Technical services provided by the RPNSG include personal dosimetry, survey meter calibration, and various test services to check for radiation levels. Please see below for the list of services provided by RPNSG.
Analysis of Wipe Test Samples for Sealed Sources
Under the Radiation Protection (Ionising Radiation) Regulations, any person who possesses or has under his control any radioactive sealed source shall ensure that a wipe test for radioactive sealed source is performed by a qualified individual at least once every year. This is to ensure that there is no leakage of radioactive substance. Radiation Monitoring and Services Division (RMSD) provides analytical laboratory services to analyse wipe test samples for any radioactive contamination.
Procedures on how to perform the wipe are described below.
Tools needed to perform the wipe:
- Wipe medium e.g. filter paper, cotton wool or any other material of high wet strength and absorbent capacity (recommended size 2 cm x 2 cm)
- Water or methylated spirit or any other liquid which will not attack the material of the housing.
- Surgical / disposable gloves
- Forceps or tongs
- 2 small re-sealable bags
- Identification labels black permanent marker
How to conduct a wipe:
- Moisten the wipe medium with water or other appropriate liquid.
- Wipe the bonding or surface of the sealed source if it is not installed in a container. For sealed source that is installed in a container (e.g. source housing), wipe the immediate container – the sides of the housing where possible leakage can be found (e.g. openings at the bottom of the housing).
- After the wipe, double-pack each wipe medium used, which is the wipe test sample, in two small re-sealable bags. The external bag should be properly labelled with information on the type of radionuclide and serial number of the source. Alternatively, you could write a description and identification on the bag with a black permanent marker.
- Surgical or disposable gloves shall be worn to protect the hands from possible radioactive contamination.
- Forceps or tongs shall be used to minimise radiation exposure of the hand.
- Before the wipe is done, ensure that the shutter is closed for sources installed in devices (e.g. gauges).
- The sealed bags containing the wipe test samples shall not be opened prior to laboratory analysis.
Measurement of radioactive contamination:
- The wipe test samples shall be sent to the laboratory to be analysed for any radioactive contamination. The measuring equipment used depends on the type of ionising radiation emitted from the radioactive sealed source tested. In general, for beta emitters, a proportional end-window counter is used, and for gamma emitters, a well-type sodium iodide (NaI) detector is used. An analysis report will be generated and sent to the company.
- If the source is found to be leaking, the source should be dismantled and put into a leak-proof container. It must not be brought into use until all necessary remediation actions have been effected. The areas affected by the leakage should be decontaminated under the supervision of the licensee or an individual approved by the Director-General of Environmental Protection as qualified to do so, and they shall be properly equipped for the purpose.
Calibration of Survey Meters
Under the Radiation Protection (Ionising Radiation) Regulations, any radiation monitor, such as survey meters, direct reading personal dosimeters, etc., used in connection with any radiation work, shall be calibrated at least once every year by a person approved by the Director-General of Environmental Protection as a qualified person for this purpose.
For the purpose of this calibration, RMSD operates a Secondary Standards Dosimetry Laboratory (SSDL) for radiation protection level dosimetry.
The SSDL is established with the support of the International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) as part of the international network of secondary reference laboratories.
The reference instruments maintained by the SSDL have calibration certificates traceable to BIPM - the International Bureau of weights and measures in France. These reference dosimeters and calibrated radiation sources are used to calibrate radiation monitoring equipment in Singapore.
Personal Dose Monitoring
Under the Radiation Protection (Ionising Radiation) Regulations, any individual who is working with ionizing radiation shall wear a personal radiation monitoring device or dosimeter. Under the IR regulations, any individual licensed to do radiation work shall make approved arrangements for the monitoring of the individual radiation dose received while performing radiation work.
