Instructional Guide for MCG Research Personnel- Laboratory Surveys
Principal Authorized Users (PAU) are required, as a condition of their authorization,
to perform weekly surveys. Surveys are used to identify and quantify radioactive
contamination and radiation levels. This guide is provided to assist you in performing
surveys and documenting routine weekly surveys.
Surveys are required to be performed by the Principal Authorized User in all labs
under a permit that allows use of radioactive material. This includes common equipment
areas where several labs are using radioactive material. One Principal Authorized
User is generally responsible for ensuring that the area is surveyed on a weekly
Types of Surveys
There are three categories of survey that are performed in the lab: fixed contamination,
removable contamination, and ambient dose rate surveys.
Fixed contamination surveys are used to locate radioactive material that can not be removed by applying
moderate pressure. Fixed contamination is quantified by :
- A Surface Emission Rate (SER), in gross counts per minute (cpm).
- Good radiological practice is to make sure that the SER is kept below twice
the ambient background.
Removable contamination are used to locate radioactive material than can be removed by applying moderate
pressure. Removable contamination presents a personnel hazard and also an internal
hazard due to the possibility of ingestion. Removable contamination is defined
in units of:
- Disintegrations per minute, divided by a surface area of one hundred centimeters
- The MCG criteria for removable contamination is 200 dpm/100cm2.
- Contaminated areas generally have removable contamination, but may have a
combination of the two types.
Dose Rate Surveys measure the amount of ionization in air, taken 30 cm from the source of radiation.
- The MCG action level is that ambient area dose rates must be kept below 2
mrem/hr. Possible sources of readings above this level are unshielded source
vials and waste containers.
One key to an effective contamination survey program is the selection of the proper
instrument. For detecting a Surface Emission or Exposure Rate the two most common
portable survey meters found in the MCG Research facilities are Geiger Mueller
(GM) survey meters and NaI scintillation survey meters.
- The GM meter is best used for P-32, a high energy beta emitter, but can also
identify areas heavily contaminated with lower energy betas such S-35 or C-14,
for which the GM has a relatively low efficiency.
- Note that exposure readings displayed in mR/hr using a GM are a conservative
- Note also that regulatory limits are expressed in units of mrem/hr. For purposes
of laboratory surveys the quality factor converting exposure rate to dose
rate is one, so that displayed units of mR/hr are equivalent to mrem/hr.
- Thin crystal NaI scintillation survey meters are used to identify I-125 contamination.
GM survey meters are poor detectors of I-125. No common portable survey meter can detect H-3.
Wipe tests must be used to survey an area for H-3 contamination. Due to their high
efficiency, wipe test counters, such as liquid scintillation counters and gamma counters
are very effective tools for identifying removable contamination. Gamma counters are
used for counting wipe tests for photon emitters, such as: I-125, I-131, Tc-99m,
The liquid scintillation counter is the best instrument for detecting removable beta
contamination. Its efficiency is high for a wide range of b -emitting nuclides. It is the best choice for removable contamination surveys in
radioactive material laboratories not working with pure photon emitters such as those
When one is unsure of the correct counting instrument to utilize, the Radiation Safety
Office should be contacted at extension 1-9826.
Routine contamination surveys are required to be performed weekly when radioactive
material is used. A good working practice is to perform a survey following each experiment
involving radioactive material. If your laboratory uses radioactive material infrequently,
you may suspend routine contamination surveys as long as you document the non-use.
A record of the survey performed after the last use must be on file, however. It is a requirement of the MCG Radiation Safety Guide that non-use of isotopes
be documented if no survey was performed for the week. For your convenience, there is a column on the survey form to easily document
non-use of isotopes for the week.
Portable Instrument Check
- Check Radiation Safety Office instrument calibration label. Contact the Radiation
Safety Office for calibration if calibration is greater than one year old.
- Check batteries.
- Turn on audio circuit.
- Perform operational check. Expose meter to attached check source to verify
that the instrument is operating.
- Determine background reading by holding the meter over an area that is not
- Record on the survey form the date of the survey and indicate the instrument
used and the required instrument information.
Survey locations should be chosen to reflect both areas where there is a likelihood
of detecting contamination and also for which contamination might be accidentally
Some suggested locations:
- Countertops, including the edges
- Fume hoods (aprons, sashes, sash handles)
- Refrigerator and freezer door handles
- Areas surrounding sinks designated for radioactive material
- Floor, around working areas and lab entrances, waste containers, and fume
- Equipment used with radioactive material, especially common equipment
- Doorknobs and the floor at entrances to the lab
Utilizing the provided laboratory survey form, indicate the survey locations with
numbers corresponding to the locations.
Fixed Contamination Survey
Slowly move the probe over designated areas in a zigzag pattern, listening for an
increase in the pulse rate as an indication of increased activity.
- If an area with a count rate more than two times background is identified,
determine the extent of the contaminated area and decontaminate.
- After decontaminating any area, resurvey to verify that the area is clean.
- If the count rate is greater than two times background, repeat the decontamination
and resurvey until levels are less than two times background.
- Fixed contamination surveys do not have to be documented, but are an extremely
good radiological practice. These surveys will help you locate possible contamination
that can be quantified with a removable contamination survey.
Removable Contamination Survey
- Identify sampling points/locations.
- Using filter paper, with a diameter less than two inches, wipe an area approximately
100 cm2. This can be done by making an S-shaped curve about 12 inches long to increase
the chance of picking up contamination.
- Count the wipes on a liquid scintillator or gamma counter.
- Divide the cpm given by the counter by the instrument efficiency to obtain
dpm/100cm2 and document on the survey form under the "R" on the left side of the survey location column corresponding to the location
where the wipe was taken.
- If an area of removable contamination is identified as being greater than
200 dpm/100cm2, decontaminate and resurvey the area.
- Repeat the cleaning and resurvey until the area has removable contamination
less than two times background.
- Record counting results, identified contamination, subsequent actions, and
Any location in which the count rate is more than 200 dpm/100cm2 should be considered contaminated.
- Clean the area with soap and water, a commercial cleaning solution, or a
commercial decontamination solution specifically designed for radioactive
- Resurvey the area to verify that the contamination has been removed. If the
contamination appears to be fixed, mark the area and notify the radiation
safety office for assistance. If high level contamination is discovered and assistance
in decontaminating the area is required, contact the Radiation Safety Office.
Dose Rate Surveys
- Dose Rate surveys are performed with the detector 30 cm from the source.
- Record the exposure readings under the "E" of the column corresponding to the location
- The MCG action level for exposure rates at 30 cm is 2 mrem /hr.
- If decontamination measures can not bring the exposure rate below 2 mrem/hr,
contact MCG Radiation Safety.
- Typically, only waste containers containing P-32 will exceed these levels
and should be shielded to bring the exposure rate to less than 2 mrem/hr and
the container should be disposed of as soon as possible.
Please feel free to contact the Radiation Safety office at extension 1-9826 with any
questions regarding laboratory surveys or other radioactive material use issues.