What is Radiation? - Ab.ust.hk

RADIATION SAFETY for
Engineering Students
En-V12
Health, Safety and Environment Office
The Hong Kong University of Science and Technology
Ionizing Radiation
• Any radiation with sufficient energy to
overcome the binding energy between
electron and nucleus to cause ionization.
hν
radiation
e.g. gamma ray
e
Atom/Molecule ---> ion
electron
Radioactivity (放射性 放射性 放射性) 放射性
• Radioactivity is measured as the number of
disintegration that a sample of radionuclide
undergoes in a certain period of time.
curie (Ci) (居禮 居禮 居禮) 居禮
1 Ci = 3.7 x 10 10 disintegration/sec
becquerel (Bq) (贝可 贝可 贝可) 贝可
1 Bq = 1 disintegration/sec
1 Bq = 27 pCi
What is Radiation?
Radiation is a kind of ENERGY.
It can be broadly classified into
• Ionizing Radiation (电离辐射 电离辐射 电离辐射) 电离辐射
• Non-ionizing Radiation (非电离辐射
非电离辐射 )
Ionizing Radiation Symbol
Physical Half-life (T ½ )
• The time in which half the atoms of a
radioactive substance disintegrated to
another nuclear form.
A = A o e -λt where A is activity at time t,
λ is decay constant,
t is time taken.
When t = T ½ , then A = 1/2 A o

Relative Activity (A/A o)
Radioactive Decay Curve
1.00
0.75
0.50
0.25
0.00
A
A o
= e -λt
0 2 4 6 8 10
Number of Half-lives
Types of Ionizing Radiation
• Alpha particles
• Beta particles, e - , β +
• Gamma/X-ray
• Neutrons
Travelling distance in air
• Alpha particles - 1-2 in.
• Beta particles - up to 10 feet
• Gamma/X-ray - several hundred ft.
• Neutrons - several hundred ft.
Relative Activity
Radioactive Decay Curve
1
0.1
0.01
0.001
0.0001
0.00001
0 2 4 6 8 10
Number of half-lives
Rule of Thumb: Less than 1% remains after 7 half-lives
Electrical Charges
• Alpha particles - +2
• Beta particles - -1
• Gamma/X-ray - neutral
• Neutrons - neutral
Shielding Materials
• Alpha particles - A sheet of paper.
• Beta particles - plastic or low atomic
number materials.
• Gamma/X-ray - high atomic number
materials such as lead or concrete.
• Neutrons - high hydrogen content
materials such as water or paraffin.

Sources of Radiation affect human
Occupational:
less than 0.3%
Manmade:
18%
Natural
Background:
82%
Sources of Radiation
Man-made Radiation
The 4 major sources of man-made radiation
exposure are:
1. Medical Radiation (医疗辐射 医疗辐射 医疗辐射) 医疗辐射
2. Radioactive Fall out (核爆扩散 核爆扩散 核爆扩散) 核爆扩散
3. Industrial Applications (工业应用 工业应用 工业应用) 工业应用
4. Consumer Products (消费产品 消费产品 消费产品) 消费产品
Biological Effects (生物效应 生物效应 )
Deterministic Effects (确定性效应
确定性效应
确定性效应):
确定性效应
• generally a threshold dose level exist.
• effect shown out when receive dose greater
threshold level.
e.g. : eye receive radioactive dose of 1 Sv, cataract
(白內障 白內障 白內障) 白內障 occurs.
Stochastic Effects (随机性效应
随机性效应 ):
• generally without a threshold dose level.
• higher the dose, higher risk of the effect.
e.g.: cancer induction.
Sources of Radiation
Natural Background - radiation received from:
1. Cosmic Rays (宇宙射线)
2. Terrestrial Radiation (陸地輻射)
3. Food
4. Radon (氡氣)
Background is generally the main source of
radiation exposure to a population
Radiation Hazard
External Hazard (外照射危害):
Neutrons > Gamma/X > Beta > Alpha
Internal Hazard (內照射危害):
Alpha > Beta > Gamma/X
(intakes of neutron sources are rare.)
Radiation Damage on Cells
• Each organ of the human body is made
up of specialized cells.
• Ionizing radiation can potentially affect
the normal functioning of these cells.
• Radiation can damage or kill cells.
Some damages are repaired. Improper
repairs may cause potential health
effects.

Radiation Damage on Cells
• Somatic Effects (躯体效应 躯体效应 躯体效应) 躯体效应 effects on the
body of the individual receiving
radiation, e.g., mutation leading to
cancer.
• Genetic Effects(遗传效应 遗传效应 遗传效应): 遗传效应 on
reproductive cells, may be inherited,
effects on chromosomes or DNA.
• Heritable Effects(继承效应 继承效应 ): genetic
effects that passed on to offspring.
Controls Against Exposures
Mainly three types:
• Engineering Controls: Use physical
barrier to prevent exposure in the first
place, most preferred.
• Administrative Controls: Use procedures
to limit unnecessary exposure and control
unauthorized access.
• Personal Protection: Last resort.
Radiation Monitoring
• Personal and work area monitoring are
needed.
• It ensures that radiation exposure at both
personal and working area are less than the
regulatory dose limit.
(a) Total Dose
(b) Dose rate
Factors Affecting
Biological Damage
(c) Types of Radiation
(d) Area of the Body Irradiated
(e) Cell Sensitivity
(f) Individual Sensitivity
Reduction of
External Radiation Dose
(a) Time
(b) Distance
(c) Shielding
(d) Source Reduction
TLD Badge
Recommended by HK Radiation Board for
occupational exposure monitoring

