miles per hour. The dosimeter measures the total
A rad is a unit of energy absorbed from
ionizing radiation, equal to 100 ergs per gram
exposure in R or in rad, without regard to time.
of irradiated material. An added factor in the
Therefore, it is like the odometer that records the total
use of a rad is that it expresses the dose from
distance traveled in miles without regard to time.
any type of radiation, whereas the roentgen
relates only to gamma radiation or X rays.
Fixed RADIAC systems are installed on most
Navy combatants. The instruments provide
information on gamma dose rates at the location of the
Information on intensity and dosage is essential in
measuring the extent and degree of radiological
detector and at the main readout installations, usually
contamination. It permits the calculation of safe entry
the bridge area and DCC (Damage Control Central).
time and stay time for personnel in contaminated areas.
The information from these instruments may be used
Also, it provides an objective means for withdrawing
to estimate the dose rates at locations on the ship other
personnel when they are nearing the critical point of
than the bridge.
radiation exposure. Finally, it is useful in anticipating
the severity of radiation sickness. Data needed for
SURVEY METERS
these and other calculations can be gathered by various
radiac instruments.
The Navy has radiac instruments that can be used
to detect or measure certain types of radiation. The
No hand-held RADIAC available for military use
following sections discuss the survey meters currently
can measure both radiation intensity and dose.
used by the Navy.
Therefore, separate instruments must be used to make
the different types of measurements. These devices are
AN/PDR-27
as follows:
The AN/PDR-27 (series J through S) shown in
DOSE RATE, or SURVEY METER--The
figure 11-1 is a portable, watertight, battery-powered,
device that measures radiation intensity is called
low-range survey radiac. Two Geiger-Mueller (GM)
a dose rate, or survey, meter. This device
tubes are mounted in an extendable probe. A spare GM
provides the information needed to calculate the
tube set is included in the carrying case. The probe is
radiological hazards of occupying a
fitted with a beta shield. Six alkaline D-cell batteries
contaminated area or handling contaminated
(BA-3030/u) power the unit. If the alkaline batteries
equipment. It also provides the information
are unavailable, you may use carbon-zinc, D-cell
necessary to calculate the approximate length of
batteries (BA-30). The AN/PDR-27 provides both
time personnel can safely remain in a
visual and audible indications of gamma and beta
radiological contaminated area.
radiation levels. The visual indication is shown on a
DOSIMETER--The device that measures the
meter. The audible indication is heard through a
total radiation received by an individual is called
headset. The radiation measurement is in
a dosimeter. Medical officers must have dose
milliroentgens per hour (mR/hr). The unit is capable of
information to predict the severity of radiation
detecting and measuring gamma radiation when the
sickness, to make the prognosis, and to provide
beta shield is in place. It is also capable of detecting
appropriate medical treatment.
beta and gamma radiation simultaneously when the
beta shield is removed. There are four linear scales on
The two types of radiation detection and
the AN/PDR-27. The scales are 0 to 0.5 mR/hr, 0 to 5
measuring instruments may be compared to
mR/hr, 0 to 50 mR/hr, and 0 to 500 mR/hr. Beta
automobile speedometers and odometers (mileage
radiation can be detected on the lower two scales only.
indicators). The dose rate, or survey, meter measures
The -27 can detect and measure gamma, but it can only
the intensity of radiation in R/hr or rad/hr like the
speedometer indicates the speed of an automobile in
detect beta.
11-2
