Radiation detection in radioactive materials areas will usually be accomplished by using some type of gas filled detector, such as a Geiger-Muller (G.M.) detectors or an ion chamber.
A. Types of Radiation Detection Instruments
1. G.M. Detectors
These instruments may be calibrated in mR/hour or in cpm. An end window or pancake probe with a thin detector window will be used (window density thickness of l.0 to 2 mg/cm2). These instruments are approved for the detection of low energy betas (>150 keV.) and most gamma radiations.
2. Ion Chambers
An air filled ion chamber will be the preferred instrument to set personnel dose rates and are required for use in high radiation areas.
3. Scintillation Detectors
Hand held scintillation detectors will be used for the detection of low energy gamma emitters such as I-125. This type detector will normally use a thin NaI(Tl) crystal (approximately 1 mm thick). Typical energies detectable are 10 to 60 keV.
4. Liquid Scintillation Detectors
Liquid scintillation counters will be used for analyzing air samples, smear samples, liquid samples, and samples supporting specific research projects for the presence of low energy βγ radiations which cannot be detected with hand held detectors.
B. Instrument Calibration
Portable radiation detection instruments will be calibrated by the Radiation Safety Office, returned to the manufacturer, or sent to a certified vendor for calibration.
Instrumentation calibrated by the Radiation Safety Office will be calibrated in accordance with procedures approved by the S.C. Bureau of Radiological Health.
1. Calibration Frequency
Calibration Frequency shall not exceed 12 months. Instruments which do not display a current calibration sticker (within the last 12 months) are not approved for used.
C. Instrument Use – preoperational checks
Before using any portable detection instrument the following pre-operational instrument checks will be made:
1. Inspect the instrument for signs of physical damage.
2. Verify that the instrument calibration is current, within the last year. Do not use an instrument that is out of calibration.
3. Turn the instrument control knob to the battery check position or depress the battery check button. If batteries are bad or weak, replace them.
4. If the instrument has a "zero" position on the control knob, move the knob to the zero position and adjust so that the instrument needle reads zero.
5. Response check the instrument by exposing the detector to a known source of ionizing radiation to insure functionality before use.
6. Most hand held instruments have several scales (X 0.1, X1, X10, X100). Set the instrument to the highest scale and begin the survey. If no indication is seen, set the instrument to successively lower scales until activity is detected.