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Survey Information

What is Radioactive Contamination?

It is the uncontrolled distribution of radioactive material in a given area. A wipe test that produces results equal to or greater than 200 dpm/100 cm² is consider contaminated. A meter survey that produces results with a continuous count rate of three times the background or more is considered contaminated. Therefore, the area will need to be decontaminated.

Why is Surveying for Contamination Important?

  • To minimize exposure from external radiation sources to levels as low as reasonably achievable (ALARA).
  • To minimize the entry of radionuclides into the human body by ingestion, inhalation, absorption or through open wounds when unconfined radioactive materials are handled.
  • To minimize cross-contamination.

Types of Contamination

  • Removable contamination:
    • It can be readily removed using proper decontamination procedures.
  • Fixed contamination:
    • It cannot be readily decontaminated. Fixed contamination generally does not present a significant hazard unless the material comes loose or is present in such large amounts that it presents an external radiation hazard.

Types of Surveys

  • Meter surveys are performed with Geiger detectors or scintillation probes. These surveys identify both fixed and removable contamination but will detect only certain isotopes.
  • Wipe surveys are performed by using a Q-tips or filter paper and gently wiping the surface of an area. The wipe media will be counted on a liquid scintillation counter or a gamma counter. Only removable contamination can be detected. Wipe tests are best with detecting low-level contamination.

Note: Wipe Test results must be documented in units of disintegrations per minute (DPM) for all surveys taken. To learn how to convert from CPM to DPM, CLICK HERE.

Surveying Instruments

Radiation cannot be detected by human senses. A variety of instruments are available for detecting and measuring radiation. These instruments must be appropriate for the type and level of ionizing radiation being used.

  • Geiger-Mueller (GM) Meter:
    • Measures gamma or high energy beta
  • Scintillation Probe:
    • Measures low energy x-ray sources and to locate I-125 contamination
  • Gamma Counter:
    • Measures gamma
  • Liquid Scintillation Counter:
    • Measures beta

Registering Survey Meters

Survey Meter Registration Form

Documentation of Contamination Surveys

It is mandatory to document surveys after every experiment, every month and any spill. As prudent practice, one shall always check for contamination periodically during an experiment, before one leaves the laboratory and before one leaves to go home.