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PROTECTION OF WORKERS Nuclear Gauges SEALED SOURCES IN GAUGES PORTABLE GAUGES CARE AND SECURITY þDO

Supervision þ Nuclear gauges are devices that use radioactive sources to Gamma and neutron sources Beta sources Portable gauges are used on-site, e.g. when laying road Make sure the source is always kept safe and secure. surfaces or well logging. þ The employer will nominate measure parameters such as thickness, density, moisture or fill þ Close the shutter when the gauge is not in use (if a level. necessary, check this using a radiation ). Officer to supervise work Transport þ Nuclear gauges normally incorporate a nuclear source, a detec- withradioactive sources. Observe any warning and obey the instructions tor and a shutter. Although radiation is being emitted all the time, Portable gauges must be carried in transport packages that þ An inventory must be kept given on signs and notices. the shutter can be closed to shield the radiation beam. comply with national and international regulations. of the radioactive sources þ Follow the procedures set out by your employer. on a site. þ þ Report any safety concerns to the Radiation Protection Shutter (open) These could be: Regular checks should be Officer. Shutter þ made to ensure that the sources are present, source control Excepted packages. containers are not damaged and no radioactive material þ Wear your personal . þ is outside the container. The radioactive material is The walls of the capsule are Type A packages. Storage held within a tough thinner to allow the beta þ Type B packages. casing. The casing prevents radiation to pass through. When a gauge is not in use, DO NOT the radioactive material from Beta sources are usually it should be made safe and

Material flow Source escaping but does not shield more fragile than gamma or secure or, if it is portable, þ Leave a portable gauge unsecured or unattended. Detector Shielding Type A and Type B packages must be labelled to indicate the radiation completely. neutron sources. it must be properly stored. þ the dose rate on the surface, and at 1 m from the package: A good storage location will be: Handle an unshielded radiation source. Gamma, beta and sources can all be used in þ Secure. þ Attempt to repair a damaged gauge or its safety nuclear gauges, depending on the application. Gamma radiation is very penetrating and is scattered by dense þ Fireproof. features unless you have been formally trained. materials. Gamma radiation is used for measuring the thick- þ Neutron radiation is very penetrating and is scattered by materials ness of materials such as , detecting fill height or mea- Weatherproof. with a high hydrogen content, e.g. water. It is frequently used for suring density by detecting scattered radiation. þ Shielded. measuring the moisture content in soil and asphalt. þ Labelled. DOSE AND EFFECTS Beta radiation is not very penetrating. It is often used for measur- Routine tests are needed to check that the source capsule is intact, and that no radioactive material has leaked out. The storage location should only be used to store the gauge ing the thickness or density of paper, plastics and textiles. and related equipment. Units of dose DOSE RATE INCREASES Marking and labelling The unit of is the (Gy). Gauges containing radioactive The unit used to quantify the dose in radiation protection is For excepted packages, the dose rate around the outside of sources should be clearly the (Sv). the package must be less than 5µ Sv/h. Dose rates are not marked as “Radioactive”. required to be indicated on the package labelling. Details of the source, such as One millisievert (mSv) is 1/1000 of a sievert. the radioisotope and its activity, The driver must carry transport documents, including the should also be displayed. Annual doses from natural vary Consignor’s Note. Placards must be displayed on vehicles on an average between 1 mSv and 5 mSv worldwide. carrying gauges, unless they are excepted packages. This radioactive source should have been disposed of as One microsievert (µ Sv) is 1/1000 of a millisievert. . However, it The typical dose from a chest X ray is 20µ Sv. was found in a scrap yard. Appropriate labelling and Dose rate A thickness gauge incorporating a beta source. In the picture above, the source The source housing of a level gauge A portable gauge used to measure proper supervision of the is contained in the housing above the product that is being measured and the incorporating a gamma source. The moisture and density, typically in soil source would have prevented Dose rate is the dose received in a given time. detector is on the opposite side. detector is on the opposite side of and asphalt. These gauges incorporate this. The unit used is microsieverts per hour (µ Sv/h). the vessel. gamma and neutron sources. If a person spends two hours in an area where the dose rate is 10 µSv/h, then they will receive a dose of 20 µSv. RADIATION PROTECTION Note: Placard not to scale PRACTICAL PROTECTION Cooperation and exchange of information Physical controls Time When a gauge is used at another employer's site, there Where shutters are used, lights Health effects of To reduce radiation doses, the time spent in radiation areas can be used to show whether the must be discussion and exchange of information in If radiation doses are very high, the effect on the body will must be kept as short as possible. The longer the time spent in advance. Many aspects will need to be agreed, including: shutter is open or closed. an area, the higher the dose received. appear relatively soon after the exposure. These acute injuries will occur if the absorbed dose is higher than a 0 minutes 15 minutes 30 minutes 1 hour 2 hours þ Physical barriers can be used to Temporary secure storage arrangements. threshold value; the sources and equipment used in In an area where the dose rate is 100µ Sv/h, the dose received stop people getting close to a þ nuclear gauges are capable of delivering such doses. It is will be: When the gauge will be used. gauge where dose rates may be therefore essential that procedures for work are followed. þ Where the gauge will be used. high. 0 µSv 25 µSv 50 µSv 100 µSv 200 µSv þ Whether it will be necessary to restrict access Even if the dose is not high enough to cause serious injury, Procedures there is still the possibility of incurring other health effects. Shielding Shielding material must be appropriate for to the area around the work. Distance If the dose rate at 1 m from a source is 100 µSv/h, The employer must set out written procedures for undertaking These effects, e.g. radiation induced cancer, are risk the type of radiation. For example: þ What warning will be used when the source the dose rate at 2 m will be 25µ Sv/h. the work. If operators follow the procedures, their doses will be based, i.e. the higher the dose received, the greater the is, or is about to be, exposed. chance of developing the effect. Toreduce the possibility of plastic lead concrete ‘as low as reasonably achievable’(ALARA). þ Who is responsible for the gauge on-site. developing late effects, radiation doses must be kept: þ Emergency procedures. 1 cm of plastic AS LOWAS REASONABLYACHIEVABLE (ALARA) will totally shield all beta radiation. WHEN THINGS GO WRONG Lead and concrete can be used to shield against gamma and X . This nuclear density gauge was left for a few moments. A 25 µSv/h 100 µSv/h Concrete can also be road roller struck the gauge used to shield against and, as a result, it was badly Example: 1 m neutron radiation. damaged. This operator must follow clear procedures for loading a well logging source. 2 m The procedures might state that he/she must prevent access to the area while he/she carries out this work, use remote handling tools and complete the task as quickly as possible.