Radiation protection for work with unsealed sources

SEMINAR1. Legislative control RSA93 & irr992. Management Structure3. Duties of Workers – ALARA + red tape4. To carry out ALARA – know isotope and hazards, know units5. Stochastic & non-stochastic damage. No way of eliminating risk – hence

ALARA6. Maximum Legal Dose7. Equivalent risks8. Minimise Dose9. Minimum Activity – counts 10,000 maximum10. Shielding11. Common Sense (demo) LOCAL RULES – tray, gloves, care12. Monitoring – 2 types of monitor demo13. Records – account for waste disposal – 3 routes14. Record Sheets15. 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 ActBPM – 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. 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)?

2. Are there procedures where a different radionuclide could be used that has a lower environmental impact (shorter half life perhaps)

3. Are the procedures currently followed best practice? Could different techniques be employed that would reduce the amount of radioactive material used.

4. Is there scope for reducing waste by ordering radionuclides in smaller amounts?

5. Could we usefully reduce emissions by increased decay storage? (I-125 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 disposalProject 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

Example1. Designation 32P

(AX)2. Activity 370MBq

(MBq or mCi)3. Radiations emitted

(, or )4. Energies of the Radiations 0.51MeV

(MeV)5. Frequency of emission 95%

(% disintegrations)6. Half-life 14 days

Common Isotopes

3H 14C 32P 125I

Type

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

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 Less serious

X Rays Whole body

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 (Bq) = 1 dps (1 disintegration per second)

1 Kilo- (kBq) = 103 dps

1 mega- (MBq) = 106 dps

1 giga- (GBq) = 109 dps

1 microcurie (Ci) = 3.7 x 104 dps

1 milli- (mCi) = 3.7 x 107 dps

1 curie (Ci) = 3.7 x 1010 dps

1 MBq = 27 Ci1mCi = 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 - 1 in 2,000 chance above average extrapolating 10 mSv - 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 cosmic radiation 300 svTerrestrial 400 sv 87%

radon decay 800 sv of totalinternal radiation 370 sv

(eg. K-40)

TOTAL NATURAL 1870 sv

• Artificial Medical procedures 250 sv Weapons fall out 10 sv

Nuclear discharge to 1.5 sv

Environment 13%

Occupational exposure 8 sv of totalMiscellaneous sources 11 sv

TOTAL ARTIFICIAL 280 sv

• Chernobyl estimate (U.K.) 40 sv (May 86 – April 87)

20 sv subsequently

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 Risk of death per year

Fishing 1 in 800

Coal mining 1 in 6,000

Construction 1 in 10,000

All employment 1 in 43,500

And (b) Average annual risk of death in the U.K. from some common causes

Cause Risk of death per year

Smoking 10 cigarettes per day 1 in 200

All natural causes for a 40 year old 1 in 850

Accidents on the road 1 in 9,500 Accidents in the home 1 in 26,000

There are three strategies for dose control

1. Planning of experiments to reduce dose, mechanical interlocks (As Low As Reasonably Achievable (ALARA)).

2. Retrospective, film badges

3. 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 DoseTotal 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.

ShieldingThe amount of shielding required depends on three things:1. The type of radiation2. The activity of the source3. 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 sensitive2. 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

Each radioisotope has a specific emission spectrum

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

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 mini-monitor 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 1ci sample at 20mm:

Radionuclide c.p.s. Principal emission125I 1610 35 keV and 27-32 keV51Cr 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 berecorded 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: Indicate type of equipment (optional)

• 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.

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: a unique code from STORES identifying the delivery (e.g.B10/09)- this

code must be marked on the outside of the radioisotope container.•  SUB-CODE: mark this as MASTER on all master sheets•  DATE RECVD: date received by stores•  ACTIVITY REF.DATE: as supplied by Amersham for short-lived isotopes•  COMPOUND: chemical composition of the isotope source

ISOTOPE: radionuclide (I-125, P-32, C-14 etc.)•  LOCATION: laboratory where isotope is to be kept•  TOTAL ACTIVITY: as delivered from Amersham (eg 5mCi)•  TOTAL VOLUME: volume of isotope delivered

ASSIGNED TO: person ordering the isotope and who is then responsible for ensuring that proper records are kept of its disposal

• (Continued below)

Waste Disposal Routes

Very Low Level Waste

Mixed with normal refuse 400 kBq per 0.1m3 (e.g. cube 46x46x46cm.)

paper, gloves in unlabelled sacks

Aqueous

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 levels- e.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.