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Radiation Monitoring Services: Frequently Asked Questions

Wearing and Handling of Dosimeters

  1. How to wear the whole body dosimeters?
  2. The whole body dosimeter should be worn on the body trunk with the name label facing towards yourself (that means the side with silver window should face outwards) for properly measuring the radiation dose absorbed by you. If you are required to wear lead apron at work, we recommend you to wear the dosimeter under the lead apron for estimating the dose of the major part of your body.

  3. How to wear the finger dosimeter?
  4. The finger dosimeter should be worn on the finger of the most exposed hand in the direction facing the radiation field at work. If you are required to wear gloves at work, we recommend you to wear it inside the glove for preventing any contamination on the dosimeter.

  5. Can I wash my hand with the finger dosimeter?
  6. Yes, you can wash your hand with the finger dosimeter as it is designed by the manufacturer to be water proof.

  7. How to return the dosimeter after use?
  8. Most of the users opt for returning their dosimeters by mail as it is the most convenient way. However, according to the conditions of service, the user will be responsible to any loss of the dosimeter in the delivery process. Therefore, if you do not want to bear such risk, we recommend our clients to return their dosimeters by hand.

  9. How to access the monthly dose report?
  10. We send the hardcopy dose report to the contact person of a company with the new batch of dosimeters every month. The individual user can also enquire his/her dose history through our Electrics Radiation Licensing and Services System (ERLS) web site with account type: Radiation Monitoring Service Person. The login user ID is the personal identification number as registered at our service and, for most of our users, it is the HKID number without the bracketed digit. The password for the first login is the same as the login user ID. We advise the users to change their password after the first login.

  11. How to keep the dosimeter after use?
  12. We recommend users to keep their own dosimeters in a secure place, for instance, a lockable cabinet after use. The users should also prevent leaving their dosimeters in the radiation area after work.

  13. Can I attach personal label on the dosimeter?
  14. We do not recommend users to attach personal labels on their dosimeters as the dosimeter cards which have fixed identification for the individual will not be put in the same dosimeter holders (the external plastic case) after the readout process. Any extra label will be detached before the final dispatch of dosimeters.

  15. What can I do if my dosimeter is lost?
  16. The users should report to us the case of dosimeter lost by completing the RMS-LOSS form which is available for downloading at . The users from the private sector should pay for the charges of the dosimeter on receiving our demand note.

Interpretation of Dose Report

  1. What is the type of radiation exposure monitored by our service?
  2. For the purpose of radiation protection, radiation exposure is categorized into three different types as medical exposure, occupational exposure and public exposure. The exposure monitored by us is the occupational one and the dose reported is the individual external radiation dose at work with the environmental radiation part being subtracted. The dose level of the environmental radiation is referred to the value measured at our laboratory as reference.

  3. What is the meaning of the abbreviation “BRL” in the dose report?
  4. The abbreviation “BRL” shown in the dose report is the short form of “Below Recording Level”. As recommended by the International Commission on Radiological Protection (ICRP) in publication 35, dose values above the recording level is considered to be worth keeping otherwise they can be discarded or treated as zero. The recording level of our monitoring program is defined to be 0.167 mSv which corresponds to one-tenth of the derived monthly dose value of the annual dose limit of 20 mSv. The reason for adopting the recording level is to prevent unrealistic attention focusing on to exposure of very small health risk and, in general, monitoring results are easy to obtain but difficult to interpret. In view of such recommendation, we indicate doses below the recording level as “BRL” in the dose report. However, as requested by some users, such BRL doses are still added to the personal dose record as cumulative lifetime dose for their reference.

  5. What is the reported dose quantity?
  6. We adopt the use of the operational dose quantities Hp(0.07) and Hp(10) for individual monitoring as recommended by the International Commission on Radiation Units and Measurements (ICRU) in its report 51.

    Hp(10), which is appropriate for both strongly and weakly penetrating radiations, is the personal dose equivalent in soft tissue at a depth of 10 mm below a specific point on the body. Hp(10) is mainly used for the estimation of the effective dose of a person.

    Hp(0.07), which is appropriate for the weakly penetrating radiations (e.g. beta radiation and low energy x-ray), is the personal dose equivalent in soft tissue at a depth of 0.07 mm below a specific point on the body. Hp(0.07) is mainly used for the estimation of the skin dose of a person.

