Survey records must be documented on a Radiation Survey Data Sheet and filed in the Radionuclide Inventory and Survey Book. These records must be kept for three years.
- Direct Radiation Surveys
It is always good practice to perform an area survey with a Geiger-Mueller (GM) meter after each procedure in which detectable beta- or gamma-emitting radionuclides are used to determine the presence of gross levels of contamination. Surveys should include the individual performing the experiment, laboratory bench, equipment, and the floor in the immediate area. If a survey is performed, whether or not it was required (per the tables below), any elevated readings warrant a more extensive survey (e.g., wipe survey) and decontamination or shielding as appropriate.
A direct survey is required and must be recorded after each experiment using unsealed quantities of the activities specified below:
AFTER EACH EXPERIMENT (Table 1)
TYPE OF RADIATION ENERGY ACTIVITY EXAMPLES Beta > 300 keV > 5 mCi 32P, 36 Cl Gamma/X-ray < 500 keV > 5 mCi 125 I, 111 In, 51 Cr Gamma/X-ray > 500 keV > 0.5 mCi 22 Na, 59 Fe, 86 Rb
A direct survey is required and must be recorded each month (calendar month) in all areas where unsealed quantities of the radionuclides specified below are used or stored:
MONTHLY (Table 2)
TYPE OF RADIATION ENERGY EXAMPLES Beta > 300 keV 32P, 36 Cl Gamma/X-ray > 100 keV 51 Cr, 111 In, 22 Na, 59 Fe, 86 Rb
Additional survey requirements may be specified on a PH=s Radionuclide Use Permit.
If the results of the direct survey indicate a radiation source, other than contamination that exceeds 2 mR/hr (or equivalent count rate) at 30 cm, shielding must be utilized. This includes stock vials, waste containers, etc.
If contamination is present, the area must be decontaminated and resurveyed (using both direct and wipe surveys) until background levels are achieved.
After removing disposable gloves and washing hands, a survey of the bare hands is recommended. Documentation of this survey is usually not required. When performing such surveys, the following points should be considered:
- A survey with a GM is adequate for most radionuclides with x-ray, gamma ray, or beta energies greater than 50 keV. Beta radiation is most efficiently detected through a thin end-window GM tube or "pancake" probe.
- For x-ray or gamma radiation less than 50 keV (e.g., 125I), only a GM meter with a scintillation probe will adequately detect the presence of contamination.
- For beta radiation less than 50 keV (e.g., 3H), a wipe survey of the hands is the only reliable survey method.
Survey of lab coats, personal clothing, and shoes are recommended following the use of radioactive material, before laundering (especially lab coats), or before leaving the laboratory.
- Contamination (wipe) Surveys
A wipe survey is required after each experiment using unsealed quantities of activity in excess of the limits specified below:
AFTER EACH EXPERIMENT (Table 3)
TYPE OF RADIATION ENERGY ACTIVITY EXAMPLES Beta < 300 keV > 10 mCi 3H, 14C, 35S Beta > 300 keV > 5 mCi 32P, 36 Cl Gamma/X-ray < 500 keV > 5 mCi 125I, 111 In, 51 Cr Gamma/X-ray > 500 keV > 0.5 mCi 22 Na, 59 Fe, 86 Rb
NOTE: In all other cases, wipe surveys must be conducted at least monthly.
Wipe surveys should be carried out in all areas listed on the permit. This includes counting rooms and other "specific-use areas". If a particular lab is not used for any radioactive work in a given month, a survey is not required provided a notation is made on the monthly survey form indicating the reason for the omission (e.g., "No use in CL 159").
Wipe surveys should be performed in radionuclide use areas such as lab benches, hood sills, sinks, etc. Also, areas where contamination would not be expected should be included as part of the survey (e.g., refrigerator handles, telephones, desks, etc.). These areas should be chosen at random in addition to the routine survey locations. One other area that should be included in the survey is the floor in the doorway of the laboratory. Contamination in this location may indicate a more widespread problem (i.e., contamination leaving the laboratory).
Preceding a wipe survey with a direct radiation survey (e.g., using a thin, end-window GM meter) may aid in locating contaminated areas within the laboratory. However, this type of survey is only applicable in laboratories where medium to high energy beta emitters (e.g., 32P and 36Cl) or gamma emitters are used. Any elevated direct radiation reading which may be associated with contamination should be followed up with a wipe survey in that location to determine if the contamination is fixed or removable.
The actual wipe survey consists of rubbing a filter paper or Q-tip over an area of approximately 100 cm2. Care should be taken to prevent cross contamination between wipe samples. These wipes should be counted in a liquid scintillation counter (LSC) or gamma counter as appropriate.
Wipe surveys from several locations which are above background but less than the levels specified in the limits below may indicate a widespread contamination problem. This may require a review of procedures. If gross ( > 50,000 cpm) or widespread contamination is detected, immediately notify the RSO.
Wipe surveys should typically be counted in the same instrument utilized for counting the samples associated with the clinical/research procedure (e.g., liquid scintillation counter or gamma counter). The instrument should be set to count for the radionuclides used in the laboratory. If wipes are to be counted for beta and gamma radionuclides, both a liquid scintillation and gamma counter should be used. In all instances, the window should be set wide enough to capture all energies or multiple windows may be used. Presets, if available on the instrument, may also be used; however, the window for the preset should be verified as appropriately established for the radionuclide in question.
The table below provides channel setting suggestions for some common radionuclides. When in doubt, a wide open window should be used (e.g., 0-2000 keV).
RADIONUCLIDE ENERGY* COUNTER SETTING 3H 6 keV LSC 0 - 18.6 keV 14C 52 keV LSC 18.6 - 200 keV 35S 56 keV LSC 18.6 - 200 keV 33P 83 keV LSC 18.6 - 250 keV 32P 570 keV LSC 500 - 1710 keV 125I 36 keV Gamma 20 - 90 keV 51Cr 320 keV Gamma 270 - 370 keV
*The energies listed in Table 4 for beta-emitting radionuclides provide the average beta particle energy.
For radionuclides not listed above, the general rule of thumb should be to set the window approximately 50 keV below and 50 keV above the energy in question. For liquid scintillation counting of beta radiation, the window should be set with regard to the average beta energy (i.e., one-third of the maximum energy).
A "background" wipe sample should be counted with the wipes from a contamination survey. Assuming a counting efficiency of greater than 10%, contamination greater than 200 cpm/100 cm2 above background should be decontaminated and resurveyed until the contamination has been reduced to acceptable levels. In addition, a direct radiation survey, if applicable, should be performed to verify that the exposure rate is less than 2 mR/hr. All results from resurveys must be included on the Radiation Survey Data Sheet. Documentation of results (including negative results) is of utmost importance. Completion of the data sheet will assure that all pertinent information is properly recorded.
The results (printout) from the counting instrument should be included and keyed to a diagram of the laboratory(s) with the wipe numbers corresponding to a number on the diagram. Make sure to include all labs and areas of radioactive material use (e.g., specific-use areas, shared labs, etc.).
The completed Radiation Survey Data Sheet must be placed in the Radionuclide Inventory and Survey Book. Although a PH may assign one individual to perform the appropriate surveys at the required frequency, all radionuclide users should know how to perform and document the surveys to prevent the omission of surveys when the responsible individual is absent. In addition, all lab personnel should know the location of this manual and the Radionuclide Inventory and Survey Book.
During time periods of inactivity (i.e., for months when radionuclides are not used), wipe and direct surveys are not required; however, documentation must be made in the survey book each month to indicate the reason for the omission of the required surveys.