b. Graphical method. The graphical method of determining the NF is based on the fact that a plot

on log-log graph paper of the NF versus the time after burst at which a reading is taken to desired

reference time is a straight line. This procedure requires that both *n *and H-hour be known. The graph in

Figure A-2 (Appendix A, page A-9) has been constructed to determine the NF for correction to H + 1. To

use the graph

Read across the bottom to locate the appropriate time after burst.

Follow the line above that point into the graph to the point where it intersects the slanted line for

the appropriate decay exponent.

From that point, follow the line to the left of the scale and read the NF.

c. Tables of values. Tables A-6 and A-7 (Appendix A, pages A-7 and A-8) are tables of NFs of

selected times after a nuclear burst and for various decay exponents. The reference times are H + 1 and H

+ 48. These tables are normally used when H-hour is known for fallout contamination and the collection

effort is initiated immediately. The tables are used after determining the time after burst when the

readings were taken. Locate that time in the left column. Read across the page taking the reading for the

time under the appropriate decay exponent. If the decay exponent is unknown, use *n *= 1.2.

EXAMPLE: What is the NF if the time of burst is 0900 and the time of reading is H + 4 hours, *n *= 1.2?

SOLUTION: Locate H + 4 hours on the left column of Table A-6 in Appendix A. Read across the chart

to the H + 4 reading under the 1.2 heading. NF = 5.27.

When the time of reading is between two of the times after burst in the left column, an accurate NF can be

obtained through interpolation between numbers. A rapid interpolation can be made by approximation.

A safe-sided NF may also be determined by going to the next higher time.

calculated as: *OCF = (CF, VCF, or AGCF) x NF*. The calculation of this factor greatly reduces the work

required to calculate the final data to be plotted. Instead of multiplying each monitoring and survey

reading by the CF and then the NF, each reading is multiplied by the OCF only.

EXAMPLE: You have received data from an aerial survey. A course leg on the survey had 15 readings.

The AGCF is computed as 4.2. The NF is determined as 2.64. What OCF would each of the 15 readings

be multiplied by to determine the H + 1 ground dose rate?

SOLUTION: *OCF = 4.2 (AGCF) X 2.64 (NF) = 11.09, *rounded up to 11.1 (see Appendix C for rounding

rules). Figure 5-1, page 5-6, shows a completed survey report using the OCF. Dose rate readings can

also be normalized using the residual radiation decay (fallout) nomogram or the ABC-M1A1 RADIAC

calculator.

(Figure 5-2, page 5-7) allows the user to find the dose rate at any time, if a dose rate at a known time after

the burst is available.

Figure 5-2 is valid only for single explosions.

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