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Doses to individuals may also be calculated indirectly if exposure rates are
known from radiation surveys (radiation measurements made in the field). Two
types of radiation survey instruments are helpful for assessing the potential for
exposure to military personnel in the field. The first type measures the radiation
exposure or dose to which personnel may be subjected. This category of instrument
includes devices such as microroentgen meters and ion chambers. The second type
of meter is represented by Geiger-Mueller (GM) or sodium iodide detectors. These
meters are used to find contamination, although the GM detector may be calibrated
to provide exposure readings. The conversion must take into account the efficiency
of the probe and a number of other factors.
An ion chamber is designed to measure exposure, that is, ionization in air
due to gamma rays (in coulombs per kilogram or roentgen). This instrument
measures the quantity of radiation energy at a point in the air. Ion chambers
normally come equipped with a moveable cover over the detection chamber. When
the cover is opened, the instrument will respond to beta, as well as gamma,
radiation. However, these instruments are not usually calibrated for beta radiation,
so the instrument reading may not be accurate for them.
A GM detector is primarily designed to measure the number of alpha, beta,
or gamma rays that emanate from a source and strike the detector in a given time.
This meter does not normally provide information about the energy of incident
radiation or about exposure. However, it can be calibrated to relate the number of
gamma rays to a known ionization in air to give readings in units of coulombs per
kilogram (or roentgen).
The devices briefly discussed above are useful for detecting or measuring
contamination on surfaces (e.g., on the ground or on a vehicle such as a tank), but
they cannot directly detect low levels of airborne radioactivity that might be

hazardous. To determine whether airborne contamination is a health problem, an
additional device—the air sampler—is required. Through the use of a filter or by
impaction on a collection plate, this device removes solid radioactive particles
from the air and concentrates them sufficiently to be measured by a detector
similar to those discussed above. Such measurements, however, must frequently be
made in the laboratory.
Determination of internal doses resulting from exposures to inhaled or
ingested radionuclides is much more difficult and time-consuming than
determining external dose. It requires measurements of levels of air (or water or
food) contamination, identification of significant radionuclides, measurement of
the amounts excreted by the exposed person, such as in the urine and feces, and the
application of sophisticated biomathematical models to determine doses to specific
organs. Gamma-emitting radionuclides deposited in the body can be detected and
measured with instruments external to the body, for example, through use of a
whole-body counter. Under battlefield conditions, rough measurements of
environmental contamination can be made as a basis for estimating both internal
and external doses. If calibration factors are available for open-window ion
chambers and GM counters, those instruments may be used to obtain a very crude

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