Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

` Ionising Radiations Code of Practice and Guidance Surface Contamination and Dose Rate Monitoring

Regulation 19 of The Ionising Radiations Regulations 1999 (IRR99) requires that the College where it has designated an area either controlled or supervised shall ensure that necessary steps are taken in regard to the nature and extent of the level of risk from exposure to ionising radiation, that levels of ionising radiation are adequately monitored for each area, and working conditions in those areas are kept under review. The Environmental Permitting Regulations 2010 (EPR10) also required users to monitor regularly for contamination and record the results.

Each Department / Group Head is responsible for ensuring that suitable radiation and contamination monitoring is carried out in their designated areas as appropriate.

The appointed Radiation Protection Supervisor (RPS) is responsible for ensuring that routine and task related monitoring is carried out in designated areas on a regular basis. This monitoring can be done by the RPS or a competent radiation user.

The radiation user is responsible for monitoring their work area before and after each use and completing record sheets, acting on any high dose-rate or contamination readings and reporting them to their RPS.

1.0 Definitions

A Radiation User / User is a person who is registered with the College Radiation User / User Safety Department to undertake work with ionising radiations. The College is classed as a radiation employer where it undertakes work or practices involving the use of ionising radiations. In EPR10 Radiation Employer Permits, Imperial College London (the radiation employer) is referred to as “the user”. RPA Radiation Protection Adviser RPO Radiation Protection Officer IRR99 Ionising Radiations Regulations 1999 RPS Radiation Protection Supervisor EPR10 Environmental Permitting Regulations 2010

2.0 Code of Practice

The College is a „radiation employer‟ and therefore has a statutory duty to ensure that levels of ionising radiations are adequately monitored in any Supervised and Controlled Areas on a periodic basis that is appropriate for its working patterns. Any department or individual radiation user working with ionising radiations shall ensure that radiation and contamination survey monitoring is done on a regular basis and the results recorded. The extent of the monitoring required will depend on the nature of the work and the findings of the risk assessment (work registration FORM J).

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

Departments are responsible for ensuring that an adequate monitoring programme is in place that is able to indicate breakdowns in control or systems, and detect changes in radiation or contamination levels.

Monitoring will be necessary both inside and outside the boundaries of the designated areas. The department must also ensure that all their staff are familiar with the proper use of the instruments available and know how to interpret the results.

The radiation user and RPS shall consult with the College RPA or RPO so far as is necessary to ensure that the correct radiation / contamination monitoring equipment will be used.

3.0 Guidance

3.1 Imperial College Monitoring Programme

 Stage 1) – Task Related Monitoring is performed by the radiation user as a standard procedure especially where ionising radiation is being used regularly during a single working day. Work areas should be monitored before and after each use.  Stage 2) – Routine Monitoring is carried out on a weekly or monthly basis by the RPS of the group or department to demonstrate that areas where ionising radiation is used are under constant review, correctly designated, and the Task Related Monitoring is being carried out effectively.  Stage 3) – Specific Monitoring is carried out by the RPS, RPO or RPA. This will sometimes involve the use of non-standard monitoring instrumentation to interpret complex data for nuclide identification. Example applications are clearance and decommissioning surveys.

Further guidance can be found for Decommissioning and clearance monitoring in IRPM-ICRP-035 (Liquid Scintillation Counting) and IRPM-ICRP-040 (Decommissioning).

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

Stage 3 – Specific Monitoring

Stage 2- Routine Monitoring

Stage 1 – Task Related Monitoring

The monitoring programme helps to ensure that all exposures are as low as reasonable practicable (ALARP).

3.2 Surface Contamination Monitoring

Surface Contamination monitoring is the process whereby ionising radiations, produced by either loose (i.e. movable) or fixed (i.e. non-movable) radioactive contamination, is monitored. The potential risk of internal exposure when radioactive material is distributed over a surface is of interest. The monitoring can be undertaken by two main methods:

 Direct Monitoring) - Using a suitable radiation monitor to detect the presence of emissions from surfaces and objects contaminated with radioactive material.  Indirect Monitoring) - A swab (wipe) is taken from the contaminated area and is then presented to a monitor in a low background area for measurement or counted in a liquid scintillation counter for a more accurate indication.

