Radiation protection for work with unsealed sources

SEMINAR 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 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? (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 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 Example Designation 32P (AX) Activity 370MBq (MBq or mCi) Radiations emitted  (,  or ) Energies of the Radiations 0.51MeV (MeV) 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 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 32P 14.3 d 1.70 33P 25 d 0.25 35S 87.2 d 0.17 36CI 3 x 105 y 0.l71 32-Phosphorus is one of the highest energy beta-emitting radionuclides commonly used in biomedical research

Hazards represented by different ionising radiations External Internal  particle None Very serious  particle Skin, eyes Serious Neutrons Whole body  Rays Less serious X Rays Positron emitter eg 18F. Positron annihilates with electron to emit 2 gamma rays in opposite directions.

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  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 - 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 sv Terrestrial  400 sv 87% radon decay 800 sv of total internal 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 total Miscellaneous 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 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

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 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. Useful in reducing doses by moving away - The other side of the coin is that if you (or your fingers) are very close- the dose rate can be very high, e.g. if handling a tube with a high-energy emitter, like 32P, directly with your fingers. Minimise this! Also 18F, positron emitter 1.6 Mev (similar energy to 32P)

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 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: The type of radiation The activity of the source 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 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. 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.

Radioactive decay process Type of active monitoring Emission  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  + 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

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

So it can be seen that the response of a monitor will vary with 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 The amount of radiation Its energy 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: 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 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 Critical organ BONE THYROID Biological stability if absorbed HIGH MOD Concentration in critical organ LOW Disposal problems

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. After completion of work monitor yourself, wash and monitor again Always discuss work procedures and get detailed advice from experienced radiation workers.