STANDARD OPERATING PROCEDURES FOR
RADIATION CONTAMINATION SURVEYS
Whenever unsealed radioactive materials (liquid solutions in vials,
ampoules, test tubes) are handled (pipetted, transported, mixed,
transferred) it is possible to contaminate laboratory benches, floors,
and equipment. Every radiation-handling laboratory must be frequently
surveyed to detect the presence of any radioactive contamination.
The purpose of this document is to provide guidelines and techniques
for laboratory personnel responsible for conducting contamination
WHAT CONSTITUTES CONTAMINATION ?
Contamination is defined as the presence of radioactivity in an
unwanted area. If the contamination is on a disposable item it may be
thrown out into the radioactive waste.
WHAT ARE THE DANGERS FROM CONTAMINATION ?
Contaminated areas in a lab can lead to 3 problems;
- external radiation exposure to lab personnel
- internal absorption if comes into contact with skin or is inhaled
- interference with experiments being conducted in the lab
WHERE DO I LOOK FOR CONTAMINATION ?
Areas that have high potential for contamination; work benches, fume
hoods, pipettes, syringes, centrifuges, the floor, inside
refrigerators/freezers should be surveyed more frequently. Door
handles, telephones, sink faucets should be surveyed once per month.
Persons responsible for conducting surveys should obtain a room
diagram and a custom made survey form from the Radiation Safety Office
(RSO) and use it to specify areas which will be frequently monitored.
The areas should be numbered and identified on the Contamination Survey
HOW FREQUENTLY MUST I SURVEY ?
Every investigator agrees, as a condition of his/her authorization,
that radiation-handling laboratories will be surveyed weekly for
contamination. However, it is good laboratory practice to do a
contamination survey after each use of radioactive materials.
If no radionuclides are handled in a particular week, no survey is
required. However, the survey report form must be filled out and sent
to the RSO or a "No Radioactive Material
Use" form can be submitted to the RSO. Since a handling lab
may also store radioactive materials, a survey must be performed at
least once per month, even
if no radioactive materials were handled during that month.
Freezers, cold rooms, counter rooms, and centrifuge rooms must be
checked monthly and the Contamination Survey Report form filled out and
sent to the RSO.
52 weekly contamination survey reports are expected each year for
each radiation handling laboratory.
12 monthly surveys are expected each year for rooms used only to
count radioactivity, and those which are used only to store
radioactivity such as cold rooms and freezers.
WHAT KINDS OF CONTAMINATION ARE THERE ?
Fixed contamination refers to radioactivity remaining on a
surface after repeated decontamination attempts fail to significantly
reduce the contamination level.
Removable contamination refers to radioactivity that can be
transferred from a surface to an absorbent material, such as filter
paper or cotton swabs, by rubbing with moderate pressure and swapping
an area of at least 100 centimeters squared.
WHAT IS BACKGROUND RADIATION ?
Every radiation detector indicates counts even without the presence of
radiation sources or contamination. This results from electronic
"noise" and from the detection of cosmic radiation and other natural
radiation sources in the environment. This is called "background"
radiation. The background counting rate for most detectors is usually
between 10 and 100 counts per minute (cpm).
You must determine the background count rate for your instrument
before each contamination survey. Here are some ways to do this;
For a survey meter (GM or NaI), the background count rate is
determined by a reading in a location that has no radiation sources
within it, such as the hallway or an office.
For a liquid scintillation counter, the background count rate is
determined by counting a non-contaminated wipe in the same volume of
scintillation cocktail that you use for your wipes to survey for
For a gamma counter, the background count rate is determined by
counting a non-contaminated wipe in the same size container that you
will use for your wipes to survey for contamination.
WHAT IS A SURVEY METER ?
A survey meter is a portable device used to measure radiation by
counting either the number of air ionizations in a GM tube or light
flashes produced in a NaI crystal as a result of radiation's
interaction with the detector. The GM detector is very efficient for
detecting the presence of high energy beta particle emitters (such as
P-32) and a NaI detector may be used to
detect gamma and xray emitting radionuclides (such as Cr-51, I-125).
