RADIATION SAFETY PROGRAM
STANDARD OPERATING PROCEDURES
(RSP- 06- 2004)
CONTAMINATION MONITORING PROCEDURES
INTRODUCTION
All radioisotope facilities using unsealed nuclear substances must be monitored for surface contamination.
Whenever monitoring is being performed standard laboratory practice for personal protective equipment
such as gloves and lab coat are required. Radioactive contamination may be measured by two methods:
a) directly using portable instruments or
b) indirectly using non portable instruments such as liquid scintillation counters, gas-flow
proportional counters, gamma counters
Contaminated areas must be cleaned without delay verified by further contamination checks.
FREQUENCY OF MONITORING
Monitoring for surface contamination is required to be done

at least weekly in a radioisotope work area

immediately after a spill or incident

before equipment is released for non-radioactive use
It is highly recommended that an active work area be surveyed at the end of each session to ensure that
radioactive contamination is not inadvertently spread about or taken home. If no radioisotopes have been
used since the previous survey, a notation of this fact can be made in the contamination survey form. No
further action is necessary until the next usage.
LOCATIONS OF MONITORING
A sketch of the floor plan of each room using unsealed nuclear substances should be prepared. The
locations of active areas in the radioisotope work area should be numbered on the sketch. These
locations should include bench tops, sinks, fume hoods, storage areas, and non-active working surfaces
such as floors, instruments and equipment, door handles, light switches, sink taps and telephone
receivers. Several random locations should also be monitored. Keep the results of the monitoring in a
log book.
MONITORING RECORD
Results from the contamination monitoring must be recorded on the Ryerson University Radioisotope
Contamination Monitoring Report (RSP-F06-2004). If readings are below the action level for contamination,
this finding may be noted in the form.
CALCULATION OF REMOVABLE CONTAMINATION
The readings detection equipment can be related to regulatory criteria if the efficiency of the instrument for
a specific radioisotope is known. The contamination criteria (expressed in Bq/cm2 ) will vary for different
radionuclides. Refer to the Radiation Safety Manual section 3.13 for contamination criteria for specific
radionuclides. For mixtures of radioisotopes, do all calculations using the radioisotope for which the
instrument has the lowest detection efficiency.
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July 16, 2004
Using the following equation, the amount of contamination can be calculated:
Removable Activity
=
N - Nb) ___
E x 60x A x F
(Bq/cm2)
Where:
N = is the total count rate in counts per minute (CPM) measured directly or on the wipe.
Nb = is the count rate of the blank (in CPM)
E = instrument efficiency for specific isotope (e.g. for 26% efficiency, E = 0.26)
60 = sec/min
A = area wiped in cm2 (not to exceed 100 cm2)
F = is the collection factor for the wipe. Use a value of F = 0.1 (i.e., 10%).
METHOD 1: DIRECT MEASUREMENT USING PORTABLE METERS
Direct measurements involve using a portable contamination monitor instruments to detect both fixed and
removable decontamination. Contamination meters are specifically designed to measure radioactive
contamination on a surface. The detector must have sufficient sensitivity to detect contamination at
levels specified and outlined in the regulatory license issued by the Canadian Nuclear Safety Commission
(CNSC), regulatory documents or internal requirements for the specific radionuclides being monitored.
Depending upon the detector and the radioisotopes, direct measurement is often convenient for
monitoring large areas. These meters may be used when background radiation levels are negligible.
All radiation detection instruments must be registered with the Radiation Safety Officer.
New
contamination meters should be tested to verify that it meets all specification stated by the manufacturer.
It is recommended that meters be calibrated annually and records kept for 3 years. To arrange for
calibration of meters, please contact the Radiation Safety Officer at extension 4212.
STEPS FOR MONITORING CONTAMINATION USING PORTABLE METER
1.
OPERATIONAL CHECK
Before monitoring contamination, portable instruments should be given operational checks as specified
the manufacturer. Before each use, operator should verify that a meter is functioning properly by
checking for:
a) battery power
b) high voltage
c) source response time
d) Measure background radiation levels at a surface that is known to be clean.
Record the operational checks and background measurements. Any monitor not operating within the
parameters of the operational checks or which show anomalous background measurements should not be
used until their proper operation can be verified.
2.
METER PLACEMENT
The reading from surface contamination monitors can be influenced by sources of radiation in the vicinity
of the surface being monitored. If possible, remove all radiation sources from the area to be monitored by
the survey instrument.
Monitor the locations marked on the plan of the working area by slowly passing the detector over each
area. Keep the detector face towards the surface being monitored and keep the distance between the
detector and the surface as small as possible without touching (and possibly contaminating) the detector.
The window of the monitor must be uncovered when monitoring is occurring. If contamination is detected,
