Transcript RADIATION - Keele University

Radiation protection for work
with unsealed sources
SEMINAR
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
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15.
Legislative control RSA93 & irr99
Management Structure
Duties of Workers – ALARA + red tape
To carry out ALARA – know isotope and hazards, know units
Stochastic & non-stochastic damage. No way of eliminating risk – hence
ALARA
Maximum Legal Dose
Equivalent risks
Minimise Dose
Minimum Activity – counts 10,000 maximum
Shielding
Common Sense (demo) LOCAL RULES – tray, gloves, care
Monitoring – 2 types of monitor demo
Records – account for waste disposal – 3 routes
Record Sheets
Dealing with spillages
Ionising Radiations Regulations
ALARA – As low as reasonable attainable. Minimising dose by reducing time
spent in vicinity of isotopes by increasing working distance and by using
appropriate shielding.
Radioactive Substances Act
BPM – all users are expected to have available for inspection, written assessments
showing the considerations taken into account in disposal of radioactive waste
and how that constitutes the use of Best Practicable Means
The Radioactive Substances Act 1993
The RSA93 is aimed at ensuring the security of radioactive materials in
industrial/research use, especially with regard to the proper disposal of any
radioactive waste that may be generated.
Registration of Sources – most radioactive materials are required to be registered
under the RSA93 act for their safe keeping and use at a specified premises.
A Registration licence is issued under the Act which specifies the number of
sources and their respective maximum activities which may be brought on to
the premises.
The keeping of radioactive material and the disposal of radioactive waste are both
highly regulated by the Environment Agency.
Ionising Radiations Regulations 1999
Made under the Health & Safety at Work Act 1974, these regulations apply to all users of
radioactive materials or radiation generating equipment and are enforced by the health
& Safety Executive.
In the UK the National Radiological Protection Board advises the Government on standards
to be adopted and fully endorses the EU recommendations for reducing worker dose
limit.
IRR99 are concerned with regulation of work with ionising radiation and dose limitation:
• Restriction of exposure
• Dose limits
• Arrangements for the control of Radioactive substances
• Monitoring of ionising radiation
• Designation of controlled and supervised areas
• Local rules, supervision and radiation protection supervisors
• Information, instruction and training
Best Practical Means
1.
2.
3.
4.
5.
Can we justify the use of radioactive tracers in all the procedures
currently using them. Is there a practical non radioactive alternative
(e.g. fluorescent dyes)?
Are there procedures where a different radionuclide could be used
that has a lower environmental impact (shorter half life perhaps)
Are the procedures currently followed best practice? Could
different techniques be employed that would reduce the amount of
radioactive material used.
Is there scope for reducing waste by ordering radionuclides in
smaller amounts?
Could we usefully reduce emissions by increased decay storage? (I125 perhaps). Currently only used for 32-P.
Management Structure set up by the University to control work with unsealed
radioactive sources – summarised by flow chart
Registrar
Ultimately responsible for all work carried out at
Keele University
URPS
Ensures compliance with the Ionising Radiations
Regulations 1999 concerning the holding and
disposal of radioactive substances
DRPS
Authorises all work including purchases of
radioisotopes, advised on safe handling and
disposal of isotopes, keeps records on use and
disposal of isotopes
Project Leader
Laboratory Manager
Designs and supervises experiments, ensure all
relevant regulations are observed within laboratory
Radiation workers
Ensure safe working practices by carrying out all
laboratory work in accordance with the ALARA
principal to ensure any dose of radiation received is
As Low As Reasonably Attainable
Scheme of Responsibility
Registrar
(Mr Simon Morris)

University Radiation Protection Supervisor (URPS)
(Dr David Dugdale)

Departmental Radiation Protection Supervisor (DRPS)

