The Principles of Radiation Monitoring and the Radiation Protection System in Hong Kong. H.M.Mok Physicist Radiation Health Unit Department of Health

Transcription

1 The Principles of Radiation Monitoring and the Radiation Protection System in Hong Kong H.M.Mok Physicist Radiation Health Unit Department of Health

2 Contents Basic properties of ionising radiation and its interactions with matter Principles of radiation detection and the measuring instruments Dosimetry and health effects of ionising radiation Radiation protection system and regulatory framework in Hong Kong

3 Basic Properties of Ionising Radiation What is radiation? Radiation is the energy emitted in the form of microscopic particles or photons Radiation interacts with matter through the fundamental interactions of our nature Predominantly through the electromagnetic (for charged particles and photons) and strong interactions (for hadrons)

4 Basic Properties of Ionising Radiation Ionising radiation The adiation that interacts with a physical medium to produce ion pairs For example, α, β, X, γ-radiation, neutron, proton, pion, muon, etc. Invisible to human such that the detection of it demands a suitable monitoring instrument

5 Basic Properties of Ionising Radiation Non-ionising radiation The adiation that does not produce ion pairs in physical medium For example, soft ultra-violet, infra-red, visible light, microwave, radio-frequency, etc.

6 Basic Properties of Ionising Radiation

7 Electromagnetic Spectrum (Photons)

8 Basic Properties of Ionising Radiation Two major sources of ionising radiation: Naturally occurring radiation Cosmic rays Natural radioactive substances in environment (e.g. uranium and thorium in rock and soil) Indoor radon Contribute to the public exposure by about 80%

9 Sources of Ionizing Radiation Cosmic rays

10 Sources of Ionizing Radiation Artificially produced radiation X-rays Artificially produced radioactive substances (e.g. Co-60, I-131, Cs-137, etc.) Nuclear reactor (e.g. PWR, AGR, etc.) Nuclear weapon (e.g. fission type, fission-fusionfission type, etc.) Particle accelerator (e.g. synchrotron, linear accelerator, cyclotron, etc.)

11 Sources of Ionizing Radiation

12 Sources of Ionizing Radiation The European Organisation for Nuclear Research (CERN) in Geneva. The large circle is the ring of the site of the upcoming 14 TeV Large Hadron Collider (LHC).

13 Sources of Ionizing Radiation

14 Applications of Ionizing Radiation Ionising properties Penetrating properties

15 Applications of Ionizing Radiation Medical and dental uses - Radiodiagnosis (e.g. conventional X-ray, Computed Tomography, nuclear medicine, PET/CT, Medical cyclotron, etc.) Radiotherapy (e.g. Gammaknife, Cyberknife, Tomotherapy, brachytherapy, etc.) Radioassay (e.g. clinical tests) Dental X-ray (e.g. Intraoral or panoramic X-ray, portable dental X-ray) Remark: Medical exposure is the major contribution of public exposure from artificial sources

16 Applications of Ionizing Radiation Industrial uses Structural analysis of materials (e.g. nondestructive testing, moisture/density testing) Quality analysis of manufactured products (e.g. XRF system) Thickness measurements, static elimination, etc.

17 Applications of Ionizing Radiation Others Smoke detectors Luminous watch Self-luminous devices (e.g. Tritium EXIT sign) Lightning preventors Anti-terrorism (various inspection scanning system)

18 Applications of Ionizing Radiation

19 Medical Uses of Ionizing Radiation

20 Industrial Uses of Ionizing Radiation

21 Other Uses of Ionizing Radiation Portal Type Vehicle and Cargo Inspection System

22 Fundamental Interactions of Nature Strong Interaction Electromagnetic Interaction Weak Interaction (unified with E.M. become electroweak interaction) Gravitation

23 Interactions with Matter through Electromagnetic Interaction Only for charged particles or photons - Interact with the atoms of matter: Scattering Excitation Ionisation Bremsstrahlung radiation production - Interact with the atomic nuclei: Scattering Excitation Production of particles (lead to change of nucleus content)

24 Interactions of Photon with Matter For photons: Photoelectric effect Compton effect Pair Production Photonuclear effect Inverse Compton effect

25 Energy Dependence of Photon Interactions with Matter

26 Interactions with Matter through Strong Interaction Only for hadrons (means strong interaction particles, e.g. proton, neutron, pion, kaon, etc.) - Interact with the atomic nucleus (lead to change of nuclear content): Scattering Activation of nucleus (e.g. neutron activation) Induce nucleus transformation (fission, fusion or fragmentation) Production of subatomic particles (e.g. pions, kaons, etc.)