See IRPM-ICRP-035 (Liquid scintillation counting).

Direct monitoring is always preferred since an instant indication of the levels of contamination present is obtained. Direct monitoring may not always be possible due to the following:

 The contamination being as a result of a radionuclide with a very low energy that cannot be measured by most portable equipment. Tritium or is a good example.

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

 The radiation background in the area being too high. This situation could occur if trying to monitor for contamination in the vicinity of a radiation source.

Indirect surface contamination monitoring (wipe testing) should be adopted for the above scenarios.

An advantage of indirect (swab or wipe testing) monitoring is that one can determine whether the radioactive material is loose or fixed. Whilst neither is desirable, in the main, fixed contamination will always be preferable to loose. This is because loose contamination can, by definition, move around in the environment and lead to inhalation or ingestion of radioactive material.

3.3 Suitable Surface Contamination Monitors

Surface contamination monitors are used to directly detect the presence of emissions from radioactive substances on surfaces and objects. Even low concentrations of such substances may present a potential internal radiation hazard.

The majority of instruments used for this application detect surface emissions in terms of count rate, either units of counts s-1 or counts min-1. Some surface contaimation instruments are programmable and the user can set the likely or typical response to that specific radioisotope with a calibration factor derived from the instruments calibration data. Contact the College RPO for information if required.

There are many types of contamination monitoring equipment, too many to describe in this guidance. However table „A‟ below shows some of the most commonlly used at Imperial College London.

If you are unsure which surface contamination monitors to use, always consult the College RPA or RPO.

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

Table A: Examples of Surface Contamination Monitors

Thermo Mini 900 Thermo Mini 900 EP15 Berthold LB1210B 44A Crystal Scintillation Gas filled end window Geiger Gas filled proportional counter. Suitable for detector with a photon- Muller Tube. Suitable for most most beta, x-ray and gamma emitters. (Due multiplier. Suitable for medium energy beta emitters to the instruments wide area detector it is not most gamma emitters C-14 suitable for monitoring around piping and I-125, I-131 S-35 confined spaces). Can detect P-32, P-33, C- Cr-51 P-32 14, I-125 and Co-60.

There is an extended list of radioisotopes used at Imperial College with the recommended instruments to be used for direct surface contamination monitoring in Appendix A. There are other instruments available but before purchase / use the RPO or RPA must be contacted regarding suitability.

3.4 Basic guidelines for Contamination Monitoring

Regardless of which stage of the monitoring programme you are undertaking:

. Make sure you have selected the correct instrument to carry out the monitoring, that it is working properly and has been calibrated. . Move the instrument detector slowly over the surface you are intending to monitor. . Distance from the face of the detector to the surface you are monitoring should be approximately 3mm. . Try not to make contact between the probe and the surface being monitored as the probe can become damaged or contaminated. . Use the audio for any initial detection indication. . Once any contamination has been found, keep the detector over the area giving the highest reading and record a reading from the display. . Record the instrument readings for the areas monitored as you go along. . Report all readings (including background readings) on the monitoring record. . Always report any contamination found and carry out appropriate cleaning procedures to reduce the level of activity as far as reasonably practicable.

Practical training in direct surface contamination monitoring techniques can be given to radiation users by the College RPA or RPO through tool box sessions. Contact your College RPO for details (Reference TB001).

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

3.5 Dose Rate Monitoring

Dose rate monitoring is the process whereby radiation dose rates can be determined from the fixed or pulsed radiation fields produced by a source of ionising radiation. A dose rate may be measured from an area of contamination; this will depend on the magnitude of the activity (disintegrations per second) and the energy of those emissions.

