Radiation Detection Instrument Calibration
EH&S operates a radiation detection instrument repair and calibration facility that can accommodate a wide variety of equipment.
Routine calibration of radiation detection instruments is a required condition of regulatory and radioactive material licensing. All portable count rate meters (commonly referred to as GM Survey meters or “Geiger “ counters) and exposure rate meters (commonly referred to as ion chambers) require annual calibration.
EH&S maintains a dedicated facility for calibrating all types of portable radiation monitoring instruments across a wide range of radiation types and levels. Instrument calibrations are performed using ANSI N323A and radiation sources certified by the National Institute of Standards and Technology (NIST) or traceable to the NIST.
The facility also specializes in the maintenance and repair of all types of portable nuclear instrumentation, including radiation detection equipment.
EH&S provides count rate calibration and exposure rate calibration of radiation detection instruments. Please contact Radiation Safety for cost rates and more information.
Labs can access EHSA to view their survey meters, liquid scintillation counters, and gamma counters; check when they were last calibrated, and see when they are due for calibration. For a step-by-step guide, click here.
Frequently Asked Questions (FAQ)
A count rate calibration is a measure of the instrument's response to a known number of counts. First, the instrument is connected to a pulsar, a device which sends a discrete number of electronic pulses to the instrument. The instrument's response is measured at several levels (i.e. 100, 1000, 10,000 pulses) to ensure that the observed counts are within 10 percent of the electronic pulses. The instrument is then exposed to different radioactive sources of known activity to determine efficiencies for each.
An exposure rate calibration is a measure of the instrument’s response to a known radiation exposure rate from a radioactive Cs-137 source.
The instrument's response is measured at several precisely measured distances to ensure that the observed counts are within 10 percent of the exposure rate emanating from the source at each of those distances.
Radiation detection instruments are only capable of detecting a percentage of the emissions interacting with the detector. For example, if a source of radiation is emitting 100,000 disintegrations per minute (dpm), the instrument might only see 1 percent, or 1000 counts per minute (cpm). The efficiency varies from instrument to instrument and from radionuclide to radionuclide. A 1 percent efficiency is a rough approximation for most portable count rate meters.