Safe Working With
Ionising Radiation Revised January 2012
John Sutherland,
University Safety and Radiation Protection
Officer
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Handout - also downloadable from Safety
Office Web Page
Programme
What is radiation?
How is it measured?
Biological harm
Doses into perspective
Legislation
Unsealed work
X-ray/Sealed - Harry Zuranski, Safety Office.
Objectives
Foundation for Training in School
Understand principles
radiation types and effects
biological effects
relative risk
legislation
university arrangements
Safe Practice
Atomic Structure
a, B, Y
neutron
X
Isotopes
•Variable neutron number
•Unstable nuclei transform
•Ionising radiation emitted
Ionisation
•Energy transfer
•Enough energy ~ 13+ eV
Half - life
Isotope Half-Life
Tritium 12.4 y
Carbon 14 5730 y
Sulphur 35 87.4 d
Phosphorus 33 25.6 d
Phosphorus 32 14.3 d
Iodine 125 60.1 d
Types of Radiation
Video
Types of Radiation
Alpha From heavy nuclei (e.g. Americium 241)
Helium nuclei (2P+2N)
1500 ionisations
Dangerous internally
Easily shielded as very large particles Sheet of paper or plastic film
Small distance of air
Dead outer layer of skin
Types of Radiation
Beta Particles (B)
High speed electrons from nucleus
Identical to orbital electrons
Neutron Proton + B-
Energy dependent penetrating power
3H - 18.6 KeV
14C - 156 KeV
32P - 1.71 MeV
Rule of thumb for maximum range of beta particles
4 metres in air per MeV of charge
P32 can travel up to 7 m in air but 3H only 6mm!
Easily shielded with perspex, higher energy needs greater thickness
10 mm will absorb all P32 betas
Cannot reach internal organs
Types of Radiation
Bremsstrahlung
X-radiation resulting from high energy ß particle
absorption in high density shielding, e.g. lead.
Risk with 32P and similar high energy ß emitters.
Shield ß with lightweight materials such as perspex.
Very large activities can still produce some
Bremsstrahlung from perspex - supplement perspex
with lead on outside to absorb the X-rays.
Types of Radiation
Gamma Radiation (Y)
Electromagnetic radiation
Emitted from nucleus
Readjustment of energy in nucleus following a or ß emission
Variable energy characteristic of isotope
Highly penetrating
5 - 25 cm lead
3m concrete
Can reach internal organs
Can pass through the body
Types of Radiation
X-Radiation
Similar to gamma but usually less energetic
Originates from electron cloud of the nucleus
Produced by machines - can be switched off!
Also produced by some isotopes
Iodine-125 produces both gamma and x-rays
Broad spectrum of energy
Types of Radiation
X-rays Incident radiation ejects electron
Outer electron fills gap
X-ray energy = difference between
orbital energy levels - characteristic
Bremsstrahlung also produced
Types of Radiation
Neutrons
Large, uncharged, physical interaction.
Spontaneous fission (Californium 252)
Alpha interaction with Beryllium (Am-241/Be)
Shield with proton-rich materials such as hydrocarbon wax and polypropylene.
Americium/Beryllium sources are used in neutron probes for moisture or density measurement in soils and road surfaces etc. These also emit gamma radiation.
Units of Radiation
SI units Becquerel, Gray, Seivert
replaced Curies, Rems, Rads
Activity
Dose
absorbed
equivalent
committed
Units of Radiation - activity
Quantity of r/a material
Bequerel (Bq; kBq; MBq)
1 nuclear transformation/second
3.7 x 1010 Bq = 1 Curie
Record keeping
Stock, disposals
Expt protocols
Units of Radiation - dose
Absorbed - Gray (Gy)
Radiation energy deposited
1 Gy = 1 joule/kg
Dose Equivalent - Seivert (Sv)
modified for relative biological effectiveness
beta, gamma, X = 1
alpha, neutrons = 10-20
Units of Radiation - committed
Internal
irradiation until decay or elimination
radiological and biological half-lives
data for 50-year effect
Annual Limit on Intake (ALI)
limit on committed dose equivalent
quantity causing dose limit exposure
Exposure to Ionising Radiation
Environment
Naturally occurring radioactive minerals remaining from
the very early formation of the planet.