The advantage of a survey meter is that it can be used to quickly
survey a large area. After determining the background count rate you
can usually detect the presence of contamination by an increase in the
rate of "clicking" of the audible signal given off by the detectors
and/or by a swing of the meter needle from left to right.
The RSO recommends that all laboratories regularly using P-32
purchase a GM detector. These detectors may be purchased for about
$600. Call the RSO for purchasing information or visit Ludlum Measurements, Inc. for
various survey meters and their prices.
Laboratories using gamma emitters (Cr-51,and I-125) should purchase
a NaI solid scintillation detector instead of a GM detector because of
the higher detection efficiency. These detectors may be purchased for
$600 - $800.
Labs using both P-32 and gamma emitters can buy a detector which has
an internal GM detector and an external NaI solid scintillation
detector. An example of such a detector is Ludlum's Model 3-98.
WHAT IS WIPE TESTING ?
Wipe testing involves the swabbing of areas of a laboratory to
determine if removable contamination exists. Swabbing may be done with
Q-tips, filter paper, or any other dry absorbent material. Use normal
pressure (equivalent to amount of pressure exerted in writing with a
number 3 pencil). On a 90 cm. x 60 cm. (3' X 2') work bench we
recommend that you
obtain five wipes. Each wipe must cover at least 100 cm2 of area.
The swabs, or "wipes" are then counted in either a liquid
scintillation detector or a gamma counter.
We recommend that you add 7 milliliters of glacial acetic acid to
every liter of toluene or xylene based scintillation cocktail to
minimize the chance of false high readings due to chemiluminescence.
HOW DO I KNOW WHEN I HAVE FOUND CONTAMINATION ?
To determine if an area has contamination, compare the background
counts/minute to the counts/minute of the wipe or survey meter. If the
ratio of counts/minute exceeds 3:1 the area contains significant
contamination and should be decontaminated and resurveyed until the
ratio is less than 3:1. For example, if your background is 25 cpm, you
must decontaminate the area if the survey exceeds 75 cpm.
WHAT INSTRUMENTS DO I USE TO DETECT CONTAMINATION ?
Contamination can only be detected with either a wipe test using a
liquid scintillation counter or a gamma counter, or an area survey
using a survey meter, depending on which radionuclides are present and
if it is fixed or removable contamination.
Survey meters cannot be used to survey for removable contamination.
This can only be done with a wipe test. However, a wipe test can not be
used to evaluate an area of fixed contamination. This can only be done
with a survey meter.
HOW RELIABLE ARE RADIATION DETECTORS ?
All survey meters must be tested before each use with a radiation check
source to see if the instrument responds. If the instrument fails to
respond to within 20% of the normal reading it must be repaired and
Contact the RSO for recommendations on the purchase of a check
source. Costs range from $50 to $100. Ludlum
Measurements, Inc. has a Cs-137 check source with a holder available.
You should also check the background count rate every time you use
the detector to ensure that it is not contaminated.
All survey meters used to survey for contamination must be
calibrated each year.
Liquid scintillation and gamma counters must also be periodically
checked to make sure that they are not contaminated and working
properly. You should also perform a Chi-square test to determine
counting reliability. The RSO can help you evaluate your counters.
WHAT IS DETECTOR EFFICIENCY ?
You must determine the efficiency of the detector which is used for
contamination surveys as this information is requested by the NRC and
is needed for the Contamination Survey Report form.
Detector efficiency is the detected fraction (usually counts per
minute) of all radiation emanating from a "standard" radiation source.
A standard is a radiation source with a known number of disintegrations
per minute (dpm).
% Detector efficiency = (observed cpm of standard / dpm of standard)
LIQUID SCINTILLATION DETECTOR EFFICIENCY
The efficiency of your liquid scintillation detector can be easily
checked by inserting a "standard" vial into the counting rack. Apply
the above formula.
A "standard" is a radiation source with a known quantity of dpm.
Unquenched H-3 and C-14 "standards" are commercially available in the
price range of $250 - $300. The RSO can provide purchasing information.
To estimate the efficiency of other radionuclides such as I-125 and
P-32, prepare a "standard" by removing between 0.1 microcuries and 0.5
microcuries from your stock vial. One microcurie is equal to 2.22 *
10E6 dpm. Place it in a vial with the same amount of scintillation
cocktail that you use with your wipe test. Take a one minute count and
use the above formula.
