(b) Use the following procedure for when the best fit line does not cross both the y- and

x-axes (see location C in Figure 4-5): From any location along the best fit line, draw a line directly down

toward the x-axis. Choose a location down slope from the first location and draw a line directly left

toward the y-axis. Measure the distance downward and leftward to the point where these two lines

intersect. Record the downward measurement as the *y *value and the leftward measurement as the *x*

value. See location C in Figure 4-5.

The *n *used in calculations is determined by an average of the *n *values determined for each location.

128mm

89mm

39mm

n

n

n

A

1.2

B

1.0

C

1.1

107mm

87mm

35mm

1.2 1.0 1.1 3.3

Average *n *

1.1

3

3

For the readings recorded in the three locations in Figure 4-5, the average *n *value is 1.1. A linear

scale is superimposed on the graph to show the determination of linear measurements.

b. To determination the decay rate using the mathematical method, use the following procedure:

(1) The formula for the mathematical determination of the decay exponent is found by solving

log

log b

Where

hours after burst) that dose rate Ra was measured.

hours after burst) that dose rate Rb was measured.

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