Outer space and passes through the atmosphere of
the planet – so-called cosmic radiation.
Man-made
medical treatment and diagnosis.
industry, primarily for measurement purposes and for
producing electricity.
fallout from previous nuclear weapon explosions and
other accidents/incidents world-wide.
Biological Effects of Radiation
Exposure
Ionising radiation affects the cells of the body through damage to DNA by: Direct interaction with DNA, or
Through ionisation of water molecules etc producing free radicals which then damage the DNA.
Some damaged cells might be killed outright so do not pass on any defect.
In some cases cell repair mechanisms can correct damage depending on dose.
Deterministic Effects.
Threshold beneath which there is no effect and
above which severity increases with exposure.
High dose effects - cells may be killed by damage
to DNA and cell structures.
Clinically observable effects include:
5 Sv to whole body in a short time is fatal.
60 Sv to skin causes irreversible burning.
5 Sv to scalp causes hair loss
4 Sv to skin causes brief reddening after three weeks
3 Sv is threshold for skin effects.
Biological Effects of Radiation
Exposure
Stochastic (Chance) Effects
No threshold dose, probability of effect increases with dose but severity of effect remains unchanged
Lower dose effects
No obvious injury,
Some cells have incorrectly repaired the DNA damage and carry mutations leading to increased risk of cancer.
Rapidly dividing cells most at risk – blood forming cells in bone marrow; gut lining.
Biological Effects of Radiation
Exposure
Cancer Risk at Low Doses
Evaluation of Cancer Risk
Studied for decades. atomic bomb explosions in
Japan,
fallout from nuclear weapons tests
radiation accidents.
medical irradiations,
work (e.g. nuclear power industry)
living in a region that has unusually high levels of radioactive radon gas or gamma radiation.
E
F
F
E
C
T
RADIATION DOSE
Main Area of Interest
for Radiation
Protection
Main Area of Available Data for
Study
Life-time risk of cancer from all causes of about 20–25%.
Exposure to all sources of ionising radiation (natural plus man-made) could be responsible for an additional risk of fatal cancer of about 1%
Dose from natural background radiation is about 2.2 mSv per year.
Dose from non-medical, man-made radiation 0.02 to 0.03 mSv per year (1/100th natural background),
0.01% of additional cancer risk.
More significant cancer risk factors include: cigarette smoking,
excessive exposure to sunlight, and
poor diet.
Cancer Risk at Low Doses
Biological Effects
4-10 Sv - death
1 Sv - clinical effects
100 mSv - clinical effects on foetus
50 mSv - max lifetime univ. dose
20 mSv - annual whole body dose limit
6 mSv - classified worker
2.5 mSv - average annual exposure (UK)
1 mSv - foetus after pregnancy confirmed
150 - 250 uSv - max annual dose at univ.
20 uSv – average annual dose at univ.
Perspective on Exposures
Nature of work AND precautions in place show risk from exposure at work is extremely low.
10-15% of those subject to dosimetry receive a measurable dose,
Average dose ~ 18uSv
0.1% of the dose limit of 20 mSv,
1% of that received from natural background radiation (2.2 mSv).