SURVEY METER EFFICIENCY
The efficiency of most survey meter depends on the type of detector and
window thickness. Place the radiation standard as close as possible to
the detector surface.
To determine the efficiency for radionuclides such as C-14, S-35,
P-32, Cr-51, and I-125, you can prepare a "standard" by removing
between 0.1 microcuries and 0.5 microcuries from your stock vial. Place
it in a planchet or on filter paper. Record the number of counts per
minute and apply the above formula.
GAMMA COUNTER EFFICIENCY
To determine the efficiency of your gamma counter for gamma ray
emitters such as I-125 and Cr-51, prepare a "standard" by removing
between 0.1 and 0.5 microcuries from your stock vial. Place it in the
same size vial that you use with your wipe test. Take a one minute
count and use the above formula.
HOW DO I DECONTAMINATE ?
Decontamination is the removal of radioactive contamination and may be
done using a commercial detergent such as "Count-Off"(New England
Nuclear) or "Isoclean"(ISOLAB). When decontaminating use a paper towel
or other absorbent material after allowing the detergent to settle on
the contaminated area for several minutes. If the contamination is
successfully removed, the absorbent material is contaminated and must
be disposed as radioactive waste. After decontaminating the surface,
repeat the survey procedure. Continue decontaminating and resurveying
until the survey indicates the contamination is less than 3 times the
HOW DO I RECORD RESULTS ?
The weekly and monthly reports must be filed with the RSO using a
personalized Contamination Survey
Report form, which can be custom made for
Most of the form is self-explanatory.
Give a brief description of the areas surveyed such as; fume hood,
bench #1, floor by fume hood, etc.
If you are doing a wipe test with a 2- or 3-channel scintillation
detector, record the results for each channel or set one of the
channels for an "open window" (the entire spectrum).
If you are doing a area survey with a survey meter, record your
results under the column labelled "GM".
If you are trying to detect only one contaminant, you can set the
detector window for that radionuclide, or you can use a wide open
window. Be consistent ! If you have calculated the efficiency of your
detector for a particular radionuclide with a wide open window, then
your wipe test results should be counted with a wide open window.
RSO CUSTOMIZED SURVEY REPORT FORMS
In order to reduce some of the paperwork for the labs, the RSO can make
survey report forms. Much of the information requested on the
Contamination Survey Report Form
repeated from week to week. Record the new information onto your
personal survey form. Make copies of the customized report form.
INSPECTIONS BY RSO
The RSO is required by our NRC license to conduct a minimum of one
annual inspection of all radiation-handling and storage rooms at UVM.
The RSO has the authority to inspect as often as necessary. Part of the
inspection involves a review of the recent history of surveys conducted
by laboratory personnel, a spot check for contamination, evidence of
smoking, eating, or drinking, and the presence of food or drinks in a
RSO personnel are available to help with any of the above areas. Call
CONTAMINATION SURVEY REPORT TO THE RADIATION SAFETY OFFICE
Working in a contamination-free laboratory builds confidence in
Surveying the laboratory for radiation contamination is essential to
cross-contamination of equipment, counting samples, and personnel.
- Please use one form for each room.
- Send a weekly report for each radiation handling laboratory
during active or inactive periods.
- Send a monthly report for each laboratory not used for radiation
handling but used for waste storage, counting, or radionuclide storage
in freezers and cold rooms.
- Use an open "window" on your scintillation counter if you are
checking for more than one contaminant.
- Survey the areas most likely to become contaminated; e.g. work
benches, floors, sinks, fume hoods, instruments, and waste storage
- If the count rate of the surveyed area exceeds three times the
background counting rate, it must be decontaminated and resurveyed
until the count rate is less than three times background. Record the
results of resurveys as indicated below.
- Call x62570 to obtain a brochure on methods of conducting surveys
and decontamination techniques.
- No smoking, eating, or drinking is permitted in a radiation
- If contamination is found, the investigator and other laboratory
personnel must be informed.
- Send the contamination report to the Radiation Safety Office,
Room 004 Rowell Building.