3/2003 Rev 1 II.1.2 – slide 1 of 32 IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources Session II.1.2 Part IIQuantities and Measurements Module 1Quantities and Units Session 2Kerma, Dose, LET and more

3/2003 Rev 1 II.1.2 – slide 2 of 32 Overview  Dosimetric quantities and associated terminology will be discussed  Students will learn about kerma (rate), exposure (rate), absorbed dose (rate), linear energy transfer (LET), lineal energy transfer, and organ dose  Underlying concepts and use of the quantities will be described

3/2003 Rev 1 II.1.2 – slide 3 of 32 Content  Kerma (rate)  Mass energy absorption coefficient  Air Kerma  Exposure (rate)  Absorbed dose (rate)  Energy imparted  Linear energy transfer (LET)  Lineal energy transfer  Organ dose

3/2003 Rev 1 II.1.2 – slide 4 of 32 Kerma Kerma (Kinetic Energy Released per unit Mass) Kerma is defined as: K = where dE tr is the sum of the initial kinetic energies of all the charged particles liberated by uncharged particles in a mass dm dE tr dm

3/2003 Rev 1 II.1.2 – slide 5 of 32 Kerma  The unit of kerma is the J kg -1  The special name for the unit of kerma is gray (Gy)

3/2003 Rev 1 II.1.2 – slide 6 of 32 Kerma Kerma is usually expressed in terms of the distribution  (E) of the uncharged particle fluence with respect to energy The kerma is then given by: K =   (E) E ( ) dE Where  tr /  is the mass energy transfer coefficient of the material for uncharged particles of energy E  tr 

3/2003 Rev 1 II.1.2 – slide 7 of 32 Kerma Rate The kerma rate, K, is the quotient of dK by dt, where dK is the increment of kerma in the time interval dt, thus: K = The unit is J kg -1 s -1 and the special name for the unit of kerma rate is gray per second (Gy s -1 )..dKdt

3/2003 Rev 1 II.1.2 – slide 8 of 32 Air Kerma The kerma in air, K a, in units of pGy, is given by: K a =  (160.22) ( ) (E  ) where: E  is the photon energy in MeV  is the photon fluence in units of cm -2  tr /  is the mass energy transfer coefficient in cm 2 g -1  tr 

3/2003 Rev 1 II.1.2 – slide 9 of 32 Mass Energy Absorption Coefficient The mass energy absorption coefficient,  en / , is related to the mass energy transfer coefficient,  tr / , by the following equation: = (1 – g) where g is the fraction of initial secondary electron energy that is radiated as bremsstrahlung  en   tr 

3/2003 Rev 1 II.1.2 – slide 10 of 32 Exposure Exposure is: A quantity used to indicate the amount of ionization in air produced by x- or gamma-ray radiation The SI unit of exposure is the coulomb per kilogram (C/kg)

3/2003 Rev 1 II.1.2 – slide 11 of 32 Exposure The exposure, X, in units of C kg -1, is related to the air kerma as follows: X = where “W” is the average energy spent by an electron to produce an ion pair and “e” is the electronic charge W K a (1 – g) e

3/2003 Rev 1 II.1.2 – slide 12 of 32 Exposure  Exposure is measured under conditions of electronic equilibrium  For photon energies above about 3 MeV, the ranges of secondary electrons become a significant fraction of the photon attenuation lengths and the departure from equilibrium may be significant  Thus, exposure is not defined above photon energies of 3 MeV

3/2003 Rev 1 II.1.2 – slide 13 of 32 Exposure Rate The exposure rate, X, is the quotient of dX by dt, where dX is the increment of exposure in the time interval dt, thus: X = The unit is C kg -1 s -1..dXdt

3/2003 Rev 1 II.1.2 – slide 14 of 32 Absorbed Dose The absorbed dose, D, is given by: D = Where d  is the mean energy imparted to matter of mass dm _ dddddt _

3/2003 Rev 1 II.1.2 – slide 15 of 32 Absorbed Dose  The unit of absorbed dose is J kg -1  The special name for the unit of absorbed dose is gray (Gy)

3/2003 Rev 1 II.1.2 – slide 16 of 32 Energy Imparted Energy imparted is the energy incident minus the energy leaving the mass (excluding the energy released in nuclear transformations to keep the dose from becoming negative when the mass contains a radioactive source)

3/2003 Rev 1 II.1.2 – slide 17 of 32 Absorbed Dose Rate The absorbed dose rate, D, is the quotient of dD by dt, where dD is the increment of absorbed dose in the time interval dt, thus: D = The unit is J kg -1 s -1 and the special name for the unit of absorbed dose rate is gray per second (Gy s -1 ).dDdt.

