Radiation Workers

Guide for Using Portable Survey Meters

What is a Survey Meter?
A survey meter is a portable handheld, electronic instrument used to detect radiation. It is recommended that a "pancake" type Geiger Mueller (GM) probe be used for isotopes which emit beta radiation and an energy compensated GM probe be used for gamma emitting isotopes with energies greater than 60keV. For low energy photon emitting isotopes (<60keV), it is recommended that a low energy gamma scintillator, such as a NaI detector, be used. 125Iodine is an example of an isotope which emits photons of energy less than 60keV. It should be noted that 3H cannot be detected with a standard lab survey meter and that only very large quantities of 14C can be detected with a Geiger counter.

How to Use a Meter to Monitor:

How to Use a Meter to Monitor Surface Contamination

  1. Verify that the meter has been calibrated by the Radiation Safety Office within the last year. The meter should have a calibration sticker with the date of calibration and the “cal due” date. If the present date is later than the “caldue” date, DO NOT USE THAT METER.
  2. Perform a battery check on the meter. This is usually accomplished by turning the meter’s control knob to the “Bat” position and verifying that the meter’s output needle swings to the battery OK position.
  3. Turn the control knob to place the meter at its most sensitive scale.
  4. With the appropriate probe, a meter survey is conducted by slowly passing the probe over the area or object to be surveyed. Be certain that the pass is at a constant velocity (1 probe width per sec is recommended) and sufficient time is allowed for the meter to respond.
  5. For surface contamination measurements, the distance from the contaminated object or area should also be constant. A distance of 1cm is suggested. Care should be taken not to contaminate the probe itself!
  6. Dose rate measurements should be performed at waist/chest level and/or one foot from the ground).
  7. Begin any survey by checking yourself first. Each finger should be checked with special attention paid to thumbs. Wrist and forearm areas should be surveyed as well as lab coat sleeves, fronts and pockets. Personal surveys should also include monitoring the bottoms of shoes. Shoe soles are an excellent indicator of the presence or absence of floor contamination.
  8. All readings should be recorded. When recording measurements, counts per minute (cpm) or milliroentgens per hour (mR/hr) should be used. The correct unit is determined by the type of probe being used. When a pancake or scintillation probe is used, cpm is the correct unit. When the energy compensated probe is used, mR/hr is the correct unit. Questions related to the correct use of units should be directed to the Radiation Safety Office.
  9. Please be certain that all readings are recorded as "net". To do this, determine the normal background reading by observing a meter reading in an area where radioactive materials are not used or stored. Subtract this reading from all other measurements taken.
  10. When recording background radiation, itis normal to observe fluctuations on the meter scale use an average of the meter fluctuation. General background readings found in UMass Lowell buildings are usually from 30 – 150 cpm with a pancake probe and 200 –500 cpm with a scintillation probe.              
How to Use a Meter to Monitor Area Dose Rates

  1. Verify that the meter has been calibrated by the Radiation Safety Office within the last year. The meter should have a calibration sticker with the date of calibration and the “cal due” date. If the present date is later than the “cal due” date, DO NOT USE THAT METER.
  2. Perform a battery check on the meter. This is usually accomplished by turning the meter’s control knob to the “Bat” position and verifying that the meter’s output needle swings to the battery OK position.
  3. Turn the control knob to place the meter at its most sensitive scale.
  4. Measure the dose rate at points which are representative of the work area, such as waist/chest level and/or one foot from the ground.
  5. If the meter reads at the extreme high end of the dose rate scale (i.e. it becomes ‘pinned’ at the high end), change the control know to the next highest scale. Continue to increase the control knob until the meter registersa dose rate in the low to upper region of the dose rate scale (i.e. the meter isnot ‘pinned’ low or high).
  6. All readings should be recorded in terms of dose rate or exposure rate(mrem/hr, mR/hr) and are determined by multiplying the dose rate observed on the meter scale by the appropriate multiplying factor associated with the control knob setting.