Project Leaders / Laboratory Managers

Radiation Workers
Summary of responsibilities of workers using unsealed sources
It is the duty of all workers to take reasonable care for the health and safety of
themselves and of other persons who may be affected by their acts or
omissions at work.
Health and Safety at Work Act, 1974 (see University Safety handbook)
University Radiation Protection Supervisor (URPS: Dr David Dugdale)
• Ensure compliance with the Ionising Radiations Regulations 1999.
Departmental radiation Protection Supervisor (DRPS:
• Authorise all work including purchase of radioisotopes
• Advise on safe handling procedures, and disposal of radioactive waste
• To keep all records of all radioactive waste disposal
Project leader (may be delegated to Laboratory Manager)
• Design and supervise experiments
• Training workers in proper handling procedures and local rules
• Ensure that all relevant regulations are observed within the laboratory
• Provide facilities for disposal of radioactive waste
• Arrange removal of radioactive waste to store
• Ensure local records of monitoring and waste disposal are kept
Radiation Workers
• Register with the URPS before beginning any work with ionising
radiations
• Proceed with work only when reasonably familiar with, and confident in,
the experimental techniques involved- under close supervision initially.
• Carry out all laboratory work in accordance with the principal of ALARA, i.e.
to ensure any dose of radiation received is As Low As Reasonable Attainable
• Dispose of all radioactive waste by the appropriate local route
• Keep local records of the generation and disposal of radioactive waste
• Monitor person and work area frequently, including the start and end of each
working period.
Important Characteristics of a Radioisotope
1.
2.
3.
4.
5.
6.
Designation
(AX)
Activity
(MBq or mCi)
Radiations emitted
(,  or )
Energies of the Radiations
(MeV)
Frequency of emission
(% disintegrations)
Half-life
Example
32P
370MBq

0.51MeV
95%
14 days
Common Isotopes
3H
14C
32P
125I




Energy (MeV)
0.018
0.159
1.71
0.035
Half-life
12 y
5760 y
14 d
60 d
Target organ
Any
Any
Bone
Thyroid
Type
Physical Properties of Common Unsealed Sources
Isotope
Half-life
Principal
Radiations
Energy (MeV)
Abundance (%)
3H
12.3y

0.018
100.0
14C
5760 y

0.16
100.0
32P
14.3 d

1.70
100.0
33P
25 d

0.25
100.0
35S
87.2 d

0.17
100.0
36CI
3 x 105 y

0.l71
100.0
32-Phosphorus is one of the highest energy beta-emitting radionuclides commonly used in biomedical research
Hazards represented by different ionising
radiations
Radiation
Hazard
External
Internal
 particle
None
Very serious
 particle
Skin, eyes
Serious
Neutrons
Whole body
 Rays
Whole body
X Rays
Whole body
Less serious
Radiological Units
Source strength (Activity)
The quantity of radioactivity, being the strength of a source or its ‘activity’, is
expressed in terms of the disintegration rate of isotopes’ atoms, or becquerels.
1 becquerel
1 Kilo1 mega1 giga-
(Bq)
(kBq)
(MBq)
(GBq)
=
=
=
=
1 dps (1 disintegration per second)
103 dps
106 dps
109 dps
1 microcurie
1 milli1 curie
(Ci)
(mCi)
(Ci)
= 3.7 x 104 dps
= 3.7 x 107 dps
= 3.7 x 1010 dps
1 MBq
= 27  Ci
1mCi
= 37MBq
DOSE
Maximum permitted dose
= 10 mSv
Permitted dose at Keele
= 1 mSv
Estimating Dose
• Measure it
dosemeter (accurate)
personal monitor
film badge
thermoluminescence detector
• Calculate it
assumptions (approximate)
Action level: positive film badge/TLD return
Effect of radiation dose:
non-stochastic effects (acute, short-term)
0-50 mSv
no visible effect
500 mSv
reversible blood changes
1 Sv
mild illness, fever
3 Sv
vomiting, hair loss
4.5 Sv
bone marrow destruction
(LD 50 (infection)
6 Sv
1st/2nd degree burns
10 Sv
diarrhoea; death in 3-5 days
Effect of radiation dose:
stochastic effects (statistical, long-term)
mainly cancers
-
leukemia (5-7 years)
others (>20 years)
difficult to get accurate statistics for low doses
50 mSv



