Ethics Guidelines
Part B - Guidelines for Projects Involving Ionising Radiation
Section 5 - Radiation Monitoring
5.1 Personal Monitoring for External Radiation
For a project using radioactive substances in the Antarctic, the user in conjunction with the Australian Antarctic Division (AAD) Radiation Safety Officer (RSO) and the Site RSO shall ensure that a suitable program of personal monitoring is set up and maintained throughout the life of the project.
5.1.1 In planning, prior consideration shall be given not only to designated users but also to the possibility of expedition personnel assisting the program. The use of unauthorised personnel handling radioisotopes is prohibited. Assistance, such as a person restraining a petrel being injected with 22Na, shall be pre-planned before departure. Assistants shall be named, appropriate training given, and personal monitoring organised.
5.1.2 Personal integrating dosimeters to be processed and read by the issuing laboratory must be used whenever practicable. It is probably best if the user continues to use the type of device and issuing centre used in Australia, where applicable, since the user will be already familiar with use of the device. Where the device normally used in Australia is not suitable, it is suggested that the user in conjunction with the Australian Antarctic Division RSO contact the Australian Radiation Laboratory personal monitoring service with a view to obtaining a suitable device.
5.1.3 Film badges are not recommended for use in Antarctica and should not be used where a more suitable device is available, whether from the user's usual personal monitoring service or elsewhere. Film badges are susceptible to ageing and are thus unsuitable for expeditions of relatively long duration compared with the normal life of the badges. Wherever practicable, TLD (thermoluminescent dosimeter) should be used in preference to film badges. Both film badges and TLD are susceptible to heating as may occur if left attached to clothing placed in hot drying cabinets.
5.1.4 Selection of the correct personal monitoring device should be made after consideration of the type(s) of radiation to which the user may be exposed. In rare cases, such as exposure to both beta radiation and neutron radiation, it may be necessary for the user to have two different monitoring devices, although monitors which measure both are available. A user having two personal monitoring devices should not wear both together unless that is necessary because of exposure to mixed radiations indicating the use of two types of badges. In such a case, if gamma radiation is also involved, and both badges record gamma radiation, then the user should wear both badges at all appropriate times and record that the gamma dose from the badges should not be summed. Similarly, where a user wears two badges of the same type but performing different measuring functions (e.g. beneath and outside a lead apron), the user should again record that the doses from the two badges are not to be summed.
5.1.5 Personal monitoring devices should normally be used as indications of whole body doses and should be worn at either waist or chest level. Once the wearing position is selected, this should be recorded and adhered to for the complete use interval of that particular monitoring device. The device should normally be worn external to clothing but under a protective device such as a lead/rubber apron. However, where it would be advantageous to afford some protection to the device under adverse conditions, it would be appropriate to wear the badge under clothing for radiation which will be essentially unattenuated by the clothing (eg. most gamma radiation).
5.1.6 Where there is handling of the radioactive material and the hands are significantly closer to the radioactive material than the body as a whole, extremities monitor(s) may be indicated (eg. finger badge) in addition to the whole body monitoring device.
5.1.7 Where the radiation field is spatially restricted (such as the narrow beam used in X-ray analysis equipment) the whole body will not be exposed and yet a small part of the body may be exposed to a significant dose. The limitations of the personal monitoring device should be recognised and the results interpreted with care and greater reliance should be put on routine surveys with appropriate instruments.
5.1.8 It should be remembered that the object of the personal monitoring device is to record the dose received by the wearer due to proximity to, or dealings with, radiation sources. To this end, the dose recorded is that which is excess to the dose recorded on the accompanying control device. Proper location of the control device is therefore essential for accurate recording of excess dose received. The control placement should reflect the dose which would be received from natural background radiation (including doses attributable to common building materials) in the absence of working with radiation sources. The control should therefore be placed beyond the influence of the radiation sources (including stored sources) but should not be shielded in case this affects the recording of background radiation. It should preferably be located in a place which would normally be assigned an occupancy of 1 (eg. a one-person office).
Care should be taken to avoid placing either control or issuable personal monitoring device next to domestic devices emitting radiation (such as older wrist watches or field compasses having radium painted radioluminescent dials).
5.1.9 Personal monitoring devices shall be uniquely identified and issued exclusively to particular individuals. The dates of actual commencement and cessation of use shall be recorded, not the nominal dates for which the monitor is issued. Any other relevant information such as type of radiation, known irregularities in use, and wearing position shall be recorded.
5.1.10 Personal monitoring devices shall not be shared. If a monitor is shared and records a dose it may be impossible to determine which person received the dose or alternatively how the dose should be shared between the persons sharing the monitor. This may lead to uncertainty or inaccuracy in the short term and lifetime dose records of the individuals participating in the sharing practice. Furthermore, shared monitors make tracking down the cause of an unacceptable dose very much more difficult. Personal monitoring devices issued for personal use shall not be used for survey monitoring. Personal monitoring devices used for survey monitoring shall be used exclusively for that purpose and shall be identified in the records as survey monitors.
