DOSE CONCEPTS QUANTITIES AND UNITS BASIC PRINCIPLES AND

DOSE CONCEPTS, QUANTITIES AND UNITS, BASIC PRINCIPLES AND PRIMARY METHODS OF RADIATION PROTECTION Module IV

Radiation exposure Traditional unit: Roentgen (R) = 2. 58 x 10 -4 coulomb/kg = 1 esu/cm 3 Module IV 2

Absorbed dose (D) Energy imparted to matter from any type of radiation D: absorbed dose E: energy absorbed by material of mass ‘m’ Module IV 3

Units of absorbed dose The SI unit: gray (Gy) 1 Gy = 1 joule/kilogram Old unit : rad 1 Gy=100 rad Module IV 4

Equivalent dose (HT) Accounts for biological effect per unit dose radiation weighting absorbed X factor ( WR ) X dose (D) HT = WR x D Module IV 5

Radiation weighting factors (WR) ICRP 60 (1991) Module IV 6

Unit of equivalent dose SI unit: sievert (Sv) HT (Sv) = WR x D (Gy) Old unit: rem (roentgen equivalent man) HT (rem) =( WR) x D (rad) Module IV 1 Sv = 100 rems 7

Effective dose (E) Risk related parameter, taking relative radiosensitivity of each organ and tissue into account E(Sv)= ΣT WT x HT WT : tissue weighting factor for organ T HT : equivalent dose received by organ or tissue T Module IV 8

Tissue and organ weighting factors Module IV 9

Conversion between units used in radiation protection Module IV 10

Committed equivalent dose HT(t) and committed effective dose E(t) Module IV 11

Projected and avertable dose Projected dose Averted dose Module IV 12

Collective effective dose (S ) Total radiation dose incurred by population Ei: average effective dose in the population subgroup i Ni: number of individuals in subgroup i Unit: man-sievert (man. Sv) Module IV 13

Sources and levels of radiation exposure to population Module IV 14

Sources of radiation dose to general population Module IV 15

Background radiation • Terrestrial radioactivity • Cosmic radiation • Internal radioactivity Natural background radiation doses in Europe Module IV 16

Terrestrial radiation: external and internal exposure U-238 Ra-222 Th-232 Ra-220 Module IV 17

Cosmic radiation Module IV 18

Internal radioactivity • Radioactivity in diet • lead-210 • polonium-210 • potassium-40 Module IV 19

‘Non-coal’ Module IV Dose in milisieverts mining 16. 3 milisieverts Average ocupational radiation doses received during various types of work 20

Dose limits recomended by ICRP (1991) - whole body Occupational exposure Public exposure 50 m. Sv maximum 5 m. Sv in any 5 in any 1 year consecutive years 100 m. Sv in 5 years (Working figure 20 m. Sv per year) Module IV (Working figure 1 m. Sv per year 21

Dose limits recomended by ICRP (1991) - tissues Annual doses to tissues Occupational Public Lens of the eye 150 m. Sv 15 m. Sv Skin (1 cm 2) 500 m. Sv 50 m. Sv Hands and feet or individual organ 500 m. Sv Module IV 22

Radiation protection Basic principles and primary methods Module IV 23

Basic principles of radiation protection l Justification of practice l Optimization of protection l Individual dose limits Module IV 24

AL ARA As low as reasonably achievable Module IV 25

Basic methods of protection against exposure to ionizing radiation l Three basic factors n Time n Distance n Shielding Module IV 26

Time Exposure rate =10 m. Gy/h X Time = Total dose 1 hour = 10 m. Gy 2 hours = 20 m. Gy Module IV 27

Distance Module IV 28

Inverse square law d=50 cm 150 m. Sv/h 0. 06 m. Sv/h Module IV 29

Shielding Module IV 30

Shielding photons Module IV 31

Half value layer (HVL) Module IV 32

Internal exposure Module IV 33

Inhalation Module IV 34

Ingestion/Absorption Module IV 35

Protective clothing and hand washing Module IV 36

Medical exposure Relative effective dose and equivalent period of exposure to natural background radiation Effective dose (m. Sv) Equivalent period of natural radiation Chest 0. 02 3 days Pelvis 1. 0 6 months IVP 4. 6 2. 5 years Barium studies 9. 0 4. 5 years CT (Chest, Abdomen) 8. 0 4 years Thyroid imaging 1. 0 6 months Bone imaging 3. 6 1. 8 years 37 Radiography Nuclear Medicine Module IV

Review points • Becquerel, coulomb per kilogram, gray, and sievert are part of International System of Units (SI). • Absorbed dose of radiation in SI units is expressed in gray. Ability of some types of radiation to cause more significant levels of biological damage taken into account with radiation weighting factor used to determine equivalent dose, expressed in sieverts • Goal of radiation safety: keep radiation exposure as low as reasonably achievable (ALARA) Module IV 38