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

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Presentation on theme: "DOSE CONCEPTS, QUANTITIES AND UNITS, BASIC PRINCIPLES AND PRIMARY METHODS OF RADIATION PROTECTION Module IV."— Presentation transcript:

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

2 - 2 Radiation exposure Traditional unit: Roentgen (R) = 2.58x10 -4 coulomb/kg = 1esu/cm 3

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

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

5 Module IV - 5 Equivalent dose (H T ) Accounts for biological effect per unit dose radiation weighting absorbed factor ( W R ) X dose (D) H T = W R x D X

6 Module IV - 6 Radiation weighting factors (W R ) Radiation weighting factors (W R ) ICRP 60 (1991)

7 Module IV - 7 Unit of equivalent dose SI unit: sievert (Sv) H T (Sv) = W R x D (Gy) Old unit: rem (roentgen equivalent man) H T (rem) =( W R ) x D (rad) 1 Sv = 100 rems

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

9 Module IV - 9 Tissue and organ weighting factors

10 Module IV - 10 Conversion between units used in radiation protection

11 Module IV - 11 Committed equivalent dose H T (t) and committed effective dose E(t)

12 Module IV - 12 Averted dose Projected dose Projected and avertable dose

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

14 Module IV - 14 Sources and levels of radiation exposure to population

15 Module IV - 15 Sources of radiation dose to general population

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

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

18 Module IV - 18 Cosmic radiation

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

20 Module IV - 20 Average ocupational radiation doses received during various types of work Non-coal mining 16.3 milisieverts Dose in milisieverts

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

22 Module IV - 22 Dose limits recomended by ICRP (1991) - tissues Annual doses to tissues OccupationalPublic Lens of the eye 150 mSv15 mSv Skin (1cm 2 )500 mSv50 mSv Hands and feet or individual organ 500 mSv

23 Module IV - 23 Radiation protection Basic principles and primary methods

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

25 Module IV - 25 ALARAALARAALARAALARA As low as reasonably achievable

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

27 Module IV - 27 Time Exposure rate =10mGy/h X Time = Total dose 1 hour = 10 mGy 2 hours = 20 mGy

28 Module IV - 28 Distance

29 Module IV - 29 Inverse square law 150 mSv/h 0.06 mSv/h d=50cm

30 Module IV - 30 Shielding

31 Module IV - 31 Shielding photons

32 Module IV - 32 Half value layer (HVL)

33 Module IV - 33 Internal exposure

34 Module IV - 34 Inhalation

35 Module IV - 35 Ingestion/Absorption

36 Module IV - 36 Protective clothing and hand washing

37 Module IV - 37 Medical exposure Relative effective dose and equivalent period of exposure to natural background radiation Effective dose (mSv) Equivalent period of natural radiation Radiography Chest0.023 days Pelvis1.06 months IVP4.62.5 years Barium studies9.04.5 years CT (Chest, Abdomen) 8.04 years Nuclear Medicine Thyroid imaging1.06 months Bone imaging3.61.8 years

38 Module IV - 38 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)


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