    The conversion from the personal dose equivalent Hp(10) to the effective dose requires the information of irradiation geometry and radiation energies. Except the case of irradiation from the back or in the low energy range < 20 keV, the personal dose equivalent due to photon radiation overestimates the effective dose.

    The effective dose received by an individual corresponds to his fatal cancer risk associated with the biological effect of radiation. As published by the International Commission on Radiological Protection, the probability of fatal cancer for the whole population and worker is 1/20 per Sv and 1/25 per Sv respectively.

  7. How to define and handle the late returned dosimeters?
  8. The dosimeters which are required to be returned in that month but received after our cut-off date (i.e. the 16th day of a month) are defined to be not returned. The dosimeters that are received within three month later than the normal month of return will still be readout and analyzed by us. However, due to the cumulative measurement nature of TLD, it is not possible for us to distinguish the dose received in terms of months in that monitoring period. The dosimeters that are returned later than three months will not be readout and the dose will not be reported.

  9. What is the meaning of 'not returned' in the dose report?
  10. In some circumstances, the dose value might not be available in the current month dose report for example, late return of dosimeter (defined as not receiving the dosimeter before our cut-off date), newly joined user etc. As there are many reasons for the unavailability of dose value in practical situations, it is complicated and difficult to cover all such cases in the dose report, we just simply adopted the use of three different status for explaining the unavailability of the dose value by 'new user', 'first dosimeter' or 'not returned' for indicating the situation. The status of 'not returned' means the dose record of that reporting month for a current user is not available which can be due to late return of dosimeter, return of dosimeter in the wrong month, etc.

  11. What is the dose alerting system?
  12. We adopt a two level dose alerting system for our users. For the monthly dose of an individual exceeded 0.5 mSv but below 1.6 mSv, a dose alert letter will be issued to the concerned company for informing them the case. The dose level of 0.5 mSv is the derived monthly dose value of 6 mSv for the definition of radiation work in the Radiation Ordinance (Cap 303) of Hong Kong.

    For the monthly dose of an individual exceeded 1.6 mSv, a warning letter will be issued to the concerned company for alerting them to identify the cause and review the operation procedures, safety conditions of the workplace and equipment. The letter will also be copied to the Radiation Board for their reference. The dose level of 1.6 mSv is the derived monthly dose value of the annual dose limit of 20 mSv for radiation workers in the Radiation Ordinance (Cap 303) of Hong Kong.

Technical Information of Dosimeters

  1. What is the principle of thermoluminescent (TL)?
  2. Thermoluminescent is the physical phenomenon that the energy stored in a material is released in the form of light on heating. The material that possesses such property is called TL phosphor. The energy source can be of the type of ultraviolet or ionizing radiation, for instance, X-rays or gamma rays. The radiation energy is absorbed by the material through the excitation or ionization processes of the electrons. The electrons released from atoms become free in the material and some of them are trapped at the impurity sites of the material as metastable state. The radiation energy is therefore stored at the impurity sites as potential energy of the trapped electrons. Such electrons can be released again on receiving the required excitation energy and, in the case of TL, it is in the form of thermal energy, for instance, through heating by planchet, gas, microwave or laser, etc.. When the TL material is being heated, the trapped electrons are released and jumped back to the ground state through electron-hole combination process which accompanies emission of photon. The light emitted can be detected by the light sensitive measuring device, for example, photomultiplier tube (PMT) or charge coupled device (CCD). The application of TL includes radiation dosimetry and dating.

  3. What is the structure and composition of the whole body type dosimeter?
  4. The whole body type dosimeter is a dosimeter card contained in a plastic case as its holder. The dosimeter card contains radiation sensitive chip elements which are made of thermoluminescent (TL) material LiF:Mg,Ti. There are filters on the dosimeter holder at the areas above the chip elements for discriminating the radiation types and measuring the appropriate dose quantities. The dosimeter card is uniquely identified by the bar code which is laser etched on the aluminum plate of the card. The dosimeter holder has a transparent window in red colour for viewing the user information on the dosimeter label. A clip is provided on each dosimeter for wearing.

  5. What is the structure and composition of the finger dosimeter?
  6. The finger type dosimeter is a ringlet dosimeter assembled with a plastic finger ring. The ringlet dosimeter is a small circular disk embedded with radiation sensitive element which is made of thermoluminescent (TL) material LiF:Mg,Ti and it is uniquely identified by the bar code printed on it.