3/2003 Rev 13/2003 Rev 1 II.3.8 – slide II.3.8 – slide 11 of 34 of 34IAEA Post Graduate Educational CourseIAEA Post Graduate Educational Course

Radiation Protection and Safe Use of Radiation SourcesRadiation Protection and Safe Use of Radiation Sources

Session II.3.8Session II.3.8

Part IIPart II Quantities and MeasurementsQuantities and Measurements

Module 3Module 3 Principles of Radiation Principles of Radiation Detection and MeasurementDetection and Measurement Session 8Session 8 Nuclear Track DetectorsNuclear Track Detectors

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OverviewOverview

Nuclear track etch detectors and principles Nuclear track etch detectors and principles of detection will be discussedof detection will be discussed

Students will learn about etchable plastic Students will learn about etchable plastic foils, detection thresholds for various foils, detection thresholds for various materials, neutron detection, approaches to materials, neutron detection, approaches to track etch detection, proton detection, and track etch detection, proton detection, and types of track etch detector systemstypes of track etch detector systems

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ContentContent

Etchable plastic foilsEtchable plastic foils Detection thresholds for various track Detection thresholds for various track

etch materials etch materials Energy window of detectabilityEnergy window of detectability Neutron detectionNeutron detection Stability of track damageStability of track damage Chemical etching proceduresChemical etching procedures

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ContentContent

Fission-foil converter approach to Fission-foil converter approach to track etch detectiontrack etch detection

Cellulose nitrate approach to track Cellulose nitrate approach to track etch detectionetch detection

Proton detectionProton detection Types of track etch detector systemsTypes of track etch detector systems

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Etchable Plastic FoilsEtchable Plastic Foils

During the 1960s, investigators found that dielectric During the 1960s, investigators found that dielectric materials became more chemically etchable by materials became more chemically etchable by exposure to ionizing radiationexposure to ionizing radiation

Materials include glass, mica and plasticsMaterials include glass, mica and plastics

Radiation induction of etchability requires a certain Radiation induction of etchability requires a certain energy deposition “threshold” per unit mass along energy deposition “threshold” per unit mass along the track of high-LET particlesthe track of high-LET particles

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Etchable Plastic FoilsEtchable Plastic Foils

After radiation exposure, chemical action by an After radiation exposure, chemical action by an etchant (e.g. HF, NaOH) causes removal of the etchant (e.g. HF, NaOH) causes removal of the radiation-damaged volumeradiation-damaged volume

This removal leaves a conical or cylindrical pit or This removal leaves a conical or cylindrical pit or holehole

This hole is large enough to see with low This hole is large enough to see with low magnification and to count and interpret magnification and to count and interpret dosimetricallydosimetrically

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Etchable Plastic FoilsEtchable Plastic Foils

For the material to be etchable, the specific energy For the material to be etchable, the specific energy imparted in the particle track must exceed some imparted in the particle track must exceed some thresholdthreshold

The threshold is characteristic of each dielectric The threshold is characteristic of each dielectric materialmaterial

Threshold minimum specific energy is given in Threshold minimum specific energy is given in terms of dT/terms of dT/dx or Ldx or L of the charged particle for a of the charged particle for a

given materialgiven material

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LL for Dielectric Materialsfor Dielectric Materials

Inorganic materials have a threshold LInorganic materials have a threshold L

mostly exceeding 15 MeV cmmostly exceeding 15 MeV cm22/mg, /mg, corresponding to 500 keV/corresponding to 500 keV/m in unit-density m in unit-density tissuetissue

Plastics tend to have lower thresholdsPlastics tend to have lower thresholds

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LL for Dielectric Materialsfor Dielectric Materials

A common radiation-vulnerable plastic in A common radiation-vulnerable plastic in use is use is cellulose nitratecellulose nitrate

Cellulose nitrate has a thresholdCellulose nitrate has a threshold LL as low as as low as

1 MeV cm1 MeV cm22/mg or 100 keV//mg or 100 keV/m in tissuem in tissue

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Energy Window of DetectabilityEnergy Window of Detectability

Kinetic energy of a given heavy charged Kinetic energy of a given heavy charged particle cannot be too high, since Lparticle cannot be too high, since L would would

be too low in this casebe too low in this case

However, the kinetic energy must be high However, the kinetic energy must be high enough for the particle to have sufficient enough for the particle to have sufficient range in the material to have recognizable range in the material to have recognizable tracks after chemical etchingtracks after chemical etching

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Energy Window of DetectabilityEnergy Window of Detectability

This situation creates an energy “window” This situation creates an energy “window” of detectabilityof detectability

Window is different for each combination of Window is different for each combination of charged particle, material, irradiation charged particle, material, irradiation conditions, and etch processingconditions, and etch processing

In many cases, this window is closed and no In many cases, this window is closed and no detection is possibledetection is possible

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Energy Window of DetectabilityEnergy Window of Detectability

