Personal Radiation Monitoring

Instructions for Administering Personal Radiation Monitoring (PRM) System

• Monitoring cards and forms will be sent to your School for the new monitoring period. The dates of the monitoring period, name of wearer, registration number and occupation code (details on back of form) will be printed on the forms. There will also be a control card sent with each issue.
• The control card is to be placed in a dry area away from radiation sources (typically in the desk of officer administering the service in the School).
• Monitoring periods are for three calendar months and begin on 1 March, 1 June, 1 September, 1 December. Replacement cards should arrive at the University on the 20^th of the preceding month.
• UWA Safety and Health will continue to provide a central distribution and collection service for all personal monitors at the University.

Thermoluminescent dosimetry (TLD) is a phenomena by which solid state detectors can be used to detect and measure exposures to ionising radiations. When exposed to these radiations, free electrons in the TLD crystals become trapped in lattice imperfections. When heated (typically to 300 ^oC) the electrons escape the traps and release light which can then be measured using a photomultiplier. The amount of light detected is related to the radiation received. TLDs can be used for personal radiation monitoring. They consist of a plastic TLD holder incorporating a number of filters and TLD card into which is imbedded the TLD materials.

Some points to observe when using TLD badges:-

• Wear the badge at chest or waist level, or if a lead apron is used in an x-ray area under the apron.
• Wear only the badge assigned to you. Don't share badges.
• Replace the badge in the rack at the end of each day - this should be in a low radiation background area. Monitors that are taken home are frequently lost or damaged.
• Don't move the card within the badge except when changing cards.
• When cards are changed, the number should be visible, the right way up in the front open window of the badge when the hinge is at the bottom.
• Damaged holders should be replaced as soon as possible.

A TLD badge does not provide protection against radiation. It measures the radiation dose received and is used to:-

• Establish that the radiation doses received by personnel are within permissible limits.
• Verify that the facilities for radiation protection are adequate.
• Show that radiation protection techniques are acceptable.

On receipt of the new issue:

1. Check the names are correct and that the correct number of cards has been received.

2. Remove the old cards from their holders and place the new cards in the card holders with the name facing the front.

3. Enter the type of radiation or isotope in the space provided on the form for the monitoring period just concluded.

4. The cards and forms collected from the previous issue should be returned immediately to the Safety and Health, not those just issued. Check that you have returned all of the cards listed on the form including the controls. TLD cards from users and the School control card need to be returned promptly to the Safety and Health at the end of the monitoring period. Please do not send these to ARPANSA. If for some reason they are not all accounted for please include a short note as to why.

5. Changes to your list of persons being monitored should be made on the attached form and sent to the Safety and Health. Two weeks notice is required for the changes to take effect.

6. Schools will be invoiced directly for cards used and for any new holders or lost badges.

7. Results will be provided to departments and will also be retained in the Safety and Health. Monitoring results should also be kept in a file in the School.

8. Regarding the dose reports received it should be noted that:

• The minimum reporting levels are 10 mSv for x-rays and 70 mSv for high energy gamma and beta radiations. A blank field indicates either no dose or a dose less than these were received.
• The control is used to subtract background radiation doses from the total dose recorded. Note that during the three month monitoring period the average background dose received from terrestrial, cosmic and internal radionuclides is less than 300 mSv and when radon is included it is around 500 mSv.
• Radiation workers are not allowed to receive more than 20,000 mSv per annum, averaged over 5 years, with no more than 50,000 mSv in any one year from both internal and external radiation exposures
• For all doses 300 mSv and above received in a three month monitoring period the Radiation Safety Committee requires that the circumstances of the exposure be investigated a written report provided to the Safety and Health.

Notes:

• The charge to the School for replacement holders is $15 and for a lost holder with card is $20. It is suggested that you ensure users are aware of these charges and it is clear on who will be required to pay these should holders and cards not be returned.
• Queries on invoices and payments should be made direct to ARPANSA on 1800 678 112 (free call).
• Schools will be charged for cards that are returned "unused".
• If you have any holders you do not require, then please return them to the Safety and Health and we will make these available to schools as required.
• Special issue monitors can be arranged - these are unnamed and come with their own control monitor. Wearing dates need to be entered onto the form and the user's name written in soft pencil on the card wrapper.
• Control cards are used to determine background radiation for each Schools issue. These must be returned with the user cards at the end of the monitoring period.
• Accuracy is typically 20% and varies depending on the radiation types being measured.
• Minimum detectable dose ranges are from 10 uSv to 70 umSv depending on the radiation types being measured.
• Natural background radiation from terrestrial gamma rays and cosmic radiation is approximately 300 uSv during a 3 month period.
• TLD wearers should not be particularly concerned at doses recorded on their badges below 300 uSv.
• Recorded doses above 300 uSv for a monitoring period should be investigated by the School Radiation Safety Officer and a written report forwarded to the Safety and Health.
• Monitoring records are kept for at least 30 years.

For further information on the above please contact Jonathon Thwaites on 6488 7932.