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The Principles of Radiation Monitoringand the Radiation Protection System

in Hong Kong

H.M.Mok

Physicist

Radiation Health Unit

Department of Health

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Contents

Basic properties of ionising radiationand its interactions with matter

Principles of radiation detection and themeasuring instruments

Dosimetry and health effects ofionising radiation

Radiation protection system andregulatory framework in Hong Kong

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Basic Properties of Ionising Radiation

What is radiation ? Radiation is the energyemitted 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) andstrong interactions (for hadrons)

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Ionising radiation

The adiation that interacts with a physical

medium to produce ion pairs

For example, , , X, -radiation, neutron, proton,

pion, muon, etc.

Invisible to human such that the detection of it

demands a suitable monitoring instrument

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Non-ionising radiation

The adiation that does not produce ion pairs inphysical medium

For example, soft ultra-violet, infra-red, visiblelight, microwave, radio-frequency, etc.

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Basic Properties of IonisingRadiation

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Electromagnetic Spectrum (Photons)

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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%

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Sources of Ionizing Radiation

Cosmic rays

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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-fusion-

fission type, etc.) Particle accelerator (e.g. synchrotron, linear

accelerator, cyclotron, etc.)

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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).

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Applications of Ionizing Radiation

Ionising properties

Penetrating properties

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Medical and dental uses - Radiodiagnosis (e.g. conventional X-ray, Computed

Tomography, nuclear medicine, PET/CT, Medicalcyclotron, 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 exposurefrom artificial sources

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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.

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Others

Smoke detectors

Luminous watchSelf-luminous devices (e.g. Tritium EXIT sign)

Lightning preventors

Anti-terrorism (various inspection scanning system)

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Medical Uses of Ionizing Radiation

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Industrial Uses of Ionizing Radiation

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Other Uses of Ionizing Radiation

Portal Type Vehicle and Cargo Inspection System

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Fundamental Interactions of Nature

Strong Interaction

Electromagnetic Interaction Weak Interaction (unified with E.M.

become electroweak interaction)

Gravitation

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Interactions with Matter throughElectromagnetic 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)

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Interactions of Photon with Matter

For photons:

Photoelectric effect

Compton effect Pair Production

Photonuclear effect

Inverse Compton effect

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Energy Dependence of PhotonInteractions with Matter

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Interactions with Matter throughStrong Interaction

Only for hadrons (means strong interaction particles, e.g.proton, neutron, pion, kaon, etc.)

- Interact with the atomic nucleus (lead to change of nuclearcontent):

Scattering

Activation of nucleus (e.g. neutron activation)

Induce nucleus transformation (fission, fusion or

fragmentation)

Production of subatomic particles (e.g. pions, kaons, etc.)

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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 themeasured quantity required

Fundamental design of detectors depends on thedosimetric quantity measured, radiation type,sensitivity, radiation energy response, effectiverange of signal (e.g. Minimum Detection Level),geometry of measurement, response time, etc.

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Principles of Detection ofIonising 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 requiresdirectional response

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Radiation dose/dose rate

measurement

Radiation contaminationmeasurement

Radiation spectroscopy

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Type of medium of radiation detector:

Gaseous type (electron and ion pairs in gas)

Ionisation chamber

Proportional counter

Geiger Muller counter

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Ionising Radiation

Schematic diagram of gas flow type proportional counter

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Ionising Radiation

Monte Carlo simulation of avalanche in proportional counter

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Ionisation chamber type portable survey meter

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Geiger Muller Type Electronic

Personal Dosimeter

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Ionising Radiation

Geiger Muller type radioactive contamination counter

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Ionising Radiation

Geiger Muller type radioactive contamination counter

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Ionising Radiation

Gas flow proportional counter type

Low Level Alpha Beta Counting System

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Ionising Radiation

BF3 proportional counter type portable neutron monitor

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Energy Dependence of the Relative

Neutron Response of Bonner Sphere

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Ionising Radiation

Solid state type (electron and hole pairs insolid)

