Radiation physics and radiation protection. University of Szeged Department of Nuclear Medicine

Transcription

1 Radiation physics and radiation protection University of Szeged Department of Nuclear Medicine

2 Radiation doses to the population 1

3 Radiation doses to the population 2

4 Sources of radiation 1 Radiation we live with Natural background radiation - Construction materials (55 %) - Radiation of the soil (26 %) - Cosmic radiation (17%) - Food (2%)

5 Sources of radiation 2 Radiation we live with Food Daily intake Radioactive levels (Bq/kg) Ra-226 ( g Th-228 / Pb-210 K-40 d ) Rice W P

6 Sources of radiation 3 Radiation we live with

7 Sources of the radiation 4 Artificial the X-ray tubes reactors and cyclotrons - Could have detrimental effects - Optimal function radiation safety

8 CT X ray tube collimators X ray emission in all directions

9 Cyclotrons

10 Decay of radionuclides Mother nuclide Type of decay Half life Daughter nuclide + particles + energy (e.g.photon)

11 Decay processes Alpha decay e.g. 224 Ra Beta decay e.g. 14 C, 99 Mo A A-4 Z X A Z 4 Z-2 Y + 2 alpha + E A X Y + e + E v + E ß Z Positron decay A Z A 0 Z-1 +1 e.g. 11 C, 18 F X Y + e + E v + E ß+ Electron capture e.g. 111 In, 125 I X + e - Y* Y + gamma A A A Z Z-1 Z-1

12 Decay scheme of 14 C

13 Principal decay scheme of 99 Mo

14 Decay scheme of 18 F

15 Ionising radiation Non ionising radiation

16 Ionising Sources of radiation 2 Particule radiation (Energia MeV) alfa (α) 2-10 beta (β) 0,01-50 protons (p) 1-10 neutrons (n) 0,02-30 ions 1-50 Electromagnetic radiation X-rays 0,005-0,5 gamma-radiation (γ) 0,005-50

17 Non ionising radiation Electromagnetic optical (light) high frequency low frequency Sound infrasound Sources of radiation 3 ultrasound

18 Path of heavy charged particle in matter close approach excitation ionization

19 Principal photon interactions in matter

20 Positron annihilation

21 Biological effects of the radiation 1 Physical phase ( s) Direct effects (ionisation and excitation) Indirect effects H 2 O radiolysis Free radicals Chemical phase ( s) DNA Molecule fragmentation Biological phase (sec-years) Stochastic effects Deterministic effects

22 Stochastic effects 1 cancer induction genetic effects No threshold dose!

23 Stochastic effects 2 Risk models

24 Deterministic effects 1 Effect Threshold dose Absorbed dose

25 Deterministic effects 2 Dermatitis Cataracta Acute radiation sickness

26 Risc assessment International Commission on Radiological Protection (ICRP) For radiation workers: 4,0 x (10-2 /Sv) For population: 5,0 x (10-2 /Sv) 20 msv: 8 x 10-4 = 1/ msv/y: 5 x 10-5 = 1/20000

27 Radiation We live with 1-3 msv Could be lethal 4000 msv Border?

28 Radiation doses 1 Absorbed dose Equivalent dose Effective dose Personal dose equivalent Committed equivalent dose Committed effective dose Collective dose

29 Absorbed dose Radiation doses 2 D = d ε /dm unite: J/ kg; gray (Gy) Equivalent dose H T,R = w R D T,R unite: J/ kg; sievert (Si); w R =1 (photons) Effective dose E = Σ w T H T = Σ w T Σ w R D T,R T T R unite: J/ kg; ievert (Sv)

30 Radiation doses 3 Commited dose long lived radionuclides 137-Cs (30 year), 90-Sr (28.5 year) - we intake them with food, water, air 137-Cs (K biological analog) accumulates in soft tissues 90-Sr (Ca biological analog) accumulates in bones

31 Dose limits 96/29/EURATOM for the Professional radiation workers: Effective dose: 100 msv/ 5 consecutive years; 50 msv/any year Organ doses: Eyes: 150 msv/ year (equivalent dose) Hands: 500 msv/ year (equivalent dose)

32 96/29/EURATOM for the Public Effective dose: 1 msv/ 1 year Dose limits Organ doses: Eyes: 15 msv/ year (equivalent dose) Hands: 50 msv/ year (equivalent dose)

33 Detection of the radiation Gas detectors Ionisation chambers Proportional counters Geiger-Müller counters Scintillation detectors (SPECT, PET, CT) X-ray films

34 Gas-filled detectors

35 Scintillation detectors Higher counting rates (fast resolving times) Gamma radiation (proportionality) Sodium iodine crystals (Tl activated) Gamma camera, SPECT, well counter BGO, LSO (PET) Semiconductors (dosimeter, camera?)

36 Scintillation detectors

37 Gamma Camera Detector

38 SPECT

39 PET

40 Personal Dosimeters X-ray films TLD dosimeters Electronic dosimeters Optical dosimeters

41 Radiation safety in NM As low as reasonably achievable (ALARA) Reducing radiation exposure: time distance shilding

42 Figure 2. Schematic illustrates the inverse-square law Brateman L Radiographics 1999;19: by Radiological Society of North America

43 1999 by Radiological Society of North America Brateman L Radiographics 1999;19:

44 Shilding 0,5 mm Pb 70 kv energy X-rays penetration: 0,36% 100 kv energy X-reay penetration: 3,2% Pb glass 30%-70%

45 International Atomic Energy Agency (IAEA) IBSS 115 (1966) standards

46 Changes in Dose Limit (ICRP) msv (Safe levels) Year

47

48

49 PET

50 Rules for working safely with unsealed radionuclide sources Always work in areas designed for handling radionuclides. To open sealed bottles use a well-designed hood or glove box. Work areas should be covered, to catch any spills and to prevent the spread of contamination. Plan all procedures in advance. Do not eat, drink or smoke in areas where unsealed radionuclides are being used or stored. Wear protective clothing and surgical gloves while working

51 Radioactive material decontamination procedures Place absorbent material over the spill to keep it from spreading. Notify others in the area and limit access to the spill area. Monitor personnel for contamination and, if necessary, decontaminate immediately. Label the boundaries of the spill area. Dispose all cleanup materials as radioactive waste.