Tipos de prediagnóstico

PROGRAMME OF MONITORING

7.1. The operating organization should establish a programme of monitoring of radiation levels in and around the workplace [13]. The adequacy of the arrangements in place for protection in radiography work should be assessed in the programme, which should include measurements of radiation levels at the following positions:

(a) For radiography in shielded enclosures:

(i) Around the walls and doors (and other openings) of the enclosure under a range of operating conditions, to ensure that an adequate level of shielding is maintained;

(ii) At the entrance to the enclosure after completion of each gamma radiography exposure, to confirm that the gamma source has been satisfactorily returned to the exposure device or that X ray emission has stopped;

(iii) Around the gamma source store, to ensure that an adequate level of shielding is provided.

(b) For site radiography work:

(i) Around barriers during a test exposure (or first exposure, depending on the circumstances) to confirm that the barriers are correctly positioned;

(ii) At the operator position during wind-out of a gamma source or when an X ray generator is energized, to confirm that radiation levels are not unacceptable;

(iii) Around the barriers during routine exposures, to confirm that dose rates remain below any values specified in national regulations or guidance or by the operating organization;

(iv) At the operator position during wind-in of a gamma source or termination of exposure of an X ray generator;

(v) Around the exposure device after each exposure, to ensure that the source has been fully returned to the shielded position;

(vi) Around any source store used on-site, to ensure that an adequate level of shielding is provided;

(vii) Around the site on completion of the radiography work, to confirm that no gamma sources have been left on the site;

(viii) Around vehicles used to transport gamma sources prior to departure to and from the site.

7.2. The monitoring programme should describe the locations to be monitored, the frequency of monitoring and the records to be kept. This information should be included in the local rules and should also be described in the radiation protection programme. Reference levels for each measurement location should be given, and the actions to be taken if these values are exceeded should be described. Records of the workplace monitoring programme should be made available to appropriate persons, including workers and the regulatory body.

SELECTION, MAINTENANCE AND CALIBRATION OF SURVEY METERS

7.3. Operating organizations should ensure that a sufficient number of suitable dose rate monitors are made available to the radiographers. While many types of monitors are suitable for measuring gamma radiation levels, some may not be

suitable for accurately measuring low energy X rays, which could result in a significant underestimation of the true dose rate. Information and guidance on the suitability of monitors should be obtained from manufacturers’ literature and qualified experts.

7.4. The operating organization should arrange for radiation monitors to be formally tested or calibrated at periodic intervals by a specialized testing laboratory. A number of operating characteristics of the radiation monitor should be assessed in these tests or in the calibration. These operating characteristics include the response to known dose rates at specific energies, the linearity and the behaviour of the monitor at very high dose rates. The frequency and the type of tests or calibration, together with appropriate records, should comply with any requirements specified either in national legislation and/or regulations or by the regulatory body. They should also follow any recommendations of the manufacturer.

7.5. Routine operational checks of the radiation monitors should be carried out by the radiographers and the radiation protection officer. These may include physical checks of whether the monitor is damaged, battery checks and zeroing of the scale. The response of the monitor to radiation should be checked before use in accordance with the regulatory requirements. This may be done, for example, by using a low activity test source, or by placing the monitor close to the surface of an exposure device when the source is in its shielded position. Some regulatory bodies may require that such checks be done in accordance with formal procedures and the results recorded.

7.6. Account should also be taken of the environmental conditions in which the monitors are to be used. Some monitors are unsuitable for use in very wet or very hot locations, and some are not robust enough to withstand heavy use on-site. On some industrial sites where site radiography work is carried out, special types of radiation monitors may have to be used. For example, in some chemical factories, radiographers may have to use radiation monitors that minimize the likelihood of accidental ignition of flammable fumes or vapours in areas of the plant (these are often called intrinsically safe monitors).

7.7. Some radiation monitors are affected by radiofrequency transmissions. If radiography is to be carried out close to radiofrequency generating equipment, then the use of specially designed radiofrequency shielded radiation monitors should be considered. Account should also be taken of noise where these devices are being used. Audible warnings should be loud enough to be heard and/or they should be supplemented by vibration or visible signals.