RADIATION SURVEYS

Introduction

Contamination Surveys

Area Surveys

Survey Instruments

Freezer Frost Surveys

Equipment Transfer / Disposal / Resale Surveys

1. INTRODUCTION

Radiation Surveys are performed in areas where radioactive materials or radiation-producing machines are used to ensure that radioactive contamination and/or exposure levels are as low as reasonably achievable (ALARA). 

Contamination surveys are performed with wipe smear samples and are used to detect removable radioactive contamination, for example, radioisotopes such as ³²P or ³⁵S.  Access to a liquid scintillation counter (LSC) or gamma counter is usually necessary to analyze wipe smear samples.  Wipe smear samples analyzed with an LSC must have scintillation cocktail in the vial, preferably a cocktail that is biodegradable.  Dry samples are not acceptable for contamination surveys.

2. CONTAMINATION SURVEYS

All laboratories should be kept clean to avoid contamination.  Laboratories using any unsealed radioactive materials are required to survey for contamination using a wipe smear.  Surveys should be taken on a regular basis to detect any contamination occurring from radiation work.  It is strongly suggested that weekly surveys be conducted, using wipe smears and a LSC.  The results should be recorded in the Radiation Safety Survey Log.  The Radiation Safety Survey Log may include an area map of the laboratory with survey locations clearly marked and the survey results.  Results may be recorded on the Survey Log form or on copies of the area map and should include the date, location, and the name or initials of the person performing the survey, as well as the LSC print-outs.  The Radiation Safety Survey Log should be stored in an easily accessible location for review by Health Physics and Federal, State, or local Inspectors.  See Appendix E for a sample Radiation Safety Survey Log Form.

Conducting Contamination Surveys

The laboratory contamination survey should include equipment and work areas used during the experiment.  For example, the survey should check floors (especially near waste containers, desks, and doorways); doorknobs; telephone receivers; buttons on equipment; hood sashes, edges, handles and switches; sink handles, edges, and drains; and lab benches.  If a contamination level in an area is more than twice background, e.g. 100 dpm/100 cm² if the background is 50 dpm/100 cm², decontaminate the area and re-survey.  Continue this process until the area is clean.  Record initial and final results in the Radiation Safety Survey Log.  Contact Health Physics for assistance with areas that are not able to be decontaminated.

Surveys should be completed each week that radioisotope is used to detect any contamination occurring from radiation work.  A week is defined as 7 days beginning Sunday and ending Saturday.  Each licensee using a “common room” is responsible for performing and recording surveys of the common room.  Surveyors should use wipe smears and a LSC with scintillation cocktail, or a gamma counter to analyze the results of the survey. 

If the laboratory is not using radioactive materials but is storing radioactive materials (including waste containers), monthly storage surveys are required.  Storage areas should be surveyed at least once each month.  The results should be recorded in the Radiation Safety Survey Log with other laboratory survey results.    

3. AREA SURVEYS

For high energy beta and any gamma emitters, area surveys are conducted with a portable (hand-held) radiation survey meter in addition to routine contamination surveys.  Area surveys are used to monitor for levels of increased radiation such as in unshielded areas or during relocation of radioactive materials.  It is important to document a background radiation survey value for comparison to the measured radiation result.

Laboratories using unsealed radioactive materials should perform area surveys periodically before, during, and after an experiment.  A final survey after completion of the experiment may be performed, but does not eliminate the requirements for taking wipe smears for the contamination survey mentioned previously.  Results may be recorded in the Radiation Safety Survey Log with the contamination survey results.

4. SURVEY INSTRUMENTS

Each laboratory using unsealed radioactive material other than ³H or ¹⁴C should either have two portable radiation survey instruments/meters or possess one instrument and have access to a second.  This is to ensure availability of a survey instrument if one is damaged, out of calibration, or otherwise unable to be used. 

While appropriate survey instruments must be available for activities involving radiation at the University of Colorado, it is the responsibility of each laboratory to supply the instrument.  Ideally, the instrument should read out in units of mR/hr and/or counts per minute (cpm) and the probe should be one which is most appropriate for the type of work performed in the laboratory.  Health Physics is available to assist with appropriate instrument selection.  Health Physics has a limited supply of loaner meters available for temporary use.

Health Physics maintains a database of all survey instruments on campus and provides calibration services for most of the models used at the University of Colorado.  Calibration is required at least once each year.  Health Physics normally collects and calibrates the survey instruments every six months to ensure compliance with the annual calibration requirement.  If a survey meter has not been calibrated within the last six months, contact Health Physics at (303) 492-6523. 

If a new instrument is obtained, contact Health Physics as soon as possible to have it placed on the calibration schedule.  If an instrument requires major repairs or more complicated calibration techniques, it will be sent to the manufacturer for these services at the expense of the laboratory.  Minor repairs may be provided by Health Physics at little to no charge to the laboratory.  Additional repair costs may be recovered from the laboratory.

Survey instruments/meters are calibrated to a National Institute of Standards and Technology (NIST) traceable ¹³⁷Cs gamma source.  Correction factors are indicated on the calibration label for use with beta emitting radionuclides.  When using b emitters, multiply the reading on the instrument by this correction factor to obtain an accurate reading.

The following types of instruments are most commonly used on campus:

Geiger-Mueller counter with thin-end window probe     Used for ³²P, ⁸⁶Rb, ¹²⁵I
Geiger-Mueller counter with “pancake” probe               Used for ³²P, ³³P, ³⁵S

These are available from several companies, including the following (Health Physics has catalogs and price lists available):

5. FREEZER FROST SURVEYS

Freezers used to store tritium (³H), are usually contaminated by the radionuclide due to hydrogen exchange with water.  The escaped tritium (³H) is then incorporated into the freezer frost (or condensation in a frost-free freezer) in the form of tritiated water (HTO).  A heavily contaminated freezer could contain several millicuries of HTO in the frost.

Freezers used to store tritium (³H) are checked every six months by Health Physics personnel.  Excessive contamination (>10,000 dpm/100 cm² or dpm/ml) requires defrosting and decontamination of the freezer by laboratory personnel.  Any liquid generated by defrosting should be considered radioactive liquid waste and collected for disposal through Health Physics.  Paper towels used to blot liquid are considered solid radioactive waste.  Please refer to the Waste chapter for additional information.

6. EQUIPMENT TRANSFER / DISPOSAL / RESALE SURVEYS

Equipment such as refrigerators, freezers, centrifuges, and other laboratory items used with radioactive materials must be surveyed prior to transfer or disposal to assure that they are free from radioactive contamination.  Refrigerators and freezers used for tritium, which may have become incorporated into the plastic of the unit, are two specific examples.  Contact Property Services at (303) 492-6524 to transfer or dispose of equipment associated with radioactivity.  A contamination survey of both the inside and outside of the unit will be required.  Maintain the survey records, including LSC print-outs, with the contamination survey results in the Radiation Safety Survey Log.  Once the unit is determined to be free from radioactive contamination, all radioactive signs and symbols must be obliterated or removed.  Property Services uses an Equipment Disposal/Resale Form that should be completed for transfer or disposal of large items.  Please refer to Appendix H for a blank Equipment Disposal/Resale Form.

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