5.2 Real-time Personal Monitoring for External Radiation
The personal monitoring devices referred to above in Section 5.1 are the type which record the integrated dose but which cannot be read until processed by a suitably equipped laboratory (usually the issuing laboratory). However, there may be operations conducted where it is desirable to determine the doses being received during the actual operation. There can be considerable benefit for radiation protection practice in conducting real-time monitoring at least once in relation to procedures with radioactive materials.
Real-time personal monitoring may be carried out as an adjunct to the type personal monitoring outlined in Section 5.1 but should not be used as an alternative.
5.2.1 Real-time personal monitoring may be carried using personal dosimeters located at the waist or chest. As with any monitoring device, the user in conjunction with the Australian Antarctic Division RSO should ensure that it is appropriate for the type of radiation of interest.
5.2.1.1 Quartz fibre dosimeters integrate the dose and may be read from time to time as the dose accumulates. These dosimeters accumulate background radiation and should be reset prior to use. Care should be taken to check the initial reading before use in case the re-setting has not been exactly to zero. Care should be taken that the model of dosimeter selected is appropriate for the type of radiation and dose rates of interest.
5.2.1.2 'Chirper' personal monitoring devices emit beeps in response to radiation, the frequency of the beeps increasing with dose rate. Most have an alarm which is adjustable on some models. Unless high exposure rates are expected, the basic 'chirper' is of limited use for real-time monitoring. However, more advanced models also integrate and display the accumulated dose and incorporate a dose alarm. Such models are useful for real-time personal monitoring in this context. The accumulated dose should be recorded or reset before each use. Again, care should be taken that the model selected is appropriate for the type of radiation and dose rates of interest.
5.2.1.3 Survey instruments may be used to determine dose rates at various points during the operation and combined with a knowledge of the occupancy times of those points, calculations can be performed to give real-time personal monitoring. Quite a number of modern meters now offer an integrating facility and this can be used for direct readout of dose received by the meter during the period of integration. Again, care should be taken that the meter used is appropriate for the type of radiation and the dose rates of interest.
5.3 Personal Monitoring for Internal Radiation
5.3.1 Internal doses to whole body and/or particular organs can be received from ingestion or inhalation of radioactive material. Simple devices equivalent to the external monitors of Section 5.1 are not available to record doses received internally.
5.3.2 Inhalation of radioisotopes can be estimated by sampling the air with an appropriate air sampler and counting the activity of radioisotopes collected on the filter paper. It is unlikely that the quantities of radioisotope or the style of experiment could justify this monitoring procedure.
5.3.3 Ingestion is best minimised by preparing and following working rules that promote a high standard of radiation hygiene.
5.3.4 Whole body monitoring is a technique that can be used to estimate body burdens of gamma emitting radioisotopes. Whole body counting facilities are usually available only at major radiation institutions. Whole body counting is unlikely to be indicated for the types and activities of radioisotopes commonly in use in the Antarctic.
5.3.5 The activity of a radioisotope excreted is a useful indicator of the activity of that radioisotope in the body. It is also a practical personal monitoring method as samples can be collected in the Antarctic even if the required measurement facilities are unavailable. It is recommended that such sampling take place if there is a real possibility that there has been ingestion and/or inhalation of 0.3 ALI or more of a radioisotope. In the case of mixed radioisotopes the suspected intakes should be converted to Annual Limit of Intakes and summed to see if the total exceeds 0.3 ALI.
5.3.6 The assessment of whether 0.3 ALI is likely to be exceeded in normal practice will depend on the total activity available, the sort of procedures carried out, the confidence the user has in the radiation hygiene methods employed and the results of the routine contamination checking carried out. For most radioisotopes used in Antarctica under normal circumstances it is unlikely that there will be a real possibility that 0.3 ALI is exceeded, provided that good radiation hygiene practices are conscientiously followed including proper contamination monitoring. Personal monitoring for ingestion and/or inhalation is thus unlikely to be indicated for most radionuclides in normal practice.
The situation may well be different as the result of an incident or accident and the user in conjunction with the Radiation Safety Officer must make an assessment of potential inhalation and/or ingestion of radioisotopes by any individual as a result of that incident or accident. Personal Monitoring for internal radiation must be undertaken in conjunction with the Australian Antarctic Division Polar Medicine Branch.
5.3.7 Tritium is an isotope for which, because of the practical difficulties of contamination monitoring, it may be advisable to carry out limited urine monitoring even though ingestion and/or inhalation of a significant quantity is not expected. The rule should be that urine sampling will occur where there is a potential for intake exceeding 0.3 ALI, even though an intake of that magnitude is considered unlikely.
