3/2003 Rev 13/2003 Rev 1 II.1.2 – slide II.1.2 – slide 11 of 32 of 32IAEA 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.1.2Session II.1.2

Part IIPart II Quantities and MeasurementsQuantities and Measurements

Module 1Module 1 Quantities and UnitsQuantities and Units

Session 2Session 2 Kerma, Dose, LET and moreKerma, Dose, LET and more

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OverviewOverview

Dosimetric quantities and associated Dosimetric quantities and associated terminology will be discussedterminology will be discussed

Students will learn about kerma (rate), Students will learn about kerma (rate), exposure (rate), absorbed dose (rate), linear exposure (rate), absorbed dose (rate), linear energy transfer (LET), lineal energy energy transfer (LET), lineal energy transfer, and organ dosetransfer, and organ dose

Underlying concepts and use of the Underlying concepts and use of the quantities will be describedquantities will be described

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ContentContent

Kerma (rate)Kerma (rate) Mass energy absorption coefficientMass energy absorption coefficient Air KermaAir Kerma Exposure (rate)Exposure (rate) Absorbed dose (rate)Absorbed dose (rate) Energy impartedEnergy imparted Linear energy transfer (LET)Linear energy transfer (LET) Lineal energy transferLineal energy transfer Organ doseOrgan dose

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KermaKerma

Kerma (Kerma (KKinetic inetic EEnergy nergy RReleased per unit eleased per unit MaMass)ss)

Kerma is defined as:Kerma is defined as:

K = K =

wherewhere

dEdEtrtr is the sum of the initial kinetic energies of all the is the sum of the initial kinetic energies of all the charged particles liberated by uncharged particles in a charged particles liberated by uncharged particles in a mass dmmass dm

dEdEtrtr

dmdm

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KermaKerma

The unit of kerma is the J kgThe unit of kerma is the J kg-1-1

The special name for the unit of kerma The special name for the unit of kerma is gray (Gy)is gray (Gy)

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KermaKerma

Kerma is usually expressed in terms of the distribution Kerma is usually expressed in terms of the distribution (E) of the uncharged particle fluence with respect to (E) of the uncharged particle fluence with respect to energyenergy

The kerma is then given by:The kerma is then given by:

K = K = (E) E ( ) dE(E) E ( ) dE

Where Where trtr// is the mass energy transfer coefficient of the is the mass energy transfer coefficient of the material for uncharged particles of energy Ematerial for uncharged particles of energy E

trtr

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Kerma RateKerma Rate

The kerma rate, K, is the quotient of dK by dt, The kerma rate, K, is the quotient of dK by dt, where dK is the increment of kerma in the time where dK is the increment of kerma in the time interval dt, thus:interval dt, thus:

K =K =

The unit is J kgThe unit is J kg-1-1 s s-1-1 and the special name for and the special name for the unit of kerma rate is gray per secondthe unit of kerma rate is gray per second(Gy s(Gy s-1-1))

..

..

dKdKdtdt

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Air KermaAir Kerma

The kerma in air, KThe kerma in air, Kaa, in units of pGy, is given , in units of pGy, is given by:by:

KKaa = = (160.22) ( ) (E(160.22) ( ) (E))

where:where:

EE is the photon energy in MeVis the photon energy in MeV is the photon fluence in units of cmis the photon fluence in units of cm-2-2

trtr// is the mass energy transfer coefficient in is the mass energy transfer coefficient in cmcm22 g g-1-1

trtr

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Mass EnergyMass EnergyAbsorption CoefficientAbsorption Coefficient

The mass energy The mass energy absorptionabsorption coefficient, coefficient, enen//, is , is related to the mass energy related to the mass energy transfertransfer coefficient, coefficient, trtr//, by the following equation:, by the following equation:

= (1 – g)= (1 – g)

where g is the fraction of initial secondary where g is the fraction of initial secondary electron energy that is radiated as electron energy that is radiated as bremsstrahlungbremsstrahlung

enen

trtr

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ExposureExposure

Exposure is:Exposure is:

A quantity used to indicate the amount of A quantity used to indicate the amount of ionization in air produced by x- or gamma-ray ionization in air produced by x- or gamma-ray radiationradiation

The SI unit of exposure is the coulomb per The SI unit of exposure is the coulomb per kilogram (C/kg)kilogram (C/kg)

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ExposureExposure

The exposure, X, in units of C kgThe exposure, X, in units of C kg-1-1, is related , is related to the air kerma as follows:to the air kerma as follows:

X =X =

where “W” is the average energy spent by where “W” is the average energy spent by an electron to produce an ion pair and “e” is an electron to produce an ion pair and “e” is the electronic chargethe electronic charge

WW

KKaa (1 – g) e (1 – g) e

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ExposureExposure

Exposure is measured under conditions of Exposure is measured under conditions of electronic equilibriumelectronic equilibrium

For photon energies above about 3 MeV, the ranges For photon energies above about 3 MeV, the ranges of secondary electrons become a significant fraction of secondary electrons become a significant fraction of the photon attenuation lengths and the departure of the photon attenuation lengths and the departure from equilibrium may be significantfrom equilibrium may be significant

Thus, exposure is not defined above photon Thus, exposure is not defined above photon energies of 3 MeVenergies of 3 MeV

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Exposure RateExposure Rate

The exposure rate, X, is the quotient of dX by The exposure rate, X, is the quotient of dX by dt, where dX is the increment of exposure in the dt, where dX is the increment of exposure in the time interval dt, thus:time interval dt, thus:

X =X =

The unit is C kgThe unit is C kg-1-1 s s-1-1

..

