Ionising Radiation Revised January 2012 John Sutherland, - - PowerPoint PPT Presentation
Safe Working With Ionising Radiation Revised January 2012 John Sutherland, University Safety and Radiation Protection Officer Remember Please make sure you have signed in - otherwise you will need to re-attend!! Handout - also
Revised January 2012
John Sutherland, University Safety and Radiation Protection Officer
Remember
Please make sure you have signed in -
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
Ionisation
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 Par
articles es (B) (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
Bremsstra
msstrahlun hlung
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
Gam
amma ma Rad adia iati tion
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-Radiat
adiation ion
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
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.
Uni nits ts of
adiat ation
SI units Becquerel, Gray, Seivert
replaced Curies, Rems, Rads
Activity Dose
absorbed equivalent committed
Uni nits ts of
adiat ation
activity ity
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
Uni nits ts of
adiat ation
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
Uni nits ts of
adiat ation
mitted tted
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
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
Comparison of Common Isotopes Safe Handling – 10 Golden Rules Decomposition
38
Commonly used isotopes
Isotope
14C 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
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
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
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
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
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
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% Radiochemical purity 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) Radiochemical purity
54
Effect of temperature
Stability of [35S]Methionine
100% 70% 90% 80%
6 3 1 Time (weeks) Radiochemical purity
55
Effect of temperature
Stability of [³H]Uridine
100% 70% 90% 80% +2º
12 6 3 9 Time (weeks) Radiochemical purity
56
Effect of free radical scavengers
Decomposition of [U-14C]Phenylalanine at 20ºC
100% 90% 80% 70% 4 2 3 1 Time (months) Radiochemical purity + 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