10 mSv
- 1 in 2,000 chance above average
extrapolating
- 1 in 10,000 chance above average
There is probably no “safe” dose:
Follow the principle of ALARA
(As Low As Reasonably Attainable)
Average Annual Dose Equivalent to an Individual (UK)
 = 10-6 m = 1-3
•
•
•
Natural
Artificial
cosmic radiation
Terrestrial 
radon decay
internal radiation
(eg. K-40)
TOTAL NATURAL
Medical procedures
Weapons fall out
Nuclear discharge to
Environment
Occupational exposure
Miscellaneous sources
TOTAL ARTIFICIAL
300 sv
400 sv
800 sv
370 sv
87%
of total
1870 sv
250 sv
10 sv
1.5 sv
8 sv
11 sv
280 sv
Chernobyl estimate (U.K.) 40 sv (May 86 – April 87)
20 sv subsequently
13%
of total
Important Dose Equivalents (Annual) relating to occupational exposure
Annual dose limit for men (radiation works)
= 10 msv
Special controls may become necessary if the dose rate exceeds 7.5 sv hr-1
(wholebody)
Risk Factors
1.
The risk factor for radiation induced fatal cancer is :
1.25 x 10-2 sv -1 (1 in 80 per Sievert)
The average dose equivalent received by a radiation worker is:
1.4 msv per year.
Therefore the annual risk of death for radiation workers due to cancer is:
1 in 57,000
2.
To put this value into perspective compare it with:
(a) Average annual risk of death in the U.K. from accidents at work
Occupation
Fishing
Coal mining
Construction
All employment
Risk of death per year
1 in 800
1 in 6,000
1 in 10,000
1 in 43,500
And (b) Average annual risk of death in the U.K. from some common causes
Cause
Smoking 10 cigarettes per day
All natural causes for a 40 year old
Accidents on the road
Accidents in the home
Risk of death per year
1 in 200
1 in 850
1 in 9,500
1 in 26,000
There are three strategies for dose control
1.
2.
3.
Planning of experiments to reduce dose, mechanical interlocks (As Low
As Reasonably Achievable (ALARA)).
Retrospective, film badges
Active monitoring, hand-held radiation detectors and swab testing.
Planning
Always plan experiments so that the minimum amount of radioactivity is used.
Always plan experiments with the minimum of sample handling
Do not linger in areas where radioisotopes are being used
Retrospective
Film badges are issued by the DRPS and any reported doses will be invesitigated
immediately
The Inverse Square Law
• The Inverse Square Law is a very powerful tool for
practical protection against external radiation.- it describes
how the intensity of radiation from a radioactive source
decreases as you move away from it.
• The simple rule to remember is that by doubling the
distance the radiation level is reduced to one quarter., by
trebling the distance the radiation level is reduced to one
ninth, and so on.
Minimising Dose
Total dose = dose rate x time
• Assess potential hazard – get to know your isotope
• Minimise external hazard:
- minimise time of exposure- planning
- keep distance from source
- use minimum activity necessary for experiment- planning
- use shielding where appropriate
• Minimise internal hazard
- good lab hygiene
- good technique
Apply liberal quantities of common sense!
Minimum activity considerations
• Statistical counting errors
• Signal/noise (background)
Statistical errors
error
 total counts
=
Total counts
Error
Error(%)
10
 3.2
31%
100
 10.0
10%
1000
 32
3%
10,000
 100
1%
10,000 counts over 5 min at 50% counting efficiency
= 4,000 dpm = 67 Bq ( 2 nCi)
Alpha particles are very easily absorbed. A thin sheet of paper is sufficient to
stop them so they never present a shielding problem.
Beta particles are more penetrating than alpha. The best shielding for beta
radiation is low density material such as perspex – 6mm thick will stop all beta
radiation up to 1MeV. Whilst relatively easy to shield, however, the dose rates
from beta radiation can be very high. High density material such as lead will
produce the ‘Bremsstrahlung’ effect where energy is emitted as penetrating X
rays.
Gamma radiation is much more penetrating and is attenuated exponentially when
they pass through any material. The most efficient absorbers are highly dense
materials such as lead or steel.
Shielding
The amount of shielding required depends on three things:
1.
The type of radiation
2.
The activity of the source
3.
The dose-rate which is acceptable outside the shielding material
Monitoring
There are 2 categories of monitors and dosemeters:
1. Contamination monitors – read out in cps and very sensitive
2. Dose ratemeters – which can calculate dose to person in Sv – less
sensitive.
Use correct monitor for the job in hand.
Contamination monitors – 2 types
1.
Geiger Muller detector used to detect beta particles, has very thin end window which
lets particles through easily. Not very sensitive to gamma rays as they pass straight
through it and do not react.
2.
Scintillation detector (900 series) has crystal in it with denser medium to stop gamma
and react. Beta particles cannot penetrate thick end window, so not detected.
Type E has a grill at the end and is most suitable for measuring low levels of leakage
radiation.
Different types of monitor for different types and energies of radiation.
NB 3H (Tritium) emits low energy beta which cannot penetrate the detector and is not
detected by either monitor. Monitor contamination by swabbing surface and liquid
scintillation counting of swab.
Active Monitoring
Types of emission
Radioactive decay
process
Type of active monitoring Emission