Scintillation counter (Plastic, NaI, CsI,)

Semiconductor detector (diode structure:

Si, Ge, CZT)

Thermoluminescent dosimeter (TLD) Film

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Ionising Radiation

The scintillation type contamination counter

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Ionising Radiation

CZT Detector Probe

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Ionising Radiation

CZT Detector Assembly

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Ionising Radiation

Alpha Spectroscopy System

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Ionising Radiation

Surface Barrier Type Silicon Detector of the

Alpha Spectroscopy System

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Ionising Radiation

Schematic diagram of surface barrier type silicon detector

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Ionising Radiation

High Purity Germanium (HPGe) Gamma Spectroscopy System

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Ionising Radiation

High Purity Germanium (HPGe) Portable Gamma Spectroscopy System

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Ionising Radiation

Radiation Portal Monitor

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Ionising Radiation

Whole Body Type

Thermoluminescent Dosimeter (TLD)

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Ionising Radiation

Finger Ring Type

Thermoluminescent Dosimeter (TLD)

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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)

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Ionising Radiation

Deterministic effect

Stochastic effect

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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 abovethreshold dose

i d l h ff f

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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

LD50 in 60 days due to bone marrow syndrome inacute exposure 3-5 Gy

D i d H l h Eff f

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Ionising Radiation

Stochastic effect Carcinogenesis

Probability coefficients mainly based onepidemiological 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

D i d H l h Eff f

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Ionising Radiation

Nominal Probability Coefficient

(10-2/Sv

-1)

Exposed

Population

Fatal

Cancer

Non-fatal

Cancer

Severe Hereditary

EffectsTotal

Adult

Workers4.0 0.8 0.8 5.6

Whole

Population

5.0 1.0 1.3 7.3

R di ti P t ti S t d

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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 andbenefit of radiation to human and the

environment


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International principles of radiologicalprotection (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 individualorganization

Radiological protection personnel, technology,equipment and facilities


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Exposure situations -

Planned exposure occupational exposure,

public exposure, potential exposure andmedical exposure

Emergency exposure unexpected situationsrequire urgent protective actions

Existing exposure (e.g. indoor radon notrelated to practices)

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Regulatory Control in Hong Kong

Licensing system established by the authority underRadiation 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 testingcertificate, safety procedures, staff supervision and training,

working instructions and code of practice, etc.

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On-site inspection, including radiation survey, documentaudits, checking of radiation protection instrument andfacility, etc., to ensure maintaining of the radiation safety

Enforcement action investigation, verbal/written warning,

legal action, corrective/preventive action and follow-upaction

Radiation incident and emergency response organisationis required to establish contingency plans for dealing with

incident or accident involving radiation, report to theauthority when incident occurs, authority response withother departments according to the government emergencyarrangements

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Dose Limits Prescribed in

Radiation Ordinance

Occupational Public

20mSv/yr 1mSv/yr

150mSv

500mSv

500mSv1mSv

Radiological Protection Services

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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


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in Hong Kong

Radiation protection courses approved by RadiationBoard -

Occupational Safety and Health Council

Hong Kong Productivity Council

Hong Kong Polytechnic University

The University of Hong Kong

Recent Development of the Perspectives

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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 periodof time

Proposed radiation weighting factor for charged pions Revised radiation weighing factors (neutron)

Revised tissue weighing factors (breast, gonads andremainder tissues)

Dose constraint for emergency situation and existingsituation

Environmental concern

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References

ICRP, 1990 Recommendations of the InternationalCommission on Radiological Protection, ICRP Publication

60, Ann. ICRP 21 (1-3), 1991;

ICRP, The 2007 Recommendations of the International

Commission on Radiological Protection, ICRP Publication103, Ann. ICRP 37 (2-4), 2007;

Knoll G.F.,Radiation Detection and Measurement, John

Wiley & Sons, Canada, 1989.

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Thank You!

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