3/2003 Rev 1 II.1.2 – slide 18 of 32 Lineal Energy Transfer Lineal energy transfer is the energy transferred from a particle to the medium traversed per unit length The magnitude is expressed in kilo-electron volts per micrometer (keV/  m)

3/2003 Rev 1 II.1.2 – slide 19 of 32 Lineal Energy Transfer  Expresses the level of energy transferred at a microscopic scale  Average value ranges from less than 1 kev/  m for electromagnetic radiation to several hundred kev/  m for heavy ions  Values for neutrons cover the whole of the range

3/2003 Rev 1 II.1.2 – slide 20 of 32 Linear Energy Transfer Linear energy transfer (LET), L , is defined generally as: L  = [ ]  where dE is the energy lost in traversing distance dl and  is an upper bound on the energy transferred in any single collision dEdl

3/2003 Rev 1 II.1.2 – slide 21 of 32 Linear Energy Transfer  A measure of how, as a function of distance, energy is transferred from radiation to the exposed matter  A high value of LET indicates that energy is deposited within a small distance

3/2003 Rev 1 II.1.2 – slide 22 of 32 Linear Energy Transfer

3/2003 Rev 1 II.1.2 – slide 23 of 32 Organ Dose  Following an intake into the body of a radioactive material, there is a period during which the material gives rise to equivalent doses delivered in the organs or tissues of the body at varying rates  The time integral of the equivalent-dose rate is called the committed equivalent dose, H T ( ), where is the integration time in years following the intake

3/2003 Rev 1 II.1.2 – slide 24 of 32 Specific Organs for Which Doses Are Calculated  Gonads  Bone marrow (red)  Bladder  Breast  Thyroid  Skin  Remainder  Colon  Lung  Stomach  Liver  Oesophagus  Bone surface

3/2003 Rev 1 II.1.2 – slide 25 of 32 Remainder Organs  Adrenals  Upper large intestine  Small intestine  Kidney  pancreas  Brain  Spleen  Thymus  Uterus  muscle

3/2003 Rev 1 II.1.2 – slide 26 of 32 Phantom for Organ Dose Calculation

3/2003 Rev 1 II.1.2 – slide 27 of 32 Organ Dose

3/2003 Rev 1 II.1.2 – slide 28 of 32 Summary  Dosimetric quantities and associated terminology were discussed  Students learned about kerma (rate), exposure (rate), absorbed dose (rate), linear energy transfer, lineal energy transfer and organ dose

3/2003 Rev 1 II.1.2 – slide 29 of 32  Knoll, G.T., Radiation Detection and Measurement, 3 rd Edition, Wiley, New York (2000)  Attix, F.H., Introduction to Radiological Physics and Radiation Dosimetry, Wiley, New York (1986)  International Atomic Energy Agency, Determination of Absorbed Dose in Photon and Electron Beams, 2 nd Edition, Technical Reports Series No. 277, IAEA, Vienna (1997) Where to Get More Information

3/2003 Rev 1 II.1.2 – slide 30 of 32  International Commission on Radiation Units and Measurements, Quantities and Units in Radiation Protection Dosimetry, Report No. 51, ICRU, Bethesda (1993)  International Commission on Radiation Units and Measurements, Fundamental Quantities and Units for Ionizing Radiation, Report No. 60, ICRU, Bethesda (1998)  Hine, G. J. and Brownell, G. L., (Ed. ), Radiation Dosimetry, Academic Press (New York, 1956) Where to Get More Information

3/2003 Rev 1 II.1.2 – slide 31 of 32  Bevelacqua, Joseph J., Contemporary Health Physics, John Wiley & Sons, Inc. (New York, 1995)  International Commission on Radiological Protection, Data for Protection Against Ionizing Radiation from External Sources: Supplement to ICRP Publication 15. A Report of ICRP Committee 3, ICRP Publication 21, Pergamon Press (Oxford, 1973) Where to Get More Information

3/2003 Rev 1 II.1.2 – slide 32 of 32 Where to Get More Information  Cember, H., Introduction to Health Physics, 3 rd Edition, McGraw-Hill, New York (2000)  Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)  International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)