An Introduction to Radiation Safety
2014
Ian Williamson / Steve Clipstone
Restricting Exposure
• Alle Ding' sind Gift, und nichts ohn' Gift; allein
die Dosis macht, daß ein Ding kein Gift ist.
• "All things are poison and nothing is without
poison, only the dose permits something not to be
poisonous."
(Paracelsus, 1493 - 1541)
This course will cover
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Main requirements of legislation
Types of radiation
Health effects
Management arrangements
Risk control measures
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Aim
The aim of the session is to
• Introduce you to some basic radiation principles
• Inform you of the arrangements and control
measures in place to keep you safe when working
with radiation
• Not to make you an expert!
Early uses of radioactivity
• Radium and thorium
Radiation Injuries
• 1896 - first injuries due
to radiation recorded
• 1902 - first skin cancers
seen
• 1911 – 94 cases of skin
carcinomas and
sarcomas reported
• H&S Legislation
needed?
Legislation
• Ionising Radiation Regulations 1999 (IRRs)
General and specific duties & rules about safe working practices, control
measures, assessments, roles and responsibilities;
Health and Safety Executive (HSE) enforcement
• Environmental Permitting Regulations 2010
Regulates the holding, storage, accumulation and disposal of radioactive
material;
Environment Agency (EA) Enforcement
Replaced the RSA93 Act
The Ionising Radiation Regulations
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Risk assessments
Control of exposure to ALARP
Maintenance of control measures
Dose limitation
Contingency Plans and Local Rules
RPA and RPS defined roles
Information. Instruction and Training
Co-operation between employers
Designation of areas
Dose Limits – For Workers
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1934
1937
1950
1956
1977
2000
2 mSv per day or 730 mSv per year
2 mSv per day or 10 mSv per week
3 mSv per week or 150 mSv per year
1 mSv per week or 50 mSv per year
50 mSv per year
20 mSv per year
Average annual dose to UK population (2.6 mSv)
Gamma rays from
ground and buildings
14%
Radon gas from the
ground 50%
Medical 14%
Cosmic rays 10%
Products 0.1%
Food and drink 11.5%
Fallout 0.2%
Occupational 0.3%
Nuclear discharges
<0.1%
Annual Dose Limits – UK
(IRRs)
Whole Body
Extremities and skin
Lens of the eye
Employees aged 18
and over
20 mSv
500 mSv
150 mSv
(20)
Trainees aged 18 and
under
6 mSv
150 mSv
50 mSv
(15)
Any other person
( e.g. Undergraduates)
1 mSv
50 mSv
15 mSv
(15)
(new proposed limits in brackets)
Women of reproductive capacity - exposure of abdomen limited to 13 mSv in any
consecutive 3 month period. Women are legally obliged to inform their employer
Basic Radiological Safety Rules
• All work must be risk assessed
• You MUST work within the Local Rules and
follow instructions
• You MUST be a registered radiation worker
• You MUST understand the instructions and
comply with them – if in doubt ask
The ALARP Principle
• Minimise the time you spend near a source
• Maximise the distance between you and a
source of radiation
• Maximise the shielding between you and a
source of radiation
Time
• Before the work make sure you know and plan
what you are going to do! Minimise the time
• Practice the task beforehand
• Do not linger in high dose rate areas
Distance
• Avoid working or standing in high dose rate
areas, whenever possible by moving away
from the source of radiation
• Use remote handling equipment
• Observe from a separate area
• Use minimal amounts / samples
Inverse Square Law
Distance
Double
Treble
Quadruple
Radiation Dose rate
Reduced to ¼
Reduced to 1/9
Reduced to 1/16
Shielding
• Use shielding provided where possible
• Do not tamper with equipment or defeat
interlocks
• View behind protective screening
• Make sure sealed sources are in good repair
• PPE
Radiation Units
Activity
• Number disintegrations per second (Becquerel) – one Bq
means one atom/nucleus decays and emits radiation every
second
• Characterised by the half life
Absorbed dose
• Mean energy per unit mass absorbed by any medium by any
type of ionising radiation (Gray – Gy (or joules/kg))
Equivalent Dose
• Dose allowing for type of radiation and effective biological
damage (Sievert - Sv)- absorbed dose by weighting factor
Old/US Units
• Rad
• Rem
• Ci
100 Rads = 1 Gray
100 Rem = 1 Sievert
1 Curie = 3.7 x 1010 Bq (dps)
Types of radiation
alpha
• 2 protons + 2 neutrons tightly bound together
- Helium nucleus
• High energy but low penetrating power
• Range in air only a few cm
• Internal hazard
beta
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Smaller than alpha
An electron (emitted from the nucleus)
Variable energy
Internal and external hazard
Gamma and x-rays
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Electromagnetic radiation
Variable energy with shorter wavelengths
External hazard
Penetrating – range in air m to km
Gamma rays emitted from the nucleus
X-rays emitted from electron orbital shells
Radiation
Penetration in air
Stopped by
Alpha
3 – 5 cm of air
Thin sheet of paper,
outer layers of skin
Beta
3 m of air
1cm perspex
3mm of aluminium sheet
Gamma
Eventually stopped
by air, depends on
the energy of
emission but can be
big distances
40 cm of lead – stops
almost all of the
radiation
Radioactive Half-Life
Not all of the atoms of a radioisotope decay at the same time,
but they decay at a rate that is characteristic to the isotope.