27 Principles of Detection of Ionising Radiation Based on the ion production property Number of events proportional to the intensity of radiation Collection of the ions produced and counting Calibration to convert the raw counting signal to the measured quantity required Fundamental design of detectors depends on the dosimetric quantity measured, radiation type, sensitivity, radiation energy response, effective range of signal (e.g. Minimum Detection Level), geometry of measurement, response time, etc.

28 Principles of Detection of Ionising Radiation Low penetrating radiation (e.g. alpha or beta radiation) requires small detector wall thickness Low intensity radiation level requires more detection material Ambient radiation measurement requires isotropic detector response Surface contamination measurement requires directional response

29 Principles of Detection of Ionising Radiation Radiation dose/dose rate measurement Radiation contamination measurement Radiation spectroscopy

30 Principles of Detection of Ionising Radiation Type of medium of radiation detector: Gaseous type (electron and ion pairs in gas) Ionisation chamber Proportional counter Geiger Muller counter

31 Principles of Detection of Ionising Radiation Schematic diagram of gas flow type proportional counter

32 Principles of Detection of Ionising Radiation Monte Carlo simulation of avalanche in proportional counter

33 Principles of Detection of Ionising Radiation Ionisation chamber type portable survey meter

34 Principles of Detection of Ionising Radiation Geiger Muller Type Electronic Personal Dosimeter

35 Principles of Detection of Ionising Radiation Geiger Muller type radioactive contamination counter

36 Principles of Detection of Ionising Radiation Geiger Muller type radioactive contamination counter

37 Principles of Detection of Ionising Radiation Gas flow proportional counter type Low Level Alpha Beta Counting System

38 Principles of Detection of Ionising Radiation BF 3 proportional counter type portable neutron monitor

39 Energy Dependence of the Relative Neutron Response of Bonner Sphere

40 Principles of Detection of Ionising Radiation Solid state type (electron and hole pairs in solid) Scintillation counter (Plastic, NaI, CsI,) Semiconductor detector (diode structure: Si, Ge, CZT) Thermoluminescent dosimeter (TLD) Film

41 Principles of Detection of Ionising Radiation The scintillation type contamination counter

42 Principles of Detection of Ionising Radiation CZT Detector Probe

43 Principles of Detection of Ionising Radiation CZT Detector Assembly

44 Principles of Detection of Ionising Radiation Alpha Spectroscopy System

45 Principles of Detection of Ionising Radiation Surface Barrier Type Silicon Detector of the Alpha Spectroscopy System

46 Principles of Detection of Ionising Radiation Schematic diagram of surface barrier type silicon detector

47 Principles of Detection of Ionising Radiation High Purity Germanium (HPGe) Gamma Spectroscopy System

48 Principles of Detection of Ionising Radiation High Purity Germanium (HPGe) Portable Gamma Spectroscopy System

49 Principles of Detection of Ionising Radiation Radiation Portal Monitor

50 Principles of Detection of Ionising Radiation Whole Body Type Thermoluminescent Dosimeter (TLD)

51 Principles of Detection of Ionising Radiation Finger Ring Type Thermoluminescent Dosimeter (TLD)

52 Dosimetry and Health Effects of Ionising Radiation The physical quantity for the radiation energy absorbed per unit of matter is known as absorbed dose The unit of absorbed dose is Gray (Gy) 1 Gy 1 Joule/kilogram (J/kg) The unit of dose equivalent is Sievert (Sv) The dose quantity associated with the fatal cancer risk is known as effective dose The unit of effective dose is also Sievert (Sv)

53 Dosimetry and Health Effects of Ionising Radiation Deterministic effect Stochastic effect

54 Dosimetry and Health Effects of Ionising Radiation Deterministic effect Occurs above certain dose threshold, usually begin around the dose order of 1 Gy Significant amount of cell death leads to loss of tissue or organ function Severity of harm increase with dose above threshold dose

