IAEA Quantities and Measurements - 3 Radiation Protection Quantities Day 3 – Lecture 1 1

IAEA Objective To study the radiation protection quantities and associated terminology and to learn about equivalent dose, radiation weighting factors, effective dose, tissue weighting factors, intake, committed dose, committed effective dose, and various operational quantities 2

IAEA Content Equivalent dose and dose rate Radiation weighting factors Effective dose Tissue weighting factors Weakly and strongly penetrating radiation Ambient dose equivalent Expanded and aligned radiation fields Directional dose equivalent Personal dose equivalent Intake Committed equivalent dose Committed effective dose 3

IAEA Equivalent Dose The equivalent dose in tissue T is given by the expression: H T = ∑r W R D T,R where D T,R is the absorbed dose averaged over the tissue or organ T, due to radiation R. 4

IAEA Equivalent Dose In radiological protection, it is the absorbed dose averaged over a tissue or organ It is weighted for the radiation quality of interest The weighting factor is called the radiation weighting factor, W R 5

IAEA Equivalent Dose W R is selected for the type and energy of the radiation incident on the body This weighted absorbed dose, called the equivalent dose, is strictly a dose The unit of equivalent dose is the joule per kilogram with the special name of Sievert (Sv) 6

IAEA Radiation Weighting Factors Type and Energy RangewRwR Photons: all energies1 Electrons : all energies1 Neutrons: energy < 10 keV5 Neutrons: 10 keV to 100 keV10 Neutrons: > 100 keV to 2 MeV20

IAEA Radiation Weighting Factors Type and Energy RangewRwR Neutrons: > 2 MeV to 20 MeV10 Neutrons: > 20 MeV5 Protons: > 2 MeV5 Alpha particles, fission fragments, heavy nuclei 20

IAEA Equivalent Dose Rate The equivalent dose rate, H T, is the quotient of dH T by dt, where dH T is the increment of equivalent dose in the time interval dt, thus: H T = The unit is J kg -1 s -1 and the special name for the unit of equivalent dose rate is Sievert per second (Sv s -1 ).. dH T dt 9

IAEA Effective Dose The effective dose is the sum of the weighted equivalent doses in all the tissues and organs of the body. It is given by: E = ∑t w T H T where H T is the equivalent dose in tissue or organ T and w T is the weighting factor for tissue T. 10

IAEA Tissue Weighting Factors Account for fact that the probability of stochastic effects depends on the organ or tissue irradiated Represent the relative contribution of irradiation of each organ or tissue to the total detriment due to the effects resulting from uniform irradiation of the whole body 11

IAEA Tissue Weighting Factors Desirable that a uniform equivalent dose over the whole body should give an effective dose numerically equal to that uniform equivalent dose Achieved by normalizing the sum of the tissue weighting factors to one 12

IAEA Tissue Weighting Factors Tissue or OrganWTWT Gonads0.20 Bone marrow (red)0.12 Colon0.12 Lung0.12 Stomach0.12 Bladder0.05 Breast0.05 Tissue or OrganWTWT Liver0.05 Oesophagus0.05 Thyroid0.05 Skin0.01 Bone surface0.01 Remainder0.05

IAEA Tissue Weighting Factors Remainder Organs Adrenals Upper large Intestine Small Intestine Kidney Pancreas Brain Spleen Thymus Uterus Muscle 14

IAEA Concept of Effective Dose The relationship between the probability of stochastic effects (primarily cancer and genetic effects) and equivalent dose is found to depend on the organ or tissue irradiated. The effective dose combines the equivalent doses to the various body organs and tissues in a way which correlates well with the total of the stochastic effects 15

IAEA Operational Quantities For radiation measurement purposes, the following operational quantities are defined: Ambient dose equivalent Directional dose equivalent Personal dose equivalent 16

IAEA Operational Quantities Where doses are estimated from area monitoring results, the relevant operational quantities are ambient dose equivalent and directional dose equivalent For individual monitoring, the use of the personal dose equivalent is recommended 17

IAEA Area Monitoring The quantities recommended for area monitoring refer to a phantom termed the ICRU sphere. The ICRU sphere (ICRU, 1980) is a 30 cm diameter, tissue-equivalent sphere with a density of 1 g cm -3 and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen, and 2.6% nitrogen 18

IAEA ICRU Reference Sphere Radiation field 19

IAEA Ambient Dose Equivalent The ambient dose equivalent, H*(d), at a point, is the dose equivalent that would be produced by the corresponding field, in the ICRU sphere at a depth d in millimeters on the radius opposing the direction of the field. For measurement of strongly penetrating radiations, the reference depth is 10 mm and the quantity denoted as H*(10). The unit is J kg -1 The special name for the unit of ambient dose equivalent is Sievert (Sv) 20

IAEA Expanded Field An expanded radiation field is defined as a hypothetical radiation field in which the fluence, and its angular and energy distributions, have the same value throughout the volume of interest as the actual field at the point of reference 21

IAEA Directional Dose Equivalent The directional dose equivalent, H‘(d,), at a point, is the dose equivalent that would be produced by the corresponding expanded field in the ICRU sphere at a depth d on a radius in a specified direction. Directional dose equivalent is of particular use in the assessment of dose to the skin or eye lens The unit is J kg -1 The special name for the unit of directional dose equivalent is Sievert (Sv) 22

IAEA Personal Dose Equivalent The personal dose equivalent, H p (d), is the dose equivalent in soft tissue, at an appropriate depth d, below a specified point on the body, H p (d) can be measured with a dosimeter which is worn at the surface of the body and covered with an appropriate thickness of tissue-equivalent material 23

IAEA Personal Dose Equivalent The unit is J kg -1 The special name for the unit of personal dose equivalent is sievert (Sv) H p (10), measured at a depth of 10 mm in soft tissue, is the operational surrogate for the effective dose, E 24

IAEA Intakes of Radioactive Material When radioactive material (RAM) is inhaled or ingested, the result is an intake into the body Intakes of RAM are usually expressed in units of Bq An intake should be contrasted with an uptake of RAM into a specific organ or tissue 25

IAEA Intakes of Radioactive Material ICRP 60 defines the annual limit on intake (ALI) for each radionuclide The ALI is based on an average effective dose limit of 20 mSv per year 26

IAEA Committed Equivalent Dose Following an intake into the body of a radioactive material, there is a period during which the material gives rise to equivalent doses 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 27

IAEA Committed Effective Dose The committed effective dose E(50) for workers is defined as: E(50) = sum w T H T (50) where H T (50) is the committed equivalent dose and w T is the specific weighting factor for the tissues and organs 28

IAEA Summary Radiation protection quantities and associated terminology were discussed Students learned about equivalent dose, radiation weighting factors, effective dose, tissue weighting factors, intake, committed dose, committed effective dose, and various operational quantities 29

IAEA 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 30

IAEA 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 31

IAEA 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 32