Swab testing
Helium nucleus
Soft 
Mini-instrument type EL
probe and swab testing
electrons
Hard 
Mini-instrument type EL
probe
electrons
 + X ray
Mini-instrument type 44
A, B or X probe
electromagnetic
Each radioisotope has a specific emission spectrum
Monitoring and dose control theory
The hazard to the worker associated with various types of emission can be divided
into two groups.
Emission
Hazard
External radiation
Internal contamination

None
Very serious

Skin and eyes
Serious

Whole body (including
internal organs)
Minor (except if target
organ is small)
X ray
Very serious
The use of mini-monitors
NB the monitor is not tropicalised or ruggedised and will not work if it is dropped
into a pond or run over by a tank!
Operation
•
•
•
Select the correct type of monitor
Switch the battery check for at least 2 minutes
Check the monitor is working with a radioactive source
Areas where work with ionising radiation is used are divided into three types:
Controlled > 1 mCi
Supervised > 100 Ci
Registered +/- 10 Ci
Various types of probes are available but commonly they are Geiger Muller eg minimonitor type EL and scintillation eg type 44A. The response of both probes varies
with the energy of the source as shown in Fig 1 and 2.
So it can be seen that the response of a monitor will vary with
a)
The amount of radiation
b)
Its energy
c)
Monitoring: Radioactivity is measured in KBq or Ci but the monitors give c.p.s.
The interpretation of c.p.s. must take into account the type of emission, the distance from
the source and the response of the probe to the energy of the emission, eg using a
type 44A probe with a 1ci sample at 20mm:
Radionuclide
c.p.s.
Principal emission
125I
1610
35 keV and 27-32 keV
51Cr
73
0.32 mev and 5 kev
CONTAMINATION MONITORING
Levels of radiation have to be routinely monitored both within and around all
controlled and supervised areas to check for:
•
•
•
•
Presence of enhanced levels of radiation exposure
Leakage from source housings, waste storage containers etc.
Presence of contamination on surfaces from use of unsealed radioactive
material
Presence of airborne contamination resulting from the release of gaseous
materials
Master Sheet Waste Disposal Section
Each time some isotope is removed from the stock bottle, its fate should be
recorded in the disposal section as follows:
•
NB the Department isotope code (e.g. B10/09) must be marked on the
stock container
• DATE:
When the isotope was removed from stock
•
AMOUNT USED: Record the amount removed from stock and amount
remaining in stock. It is essential that the master sheet
completely account for ALL of the isotope originally
delivered. For long-lived isotopes, this account must be in
activities. For isotopes that significantly decay with time
accounting procedures can be in volumes.
•
PURPOSE:
•
DISPOSAL ROUTE: If the activity is all used up in one experiment, then the
amount used should be accounted for in the first three
waste disposal route columns. NB. The disposal limited
for liquid organic waste is only 20 Ci/month so be
accurate. If the procedure involves preparation of a
derivative source to be used in several experiments (eg a
radiolabelling prep, make sure you keep track of all the
radioactivity.
Indicate type of equipment (optional)
Master Sheet Header Section
(A new sheet every time some isotope arrives in the School)
This should be filled in as soon as possible after delivery, as follows:
DEPT CODE:
•
SUB-CODE:
•
DATE RECVD:
•
ACTIVITY REF.
DATE:
•
COMPOUND:
a unique code from STORES identifying the delivery (e.g.B10/09)- this
code must be marked on the outside of the radioisotope container.
mark this as MASTER on all master sheets
date received by stores
as supplied by Amersham for short-lived isotopes
chemical composition of the isotope source
ISOTOPE:
•
LOCATION:
•
TOTAL ACTIVITY:
•
TOTAL VOLUME:
radionuclide (I-125, P-32, C-14 etc.)
ASSIGNED TO:
person ordering the isotope and who is then responsible for ensuring that
proper records are kept of its disposal
•
(Continued below)
laboratory where isotope is to be kept
as delivered from Amersham (eg 5mCi)
volume of isotope delivered
Waste Disposal Routes
Very Low Level Waste
Aqueous
Mixed with normal refuse 400 kBq
per 0.1m3 (e.g. cube 46x46x46cm.)
paper, gloves in unlabelled sacks
Designated sink 400 MBq per
month all isotopes
Solid Waste
Incinerators 200 MBq per month
includes sample tubes
14C, 3H and 1251 only designated
bins
Liquid organic
Incinerators 400 kBq per month
includes scintillation vials 14C, 3H
only 4 litre plastic containers
Note that short-lived isotopes, eg 32P, are often best disposed of by storing in
shielded areas until decay has reduced the radioactivity to negligible levelse.g. 6 months storage for less than 1 mCi 32P, then, unlabelled, into very low
level waste
KEY FEATURES CONCERNING RADIATION PROTECTION FOR
TWO COMMONLY USED RADIONUCLIDES
Feature
P-32
I-125
Radiation type


