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 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