaminationcontaminationIf contamination readings exceed action If contamination readings exceed action levels, remove or treat objectlevels, remove or treat object

Removable Contamination Surveys

Removable contamination Removable contamination Readily removed by wipingReadily removed by wipingInternal and external hazardInternal and external hazardCan be transferred to contaminate other areasCan be transferred to contaminate other areas

Wipe samples collected from surfaces with the Wipe samples collected from surfaces with the potential for contamination:potential for contamination:

Freezers, refrigerators, fume hoods, bench tops, Freezers, refrigerators, fume hoods, bench tops, floors, sinks, waste containersfloors, sinks, waste containers

Results in dpm/100 cmResults in dpm/100 cm22

Treat and retest if contamination foundTreat and retest if contamination found

Sealed Source Leak TestSealed sources can be found in air Sealed sources can be found in air monitoring devices, gamma irradiators, monitoring devices, gamma irradiators, industrial gaugesindustrial gaugesLeak tests required to assess for leakage and Leak tests required to assess for leakage and external contamination external contamination Conducted every six monthsConducted every six monthsSwab used to wipe external surfacesSwab used to wipe external surfacesLimit = 0.005 Limit = 0.005 µµCiCi

X-Ray Leakage Surveys

XX--Ray generating devices are found in scientific, Ray generating devices are found in scientific, medical and industrial applicationsmedical and industrial applicationsSurveys to detect leakage periodically and after Surveys to detect leakage periodically and after shielding is disturbedshielding is disturbedPortable survey meter Portable survey meter moved slowly along surfacesmoved slowly along surfacesReadings above backgroundReadings above backgroundmay indicate damaged may indicate damaged

shieldingshielding

Detecting Radiation

Fixed Laboratory Analytical InstrumentsFixed Laboratory Analytical InstrumentsMeasure activity of removable contamination Measure activity of removable contamination on wipes or swabson wipes or swabs

Rate Measuring Instruments (Survey Meters)Rate Measuring Instruments (Survey Meters)Measure intensity of radiation Measure intensity of radiation

Dose Measuring Instruments (Dosimeters)Dose Measuring Instruments (Dosimeters)Measure total amount of radiation received Measure total amount of radiation received during a period of timeduring a period of timeProvide a dose measure Provide a dose measure

Fixed Laboratory InstrumentsLiquid Scintillation CounterLiquid Scintillation Counter

OperationOperationRadiation in the sample causes liquid scintillation Radiation in the sample causes liquid scintillation cocktail to produce light, which is amplified and cocktail to produce light, which is amplified and converted into an electrical signalconverted into an electrical signal

AdvantagesAdvantagesSensitive to low energy Sensitive to low energy ββOnly method to detect tritiumOnly method to detect tritiumGood efficiencyGood efficiency

LimitationsLimitationsLarge, bulky, expensiveLarge, bulky, expensiveQuenching can led to decreased efficiencyQuenching can led to decreased efficiency

Portable Survey MetersSelection CriteriaSelection Criteria

Type of radiationType of radiationEnergyEnergyPurpose Purpose –– contamination, evaluating leakage, dose contamination, evaluating leakage, dose estimation, identification of nuclidesestimation, identification of nuclides

GasGas--Filled Detectors Filled Detectors –– radiation ionizes gas molecules in radiation ionizes gas molecules in chamber, ion pairs are attracted to electrodes and create an chamber, ion pairs are attracted to electrodes and create an electrical signalelectrical signal

Ionization ChamberIonization ChamberProportional CounterProportional CounterGeigerGeiger-- MMüüller Counterller Counter

Scintillation Detectors Scintillation Detectors –– radiation interacts with crystals to radiation interacts with crystals to produce light photonsproduce light photons

Ionization ChambersRelatively low voltageRelatively low voltage

Only the charge from the initial Only the charge from the initial ionization event is countedionization event is counted

Uses and advantagesUses and advantagesββ, , γγ , X, X--RaysRaysUsed to estimate doseUsed to estimate doseNo dead timeNo dead time

LimitationsLimitationsUnderestimation of dose if exposure is Underestimation of dose if exposure is

not uniformnot uniformExpensive electronics Expensive electronics Sensitive to environmental effectsSensitive to environmental effects

Proportional CountersSomewhat higher voltageSomewhat higher voltage

Leads to a cascade of ion pairsLeads to a cascade of ion pairsNumber of pairs is proportional to the number of ions from Number of pairs is proportional to the number of ions from the initial radiationthe initial radiation

Uses and advantagesUses and advantages

α, βα, β, , γγ , X, X--RaysRays

Measures energy of incident radiationMeasures energy of incident radiation

Useful for accurate measurements over a range of energiesUseful for accurate measurements over a range of energies

LimitationsLimitations

Expensive electronicsExpensive electronics

Bulky and heavyBulky and heavy

Dead time up to 10 Dead time up to 10 µµsecsec

Geiger- Müller Counters

LimitationsLimitationsLack the ability to discriminate between different energy Lack the ability to discriminate between different energy radiationradiationNonNon--continuous measurement continuous measurement Dead time > 100 Dead time > 100 µµsecsec

Higher voltageHigher voltageCascade of ion pairs saturates the detectorCascade of ion pairs saturates the detectorSize of the pulse created is independent of the Size of the pulse created is independent of the

size of he original ionization eventsize of he original ionization eventUses and advantagesUses and advantages

α, βα, β, , γγ , X, X--RaysRays

Relatively low cost and ruggedRelatively low cost and ruggedMore sensitive to lowMore sensitive to low--level radiationlevel radiation