Because of the energy window, nuclear track Because of the energy window, nuclear track etch radiation detection has not generally etch radiation detection has not generally been practical for electrons or gamma raysbeen practical for electrons or gamma rays

Its greatest application has been in the area Its greatest application has been in the area of of neutron dosimetryneutron dosimetry

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Threshold LThreshold L vs RBE vs RBE

The lowest threshold LThe lowest threshold L in tissue in tissue

(= 100 keV/(= 100 keV/m for cellulose nitrate) occurs m for cellulose nitrate) occurs around where the RBE reaches a maximum around where the RBE reaches a maximum in many mammalian biological systemsin many mammalian biological systems

The RBE range of greatest interest occurs The RBE range of greatest interest occurs from Lfrom L = 0.2 keV/ = 0.2 keV/ m to Lm to L = 100 keV/ = 100 keV/ m m

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Stability of Track DamageStability of Track Damagein Plasticsin Plastics

Latent-damage track in plastics is stable Latent-damage track in plastics is stable against spontaneous repair at storage against spontaneous repair at storage temperatures below 50temperatures below 50° C° C

Approaching the softening temperature of a Approaching the softening temperature of a plastic results in rapid annealing and repair, plastic results in rapid annealing and repair, thus removing etchabilitythus removing etchability

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Chemical Etching ProceduresChemical Etching Procedures

Becker (1973) has reviewed many details of Becker (1973) has reviewed many details of various etching proceduresvarious etching procedures

Combination of an etchant with high-voltage Combination of an etchant with high-voltage AC across the film has been found to AC across the film has been found to improve etching speed and reproducibility in improve etching speed and reproducibility in some casessome cases

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Two Approaches toTwo Approaches toTrack Etch DetectionTrack Etch Detection

Fission-foil convertersFission-foil converters

Direct interaction of neutrons in Direct interaction of neutrons in etchable film and overlying plastic etchable film and overlying plastic layerlayer

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Neutron Track Etch Dosimetry Neutron Track Etch Dosimetry Using Fission-Foil ConvertersUsing Fission-Foil Converters

When a foil of fissionable material is struck When a foil of fissionable material is struck by neutrons of energies above its fission by neutrons of energies above its fission threshold energy, very heavy energetic threshold energy, very heavy energetic charged particles are generatedcharged particles are generated

If the foil is adjacent to a plastic film, If the foil is adjacent to a plastic film, etchable damage tracks are efficiently etchable damage tracks are efficiently producedproduced

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Neutron Track Etch Dosimetry Neutron Track Etch Dosimetry Using Fission-Foil ConvertersUsing Fission-Foil Converters

Number of such etchable tracks has been found to Number of such etchable tracks has been found to be 1.16 x 10be 1.16 x 10-5-5 per neutron barn per neutron barn

This simple relationship arises from the nearly This simple relationship arises from the nearly constant detection efficiency of plastics for fission constant detection efficiency of plastics for fission fragments,and fragments,and

The fact that the common fissile materials yield The fact that the common fissile materials yield similar distributions of fragment speciessimilar distributions of fragment species

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Neutron Track Etch Dosimetry Neutron Track Etch Dosimetry Using Fission-Foil ConvertersUsing Fission-Foil Converters

A typical chemical etching scheme, A typical chemical etching scheme, used with polycarbonate films, used with polycarbonate films, consists of a bath in 30% KOH at 60consists of a bath in 30% KOH at 60C C for 5 to 50 minfor 5 to 50 min

Track concentrations range from 10Track concentrations range from 1066 to to 101033 tracks/cm tracks/cm22

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Track Etch Using Track Etch Using Cellulose NitrateCellulose Nitrate

Neutron dosimetry can also be Neutron dosimetry can also be performed by neutron interactions in performed by neutron interactions in plastic filmsplastic films

Fast neutrons striking cellulose nitrate Fast neutrons striking cellulose nitrate films cause recoiling C, O, and N films cause recoiling C, O, and N atomsatoms

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Track Etch Using Track Etch Using Cellulose NitrateCellulose Nitrate

Tracks are inconveniently small under Tracks are inconveniently small under ordinary etching proceduresordinary etching procedures

Track size can be greatly enhanced by Track size can be greatly enhanced by application of an AC voltage (2000 V at application of an AC voltage (2000 V at 1 kHz) across the film in the etching 1 kHz) across the film in the etching bathbath

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Proton Detection Using Proton Detection Using Commercial PlasticsCommercial Plastics

A commercial plastic called CR-39 has a low A commercial plastic called CR-39 has a low enough Lenough L to detect protons resulting from to detect protons resulting from

elastic collisions with hydrogen elastic collisions with hydrogen

The L The L threshold, below which the proton threshold, below which the proton

tracks are not dense enough to cause tracks are not dense enough to cause etchable damage, is about 100 MeV cmetchable damage, is about 100 MeV cm22 /g or /g or 10 KeV/10 KeV/m in tissuem in tissue

