Technical services provided by the RPNSD 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 RPNSD.
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. RPNSD 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, RPNSD 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.
RPNSD provides Thermo-Luminescence Dosimeter (TLD) personal radiation monitoring service. The TLD badge consists of a TLD card and a TLD cardholder. The TLD card consists of two Lithium Fluoride (LiF) crystalline chips. The TLD card has to be placed into the TLD cardholder in the manner that the LiF chips coincide with the filters on the cardholder. The TLD card must be placed into the TLD cardholder before use as the TLD cardholder consists of filters to correct for readings for skin and body doses respectively. TLD is a passive monitoring device and it will reflect 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 for the next monitoring period, all previously issued TLD cards shall be returned to RPNSD for analysis. A dose report will be generated and sent to the contact person of the organisation.
TLD card and TLD cardholder
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 card carries a unique barcode. The issued TLD card 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 card into the TLD 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.
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
|Instructions on the proper use of TLD badge |
|1 ||Please store the TLD badge away from radiation area when not in use. Do not store the TLD badge 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. |
|3 ||If the TLD badge is accidentally irradiated, e.g. if it is dropped in a place where radiation work is being carried out, please bring the TLD badge to RPNSD immediately and state that the TLD badge 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 to RPNSD immediately for evaluation of the dose received. |
|5 ||User/Company should report to RPNSD in writing by mail or email immediately if a TLD card/badge is lost. Company shall be liable to pay for the cost of any unreturned, lost or damaged TLD cards at $54.60 each, (GST inclusive). Please note that late payment interest (LPI) will be imposed in the case of any late payment. |
|6 ||TLD cardholders are sold separately at the NEA Customer Service Centre at $25.20 each (GST inclusive). |
|7 ||TLD cards are issued periodically (e.g. monthly, bi-monthly, quarterly, four-monthly). The TLD card is a property of RPNSD and must be returned immediately when the user has resigned or posted to a different department/institution/organisation. |
|8 ||Depending on the monitoring cycle (e.g. monthly/bi-monthly/quarterly/four-monthly), all TLD cards will be issued by RPNSD during the last week of the month. Upon receipt of the new cards, users shall return all previously issued TLD cards to RPNSD 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.
Each report will provide information on: a) dose received during the monitoring period which the TLD card 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
RPNSD 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.