The Principles of Radiation Monitoring and the Radiation ...ne.hkie.org.hk/upload/doc/8b807efa-fc12-4853-8a60-c204352209ec_se… · dose in testes – 0.15 Gy ... International principles

The Principles of Radiation Monitoringand the Radiation Protection System

in Hong Kong

H.M.MokPhysicist

Radiation Health UnitDepartment of Health

Contents

Basic properties of ionising radiation and its interactions with matterPrinciples of radiation detection and the measuring instrumentsDosimetry and health effects of ionising radiationRadiation protection system and regulatory framework in Hong Kong

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 naturePredominantly through the electromagnetic (for charged particles and photons) and strong interactions (for hadrons)


Ionising radiationThe radiation 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


Non-ionising radiation The radiation that does not produce ion pairs in physical mediumFor example, soft ultra-violet, infra-red, visible light, microwave, radio-frequency, etc.

Basic Properties of IonisingRadiation

Electromagnetic Spectrum (Photons)


Two major sources of ionising radiation:

Naturally occurring radiationCosmic raysNatural radioactive substances in environment (e.g. uranium and thorium in rock and soil) Indoor radon

Contribute to the public exposure by about 80%

Sources of Ionizing Radiation

Cosmic rays


Artificially produced radiation X-raysArtificially 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-fusion-fission type, etc.)Particle accelerator (e.g. synchrotron, linear accelerator, cyclotron, etc.)



The European Organisation for Nuclear Research (CERN) in Geneva. The large circle is the ring of the site of the upcoming14 TeV Large Hadron Collider (LHC).


Applications of Ionizing Radiation

Ionising properties Penetrating properties


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


Industrial uses– Structural analysis of materials (e.g. non-

destructive testing, moisture/density testing)– Quality analysis of manufactured products (e.g.

XRF system)– Thickness measurements, static elimination, etc.


Others– Smoke detectors– Luminous watch– Self-luminous devices (e.g. Tritium “EXIT” sign)– Lightning preventors– Anti-terrorism (various inspection scanning system)


Medical Uses of Ionizing Radiation

Industrial Uses of Ionizing Radiation

Other Uses of Ionizing Radiation

Portal Type Vehicle and Cargo Inspection System

Fundamental Interactions of Nature

Strong InteractionElectromagnetic InteractionWeak Interaction (unified with E.M. become electroweak interaction)Gravitation

Interactions with Matter through Electromagnetic Interaction

Only for charged particles or photons - Interact with the atoms of matter:

ScatteringExcitationIonisationBremsstrahlung radiation production

- Interact with the atomic nuclei:ScatteringExcitationProduction of particles (lead to change of nucleus content)

Interactions of Photon with Matter

For photons:Photoelectric effectCompton effectPair ProductionPhotonuclear effectInverse Compton effect

Energy Dependence of Photon Interactions with Matter

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):ScatteringActivation of nucleus (e.g. neutron activation)Induce nucleus transformation (fission, fusion or fragmentation) Production of subatomic particles (e.g. pions, kaons, etc.)

Principles of Detection of Ionising Radiation

Based on the ion production propertyNumber of events proportional to the intensity of radiationCollection of the ions produced and countingCalibration to convert the raw counting signal to the measured quantity requiredFundamental 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.


Low penetrating radiation (e.g. alpha or beta radiation) requires small detector wall thicknessLow intensity radiation level requires more detection materialAmbient radiation measurement requires isotropic detector responseSurface contamination measurement requires directional response


Radiation dose/dose rate measurementRadiation contamination measurementRadiation spectroscopy


Type of medium of radiation detector:Gaseous type (electron and ion pairs in gas)