Finger-Ring Dosimeter Radiation Survey Meter
Conclusion
• Ionizing radiation can cause biological effects
to human.
• Control measures for protection must be
established before start working.
• Safety procedures for occupational use of
radiation should be reviewed frequently.
• Personnel and work area monitoring are
needed to ensure that safety procedures and
controls are really working effectively.
Electromagnetic Wave Components
Survey the work area
Non-Ionizing Radiation (非电离辐射
非电离辐射 )
• NIR is a kind of energy which does not has
sufficient energy to ionize atoms or molecules.
• NIR are Electromagnetic Fields (EMFs)
having wave properties.
Non-Ionizing Radiation Symbol

Interactions with matter
• Absorption is the most important to affect human.
• Absorption depends on electrical properties,
object size and polarization (all frequency
dependent)
Example of Resonant
Molecular size of water is 3.8 x 10 -10 m.
Water molecules resonate at 2480 MHz
(4 x 10 -10 m) to produce large amount of
heat.
1 gram of water absorbs microwave at
2480MHz giving out 334 J.
Non-Ionizing Radiation Spectrum
• Subradiofrequency range
• f: 0 - 3 kHz, λ: 0 - 100 km
• Radiofrequency range
• f: 3 kHz - 300 MHz, λ: 100 km - 1 m
• Microwave range
• f: 300 MHz - 300 GHz, λ: 1m - 1 mm
• Infrared range
• f: 3 GHz – 30 THz, λ: 1 mm - 1000 nm
• Visible/Ultraviolet range
• f: 30 THz – 30000 THz, λ: 1000 nm - 100 nm
Object size affects absorption
Radiofrequency / Microwave
(RF/MW) Radiation

Radiofrequency / Microwave
(RF/MW) Radiation
Example of RF sources
- Radar
- Electrical cable tower
Example of MW sources
- Microwave antenna
- Mobile phone
- Microwave oven
Specific Absorption Rate (SAR)
• Specific Absorption Rate (SAR) is a
absorption unit for the RF/MW exposure.
• Measure in vivo.
• Standard whole body limit is 0.4 W/kg based
on 6 minutes average.
Average power density
RF/MW Exposure Guidelines
Induced
current
Body
resonance
30 300
Frequency
Surface
heating
MHz
RF/MW Wavelength Are About the
Size of Humans
• People are good antennas when the
wavelengths of RF are similar in size.
• Induced AC electricity dominate close to RF
sources rather than radiation.
• Heating effect to human body caused by
microwave sources.
Power Density (Energy Flux Density)
• It is a derived limits of exposure measured in
the body-absent situation.
• The radiant power incident on a small sphere is
divided by the cross-sectional area of that
sphere.
• The SI unit of power density (S) is watt per
square meter (W/m 2 ).
Biological Effects to RF/MW
• RF/MW absorption may produce heating
effect.
• Hyperthermia (體溫過高): damage mainly to
eyes and testicles.
• Causing cataract (白內障) and temporary
sterile (短暫不育).

Protective Measures
• Shielding:
Metal enclosure or metal mesh gauze (pore size 1400 nm.
• Corneal absorption increases with increasing
wavelength.
• The damage in IR-B and IR-C regions is
primarily to the cornea (眼角膜).
• Heat stress (熱衰竭).
Ultraviolet Radiation (UV)
Sources
• Sunlight
• Arc lamps
• Germicidal lamps
• UV transilluminator
• Arc welding

Ultraviolet Radiation (UV)
The bands:
- UV-A: 400 – 315 nm (near UV)
- UV-B: 280 – 315 nm (far UV)
- UV-C: 100 – 280 nm (vacuum UV)
• The wavelength of 260 – 280 nm UV light is
generally considered the most hazardous to the
eyes.
Biological Effect to UV
• Effects on skin
- Acute effects (急性效應)
o Erythema (reddening skin) (紅斑) is a photochemical
response of the skin. (UV-B and UV-C).
- Chronic effects (慢性效應)
o Accelerate skin aging (UV-B)
o Develop skin cancer (UV-B and UV-A) strongly
correlated with latitude, altitude and cloud cover.
o Vitamin D synthesis.
UV Radiation Hazard
• High intensity of UV can generate ozone in air.
(usually at UV-B and UV-C).
• Ozone is a irritation gas.
• Adverse effect to lung function when receive
large dose of ozone gas.
• Photo-chemical smog formation to cause air
pollution in urban city.
Smog formation = NO x + Ozone + hydrocarbon
Solar UV
• The solar UV is greatly attenuated by the
earth’s ozone layer(臭氧層), limiting
terrestrial UV to wavelength up to 290 nm.
• Component of solar UV reaches earth’s
surface:
• 5 - 10% of UV-C;
• 50 - 60% of UV-B;
• 80 – 90% of UV-A.
Biological Effects to UV
• Effect on the eyes
- Acute effects
o Photokeratitis (光化性角膜炎)(snowblindness)
commonly referred to as welder’s flash / arc-eye.
o Painful last from 6 to 24 hours, disappear within 48
hours.
- Chronic effects
o Protein deposit or growth in the cornea.
o Cataracts (白內障)
o Conjunctiva (結膜炎)
Protective Measures
• Depending upon whether the UV radiation
exposure occurs indoors or outdoors.
• Outdoor: the use of hats, eye protectors, facial
shields and clothing are practical.
• Indoor: engineering control measures are
preferable.

UV Radiation Control
• Engineering Control
- Interlocked enclosure
- UV protective shield / filter
- Cover reflective surfaces
• Administrative Control
- Warning signs
- Access control
- Reduce exposure time
• Personal Protective Equipment
- Face shield / eye goggles
- Opaque gloves
Radiation Safety
Depends on You !!
The End