Scintillation DetectorsOperationOperation

Radiation interacts with crystals to produce Radiation interacts with crystals to produce light photonslight photonsPhotomultiplier tube converts to pulsesPhotomultiplier tube converts to pulsesNumber of pulses proportional to intensityNumber of pulses proportional to intensityMagnitude of pulses proportional to energyMagnitude of pulses proportional to energy

Uses and advantagesUses and advantagesLow energy XLow energy X--RaysRaysMore sensitive than gasMore sensitive than gas--filled detectorsfilled detectors

LimitationsLimitationsCannot detect Cannot detect αα and and ββ

Dosimetry

When likely exposure >10% of limitsWhen likely exposure >10% of limitsPocket DosimetersPocket Dosimeters

DirectDirect--readingreadingDigitalDigital

Film BadgesFilm BadgesThermoluminescent DosimetersThermoluminescent Dosimeters

Direct-Reading Pocket Dosimeters

OperationOperationSmall ionization chamber with deflected fiberSmall ionization chamber with deflected fiberIncident radiation lessens the deflectionIncident radiation lessens the deflectionRead by viewing fiber through a calibrated exposure scaleRead by viewing fiber through a calibrated exposure scale

Advantages Advantages Compact, Reusable, fairly sensitive Compact, Reusable, fairly sensitive Provides immediate exposure readings Provides immediate exposure readings

LimitationsLimitationsNo permanent exposure recordNo permanent exposure recordLimited rangeLimited rangePotential for discharge if droppedPotential for discharge if droppedMust be zeroed and recharged dailyMust be zeroed and recharged daily

Digital Pocket Dosimeters

OperationGeiger- Müller Counter Digital output of accumulated dose and dose rateAudible alarm if threshold dose exceeded

Advantages Reduced reading errorsHigher exposure range than direct-readingReusability

LimitationsNo permanent exposure record

Film BadgesOperationOperation

Gamma, XGamma, X--Ray, Beta ExposuresRay, Beta ExposuresRadiationRadiation--sensitive filmsensitive filmFilters attenuate different energies, discriminating Filters attenuate different energies, discriminating between types of radiationbetween types of radiation

AdvantagesAdvantagesPermanent exposure recordPermanent exposure recordGood accuracy at higher exposuresGood accuracy at higher exposures

LimitationsLimitationsExposure not read immediatelyExposure not read immediatelySensitivity to heatSensitivity to heatLess accuracy at lower exposuresLess accuracy at lower exposures

Thermoluminescent DosimetersOperationOperation

Gamma and XGamma and X--Ray, high energyRay, high energy ββRadiation ionizes atoms in a phosphor crystal, electrons are Radiation ionizes atoms in a phosphor crystal, electrons are deposited in crystal structure and released when heateddeposited in crystal structure and released when heatedReleased electrons produce light, which is measured by a Released electrons produce light, which is measured by a photomultiplier tubephotomultiplier tube

AdvantagesAdvantagesReusableReusableSensitive to low dosesSensitive to low doses

LimitationsLimitationsNo permanent recordNo permanent recordNo reNo re--readabilityreadabilityCostCost

Survey and Dosimetry Recordkeeping

Purpose Purpose Serves as a permanent record of surveys, Serves as a permanent record of surveys, exposure rates and dosesexposure rates and dosesSatisfies regulatory requirementsSatisfies regulatory requirementsDemonstrates compliance with regulations and Demonstrates compliance with regulations and internal practicesinternal practices

RetentionRetentionUntil termination of license Until termination of license –– Dosimetry and Dosimetry and dose survey recordsdose survey records3 years 3 years –– All other recordsAll other records

Survey and Dosimetry Recordkeeping

Area and Contamination SurveysArea and Contamination SurveysDate, area surveyed, radionuclides, survey Date, area surveyed, radionuclides, survey instrumentation, calibration dates and instrumentation, calibration dates and correction factors, background levels, correction factors, background levels, responsible person, supervisory reviewresponsible person, supervisory reviewMap of area showing locations surveyed or Map of area showing locations surveyed or wipedwipedDose rates and contamination levels recorded, Dose rates and contamination levels recorded, corrective actions needed or completedcorrective actions needed or completed

Survey and Dosimetry Recordkeeping

XX--Ray Leakage SurveysRay Leakage SurveysLocation, XLocation, X--Ray generator model#, serial #, Ray generator model#, serial #, maximum energy, survey instrumentation, maximum energy, survey instrumentation, responsible personresponsible personBackground readings and results, identification Background readings and results, identification of of ““hot spotshot spots””

Sealed Source leak testingSealed Source leak testingGauge or source serial #, radionuclide, activity, Gauge or source serial #, radionuclide, activity, location, results, responsible personlocation, results, responsible person

Survey and Dosimetry Recordkeeping

Dosimetry RecordkeepingDosimetry RecordkeepingRecord dosimetry results on NRC Form 5 Record dosimetry results on NRC Form 5 or equivalentor equivalent

Licensee name and ID #Licensee name and ID #Name, ID#, Sex, Age, Monitoring Name, ID#, Sex, Age, Monitoring PeriodPeriodIntake and doseIntake and dose

Sources of Additional Information

4040--hour RSO training coursehour RSO training courseAIHCe PDC AIHCe PDC ““Managing Radiation Programs for Managing Radiation Programs for Industrial HygienistsIndustrial Hygienists””Dosimeter and survey meter manufacturersDosimeter and survey meter manufacturersHPS website HPS website www.hps.orgwww.hps.org

AIHA Ionizing Radiation Committee website: AIHA Ionizing Radiation Committee website: www.aiha.org/Content/InsideAIHA/Volunteer+Groups/IRcomm.htm