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Track Etch Detector System –Track Etch Detector System –Autoscan 60Autoscan 60

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Track Etch Detector System - Track Etch Detector System - Autoscan 60 ReaderAutoscan 60 Reader

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Track Etch Detector System – Track Etch Detector System – Polymer DetectorsPolymer Detectors

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Track Etch Detector System Track Etch Detector System

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Glass Track-Etch DetectorsGlass Track-Etch Detectors

Developed by University of California at Developed by University of California at Berkeley in the United StatesBerkeley in the United States

Called BP-1 (barium-phosphate) glass and Called BP-1 (barium-phosphate) glass and has high sensitivity and resolutionhas high sensitivity and resolution

Used in experiments in high-energy Used in experiments in high-energy physics, and cosmic-ray physics in outer physics, and cosmic-ray physics in outer spacespace

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Typical Track Etch PitTypical Track Etch Pit

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Etch-pits In the Trek Detector ProducedEtch-pits In the Trek Detector Produced By Cosmic Rays By Cosmic Rays

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SummarySummary

Nuclear track etch detectors and principles Nuclear track etch detectors and principles of detection were discussedof detection were discussed

Students learned about etchable plastic Students learned about etchable plastic foils, detection thresholds for various foils, detection thresholds for various materials, neutron detection, approaches to materials, neutron detection, approaches to track etch detection, proton detection, and track etch detection, proton detection, and types of track etch detector systemstypes of track etch detector systems

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Knoll, G.T., Knoll, G.T., Radiation Detection and Radiation Detection and MeasurementMeasurement, 3, 3rdrd Edition, Wiley, New York (2000) Edition, Wiley, New York (2000)

Attix, F.H., Attix, F.H., Introduction to Radiological Physics Introduction to Radiological Physics and Radiation Dosimetryand Radiation Dosimetry, Wiley, New York (1986), Wiley, New York (1986)

International Atomic Energy Agency, International Atomic Energy Agency, Determination of Absorbed Dose in Photon and Determination of Absorbed Dose in Photon and Electron Beams, 2Electron Beams, 2ndnd Edition, Technical Reports Edition, Technical Reports Series No. 277, IAEA, Vienna (1997)Series No. 277, IAEA, Vienna (1997)

Where to Get More InformationWhere to Get More Information

3/2003 Rev 13/2003 Rev 1 II.3.8 – slide II.3.8 – slide 3232 of 34 of 34

International Commission on Radiation Units International Commission on Radiation Units and Measurements, Quantities and Units in and Measurements, Quantities and Units in Radiation Protection Dosimetry, Report No. 51, Radiation Protection Dosimetry, Report No. 51, ICRU, Bethesda (1993)ICRU, Bethesda (1993)

International Commission on Radiation Units International Commission on Radiation Units and Measurements, Fundamental Quantities and and Measurements, Fundamental Quantities and Units for Ionizing Radiation, Report No. 60, ICRU, Units for Ionizing Radiation, Report No. 60, ICRU, Bethesda (1998)Bethesda (1998)

Hine, G. J. and Brownell, G. L., (Ed. ), Hine, G. J. and Brownell, G. L., (Ed. ), Radiation Radiation DosimetryDosimetry, Academic Press (New York, 1956), Academic Press (New York, 1956)

Where to Get More InformationWhere to Get More Information

3/2003 Rev 13/2003 Rev 1 II.3.8 – slide II.3.8 – slide 3333 of 34 of 34

Bevelacqua, Joseph J., Bevelacqua, Joseph J., Contemporary Health Contemporary Health PhysicsPhysics, John Wiley & Sons, Inc. (New York, , John Wiley & Sons, Inc. (New York, 1995)1995)

International Commission on Radiological International Commission on Radiological Protection, Data for Protection Against Ionizing Protection, Data for Protection Against Ionizing Radiation from External Sources: Supplement to Radiation from External Sources: Supplement to ICRP Publication 15. A Report of ICRP ICRP Publication 15. A Report of ICRP Committee 3, ICRP Publication 21, Pergamon Committee 3, ICRP Publication 21, Pergamon Press (Oxford, 1973)Press (Oxford, 1973)

Where to Get More InformationWhere to Get More Information

3/2003 Rev 13/2003 Rev 1 II.3.8 – slide II.3.8 – slide 3434 of 34 of 34

Where to Get More InformationWhere to Get More Information

Cember, H., Introduction to Health Physics, 3Cember, H., Introduction to Health Physics, 3rdrd Edition, McGraw-Hill, New York (2000)Edition, McGraw-Hill, New York (2000)

Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8Table of Isotopes (8thth Edition, 1999 update), Wiley, Edition, 1999 update), Wiley, New York (1999)New York (1999)

International Atomic Energy Agency, The Safe Use International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)IAEA, Vienna (1995)