Safe Working With Ionising Radiation Programme What is

1
Safe Working With Ionising Radiation
2
Programme

• What is radiation?
• How is it measured?
• Biological harm
• Doses into perspective
• Legislation
• Unsealed work
• Isotope selection
• Safe working
• Decomposition

3
Objectives

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

4
Atomic Structure
5
Isotopes

• Variable neutron number
• Unstable nuclei transform
• Ionising radiation emitted

6
Ionisation

• Energy transfer
• Enough energy 13 eV

7
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
8
Types of Radiation

• Video

9
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

10
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

11
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.

12
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

13
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

14
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.

15
Units of Radiation

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

16
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

17
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

18
Units of Radiation - relationship

• quantity x energy dose rate (uSv. hr-1)
• number of DPS (Bq)
• energy in electron volts
• 1 eV 1.6 x 10-13 joules
• e.g. 1 MBq of a 1MeV source, thus
• 1 MeV 1.6 x 10-7 joules, and
• 1 MBq 106 disintegrations per second, hence
• Energy flux 1.6 x 10-1 joules/second
• 576 joules/hour
• Note 1 Sv/h 1 joule/kg/h deposited in tissue

19
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

20
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.

21
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.

22
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.

23
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.

24
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.

25
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.

26
Cancer Risk at Low Doses

• Most simplistic assumption is linear relationship
  between dose and risk
• This produced the following risk probabilities
• Fatal Cancer 1 in 25,000 per mSv
• Non-fatal cancer 1 in 125,000 per mSv
• Hereditary Effect 1 in 125,000 per mSv
• Combined risk 1 in 18,000 per mSv

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
• Radioactive Substances Act 1993

31
Ionising Radiations Regulations 1999

• Worker protection
• dose limits
• justification
• risk assessment for exposure
• restrict exposure through
• equipment, procedure, expt design
• time, distance , shielding

32
Protection through distance

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

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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
• Secure storage and accounting
• Movement
• packaging and labelling
• No posting or carriage on public transport

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Radioactive Substances Act 1993

• 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

36
Administrative Controls

• Project Registration
• Isotopes
• Quantities
• Disposal routes
• Lab Facilities
• Worker Registration
• Project
• Dosemeter - Care
• Amend Details if Work Changes

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End of Part One

• X-ray and Sealed Source Users to Other Room
• Harry Zuranski
• Sign in.

38
Isostock - Computer Recordshttp//www.nottingham.
ac.uk/safety/publications/radiation.html
39
The Use of Radiochemicals in Life Science Research
Safe handling and choice of Isotope
Slide Set Provided by Amersham Biosciences
A
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Definitions

• Radioactivity - the property of certain nuclides
  of emitting radiation by the spontaneous
  transformation of their nuclei
• Specific activity - Activity per unit mass of a
  compound
• Radioactive concentration - The activity per unit
  quantity of any material in which a radionuclide
  occurs
• Radiochemical purity - the amount of
  radioactivity in the stated chemical form ( does
  not take into account non-radioactive impurities)

41
Production of radiochemicalsneutron in / proton
out
42
Isotope production

• Isotope
• 3 Hydrogen (Tritium)
• 14 Carbon
• 35 Sulphur
• 32 Phosphorus
• 33 Phosphorus
• 125 Iodine

• Stable daughter nuclide
• Helium -3
• Nitrogen -14
• Chlorine - 35
• Sulphur -32
• Sulphur - 33
• Tellurium - 125

43
Commonly used isotopes
44
14C maximum specific activity
45
Commonly used isotopes
46
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
• Label is part of the backbone of molecule
• Labelled molecules are natural species - no
  artefacts

47
14C is in the backbone
48
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
• Label is part of the backbone of molecule
• Labelled molecules are natural species - no
  artefacts

49
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
• Label on periphery of molecule - no confidence in
  label position
• Labelled molecules are natural species - no
  artefacts

50
Label moves around the molecule
51
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
• Label on periphery of molecule - no confidence in
  label position
• Labelled molecules are natural species - no
  artefacts

52
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
• Label covalently bound to molecules - position of
  label fixed
• Not often part of natural molecule - artefacts

53
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

54
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
• Label covalently bound to molecule - position
  fixed
• Labelled molecules natural species - no artefacts

55
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
• Label covalently bound to molecule - position of
  label fixed
• Labelled molecules are natural species - no
  artefacts

56
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
• Label covalently bound to molecule - position of
  label fixed
• Labelled molecules may be natural (S-35 Met) or
  not (S-35 nucs)

57

Deoxynucleotide triphosphate structure
g b a
Base
O
OCH
P
P
P
2
H
H
OH
H
58
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
59
Comparison P-32/P-33/S-35

• Resolution in autoradiography
  
• S-35 gt P-33 gt P-32
• Sensitivity in detection
• P-32 gt P-33 gt S-35
• Probe stability
• S-35 gt P-33 gt P-32
• Decay rate
• P-32 gt P-33 gt S-35

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Choosing an isotope

• Detection method
• Resolution required
• Sensitivity
• Specific activity
• Formulation - aqueous/ethanol
• Position of label - important in metabolic
  studies / can affect protein binding

61
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

62
Radiation Decomposition

• The chemical decomposition of a compound caused
  by, or accelerated by, the presence of one or
  more radioactive atoms in the molecule

63
Modes of decomposition
64
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

65
Stability of 2,4,6,7-³HOestradiol
100
Radiochemical purity
90
80
4
8
12
20
15
Time (weeks)
66
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)
67
Effect of temperature
Stability of 35SMethionine
100
-140º
-80º
90
Radiochemical purity
80
-20º
70
Time (weeks)
6
1
3
68
Effect of temperature
Stability of 35SCysteine
100
-140º
-80º
90
Radiochemical purity
60
30
-20º
1
5
3
2
4
Time (weeks)
69
Effect of temperature
Stability of ³HUridine
100
2º
90
Radiochemical purity
80
-20º
70
12
6
3
9
Time (weeks)
70
Effect of slow freezing
Slow freezing concentrates the solute
71
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
72
Effect of free radical scavengers
Stability of 35SMethionine
100
90
50
Radiochemical purity
Control (SJ204)
Stabilised 35Smethionine (SJ1515)
0
30
20
10
Time (days)
73
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 RedivueTM formulations
• Tritium - Store just above freezing point or -140
• Reanalyse immediately prior to use
• Aliquot if long storage expected

74
END