stop and obtain a measurement. If a reading is off-scale, the monitor shall be moved to a distance where
readings can be made, and the distance and reading and location noted.
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July 16, 2004
3.
CONTAMINATION
If a reading greater than the contamination criterion is found, the area must be decontaminated. Clean
the area and perform monitoring again. Repeat cleaning if monitoring indicates contamination. A reading
in excess of the contamination criteria after repeated cleaning is an indication of fixed contamination or a
high radiation background. Identify and mark the contaminated area on the plan. Record the highest
measurement for each area and the final measurement after cleaning.
METHOD 2: INDIRECT MEASUREMENT OF CONTAMINATION
Indirect measurement detects removable contamination by means of wipe tests and non portable
detectors such as liquid scintillation counters. Indirect measurement of contamination is used when
portable instruments are not sensitive enough for the radionuclides being monitored. For low energy beta
emitters such as Tritium (H-3), Sulphur -35 (S-35) or Carbon 14 (C-14), monitoring through the use of
wipes and liquid scintillation counting is the most effective for contamination monitoring. This type of
measurement is also effective in areas with high background. As with other detection equipment, the
efficiency of the counter should be determined for the specific isotope being counted, prior to
contamination monitoring.
STEPS FOR MONITORING CONTAMINATION USING WIPES
a)
b)
c)
d)
e)
f)
g)
h)
Select an absorbent analytical grade of filter paper with a diameter of about 5 centimetres.
With the filter, wipe each of the locations shown on the plan of the working area. Hold the filter
paper on the edge with thumb and index finger use uniform and constant pressure to ensure the
entire area is wiped. Wipe an area of approximately 100 cm2 with an S-shaped pattern.
Use one numbered wipe per location.
Place wipe in a scintillation vial, add scintillation fluid, and cap the vial.
Count the wipes (typically 1-2 minutes) in a low-background area and record all results. Include
a blank wipe to determine the net count-rate above background and standard with each set of
wipes. When using the wipe method of measurement, only a fraction of the contamination will be
removed, assume a wipe efficiency (i.e. collection factor) of 10%.
Record the wipe test measurements.
If contamination is found, the areas must be identified and decontaminated. After cleaning, rewipe the area again and continue until the area has been cleaned.
Record the results before and after the decontamination including the printout from the liquid
scintillation counter and keep the printout from the counter with the contamination monitoring
records.
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BACKGROUND INFORMATION
CONTAMINATION MONITORING
(RSP-06-2004)
Not all monitors are suitable for or sensitive enough to detect contamination from all types of
radionuclides. Portable contamination monitors cannot be used to detect tritium (H-3) and typically
have very low efficiencies for other low energy beta emitters such as Carbon -14 and Sulphur 35. The
most effective method for surface contamination monitoring for these low energy beta emitters is by using
wipe tests and liquid scintillation counting method. High energy beta emitters such as Phosphorus-32 or
gamma emitters can be effectively monitored using a portable contamination monitor with an appropriate
detector, (for example an end-window GM pancake probe) as shown in the photo below.
BACKGROUND RADIATION
The typical background readings (i.e., the naturally occurring radiation readings) should be known for the
general area before monitoring begins in a radiation area. In this way a valid comparison can be made of
the radioactive area being monitored.
METER EFFICIENCY
For each instrument the detection efficiency especially for contamination meters should be known prior to
start. For contamination monitors, the detection efficiency will vary by isotope.
Efficiencies for all meters and scintillation/gamma counters must be obtained for those isotopes that will
be used in the laboratory. A detector efficiency depends upon several factors including, the type of
detector, size and shape – larger surface areas are more sensitive), distance of detector from nuclear
substance, type of radioisotope and type of radiation measures, backscatter towards detector and
absorption by air of radiation before reaching detector. Efficiencies can be obtained using a standard
source with a known activity.
Efficiency = {detector count rate – background rate}
known activity of standard source
(cpm)
(dpm)
MAINTENANCE
The Permit Holder is responsible to ensure radiation detection equipment is maintained. Portable meters
will be examined by Radiation Safety Officer during regular lab inspections. Any meter found not to be
functioning properly will be removed by the RSO until the equipment is serviced and functioning. The
RSO can assist in arranging repairs and required calibration services.
APPLICABLE LEGISLATION, STANDARDS AND GUIDELINES:



Canadian Nuclear Safety and Control Regulations - Sections 24 and 26
Canadian Nuclear Safety Commission: Regulatory Document (INFO-0545): “Radioisotope
Safety: Monitoring for Radioactive Contamination”.
Canadian Nuclear Safety Commission: Regulatory Guide G-121 “Radiation Safety in
Educational, Medical and Research Institutions” (May 2000)
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