Lesson 2/Learning Event 1
The information received from NBC 4 (Nuclear) Reports must be evaluated. During the evaluation
process, monitoring reports will provide dose-rate information about the contaminated area. This dose-
rate information must be converted to the ground dose rates at a reference time (normally H + 1 if fallout
is less than 48 hours old). If the report is from a location where the fallout is 48 or more hours old, a
reference time of H + 48 hours is normally used. To accomplish processing, a reference time (H-hour)
must be established and the decay rate of the contamination determined. The procedure to be followed
in determining these two factors will depend upon the source of the contamination and the operational
situation existing at the time.
Evaluate NBC 4 (Nuclear) Report Data
Personnel processing NBC 4 (Nuclear) Report data must evaluate the report to determine if correlation
factor information is needed. A correlation factor (CF) is used when monitoring readings are taken in a
shielded position. Shielded dose-rate readings must be converted to unshielded ground dose-rate
readings. This conversion is accomplished by using a correlation factor. The shielded dose-rate reading
is converted to an unshielded ground dose-rate by multiplying the shielded reading by the correlation
factor. Space is provided on the Radiological Data Sheet for both the required dose-rate information and
the calculation of the correlation factor.
Correlation Factor for Vehicles. Data for the vehicle correlation factor are provided by the monitor and
consist of a set of two readings taken at the same location. One reading is taken inside the vehicle with
the instrument located as indicated in figure 6 on page 33. All subsequent inside readings must be taken
with the meter in this same position. The other reading is taken outside the vehicle as a normal ground
monitoring reading at the same location with the vehicle pulled away at least 10 meters. The outside
reading should be taken within three minutes of the inside reading. One or two additional sets of data
should be taken at different locations so that the control party can use an average vehicle correlation
factor. The sites for obtaining vehicle correlation factor data should be selected to approximate average
foliage and ground surface conditions for the contaminated area. New data must be obtained if these
conditions change significantly or if the survey meter or vehicle is changed. Accuracy of the correlation
factor data is extremely important. If correlation factor data are not provided, but only the type of
shielding is provided, correlation factors from figure 6 may be used.
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