RMSD provides personal radiation monitoring service using Thermo- Luminescent Dosimeters (TLD). The TLD dosimeter consists of a TLD card/ring and a TLD cardholder/ring holder. TLD is a passive monitoring device which measures the dose received by the radiation worker after the TLD card is analysed after every monitoring period. Within two weeks upon receipt of new TLD cards/rings for the next monitoring period, all previously issued TLD cards/rings shall be returned to RMSD for analysis. A dose report will be generated and sent to the contact person of the organisation.
Radiation Dose Monitoring (RDM) - Radiation dose monitoring provides users with information on their exposure to radiation in their course of work. The TLD-2 card used for radiation dose monitoring consists of two Lithium Fluoride (LiF) crystalline chips. The TLD-2 card must be placed in the TLD-2 cardholder before use as the TLD-2 cardholder consists of filters to correct the readings for skin and effective doses respectively.
Neutron Dose Monitoring (NDM) - In neutron dose monitoring, a TLD card with four Lithium Fluoride (LiF) crystals, placed within a TLD-4 card holder, will be issued. The TLD-4 card used for neutron monitoring is a form of albedo dosimeter which relies on the body to slow down the fast neutrons and scatter them towards the dosimeter. Therefore, the dosimeter must be worn close to the body for better accuracy. The dose received from neutron exposure will be considered as part of the effective dose to the body.
Extremities Dose Monitoring (ExDM) - Extremities dose monitoring allows the users to track their radiation exposure to their extremities, e.g. hand or feet, when radioactive materials are handled at proximity in their work processes. A TLD ring will be issued to the user, which consists of a TLD ring chip that is encapsulated within the ring holder. The ring chip is a Lithium Floride (LiF) crystal which measures the dose received by the user after the TLD ring chip is analysed. Extremities dosimeter provides better representation of the skin dose as compared to RDM if the work process requires the handling of radioactive material at proximity.
When the LiF crystalline chips are exposed to ionizing radiation, some energy is absorbed and stored in the chips. This stored energy is released in the form of luminescence when the chips are heated during the analysis. The amount of light emitted on heating the chips is proportional to the amount of radiation the chips received.
Information on the TLD card:
Each TLD dosimeters carries a unique barcode. The issued TLD-2 card for RDM is sealed in a plastic sleeve labelled with the user’s name, identification number, company code, TLD number and the monitoring period for the issuance. User shall place the TLD-2 card into the TLD-2 cardholder such that the cut-away corner fits the groove in the TLD cardholder nicely. The user’s name shall be visible through the window of the TLD cardholder.
TLD-2 card with TLD card holder for Radiation Dose Monitoring
TLD-4 card and TLD ring are issued together with their respective holder and user shall use the dosimeter as provided. User shall not pry open the holder to remove the TLD-4 card or ring chip within. The TLD-4 cardholder/ring holder is labelled with the user’s name, identification number, company code, TLD number and the monitoring period for the issuance.
TLD-4 card with TLD card holder for Neutron Dose Monitoring
TLD ring chip and TLD ring holder
How to wear the TLD badge:
User may attach the TLD badge to the trunk of their body at the chest or waist level. If a protective apron is worn, the user shall wear the TLD badge under the apron. The TLD badge must be worn by the radiation worker at all times during the course of the radiation work. The picture below shows the proper way to wear the TLD badge:
TLD badge worn at chest level
User of TLD ring may wear the dosimeter on the middle finger of their hand which is exposed to most radiation during their course of work. Example: If user is supporting a vial of radioactive material on your left hand while withdrawing the material using a syringe on your right hand, please wear the TLD ring on the middle finger of your left hand. The TLD chip will need to be on the same plane as the palm of the hand (facing inwards). If protective gloves are worn, the wearer shall wear the TLD ring underneath the gloves. The TLD ring must be worn by the radiation worker at all times during the course of the radiation work to correctly register the extremities (finger) dose received by the radiation worker. You may refer to the following picture as a guide on how to wear the TLD ring.
