Radiation Protection Program: Survey Meter Information

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Radiation Protection Program
Survey Meters

How to Specify a Meter

We Do NOT Recommend

Table of Meters

All authorized users of radioactive material must have a survey meter which is sensitive to (i.e., is able to detect) the type and energy of radiation emitted by the radioactive material being used. Thus, researchers working with beta-gamma emitting nuclides are required to have a meter with a thin-window GM detector. Users working with radioactive material emitting gamma radiation are required to have a scintillation detector.

Geiger counters are used for radiation surveys at the University because of their high sensitivity for beta particles. Nearly every beta particle that penetrates the detector will cause a discharge and produce a count. A thin-window GM has a conducting shell with one surface covered by a thin (e.g., 1.5 - 4 mg/cm²) mica or mylar cover. this "window" allows particles to enter the chamber. The shell of the detector is usually made of steel or coated glass approximately 200 mg/cm² that does not let beta particles penetrate.

Low energy gamma (LEG) probes are highly efficient for low energy gamma rays in the 20 to 70 keV range. They normally use NaI crystals approximately 0.04" to 0.08" thick. Because higher energy gamma rays are more penetrating, scintillation detectors designed to detect and measure photons with energies between 100 keV and 2 MeV are thicker, often more than 1" thick.") NaI crystals to produce a portable system sensitive to both low energy gamma rays and beta particles. This type of detector would be an Ludlum 3 with Low Energy Gamma Probe excellent choice for a lab
group that uses both beta emitting nuclides and ¹²⁵I or ⁵¹Cr.

Many labs use both gamma-emitters as well as beta emitters in their research. Several detectors are on the market which combine detector elements to be capable of detecting both beta emitters and low-energy gamma emitters. The two most common type of detectors are the sandwich and the single crystal. The sandwich probe (e.g., Ludlum Model 44-21) is a NaI crystal fronted by a thin plastic scintillator (similar in function to liquid scintillation cocktail). The single crystal (e.g., Ludlum Model 44-98) uses a single BGO [bismith - germanium - oxide] that produces light when either beta or low energy gammas are absorbed in the crystal. One caution about these, and all scintillation detectors, the detector is fragile and shock sensitive, that means in a lab it may be easily broken if mishandled. For that reason, we recommend labs stick with thin-window GM detectors unless a specialty detector is needed and the personnel understand how to properly handle the detector to prevent damage.

Meters must be calibrated annually (at least once per year). The Environment, Health & Safety Department is able to calibrate most types of meters at no charge. All meters listed n this Web page are able to be calibrated by UW Environment, Health & Safety. Meters that can not be calibrated by the Environment, Health & Safety Department must be sent to an approved calibration service; the authorized user is then responsible for calibration fees and other charges.

Acceptable survey meters and pricing information are listed in the table for acceptable vendors. The meters have been divided into 3 general categories: beta detectors, beta + gamma detectors, gamma (LEG) detectors.

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