Energy
1.7 MeV
35 keV
Proection afforded by
distance
Inverse Square
Law
Inverse
Square Law
Easily air borne
NO
YES
Radiological half life
14.3 days
60 days
Finger dose problems
YES
NO
Critical organ
BONE
THYROID
Biological stability if
absorbed
HIGH
MOD
Concentration in critical
organ
LOW
HIGH
Disposal problems
NO
YES
Eleven Golden Rules
1. Understand the nature of the hazard and get practical training.
2. Plan ahead to minimise time spent handling radioactivity.
3. Distance yourself appropriately from sources of radiation and use appropriate shielding
for the radiation
4. Always get detailed instruction and advice from supervisor and/or other experienced
radiation workers before starting work- do initial work under direct supervision.
5. Contain radioactive materials in defined work areas.
6. Wear appropriate protective clothing and dosimeters.
7. Monitor the work area frequently for contamination control.
8. Follow the local rules and safe ways of working.
9. Minimise accumulation of waste and dispose of it by appropriate routes.
10.
After completion of work monitor yourself, wash and monitor again
11.
Always discuss work procedures and get detailed advice from experienced radiation
workers.
If Radioactive Material is Spilled:
Before starting work with any unsealed radioisotope, make sure a supply of absorbent
tissues is nearby, and that wherever possible all work is performed within trays which
will contain any spillage.
In any accident involving the spillage of radioactive material priority should be given to
the treatment of any personal injury or personal contamination.


Personal Decontamination
o Persons carrying out decontamination of a colleague should use gloves and
take care to avoid contaminating themselves or transferring contamination
to other areas- i.e. phone for assistance rather than leaving the laboratory.
o Use appropriate radiation monitors to determine the extent of any
contamination. For contamination by soft beta emitters (eg H-3) an initial
judgement based on visual examination may be needed before the results
of swab tests are available.
o Remove clothing as necessary and place them in plastic bag in a suitable
shielded waste receptacle. Those areas of skin where contamination is
indicated should be washed with soap and water or Decon solution. Use a
shower if one is available but take care not to wash contamination into the
eyes or mouth
o If necessary irrigate the eyes using an eye wash bottle and wash the mouth
several times.
o Monitor again. If contamination persists wash again .
o Continue this process until no contamination can be detected.
o Report the incident immediately to RPS and research group leaders.
o If ingestion of radioactive material is suspected then a medical examination
should be sought
Area Decontamination
o For personal protection use gloves and forceps. If dry powder spills are
involved an appropriate face mask should also be used.
o For minor spills ( < 1mCi ; likely conditions within Life Sciences
biochemical and molecular biological laboratories) use absorbent paper
tissues or other absorbent material to mop up the spill, working inwards
towards the centre of the spill. Place contaminated swabbing material in
plastic bags and store in a suitable shielded enclosure for latter disposal.
o For larger spills ( > 1 mCi) it may be necessary to set up radiation shields
to give protection to those carrying out the decontamination procedure.
Advice should be sought from the RPS or URPS
o Wash the affected area with water or Decon solution until monitoring
shows that all traces of contamination have been removed.
Please ask Radiation Protection Supervisor about training if required.