Ionisation chamberProportional counterGeiger Muller counter


Schematic diagram of gas flow type proportional counter


Monte Carlo simulation of avalanche in proportional counter


Ionisation chamber type portable survey meter


Geiger Muller Type Electronic Personal Dosimeter


Geiger Muller type radioactive contamination counter


Geiger Muller type radioactive contamination counter


Gas flow proportional counter typeLow Level Alpha Beta Counting System


BF3 proportional counter type portable neutron monitor

Energy Dependence of the Relative Neutron Response of Bonner Sphere


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


The scintillation type contamination counter


CZT Detector Probe


CZT Detector Assembly


Alpha Spectroscopy System


Surface Barrier Type Silicon Detector of the Alpha Spectroscopy System


Schematic diagram of surface barrier type silicon detector


High Purity Germanium (HPGe) Gamma Spectroscopy System


High Purity Germanium (HPGe) Portable Gamma Spectroscopy System


Radiation Portal Monitor


Whole Body TypeThermoluminescent Dosimeter (TLD)


Finger Ring TypeThermoluminescent Dosimeter (TLD)

Dosimetry and Health Effects of Ionising Radiation

The physical quantity for the radiation energy absorbed per unit of matter is known as absorbed doseThe 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 doseThe unit of effective dose is also Sievert (Sv)


Deterministic effectStochastic effect


Deterministic effectOccurs above certain dose threshold, usually begin around the dose order of 1 GySignificant amount of cell death leads to loss of tissue or organ functionSeverity of harm increase with dose above threshold dose


Temporary sterility in male for a single absorbed dose in testes – 0.15 GyPermanent sterility – 3.5 to 6 GyDepression of blood forming process – 0.5 GyGastrointestinal damage – 10 GyLD50 in 60 days due to bone marrow syndrome in acute exposure 3-5 Gy


Stochastic effectCarcinogenesisProbability 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


Nominal Probability Coefficient (10-2/Sv-1)

Exposed Population

Fatal Cancer

Non-fatal Cancer

Severe Hereditary Effects Total

Adult Workers 4.0 0.8 0.8 5.6

Whole Population 5.0 1.0 1.3 7.3

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


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 servicesInternal safety management system of individual organizationRadiological protection personnel, technology, equipment and facilities


Exposure situations -Planned exposure – occupational exposure, public exposure, potential exposure and medical exposureEmergency exposure – unexpected situations require urgent protective actionsExisting exposure (e.g. indoor radon not related to practices)


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)

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.

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 safetyEnforcement action – investigation, verbal/written warning, legal action, corrective/preventive action and follow-up actionRadiation incident and emergency response – organisationis 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

Regulatory Control in Hong KongDose Limits Prescribed in

Radiation Ordinance

Occupational Public Effective Dose 20mSv/yr 1mSv/yr Dose Equivalent Eye 150mSv Skin 500mSv Extremity 500mSv Fetus 1mSv

Radiological Protection Services in Hong Kong

Competent laboratories approved by Radiation Board -

The University of Hong KongThe Chinese University of Hong KongHong Kong University of Science & TechnologyThe Hong Kong Polytechnic UniversityCity University of Hong KongPamela Youde Nethersole Eastern Hospital

Radiological Protection Services in Hong Kong

Radiation protection courses approved by Radiation Board -

Occupational Safety and Health CouncilHong Kong Productivity CouncilHong Kong Polytechnic UniversityThe University of Hong Kong

Recent Development of the Perspectives of Radiation Protection (ICRP 103)

Retain the assumption of a simple proportionate relationship between increments of dose and increased riskCollective dose is inappropriate for risk projections and aggregated very low individual doses over extended period of timeProposed radiation weighting factor for charged pionsRevised radiation weighing factors (neutron)Revised tissue weighing factors (breast, gonads and remainder tissues)Dose constraint for emergency situation and existing situation Environmental concern

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.

Thank You!

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The Principles of Radiation Monitoring and the Radiation ...ne.hkie.org.hk/upload/doc/8b807efa-fc12-4853-8a60-c204352209ec_se… · dose in testes – 0.15 Gy ... International principles