July 2011 Page 1 of 2 www.nt.gov.au/health/radiationprotection
R ADIATION P ROTECTION – C ODE OF P RACTICE
S ERVICE C HECKS FOR S EALED R ADIOACTIVE M ATERIAL
BACKGROUND
Third party service providers, who undertake maintenance on this type of radiation source, may use this code to issue a certificate of compliance for sealed radioactive material. The third party service provider is accredited to carry out work under the Radiation Protection Act. Work is defined as install, test, repair, service and decommission. Conditions may be imposed on the holder of a certificate of accreditation.
All certificates for special form design that is in accordance with the international standard ISO 2919 for a sealed, radiation source, containing radioactive material, must be retained until the source is sold or properly disposed of.
INTRODUCTION
A source that is damaged or corroded may leak radioactive material. This leakage of material needs to be found and the source isolated and enclosed. The wipe test is a procedure to check for loss of radioactive material from a radiation source. It is not a check of the amount of transmission of penetrating radiation. The wipe test, for this purpose, is also given the names of smear, swipe or leak test. The principle of the wipe test is that any material that escapes from the source is trapped on a swab and the swab is checked for radioactivity.
RADIATION PROTECTION GOALS
The goal of all wipe tests is to locate, identify and contain any loss of radioactive material.
Do not expose the tester to unnecessary levels of radiation. No attempt must be made to disassemble or unsafely deal with any radiation source, which must be made safe before testing.
FREQUENCY OF TESTING
All radiation sources in storage are wipe tested at least every ten years. For sources in regular use, wipe testing should be more often and correspond to the length of time of the licence to possess the radiation source i.e. three yearly. Roughly treated sources and older radiation sources are wiped much more frequently. Check sources that contain radioactivity slightly greater than exemption levels may be checked less frequently.
GENERAL POINTS
The wipe test should be performed by a person who understands the source and the containment of the source;
It is the outer containment of the source that is wiped not the sealed source;
The use of personal dose meters is needed as part of the procedure as well as disposable gloves and all relevant personal protective equipment;
The outside of the source containment is checked for contamination but if a loss of material is suspected, source attachments and areas near the source are wiped;
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If possible, wiping should spiral into the middle of the wipe area in order to avoid wiping material outside of the area;
Swabs may be sealed in plastic bags with a seal and labelled with date, location, source type, activity and any other relevant information;
A number of companies can measure the activity on the swabs;
These companies will give guidance on types of swabs and sizes recommended;
Documentation must be completed for each sample to establish a chain of possession of the swab;
The swab should not be touched with bare hands and simple precautions are needed in the event that radioactive material is trapped on the swab;
A quick check of the swab with an appropriate surface contamination monitor is recommended before dispatch, in order to take sensible precautions with each source;
Ambient radiation levels around a radiation source must be in accordance with all codes contained in conditions of licence to possess;
The radiation source is in accordance with general provisions of the code; and
It is always good practice to wash hands regularly because other contaminants may be present.
MINIMUM DETECTION LIMIT
Wipe tests using counting equipment can detect radiation levels down to hundreds of becquerel (Bq). A truly representative background sample is not often practical to obtain. In general, when activity on all swabs from a radiation source is less than 200 Bq of unspecified, surface material (1 count/s over 20 cm2 or so, which is generally just at the detection limit for a surface contamination monitor), no action is needed.
A noticeable increase in audio-output can be used to detect contamination and the swabs must be sent to a testing laboratory and the radiation source needs to be safely isolated. Check the swabs some distance from the source and a radiation protection adviser should be consulted.
FAILED WIPE TEST
Assume a 10 % pick up of the contamination on the swab. If more than 200 Bq of the specific radionuclide that is used in the sealed, radiation source, including decay product, may have leaked, you must report a failed wipe test to the Radiation Protection Branch and further advice must be obtained from your radiation protection adviser. Emergency response actions must be implemented.
FURTHER INFORMATION
Further information may be obtained from Radiation Protection
Northern Territory Department Health PO Box 40596 CASUARINA 0811 phone: 08 89227489 fax: 08 89227334 Email: [email protected]
http://www.nt.gov.au/health/radiationprotection
