Step 1: On a sheet of log-log paper (two or three-cycle) write, "Dose rate (cGyph)" on the left side
of the paper (ordinate).
Step 2: Along the bottom of the paper write, "Time after burst (H + ___ hours)" x-axis (abscissa).
Step 3: Establish the numbering limits to be used and record at the end of each log-log-cycle.
Step 4: Plot the NBC 4 series reports on the log-log paper.
Step 5: Connect the plotted NBC 4 with a "best fit" straight line.
EXAMPLE: Suppose a set of NBC 4 (nuclear) series reports as shown in Figure 4-2 is received for decay
rate determination. H-hour is known or determined to be 0930. Plot this information on log-log paper as
illustrated in Figure 4-3, page 4-8.
Time of Reading
1000
1030
1100
1130
1200
Location
Dose rate (cGyph)
A
40
21
14
11
9
B
12
8
6
5
C
79
60
50
Figure 4-2. Dose Rate Readings
(1) The value of n may then be determined for each location and an average n is determined
as follows: Place a piece of acetate, overlay paper, or other transparent material over the graph in Figure
4-4, page 4-9, and trace it. Next, orient the transparent material over the log-log paper in Figure 4-3.
Position the arrow on the transparent device at the point where the slope intersects the x-axis. Holding
this position, align the y-axis indicator so that it is parallel with the y-axis of the log-log paper.
(2) Note the slope on the transparency that most closely matches the slope on the log-log
paper. The slope that most closely matches has an n value printed along the left side (y-axis) of the
transparency. This is the decay rate for these plotted dose rates.
CM2306
4-7
Previous Page