..

dXdXdtdt

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Absorbed DoseAbsorbed Dose

The absorbed dose, D, is given by:The absorbed dose, D, is given by:

D =D =

Where dWhere d is the mean energy imparted to is the mean energy imparted to matter of mass dmmatter of mass dm

__dddtdt

__

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Absorbed DoseAbsorbed Dose

The unit of absorbed dose is J kgThe unit of absorbed dose is J kg-1-1

The special name for the unit of absorbed The special name for the unit of absorbed dose is gray (Gy)dose is gray (Gy)

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Energy ImpartedEnergy Imparted

Energy imparted is the energy incident minusEnergy imparted is the energy incident minus

the energy leaving the mass (excluding the the energy leaving the mass (excluding the energy released in nuclear transformations to energy released in nuclear transformations to keep the dose from becoming negative when keep the dose from becoming negative when the mass contains a radioactive source)the mass contains a radioactive source)

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Absorbed Dose RateAbsorbed Dose Rate

The absorbed dose rate, D, is the quotient of The absorbed dose rate, D, is the quotient of dD by dt, where dD is the increment of dD by dt, where dD is the increment of absorbed dose in the time interval dt, thus:absorbed dose in the time interval dt, thus:

D =D =

The unit is J kgThe unit is J kg-1-1 s s-1-1 and the special name and the special name for the unit of absorbed dose rate is gray per for the unit of absorbed dose rate is gray per second (Gy ssecond (Gy s-1-1))

..dDdDdtdt

..

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Lineal Energy TransferLineal Energy Transfer

Lineal energy transfer is the energy transferred Lineal energy transfer is the energy transferred from a particle to the medium traversed per unit from a particle to the medium traversed per unit lengthlength

The magnitude is expressed in kilo-electron The magnitude is expressed in kilo-electron volts per micrometer (keV/volts per micrometer (keV/m)m)

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Lineal Energy TransferLineal Energy Transfer

Expresses the level of energy transferred at a Expresses the level of energy transferred at a microscopic scalemicroscopic scale

Average value ranges from less than 1 kev/Average value ranges from less than 1 kev/m m for electromagnetic radiation to several for electromagnetic radiation to several hundred kev/hundred kev/m for heavy ionsm for heavy ions

Values for neutrons cover the whole of the Values for neutrons cover the whole of the rangerange

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Linear Energy TransferLinear Energy Transfer

Linear energy transfer (LET), LLinear energy transfer (LET), L, is, is defined defined

generally as:generally as:

LL = [ ] = [ ]

where dE is the energy lost in traversing where dE is the energy lost in traversing distance dl and distance dl and is an upper bound on the is an upper bound on the energy transferred in any single collision energy transferred in any single collision

dEdEdldl

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Linear Energy TransferLinear Energy Transfer

A measure of how, as a function of distance, A measure of how, as a function of distance, energy is transferred from radiation to the energy is transferred from radiation to the exposed matterexposed matter

A high value of LET indicates that energy is A high value of LET indicates that energy is deposited within a small distancedeposited within a small distance

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Linear Energy TransferLinear Energy Transfer

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Organ DoseOrgan Dose

Following an intake into the body of a Following an intake into the body of a radioactive material, there is a period during radioactive material, there is a period during which the material gives rise to equivalent which the material gives rise to equivalent doses delivered in the organs or tissues of doses delivered in the organs or tissues of the body at varying ratesthe body at varying rates

The time integral of the equivalent-dose rate The time integral of the equivalent-dose rate is called the committed equivalent dose, is called the committed equivalent dose, HHTT((), where ), where is the integration time in years is the integration time in years following the intakefollowing the intake

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Specific Organs for WhichSpecific Organs for WhichDoses Are CalculatedDoses Are Calculated

GonadsGonads Bone marrow (red)Bone marrow (red) BladderBladder BreastBreast ThyroidThyroid SkinSkin RemainderRemainder

ColonColon LungLung StomachStomach LiverLiver OesophagusOesophagus Bone surfaceBone surface

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Remainder OrgansRemainder Organs

AdrenalsAdrenals Upper large intestineUpper large intestine Small intestineSmall intestine KidneyKidney pancreaspancreas

BrainBrain SpleenSpleen ThymusThymus UterusUterus musclemuscle

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Phantom for Organ Dose Phantom for Organ Dose CalculationCalculation

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Organ DoseOrgan Dose

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SummarySummary

Dosimetric quantities and associated Dosimetric quantities and associated terminology were discussedterminology were discussed

Students learned about kerma (rate), Students learned about kerma (rate), exposure (rate), absorbed dose (rate), linear exposure (rate), absorbed dose (rate), linear energy transfer, lineal energy transfer and energy transfer, lineal energy transfer and organ doseorgan dose

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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.1.2 – slide II.1.2 – slide 3030 of 32 of 32

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

International Commission on Radiation Units and International Commission on Radiation Units and Measurements, Fundamental Quantities 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)

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Where to Get More InformationWhere to Get More Information

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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 Committee ICRP Publication 15. A Report of ICRP Committee 3, ICRP Publication 21, Pergamon Press (Oxford, 3, ICRP Publication 21, Pergamon Press (Oxford, 1973)1973)

Where to Get More InformationWhere to Get More Information

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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)