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Safe Working With Ionising Radiation Revised January 2012

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Safe Working With Ionising Radiation Revised January 2012 John Sutherland, University Safety and Radiation Protection Officer – PowerPoint PPT presentation

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Title: Safe Working With Ionising Radiation Revised January 2012


1
Safe Working With Ionising RadiationRevised
January 2012
  • John Sutherland,
  • University Safety and Radiation Protection
    Officer

2
Remember
  • Please make sure you have signed in - otherwise
    you will need to re-attend!!
  • Handout - also downloadable from Safety Office
    Web Page

3
Programme
  • What is radiation?
  • How is it measured?
  • Biological harm
  • Doses into perspective
  • Legislation
  • Unsealed work
  • X-ray/Sealed - Harry Zuranski, Safety Office.

4
Objectives
  • Foundation for Training in School
  • Understand principles
  • radiation types and effects
  • biological effects
  • relative risk
  • legislation
  • university arrangements
  • Safe Practice

5
Atomic Structure
6
Isotopes
  • Variable neutron number
  • Unstable nuclei transform
  • Ionising radiation emitted

7
Ionisation
  • Energy transfer
  • Enough energy 13 eV

8
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
9
Types of Radiation
  • Video

10
Types of Radiation
  • Alpha
  • From heavy nuclei (e.g. Americium 241)
  • Helium nuclei (2P2N)
  • 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

11
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

12
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.

13
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

14
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

15
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

16
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.

17
Units of Radiation
  • SI units Becquerel, Gray, Seivert
  • replaced Curies, Rems, Rads
  • Activity
  • Dose
  • absorbed
  • equivalent
  • committed

18
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

19
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

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

21
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.

22
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.

23
Biological Effects of Radiation Exposure
  • 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.

24
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.

25
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.

26
Cancer Risk at Low Doses
  • Life-time risk of cancer from all causes of about
    2025.
  • 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.

27
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.

28
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

29
Properties of Main Isotopes
30
Legislation
  • Health and Safety
  • Ionising Radiations Regulations 1999
  • Environmental
  • Environmental Permitting Regulations 2010
  • (Supersede Radioactive Substances Act 1993)

31
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)

32
Protection through distance
  • Inverse square law applies
  • Distance Dose rate (uSv/hr)
  • 1m 1
  • 2m 0.25
  • 4m 0.06

33
Protection through distance
  • HOWEVER !!!!!!
  • Distance Dose rate (uSv/hr)
  • 100cm 1
  • 50cm 4
  • 30cm 9
  • 10cm 100
  • 1cm 10,000
  • 1mm 1,000,000

34
Ionising Radiations Regulations 1999
  • Local Rules
  • RPSs 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

35
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

36
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

37
The Use of Radiochemicals in Life Science Research
  • Comparison of Common Isotopes
  • Safe Handling 10 Golden Rules
  • Decomposition

38
Commonly used isotopes
39
Carbon-14
  • Low energy b 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 b 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
  • g 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 b emission - shielding required
    (perspex and lead)
  • 1 MBq in 1ml plastic vial _at_ 1m 2.5uSv/hr
  • _at_ 10cm 200uSv/hr
  • 30MBq in 1ml plastic vial _at_ 10cm 6mSv/hr
  • 25 hours of work 150mSv, i.e.Classified
    Worker
  • NEVER HOLD VIAL IN FINGERS

43
Phosphorus - 32
  • High energy b 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 b 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 b 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
Intensifying screen
Plastic base
aasAS
Emulsion
Anti scratch
H-3 C-14/ S-35/ P-33 P-32/ I-125
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
The Ten Golden Rules
  • 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

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
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 2,4,6,7-³HOestradiol
100
Radiochemical purity
90
80
4
8
12
20
15
Time (weeks)
53
Effect of Specific Activity
Decomposition of g-³²PATP at 20C
100
0.17
1.7
90
Radiochemical purity
60
Specific activities in Ci/mmol
17
30
7
Time (days)
54
Effect of temperature
Stability of 35SMethionine
100
-140º
-80º
90
Radiochemical purity
80
-20º
70
Time (weeks)
6
1
3
55
Effect of temperature
Stability of ³HUridine
100

90
Radiochemical purity
80
-20º
70
12
6
3
9
Time (weeks)
56
Effect of free radical scavengers
Decomposition of U-14CPhenylalanine at 20ºC
100
3 ethanol
90
Aqueous solution
Radiochemical purity
80
70
Time (months)
4
2
3
1
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

58
Contamination Control Video
59
END
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