Basics of Radiation
Types of Radiation
How to Detect Radiation
Radiation cannot be detected by human senses. A variety of
instruments are available for detecting and measuring radiation.
Examples of radiation survey meters:
This probe is used for the detection of alpha radiation.
|The most common type of
radiation detector is a Geiger-Mueller (GM) tube, also called a Geiger counter.
Using a Typical
Geiger-Mueller (GM) Counter to Survey
Get the GM counter and batteries from
storage; prepare the instrument and determine background level.
Preparing the Meter:
- Position the Geiger counter with the meter
away from you. Locate and open the battery compartment.
- Put the batteries in the meter using proper
- Close and latch the battery compartment.
- Check the batteries using the
"range" switch or "bat" button; the method depends on the type of
instrument. The meter needle should move to area on scale marked battery, indicating the
batteries are good. If the batteries are not good, find a flashlight or other source of 2
D-cells and put them in the meter -- check these batteries also.
- Turn the "F/S" switch to
- Turn the "audio" switch to
Measuring the Background Radiation:
- Check that the "F/S" switch is on
- Move the range switch to the most sensitive
- Remove the probe cover if one is in place.
- Measure the background radiation for 60
seconds: write down the reading. Since background radiation varies with time, it
may be desirable to make several counts and average the results. Record the reading.
- Expect a reading of 40-100 counts/min or a
reading of approximately 0.02 mR/hr (i.e. 0.2 on the 0.1 range setting), or 0.2 micro
- Record background reading.
How to Survey
Using the instrument:
- Move the "F/S" switch to
"F" (Fast response).
- Set the instrument selector switch to the
most sensitive range of the instrument.
- Holding the probe approximately 1/2 to 1
inch from the persons skin, systematically survey the entire body from head to toe
on all sides.
-- Move the probe slowly (about 1
inch per second).
-- Do not let the probe touch anything.
-- Try to maintain a constant distance.
-- Pay particular attention to hands, face
-- Note that some GM instruments cannot
detect alpha radiation and some low-energy beta radiation. Because alpha radiation is
non-penetrating, it cannot be detected through even a thin film of water, blood, dirt,
clothing, or through probe cover.
An increase in count rate or exposure
rate above background indicates the presence of radiation.
-- Locate the point that produces the most
clicks. (Turn the "F/S" switch to "S" to take a reading at this
location. Remember to reset it to "F" before continuing survey.)
-- When necessary, adjust the range of the
instrument by moving the range selector switch.
-- Document time and radiation
-- In general, areas that register more
than twice the previously determined background level are considered contaminated. For
accidents involving alpha emitters, if the reading is less than twice the background
radiation level, the person is not contaminated to a medically significant degree. If the
accident circumstances indicate that an alpha emitter (such as plutonium) or low energy
beta emitter could be a contaminant, a health physicist should always be consulted.
Ending the radiation survey:
- Switch off the meter.
- Replace the cap on the meter probe.
- Take the batteries out.
- Put the Geiger counter back in its case.
The following procedures are recommended
for personnel monitoring:
- Have the person stand on a clean pad.
- Instruct the person to stand straight, feet
spread slightly, arms extended with palms up and fingers straight out.
- Monitor both hands and arms; then repeat
with hands and arms turned over.
- Starting at the top of the head, cover the
entire body, monitoring carefully the forehead, nose, mouth, neckline, torso, knees, and
- Have the subject turn around, and repeat the
survey on the back of the body.
- Monitor the soles of the feet.