Follow Safe Procedures
Properties of Main Isotopes
Isotope Half-
Life
Radi
ation
Type
Energy Range in
Air
Dose
Rate at
10 cm
from
1 MBq**
Annual
Limit on
Intake*
Tritium
Water
(organic)
12.4 y B 18.6 keV 6 mm
1 GBq
480 MBq
Carbon 14
5730 y B 156 keV 24 cm 15 MBq
Sulphur 35
87.4 d B 167 keV 26 cm 34 MBq
Phosphorus
33
25.6 d B 250 keV 46 cm 14MBq
Phosphorus
32
14.3 d B 1.71 MeV 790 cm 1 mSvh-1
6 MBq
Iodine 125
60.1 d X
Y
30 keV
35 keV
metres 14 uSvh-1
1 MBq
Legislation
Health and Safety
Ionising Radiations Regulations 1999
Environmental
Environmental Permitting Regulations 2010
(Supersede Radioactive Substances Act 1993)
Ionising Radiations Regulations
1999
Worker protection
dose limits
Justification Radiation Project Proposal Forms (Rad 1-3)
risk assessment for exposure Risk Assessment Forms (Rad 5 or 6)
restrict exposure through equipment, procedure, experimental design
time,
shielding,
distance (inverse square law)
Protection through distance
Inverse square law applies
Distance Dose rate
(uSv/hr)
1m 1
2m 0.25
4m 0.06
Protection through distance
HOWEVER !!!!!!
Distance Dose rate (uSv/hr)
100cm 1
50cm 4
30cm 9
10cm 100
1cm 10,000
1mm 1,000,000
Ionising Radiations Regulations 1999
Local Rules
RPS’s for all areas
Worker/Project registration
Designation of areas
access control
contamination monitoring
Worker responsibility
Regular checks by RPS
Secure storage and accounting
Movement
packaging and labelling
No posting or carriage on public transport
Environmental Permitting
Regulations 2010
Enforced by Environment Agency.
Licensing regime
stocks
accumulation and disposal of waste
specific limits on
isotope and quantity,
disposal route and disposal period
Strict record keeping essential
Isostock for Radiochemicals
Must be kept up to date
Administrative Controls
Project Registration (Rad 1-3)
Isotopes
Quantities
Disposal routes
Lab Facilities
Worker Registration (Form)
Project
Dosemeter
Look after it
Return at end of quarter – charges for late/lost badges
Amend Details if Work Changes
The Use of Radiochemicals
in Life Science Research
Comparison of Common Isotopes
Safe Handling – 10 Golden Rules
Decomposition
38
Commonly used isotopes
Isotope 14
C 3H
125I
32P
33P
35S
Emission
Energy
(Mev)
0.156 0.0186 0.035 1.709 0.249 0.167
Half Life 5730 years 12.35years 60 days 14.3 days 25.4 days 87.4 days
Max. Spec.
Activity
62.4
mCi/mAtom
29
Ci/mAtom
2000
Ci/mAtom
9000
Ci/mAtom
3500
Ci/mAtom
1500
Ci/mAtom
Mean path 42 0.47 - 2710 300 40
length (mm)
39
Carbon-14
Low energy emission - no shielding required
Long half-life - less time pressure
Low specific activity - low sensitivity
Detection
scintillation counter
autoradiography
Geiger counter
phosphorimager
Labelled compounds generally stable - few
decomposition problems
40
H-3 (Tritium)
Very low energy emission - no shielding required
Long half - life
High specific activity - reasonably sensitive, but
weak emission
Detected by scintillation counter detection less easy
autoradiography less accurate and
fluorography less efficient than 14C
phosphorimager
Labelled compounds less stable - radiation
decomposition problems
41
Iodine -125
emission - lead shielding required
Short half-life - time pressures
Very high specific activities - high sensitivities
Detection
Gamma counter
Scintillation probe
Autoradiography
phosphorimager
Labelled compounds stable - some decomposition
problems
42
Phosphorus - 32
High energy emission - shielding required (perspex
and lead)
1 MBq in 1ml plastic vial @ 1m 2.5uSv/hr
@ 10cm 200uSv/hr
30MBq in 1ml plastic vial @ 10cm 6mSv/hr
25 hours of work = 150mSv,
i.e.Classified Worker
NEVER HOLD VIAL IN FINGERS
Phosphorus - 32
High energy emission - shielding required (perspex
and lead)
Short half-life - time pressures
Very high specific activity - very high sensitivity
Detection