TLD ring worn on the middle finger of the less-dominant hand (left hand in this picture)
|Instructions on the proper use of TLD badge |
|1 ||Please store the TLD badge/ring away from radiation area when not in use. Do not store the TLD badge/ring in places where it can be potentially exposed to radiation as this will lead to false indication of dose received by the user. |
|2 ||Extreme heat, direct sunlight and pressure (e.g. by finger nails, bending, stapling, etc.) shall be avoided as these can damage the TLD card/ring. |
|3 ||If the TLD badge/ring is accidentally irradiated, e.g. if it is dropped in a place where radiation work is being carried out, please bring the TLD badge/ring to RMSD immediately and state that the TLD badge/ring was accidentally irradiated. Failure to inform may result in an excessive dose being recorded. You may be temporarily suspended from radiation work until further notice, depending on the amount of dose recorded. |
|4 ||If you suspect that you have received an excessive dose due to an accident, please bring your TLD badge/ring to RMSD immediately for evaluation of the dose received. |
|5 ||User/Company should report to RMSD in writing by mail or email immediately if a TLD card/badge/ring chip is lost. Company shall be liable to pay for the cost of any unreturned, lost or damaged TLD card/badge/ring chip as follows: i) TLD-2 card at $100 each; ii) TLD-4 card at $265 each; iii) TLD ring chip at $148 each. All prices are inclusive of GST. Please note that late payment interest (LPI) will be imposed in the case of any late payment. |
|6 ||TLD-2 cardholders and TLD-4 cardholders are sold separately at $63 and $68 per piece respectively (GST inclusive). |
|7 ||TLD cards are issued periodically (e.g. monthly, bi-monthly, quarterly, four-monthly) based on the subscription frequency. The TLD card is a property of RMSD and must be returned immediately when the user has resigned or moved to a different department/ institution/ organisation. |
|8 ||Depending on the monitoring cycle (e.g. monthly/bi-monthly/quarterly/four-monthly), TLD cards will be issued by RMSD before the next monitoring cycle begins. Within two weeks upon receipt of the new cards/rings, users shall return all previously issued TLD cards/rings to RMSD for analysis. |
Dose Report and Dose Limits
After the TLD cards are analysed, a dose report will be generated and sent to the user’s company/organization. This dose report shall be kept by the licensee, safety officer or employer and made available to any radiation worker in the company/organization who wants to find out his/her dose received during the course of radiation work.
The radiation dose received by an individual exposed to radiation is expressed in millisievert (mSv). Under the Radiation Protection (Ionising Radiation) Regulations, the effective dose limit to the whole body for occupationally exposed individuals is 20 mSv a year, averaged over defined periods of five years; and with the further provision that the effective dose shall not exceed 50 mSv in any single year. The dose limit to extremities, e.g. hand and feet for occupationally exposed individual is 500 mSv a year. For skin, the limit is 500 mSv averaged over areas of no more than 1cm2 regardless of the area exposed.
Each report will provide information on: a) dose received during the monitoring period which the TLD dosimeter was issued and worn, b) annual accumulated dose from 1st January of that year, c) five-year accumulated dose, and d) lifetime accumulated dose.
Radiofrequency radiation and electromagnetic field measurement
RPNSG provides radiofrequency radiation and electromagnetic field measurement services to industries, government agencies and the public. These services are done using broadband measurement meters.
Training and Education
To promote the safe use of ionising and non-ionising radiation, Ngee Ann Polytechnic and Republic Polytechnic conduct courses for radiation workers on various aspects of radiation safety.
The courses in the Radiation Safety Series are:
- Basic Ionising Radiation Safety (General) / Short Notes [DOC, 158.5 KB]
- Basic Ionising Radiation Safety (NDT)
- Basic Laser Radiation Safety / Notes about laser radiation [DOC, 88 KB] , Course Syllabus [DOCX, 17.27 KB]
- Please refer to the respective websites of Ngee Ann Polytechnic and Republic Polytechnic for information on the Radiation Safety Series courses.