Dose rate measuring instruments are used to detect and quantify the harm level of external exposure from penetrating radiations emitted from a source of ionising radiation. These tend to measure gamma, X-ray photons and secondary interactions from fast neutron fields, some can be used to measure beta dose-rate in terms of equivalent dose rate of µSv h-1 or mSv h-1. Although some instruments measure absorbed dose or air kerma for environmental dose rates in µGy h-1.

Some example applications for dose rate monitoring are: measuring the scattered low energy X- rays through gaps in shielding around X-ray sets or high activity gamma source irradiators. Count rate scintillation monitors can be used to detect the presence of X-ray leakage, a dose rate measurement can be made using a suitable dose-rate instrument.

It is important to note that contamination monitors are not suitable for dose rate monitoring as they are specifically designed for determining the level of surface emissions in terms of count rate. They cannot be used to make measurements in terms of equivalent dose or absorbed dose.

3.6 Beta Dose Rate Monitoring

With use of some radioisotopes it is possible for high beta flux rates to affect the eyes, or to receive a dose from contamination in contact with skin.

This poses a dual radiation hazard where the contamination with loose material provides a risk of internal exposure through absorption, inhalation or ingestion of radioactive material, and an external radiation hazard. Examples in this category are high energy beta emitting radioisotopes e.g. P-32 and Sr-90.

To measure this „Shallow‟ dose rate some instruments have a chamber window with a material thickness similar to the depth of skin, thickness (around 7.0mg/cm2) as part of their detector and can be used to determine the beta dose rate.

3.7 Suitable Dose Rate Monitors

Table „B‟ below shows a small selection of typical dose rate instruments used at Imperial College London that are suitable for measuring gamma, X-ray photons and neutron fields.

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

Table B: Examples of Dose Rate Monitors

Thermo Mini Smart-Ion Thermo Mini-rad 1000 Thermo Eberline Neutron Monitor Ion-chamber based detector Gas filled steel walled Geiger Boron triflouride Gas filled with beta dose rate window. Muller Tube detector. Suitable proportional counter. Suitable Suitable for gamma, X-ray for gamma and X-ray photons. for most fast neutron photons and beta dose rates. Measures in terms of Ambient measurements for neutrons up Measures in terms of Ambient Dose Equivalent Rates H*(10) to 14 MeV. (Instrument can be Dose Equivalent Rates H*(10) tissue depth. Energies 60 keV a manual handling issue due to Tissue and Directional Dose to 1.3 MeV. its weight). US instruments are Equivalent Rates H‟(0.07) Skin. scaled in terms of exposure Energies 17 keV to 1.3 MeV. Non-SI units Roentgens R h-1.

Dose rate monitoring is generally more specialised and radiation dose rates are a better indication of risk than count rates for external radiation hazards. If you are in doubt as to which monitors to use always consult the College RPA or RPO.

3.8 Monitor Selection and Testing. It is important to remember that using the wrong monitor can result in missing the presence of significant surface contamination or dose rate. Some instruments are inefficient for certain types of ionising radiations. Also, some alternative instruments available may not comply with UK standards. For further guidance on correct monitor selection and testing of instruments contact the College RPO or RPA.

3.9 Responsible Persons Where work is undertaken with ionising radiations, an RPS must be appointed in writing by the department undertaking the work. The RPS should be suitably trained and is responsible for ensuring that the work is done safely and in accordance with the department local rules. The RPS should be able to give advice on the selection and use of the correct instruments, but where they are unsure of the correct choice they should consult the College RPA or RPO.

3.10 Monitoring is essential for Radiation Protection

Monitoring instruments should be used when they can help prevent exposure of persons to ionising radiations or protect the environment. Monitors are relatively inexpensive compared with other aspects of the work and should therefore be considered from the start. The requirement for adequate monitors should be considered as part of the risk assessment, which must be carried out before work starts.

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

3.11 Instrument Function Checks

Before any monitoring takes place the instrument must be given a basic function check to ensure it is fit for purpose and in satisfactory condition.

The checks involved:

. Calibration Check. The instrument must have a calibration / test sticker on the case which is in date. i.e. within the calibration period. This will be a 12 month period.