55 Dosimetry and Health Effects of Ionising Radiation Temporary sterility in male for a single absorbed dose in testes 0.15 Gy Permanent sterility 3.5 to 6 Gy Depression of blood forming process 0.5 Gy Gastrointestinal damage 10 Gy LD 50 in 60 days due to bone marrow syndrome in acute exposure 3-5 Gy

56 Dosimetry and Health Effects of Ionising Radiation Stochastic effect Carcinogenesis Probability coefficients mainly based on epidemiological studies of atomic bomb survivors in Hiroshima and Nagasaki (RERF) Linear-no-threshold hypothesis (LNT) Assume a simple proportionate relationship between increments of dose and increased risk

57 Dosimetry and Health Effects of Ionising Radiation Exposed Population Adult Workers Whole Population Nominal Probability Coefficient (10-2 /Sv -1 ) Fatal Cancer Non-fatal Cancer Severe Hereditary Effects Total

58 Radiation Protection System and Regulatory Framework in Hong Kong An effective control system for radiation protection is of prime importance to achieve a suitable balance between the risk and benefit of radiation to human and the environment

59 Radiation Protection System and Regulatory Framework in Hong Kong International principles of radiological protection (ICRP 60 and 103) Regulatory control - Laws and regulations (Radiation Ordinance (Cap 303)) Regulatory authority (Radiation Board) Policies and licensing system Radiological protection services Internal safety management system of individual organization Radiological protection personnel, technology, equipment and facilities

60 Radiation Protection System and Regulatory Framework in Hong Kong Exposure situations - Planned exposure occupational exposure, public exposure, potential exposure and medical exposure Emergency exposure unexpected situations require urgent protective actions Existing exposure (e.g. indoor radon not related to practices)

61 Radiation Protection System and Regulatory Framework in Hong Kong Principles of Radiological Protection - Justification Do more good than harm (sufficient individual or societal benefit to offset radiation detriment) Optimisation As low as reasonably achievable (take into account economic and societal factors) Limitation Limit the individual dose in planned exposure situation (except medical exposure)

62 Regulatory Control in Hong Kong Licensing system established by the authority under Radiation Ordinance (Cap 303) Radiation safety requirements for protecting the workers and public as prescribed in the conditions of licence for the specific use of radiation Licensing assessment on the radiation safety of the concerned device and installation, its conformance to the relevant international/national standards, safety testing certificate, safety procedures, staff supervision and training, working instructions and code of practice, etc.

63 Regulatory Control in Hong Kong On-site inspection, including radiation survey, document audits, checking of radiation protection instrument and facility, etc., to ensure maintaining of the radiation safety Enforcement action investigation, verbal/written warning, legal action, corrective/preventive action and follow-up action Radiation incident and emergency response organisation is required to establish contingency plans for dealing with incident or accident involving radiation, report to the authority when incident occurs, authority response with other departments according to the government emergency arrangements

64 Regulatory Control in Hong Kong Dose Limits Prescribed in Radiation Ordinance Occupational Public 20mSv/yr 1mSv/yr 150mSv 500mSv 500mSv 1mSv

65 Radiological Protection Services in Hong Kong Competent laboratories approved by Radiation Board - The University of Hong Kong The Chinese University of Hong Kong Hong Kong University of Science & Technology The Hong Kong Polytechnic University City University of Hong Kong Pamela Youde Nethersole Eastern Hospital

66 Radiological Protection Services in Hong Kong Radiation protection courses approved by Radiation Board - Occupational Safety and Health Council Hong Kong Productivity Council Hong Kong Polytechnic University The University of Hong Kong

67 Recent Development of the Perspectives of Radiation Protection (ICRP 103) Retain the assumption of a simple proportionate relationship between increments of dose and increased risk Collective dose is inappropriate for risk projections and aggregated very low individual doses over extended period of time Proposed radiation weighting factor for charged pions Revised radiation weighing factors (neutron) Revised tissue weighing factors (breast, gonads and remainder tissues) Dose constraint for emergency situation and existing situation Environmental concern

68 References ICRP, 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Ann. ICRP 21 (1-3), 1991; ICRP, The 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103, Ann. ICRP 37 (2-4), 2007; Knoll G.F., Radiation Detection and Measurement, John Wiley & Sons, Canada, 1989.

69 Thank You!