The rate of decay is a fixed rate called a half-life.
The half-life of a radioisotope describes how long it takes for
half of the atoms in a given mass to decay. Some isotopes decay
very rapidly and, therefore, have a high specific activity. Others
decay at a much slower rate – so decay at an “average rate”
After two half-lives, there will be one quarter the original
sample, after three half-lives one eighth the original sample, and
so forth.
It is an exponential decay process
= radioactive
At start there
are 16
radioisotopes
100%
After 1 half
life half have
decayed.
There are 8
remaining
50%
= stable, although not a precise figure
After 2 half
lives another
half have
decayed.
There are 4
remaining
After 3 half
lives another
2 have
decayed.
There are 2
remaining
25%
12.5%
How can we work out the half-life of a radioisotope?
We can plot a graph of activity against time
1 Half-Life
2 Half-Lives
Routes of exposure
Eye dose
Inhalation
Skin dose
Ingestion
Whole body dose
Abdomen/Foetal Dose
Extremity dose
Injection
Routes of Entry
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Ingestion
Inhalation
Puncture wounds or cuts
Absorption through the skin
Absorption of Nuclear Radiations
The most massive of the radioactive emissions – alpha particles –
have the shortest range. Due to their size they interact strongly
with matter (lots of collisions with atoms) causing large amounts
of ionization. This makes them very harmful to living tissue.
Absorption of Radiation
Beta particles being smaller have a weaker
interaction but can still cause ionization as they
interact with the electrons surrounding atoms.
Since gamma radiation is electromagnetic waves it
is the most penetrating and least ionizing.
However the deep penetration makes it dangerous
to living tissue.
Biological Effects of Ionising
Radiation
• Health Effects are
determined by the type
and intensity of the
radiation and the period
of exposure.
Biological Effects
The occurrence of particular health effects from exposure to ionizing radiation is a
complicated function of numerous factors including:
•Type of radiation involved. All kinds of ionizing radiation can produce health
effects. The main difference in the ability of alpha and beta particles and Gamma
and X-rays to cause health effects is the amount of energy they have. Their energy
determines how far they can penetrate into tissue and how much energy they are
able to transmit directly or indirectly to tissues.
•Size of dose received. The higher the dose of radiation received, the higher the
likelihood of health effects.
•Rate the dose is received. Tissue can receive larger dosages over a period of
time. If the dosage occurs over a number of days or weeks, the results are often
not as serious if a similar dose was received in a matter of minutes.
•Part of the body exposed. Extremities such as the hands or feet
are able to receive a greater amount of radiation with less resulting
damage than blood forming organs housed in the torso.
•The age of the individual. As a person ages, cell division slows and
the body is less sensitive to the effects of ionizing radiation. Once
cell division has slowed, the effects of radiation are somewhat less
damaging than when cells were rapidly dividing.
•Biological differences. Some individuals are more sensitive to the
effects of radiation than others. Studies have not been able to
conclusively determine the differences.
