multiplying the unshielded dose rate by a NF. The NF is the ratio of the ground dose rate at a reference
time (R1) to the ground dose rate at any other known time (R2) after the completion of fallout in the area
of interest, or
R
ground dose rate at a reference time
1
NF
ground dose rate at another known time R2
5-5. Normalizing Factors. NFs may be found mathematically, graphically, or from a table of values.
Each method is described in the following paragraphs:
a. Mathematical method. The equation below is used to determine the NF to convert an R2 dose
rate to a reference time R1 dose rate.
T2 = the time in H-hours that R2 was taken.
T1 = either H + 1 or H + 48 hours.
n = the decay rate.
n
R
T
The equation 1 2n is used in determining the NF by the mathematical method.
R2 T1
n
n
R1
R1 T2
T2
Thus, since NF
, and since
n , it follows that NF n .
R2
R2 T1
T1
n
T
(1) To determine a reference time of H + 1, T1n 1 and NF 2n .
T1
EXAMPLE: A nuclear burst occurred at 1030. At 1400, a reading was taken. What NF would be used to
normalize the reading to H + 1 if the decay exponent n was 1.2?
n
3.51.2 4.496
T2
SOLUTION: NF
4.50
n
1
1
T1
n
T2
(2) To determine a reference time of H + 48, T1 48 and NF
.
n
T1
EXAMPLE: A dose rate of 16 cGyph measured at H + 50 in a fallout area where the decay exponent n
was 0.6. What NF would be used to normalize the reading to a reference time of H + 48?
n
50 0.6
T2
10.45
SOLUTION: NF
1.02
n
480.6
10.20
T1
NOTE: See Appendix C for rounding rules. Using a scientific calculator, you can solve these
computations easier.
5-3
CM23066
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