Use of a tritium monitor, whether surface or air sampling, may give the user sufficient confidence in the protocols to obviate the need for urine sampling, but it should be noted that measurement of air or surface tritium levels will not generally be done with the degree of confidence available for contamination measurements of other commonly used unsealed radionuclides. Tritium in air monitors are generally available for projects through the Australian Antarctic Division RSO.
5.3.8 In the event of excessive intake of a radioisotope, medical advice should be sought through the Australian Antarctic Division Polar Medicine Branch, and the recommendations of NCRP Report No. 65 should be taken as observed.
5.3.9 The table below provides information on the ALI of radionuclides by workers and was obtained from information in ICRP Publication 68 (Dose Coefficients for Intakes of Radionuclides by Workers, 1994).
|
Nuclide
|
Half-life
|
ALI inhalation (Bq)
|
ALI ingestion (Bq)
|
|---|---|---|---|
|
tritium |
12.3 years |
|
|
|
carbon-14 |
5730 years |
|
3.5 x 107 |
|
silicon-32 |
450 years |
1.8 x 105 * |
3.57 x 107 |
|
iron-55 |
2.7 years |
2.2 x 107 * |
6.06 x 107 |
5.4 Radiation Survey Monitoring
Radiation survey monitoring is an important part of radiation protection. It is used as an aid to minimise doses, to minimise contamination in the laboratory, and to minimise contamination of the environment. It is also used to check the degree of contamination of the environment for experiments where release of radioisotopes to the environment is inevitable.
Radiation surveying may be carried out directly using portable instrumentation or indirectly by taking swabs, wipes or samples for analysis of the activity and types of radionuclides present.
5.4.1 Every operation using radioisotopes in the Antarctic must have an appropriate portable survey monitor. The only exemption likely to be granted is for tritium users. Tritium users having access to suitable liquid scintillation facilities in Antarctica and having a satisfactory program of sampling for contamination will be exempted from the requirement for portable survey instrumentation provided that the activities of tritium used are not excessively large.
5.4.2 The survey instrumentation must be suitable for:
- the types of radiation to be measured (e.g. alpha, beta, gamma, neutron);
- the lowest dose rates or lowest contamination levels required to be measured;
- the highest dose rates or highest contamination levels required to be measured;
- the energies of the radiation to be measured.
5.4.3 Humans have no sense response to radiation. The dial of the meter and its speaker become one's visual and aural response to radiation. Therefore, the survey meter must be equipped with aural as well as visual indication and both facilities should be used.
5.4.4 Radiation survey meters must be kept in calibration so that quantitative measurements shall have an uncertainty of not more than +/-25% (after due correction for energy response, which shall be known with a certainty which will not increase the overall uncertainty to greater than +/-25%). Radiation survey meters should be issued with a project, those meters being returned to Kingston with the researcher.
5.4.5 Radiation survey meters shall continue to indicate, either visibly or audibly, when radiation levels exceed the maximum scale readings for any scale.
5.4.6 Some applications may require gamma reading survey meters, some may require contamination meters and some may require both. Unsealed radioisotope use will normally require at least a contamination meter. Dual role meters are available, and if used for contamination measurements the user must ensure that the window shield (if fitted) is removed or opened.
5.4.7 The instrumentation is to be used generally as an extra sense to build up a mental image of what is going on with the radiation. The instrument is not simply to be put in the cupboard and brought out in the event of an accident. Rather, it should become an extension of the user so that it is used with conscious thought being trained on the pattern of the radiation rather than on using the meter.
5.4.8 Some of the required applications of the radiation survey equipment are referred to in other sections. The surveys undertaken must be appropriate for the program and type of work undertaken. As a guide for unsealed radionuclide work in the laboratory:
- contamination monitoring of work areas should be performed after every procedure or (related series of procedures) and should be performed at least daily while the laboratory is in use;
- hands, footwear and clothing should be checked at frequent intervals and prior to leaving the laboratory;
- equipment (glassware, etc.) should be checked after use;
- a comprehensive survey should be performed weekly or monthly (depending on use and type of use) or when there will be a break in using the laboratory and the results should be recorded.
Wipe tests shall be taken as part of this survey.
As a guide to strong gamma emitters, whether sealed sources or unsealed sources, a dose survey should be carried out with the source in the various user configurations and the doses to all areas of occupancy or potential occupancy determined. If the source is normally shielded but exposed (or a beam allowed to be emitted) during use then the dose survey meter must be switched on and appropriately positioned during use.
5.4.9 The user shall also employ wipe testing as a method of contamination detection.
(ASP&C)
May 2002
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