Scintillation counter
Cerenkov counter
Geiger counter
Autoradiography
phosphorimager
Labelled compounds unstable - decomposition
problems
44
Phosphorus - 33
Low energy emission - low shielding required (1cm
perspex)
Short half -life - time pressures
High specific activity - high sensitivity
Detection
Scintillation counter Easy to detect
Proportional counter and accurate counting
Geiger counter
Autoradiography
phosphorimager
Labelled compounds generally stable - few
decomposition problems
45
Sulphur -35
Low energy emission - low shielding required (1cm
perspex)
Shortish half-life - some time pressures
High specific activity - high sensitivity
Detection
Scintillation counter
Proportional counter
Geiger counter
Autoradiography
phosphorimager
Labelled compounds generally stable - few
decomposition problems
46
Resolution
Plastic base
Emulsion
Anti scratch
Intensifying
screen
H-3 C-14/ S-35/ P-33 P-32/ I-125
aasAS
Image on film: Blank
47
Choosing an isotope
Detection method
Resolution required
Sensitivity
Specific activity
Formulation - aqueous/ethanol
(stabilised/free radical scavenging)
Position of label - important in metabolic
studies / can affect protein binding
48
Working safely with radioactivity
Understand the nature of the hazard and get practical training
Plan ahead to minimise handling time
Distance yourself appropriately from sources of radiation
Use appropriate shielding
Contain radioactive materials in a defined work area
Wear appropriate protective clothing and dosimeters
Monitor the work area frequently
Follow the local rules and safe ways of working
Minimise accumulation of waste and dispose of it correctly
After completion of work monitor yourself and work area
The Ten Golden Rules
49
Decomposition
Chemical decomposition caused by, or
accelerated by:
the presence of one or more radioactive atoms in
the molecule
Free radicals
Micro-organisms
Stock solutions and aliquots will decompose
over time and become unusable.
50
Modes of decomposition
Mode of decomposition
Cause Method for control
Primary (internal) Natural isotopic decay None for a given specific activity
Primary (external)
Direct interaction of the radioactive emission with molecules of the compound
Dispersal of labelled molecules
Secondary Interaction of the excited species with molecules of the compound
Dispersal of labelled molecules, cooling to low temperatures, add free radical scavenger
Chemical and microbiological
Thermodynamic instability of the compound and poor environment
Cooling to low temperatures, removal of harmful agents
51
Typical rates of decomposition
Carbon -14 1-3% per year
Tritium 1-3% per month
Sulphur -35 1-3% per month
Phosphorus -32 1-3% per week
Iodine -125 5-10% per month
52
Stability of [2,4,6,7-³H]Oestradiol 100%
80%
90%
Rad
ioch
em
ica
l p
uri
ty
4 8 12 20 15
Time (weeks)
53
Effect of Specific Activity Decomposition of [-³²P]ATP at 20°C
100%
30%
90%
60%
0.17
1.7
17
Specific activities in Ci/mmol
7 Time (days)
Rad
ioch
em
ica
l p
uri
ty
54
Effect of temperature Stability of [35S]Methionine
100%
70%
90%
80%
-140º
-80º
-20º
6 3 1
Time (weeks)
Rad
ioch
em
ica
l p
uri
ty
55
Effect of temperature
Stability of [³H]Uridine
100%
70%
90%
80%
+2º
-20º
12 6 3 9
Time (weeks)
Rad
ioch
em
ica
l p
uri
ty
56
Effect of free radical scavengers Decomposition of [U-14C]Phenylalanine at 20ºC
100%
90%
80%
70%
4 2 3 1
Time (months)
Rad
ioch
em
ica
l p
uri
ty
+ 3% ethanol
Aqueous solution
57
Control of decomposition
Store at lowest specific activity
Store at lowest radioactive concentration
Disperse solids - store under inert atmosphere
Add 2% ethanol to aqueous solutions
Store in the dark
Use stabilised formulations
Tritium - Store just above freezing point or -140
Reanalyse immediately prior to use
Aliquot if long storage expected
Contamination Control Video
59
END