Radiation Effects
• Direct ionisation
– Structural cell damage,
weakens links between
atoms
– Affects cellular function
– DNA mutations
• Indirect ionisation
– Damage to chemical
constituents, e.g. water
– Formation of free radicals
Examples of various tissues and their relative radiosensitivities:
High Radiosensitivity - Lymphoid organs, bone marrow, blood, testes,
ovaries, intestines
Fairly High Radiosensitivity- Skin and other organs with epithelial cell
lining (cornea, oral cavity, esophagus, rectum, bladder, vagina, uterine
cervix, ureters)
Moderate Radiosensitivity - Optic lens, stomach, growing cartilage, fine
vasculature, growing bone (note optic lens may move up to high radiosensitivity)
Fairly Low Radiosensitivity - Mature cartilage or bones, salivary glands,
respiratory organs, kidneys, liver, pancreas, thyroid, adrenal and pituitary
glands
Low Radiosensitivity - Muscle, brain, spinal cord
Effects can take between 5 – 30 years
Radiation effects
• Stochastic effects – somatic and hereditary effects
• No safe dose or threshold – governed by chance
• Deterministic effects – loss of function
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There is no such thing as a safe level of radiation. A single electron could
damage a cell irreversibly and initiate cancer However the likelihood of
damage and the severity of damage increases with the amount of radiation.
Types of exposure
• Acute exposure
Takes place over a short period of time
Usually high exposures
• Chronic exposure
Takes place over a long period of time
Usually low level exposures
Stochastic effects
Probability
Effect, e.g. malignancy
and hereditary effects
Not immediately
observable
Dose
probability increase as dose received increases
Deterministic Effects
Severity
Threshold
Effect, e.g. cataracts,
fetal damage, skin
effects
Large dose can be
fatal
Dose
Degree of cells killed increases with dose
impairing organ function
Deterministic Effects
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50 mSv body repairs itself
1 Sv nausea and vomiting
3 Sv Erythema, blistering and ulceration
6 Sv LD50 depletion white blood cells, 50%
population exposed die of infection death
• 10 Sv severe depletion of cells lining
intestine, death due to secondary infections
Radiation Detectors
• Geiger counters, scintillation counters,
ionisation chambers;
• Count and sensitivity of the detector to
interpret the readings
Monitors
• Use portable radiation detectors to monitor
laboratory or facility radiation levels
• Use film badges or TLDs for retrospective
personal dose monitoring
• Calibrated contamination monitors are only
valid for a particular type of radiation – there
is no universal monitor
Work Areas
• Controlled areas
• Supervised Areas
Dosimetry
• In controlled areas radiation dose is measured
using dose meters or badges – you must wear
them every time you enter a controlled area
• You will be given specific instructions by your
RPS
Restricting Exposure
• All doses are kept to the ALARP principle
Design – fail to safety and cannot be bypassed
Engineered – shielded, fail to safety (interlocked), warning lights
Administrative – Local Rules, supervision, disposal
PPE – gloves , lab coats
• Dose limits should not be exceeded
Risk Assessment
All work requires a risk assessment where the risk is significant and
foreseeable. IRRs require:
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Nature and source of ionising radiation to be used
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Estimated dose rates to anyone exposed
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Likelihood of contamination arising and being spread
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Results of previous monitoring if relevant
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Control measures and design features
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Requirement to designate areas and personnel
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Planned systems of work
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Estimated levels of airborne or surface contamination likely to be
encountered
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Requirement for PPE
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Possible accident situations, potential severity
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Consequences of failure of control measures
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Steps to limit consequences of accident situations
Local Rules
• Brief and concise describing nature of work in the designated
area
• Identify key work instructions to restrict exposure
• Covers normal circumstances and contingency plans
• Contains realistic and achievable work instructions
• Reviewed periodically to ensure effectiveness
• Summary of arrangements for access restriction
• Name / contact details of RPS should be in the local rules
Waste
• Consult with your RPS regarding waste issues
Roles and responsibilities
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Keele University – VC and the Committee Structure
Radiation Protection Advisor
University Radiation Protection Officer
Radiation Protection Supervisor
Registered Radiation Worker
Agencies / Regulatory bodies
Radiation Protection Advisor
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Legal requirement
Specialist role and appointed in writing
Accredited
Currently Radman Associates
Radiation Protection Advisor
Consulted on
• Prior examination of plans for new facilities
• Critical examination of equipment
• Setting up of controlled or supervised areas
• Calibration of monitoring equipment
• Periodic examination and testing of control measures
• Investigations
• Compliance with IRRs
Radiation Protection Supervisor
• Legal requirement
• Training and development of staff / students in
correct working procedures
• Some supervisory duties
• Crucial role to ensure compliance with Local Rules,
Contingency Plans and general arrangements etc
• Familiar with work in their area
• Regular checks and record keeping
Key Contacts
• Radiation Protection Supervisors – list available
• University Radiation Protection Adviser (RPA)- Radman
Associates
• University Radiation Protection Officer – Steve Clipstone
• Head of Occupational Health and Safety – Ian Williamson
Further information
• Keele webpages
• HSE
Any questions?