. Battery and power level check. Open up the battery box and visually check battery connections and cables (Mini 900 series only). Then turn on the instrument and watch the needle indication move on the power bar for a few seconds (usually a green or blue bar on the meter). For other types use the instruments battery check function.

. Audio check. Good audible sound from the instrument in the form of “clicks” when it is turned on and detecting natural background radiation.

. Cable check. Run your hand back and forth along the cable and gently pulling each end listen for a spike in noise level or increased crackling.

. Display indication. Clear display easy to be read make sure needle moves on instrument when recording background or near a source.

. Detector Check. Probe should be clean with its grill in place and no signs of physical damage or puncture marks on window.

. Background level confirmation. A typical background reading must be taken in a low background area where no sources of ionising radiation are present.

. Source check. If the instrument does not have a check source attached, place the detector of the instrument near a source of ionising radiation (e.g. the fridge in the designated area where the stock pots of P-32 or I-125 are stored). Instruments should be able to detect this source of radiation demonstrating that they are functioning correctly.

3.12 Basic Storage

Like most pieces of sensitive laboratory equipment, contamination & radiation monitors are delicate instruments and should be treated with care and stored appropriately e.g. avoiding damp or wet areas.

3.13 The Purchase of Monitors

Monitors can be purchased from several radiation detection equipment suppliers and will typically cost from seven to sixteen hundred pounds for a contamination monitor and maybe more for a dose rate monitor. The Department Head is responsible for funding. Advice and information can be obtained from the College RPA or RPO.

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Safety Department Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0) 020 7594 9423 [email protected] www.imperial.ac.uk

The college RPA must be consulted before any type of instrument used for monitoring ionising radiation can be purchased and information on the nature of the work with ionising radiation given so that the correct selection can be made.

3.14 Testing and Calibration of Instruments

All radiation monitoring equipment should be tested at regular intervals; a „competent‟ person must test those used in designated areas annually. The College RPO carries out testing for all contamination monitors across Imperial College London. There is currently no in-house facility for the testing of dose rate instruments. For the periodic testing of dose rate instruments the College RPA and RPO can help departmental RPS to arrange the testing through a suitable external calibration house.

The Department Head is responsible for funding such tests and ensuring that all instruments in their departments are tested and maintained.

4.0 Appendix A

Radioisotope Suitable Surface Contamination Monitor 3H* Liquid Scintillation Counter (LSC) 14C Mini 900/5.10 EP15, EL, Berthold LB1210B or LSC 32P Mini 900/5.10 EP15, E, EL, Berthold LB1210B 33P Mini 900/5/10 EP15, EL, Berthold LB1210B 35S Mini 900/5.10 EP15, EL, Berthold LB1210B 36Cl Mini 900/5.10 EP15, EL, Berthold LB1210B 45Ca Mini 900/5.10 EP15, E, EL, Berthold LB1210B 51Cr Mini 900/5.40 42B or 44B 55Fe Mini 900/5.40 44B 57Co Mini 900/5.40 44A or 44B 59Fe Mini 900/5/10 EP15, EL, Berthold LB1210B 75Se Mini 900/5.40 44A or 44B, Berthold LB1210B 86Rb Mini 900/5.10 EP15, E, EL, Berthold 1210B 99Tcm Mini 900/5.40 44A or 44B, Berthold LB1210B 111In Mini 900/5.40 44A or 44B, Berthold LB1210B 123I Mini 900/5.40 44A or 44B, Berthold LB1210B 125I Mini 900/5.40 42A or 44A 131I Mini 900/5.40 42A or 44A 201Tl Mini 900/5.40 44A or 44B 238U** Mini 900/5.10 EP15, E, EL, Berthold 1210B

Notes: *( Liquid scintillation counter can be used for all the radioisotopes listed, but it is more suitable to use direct monitoring to determine the activity from contamination using a portable monitor as it provides the user with an instant reading).

** (This is assuming that the Uranium daughter products are at or close to secular equilibrium at the time of monitoring).

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